The AM Forum

I recently purchased an used SB220 amplifier. Are there any special modifications needed to allow its use on AM? I intend to drive it with a Johnson Ranger II.

My 2c, you can use a sideband amp in AM service (I'm talking about tube amps in this case) if they are rated at high enough power out to make it worthwhile and you take a few precautions.  desk top amps designed for SSB and CW usually have lightweight plate supplies.  The limiting thing, is the current rating of the plate transformer, usually something like 500 ma CCS.  The other things are the plate dissipation of the tubes, cooling, and the tank circuit (band switch for example).   So you have this envelope you have to operate within and if you know your limits and calculate say, how much current a 200 w. carrier demands, then figure 800 w. when you fully modulate it you get an idea of what the stock plate tranny can do for a few minutes.   you have two 3-500s so you know right away you can dissipate up to 1000 w.  Cooling--most SSB amps are made to be quiet which means their cooling stinks.  One easy mod you can do is get a fan for the 220 that moves more air through it.  Get the highest volume fan you can find that will work in one.  200 CFM isn't too much.  It will be loud but ur amp will love you for it if you operate it in AM.  keeping the plate supply and tubes cool will dramatically extend your transmit time.   I know guys who run the 220 on AM with around 200 to 300 watts but I think they limit their transmissions to just a minute or two.  They don't do a 10 minute buzzard tx b/c it will melt down. 

Or, you can blow all this off and get a high level plate modulated rig which is what I'm trying to do  :D

I think you wrote you have a Ranger exciter?   You need a Johnson Desk  ;D  kidding aside, good luck

Rob K5UJ

My two cents worth:

Add a couple more volts of bias to the bias zener.  Best way is to put a few 6A10 diodes in series, and a largish cap across them (to keep dynamic regulation up).

Directly ground the grids of the amplifier.  This will cause a heapin helpin of people screaming yes and no, but if you do, drive goes down about 20 percent.  If you NEED the extra drive option, keep the chokes and caps from pins 2, 3 and 4 as stock. 

Directly grounding the grids also seems to help with stability on that, and a few other similiar designs.  Of course, this will get the "toaster wire" guys to come up and say it's the best, blah blah blah.  I'm giving you what I've done to mine.

Check the caps in the plate supply.  They are old.  They need to be replaced.

Don't count on the HV resistors to be anywhere near accurate, meaning, don't count on your HV meter being anywhere near 10 percent within tolerance.  Replace the two (IIRC) resistors with 4 or so... They need it, because they are across the entire HV...  If not, you will be replacing them again, when you notice your HV falling off (not really, but the meter will start to read high or (more likely) low, and then it's time to get the HV probe out, etc).

That will get you up and running.  I also go through the tuned inputs on them...  Some will say they are fairly close, but I find that not to be the case.

If you REALLY know how to work on the amp, go through the tank network as well.  Stock, 1150 watts on 10 meters.  After moving the tap on the output coil, and touching up the input, I see 1400++ watts.

It's not hard to get 1600+ on the lower bands, with the tank circuit optimized.  It's not easy, but not hard, as you have to have the "RF Shield" in place when  making the RF deck output 'enhancements'.

Hope that helps.  Total cost should be around 100 dollars + shipping, caps included.  This will give you almost a legal limit amplifer, albeit one that can't be held keydown.

Mine will do 300 watts AM carrier for 5 minutes.  I run QUITE a bit of bias on it, though.  Stock, I'd not go above about 250 for any buzzardliness. 

Hope it helps.

--Shane

    I have been running an SB220 on AM for thirty years with little or no trouble at 250-300 watts carrier. I run the amp on 220, in the SSB position, driven by a lightly loaded Collins 32V2 in it's tune position. I also recently acquired a stock SB220 that I run more conservatively on 110. the weak points I found over the years are the fixed loading caps on 75 and 40- I replaced them with rather large "bathtub" style mica caps, and the Zener bias diode. I replaced that with a 50 ohm 50 watt adjustable wirewound resistor and 470 MFD 100 volt cap in paralell and set the resting current to 200 mils. grounding the grids directly defeats a crude inverse feedback circuit and blows the third order IMD spec of the amp all to hell. biasing the amp to a lower resting current also screws the 3rd order IMD spec. I tried it and came out with a dirty amp, so I went back to the RF choke and mica cap from grid to ground, and fairly high resting current. it's cleaner  easier to drive that way, providing you drive it with a clean signal in the first place, otherwise you just amplify the crud from the exciter and add the amp's distortion to that crud.

    a few years ago one of the origional tubes in my older SB220 shorted and took out a lot of stuff. at that time I installed the Harbach power supply board,filter cap block, and hi output fan. I highly recomend all three of those mods. the amp runs cooler, and the issues with inaccurate metering etc are resolved. I did keep my cathode bias setup though. it just works. step back from the amp and take critical a look at the tank circuit and bandswitch before you try to get more than about 1200 PEP out of it (on any mode). the bandswitch WILL melt if you beat on it on the higher bands, as will the tank coil. run it intelligently on AM and you will get years of service from it, even stock. but like all rigs, that extra few hundred watts that most hammy's go for are allways the downfall of most amps. remember- it's a nice green box, but the lable on it says Heathkit- not Harris or Collins.

I'd like to see the testing parameters for that.

I have emails galore, as does quite a few others, that show the SB220 with directly grounded grids causes the drive power to drop approximately 20-25 percent Vs. stock SB220.

I can't get the IMD to raise any amount measurable with locals listening a few Kc away from me.  No popcorn, etc.

Keep in mind, this IS for AM use.

Using the stock NFB garbage causes the bias voltage to run up and down, varying with the PEP values of drive.  To me, that's bad engineering.

As to the slide resistor...  You're only using R now, no fixed voltage regulation?  Was this BEFORE or AFTER you played with the grids.

I've been told both possibilities before, and have been involved in quite a few arguments, and listened to both sides. 

Running the SB220 into a single 3CX3000, a 6000 and a 10,000 also showed little to no difference between it and an Alpha for IMD and "crud" in "Crud" out....  This was an SB220 modified as I stated above.

I'd really be interested in what caused your amp to go down the toilet, with the mods posted above... That is, unless, the resistor taking out the fixed voltage regulator for bias was done BEFORE the rest of the mods.  If that's the case, I rest mine.


--Shane

Thanks guys, you have all given me much to consider. I will consider all of your opinions before I start modifying the amplifier.

You spend too much time with the CB and know little crowd on Yahoo Shane
 ;D Youre dealing with the big boys over here.

Ive already posted the IMD degradation results from controlled measurements when the grids are grounded at least twice over there.

I'll take what a HP SA shows over some over the air bozo report any day.

1600W out of a stock 220? Key down? Absolutely impossible at that voltage and xfmr.

Carl
KM1H

Another reason why many do not notice any apparent degradation of IMD when modifying amps is that the exciter they are using has an IMD that is worse than the amp they are testing. Many recent SS transceivers have horrible IMD, some as much as 10 dB worse than tube rigs like the Collins S-line and the TS-520s of yesteryear. As you said in another thread Carl, GIGO.

Carl, I haven't seen any results posted, from any type of measuring equipment.  Not arguing, as I seem to miss a LOT of posts on it, I'll go through the archives and check.

Making comments about service or people on other reflectors means little.  I know of little to no amateurs running a pair of 20,000s, but still listen to their opinions about high power.  Few amateur operators take weather into account when they are deciding if they will talk on their stations or not, but quite a few "CBers" have to.  Very few amateur operators have a relationship with Reid Brandon where they can call up and have a tube built to spec.  More than a handful of the "idiots" on 11 can.  Big deal.

I never said 1600 watts key down.  That's physically impossible, mine won't do more than about 800 watts KEY, but won't modulate that anywhere near linearly....  I typically run mine (AM service) at anywhere from 75 watts to 300 watts of carrier.  Usually at the 200-300 watt level.  SSB tap, but I use a bit more bias, as well as grounded grids.

My Kenwood 440 exciter has better IMD performance at 75 PEP than it does at 100 PEP.  I don't have test results to back it up, but I can sure see a difference when listening to a rx plugged into a dummy load next to it.  About 10 dB, give or take, depending on the accurace of the S-Meter (1-1.5 S Units lower).  Increasing the gain of the amplifier means if your exciter is running cleaner, GIGO applies.

As I said, I knew my post would stir up a hornets nest.  I'd LOVE to see a pic of the Spec An, a picture is worth a hell of a lot more than numbers being thrown out.... BUT, even then, numbers are nice if that's all you can get.

Regardless, mine is grounded.  I don't have neighbor complaints (with someone living 3 houses down on HF at this QTH) from anything other than front end overload when I didn't realize he was there, and he was in line with my 10 dB gain antenna, and the 10 dB gain linear.  One or the other, I'm fine.  Both, and every time I key up, almost anywhere in the HF region, I KILL his Yeasu 450.

Anywho, guests just arrived at the door, so I gotta run.

If you have some plots of the Spec An, I'd LOVE to see them.  I'd also like to see what your 950's do at 100 and 75 watts, if the xmitters haven't been highly modded....  I know you've hotrodded them quite a bit.

--Shane

You obviously don't know very many amateurs. I can think of quite a few hams right off the top of my head that run WAY more than the power you are talking about. And they are doing it correctly, because they have to - it's a BC station.  ;)

See these guys know what they are doing. That's the difference between them and the CB amp guys. Sure the CB guys can build a big amp. But the specs are terrible. They would never fly in a commercial application. So, you can listen to guys that do it professionally and have decades of proven experience, or you can listen to those who don't.

the cber's do know one thing better than most hams - how to generate & deliver the juice to hi powered amps. I dont know many hams who can set up 8 to 12 alternators to run 15 to 30 K Bird watts mobile. running 7/8" heliax for feedline.

Their amps may sound terrible, maybe 100kc wide, but they are not made for clean signals. They are made for competition in keydown contests, where you can have thousands of dollars on the line. 

The 2 worlds are so at cross purposes with each other that no valid comparisons can be made.

It's like saying "well, I axed this guy down in hell and he said this...." vs. "I axed this guy in heaven that, and he said...."

the perspectives you get MIGHT be a little far apart.

Oh brother.. Because Shane is known in the CB world he knows nothing about ham gear?  Give me break.

I have know Shane for 15 years.  If the guy says something you should listen.

As for the SB220.  I think its a waste of time as an AM amplifier.  I have three of them.  Its really only going to do 200 watts AM max. If you try to push it more then that its going to overheat and groan about it. The heat comming off that thing at 200 watts is just silly.  Cherry plates, Power trans that is screaming hot and waiting to blow.. A tuned tank thats about to flash over.

Not a bad little amp for SSB use though.


I have owned 5 of them.  I grounded the Grids on most of them. Makes a Big difference. Does not inrease IMD. I have an HP Spec AN here. The stock config is horrible.  I have plotted the amp with and without grounded Grids. If you say otherwise,  Post your picture of the spec AN showing this.

I also add diodes to the Bias. Really helps for AM use. The last one I built has the Harbach boards, caps and Grounded Grids. Diff bias on that board as well.


T

Ran out of room.

The last one is sitting right here.. Its plugged into a Stiff 240 volt line. It makes 1550 PEP with the original Eimac tubes. Runs Clean on the spec An and never arcs over or gives me trouble.  But I dont like using it on AM much.  I nice old SSB amp that will do full legal pep.  But, A 175 watt AM amp.

Clark

   I like CB amps. If I can get them cheap enough, some actually have a few good usable parts in them.
Phil KC4VWU

Call me uninformed but I always thought the SB-220/1 grid pin circuit was there to counteract lead inductance of the tubes for parasitic suppression. If that is indeed a negative feedback circuit how does if work on all bands?

Who said that he knows nothing? The comments weren't even about him. They were about these mythical people in the CB world with superior knowledge in high power RF to those in ham radio world. I don't know nor ever heard of one CBer who has designed, run or maintained high power RF systems in the commercial world. I know many hams who have. That was my point. I will judge the merits of Shane's (or any one else's comments) on the body of proven knowledge in the field.

I ran the SB-220 SA tests in the early 80's when I borrowed one from work at Wang Labs for a weekend. My tests were on a 6M conversion and the Director of the RF Division bought over his SB-221. Both showed a repeatable 2-3dB improvement with the grids as designed. There was no Internet then and GPIB wasnt even available.

The Drake L-4 was designed the same and the designer recently stated that they also saw a 3 dB improvement in IMD.

Both of the above have been discussed on the other group Shane and I doubt if results have changed ::) However I now have my own SA.
I'll be glad to redo the tests the next time a SB-220 comes in for conversion but that business has been a bit slow recently altho SB-200's keep coming in.

Since the chokes provide some level of degeneration due to their 26 Ohms DC resistance it is easy to see why output decreases compared to direct grounding. It should also follow that the process will also improve linearity. I havent tried the cap across the zener or measuring IMD with a string of diodes. Those are ideas I will try.

Clark, since you have a 220 and SA handy why dont you do as you say:
 

Carl
KM1H

Carl,

Here's a ? for ya then.  Would it be "better" to use a different style of choke then, maybe something with BIGGER wire and a core?  That way, you'd get the L you need for NFB, but reduce the ohmic value of the choke.  Bias wouldn't shift with drive level, AND the gain would go back up to the levels we see with the grids grounded.

I undertstand the problems with the core getting hot, and you could semi-negate (no pun intended) that by ensuring it was within the airflow (which it would be)...  Come to think of it, the 220 would cool them fine in stock cooling config, pretty much.

I'd love to find a way to improve the 220.  I LOVE mine.  However, it is a pissweak amp, in comparison to others, and any way to increase performance is OK with me.

As I said, redoing the tank circuit (in and out), made a BIG increase, especially on the upper bands.

--Shane

Steve,

I'm not talking about the handful of US amateur operators that have a job as a broadcast engineer, nor am I talking about the handful that have QRO power AT HOME.  I'm not talking about in the commercial world.

What I'm talking about is there isn't that many amateur operators (if you look at it statistically) that can actually BUILD anything of that nature.  I mean, seriously, are you going to debate that the amateur radio community as a whole is NOT a bunch of appliance operators?  (YES, this is a generalization).

Yeah, we have BE's in the amateur radio ranks.  We also have them in the CB radio world.  I know of 3 BE's that run 15kw plus, 2 FCC engineers (one running my amp) that operate on 27.025, etc., etc., etc.  Who CARES!

My comment was based on the fact that there are people in other services doing QRO.  Just because they don't have an amateur radio license means little to nothing.  Dennis O. can run circles around most "Broadcast Engineers" that I've had the pleasure of meeting, but refuses to use amateur radio.  He now works at Motorola.  Does it mean ANYTHING that he works on CBs to supplant his income?

The problem with the CB'ers coming 'clean' about operating there is the stigmata that goes along with it.  You can't discount, most amateur operators wouldn't even be able to figure out how to build a 75 kw carrier amplifier, much less figure out how to get enough power to it.  They'd rather just pick up an (insert appliance here), throw the G5RV up in the air, and be DONE with it.  Incidentally, these are NOT the types I find here.

IOW, the only place I've found extreme QRO is either VOA Delano, or a couple CBers running water cooled 40,000 triodes.  Me, Ive only got a 30kw water cooled triode, so I don't count in the big boy club :(  lol

It wasn't bashing anyone, it was a statistical thing.  Lots of hams are engineers.  Doesn't mean any of them are running more than 50 thousand watts out of their house!

--Shane

I totally agree. But the same is true of most CBers. So, statistically, it's a wash in that department.

All this is very irrelevant in the realm of discussing an SB-220 or other similarly powered amps, and the relative IMD levels. In this area, I think you will find the amateur population is vastly more educated and experienced than the CB population.

Kinda squares with my experience.  I owned a SB220 -- loved it a lot.  Like an idiot, I sold it when I moved back in '84.  My problem with the SB220 is in how the toobs are cooled.  I wouldn't recommend running "legal" -- with the SB220.  Probably 200 watts would be OK.  Some of the newer designs that allow for proper cooling would work just fine. But the pins have to have air running by them -- a chimney really is necessary if you're going to run the SB220 for the kinda power that AM legal limit runs.  I also had a RTTY station but did NOT run the SB220 with that either.  I had a HB 2 x 813 xmtr for that. The SB220 is a nice SSB linear.  Be sure to run it on 220 VAC

Here's a pic of my old station.  You can see the SB220 in the middle and the HB xmtr on the right.

73, Al VTP

Black & White QSL? I should talk, I never had any printed. 

The BS detector has a lower MDS here.

Speaking of cooling, the original Drake L-4 and L-4B used chimneys and a blower.  The later L-7 (same basic RF circuit with the same PS) uses a fan like the SB-220 except it is a 2 speed thermal controlled model.  I have used my L-7 a couple of times on AM for a local 160 meter net but I keep it at 150 to 175 watts carrier out.
160 is the only advantage the L-7 has over the L-4B but the cooling system is much better on the L-4B.  The cooling system on the SB-220 seems superior to the Drake L-7 given the well perforated case on the Heathkit.

The odd thing is that the T-4 series rigs are controlled carrier and very friendly to linear amplifiers while the TR-7A is a typical SS rig with continuous carrier which generates a lot of heat in the L-7.  I wouldn't use it for lengthy transmissions on AM although it would do fine with the early 4 line gear.

My SB-220 was the first Heathkit I built back in 1976 (and $369 was pretty pricey for a high school student!).  The 3-500Z tubes it came with have a spacer built around the pins so that the tube base/pin seal is elevated a bit for better cooling.  I still have it and use it from time to time and it still has the original finals.  Of course for many years it didn't get a lot of use with all of the time I spent in college and once I finally had more radio time I soon built a new homebrew amp that covered 160 and was better suited for contest use.  But the SB-220 is a pretty well built amp and works great on SSB/CW.  I worked a lot of CW DX with it and a bit of RTTY many years ago.  It does need a standby switch and I implemented that several years ago in the form of an external switch that switched the amp between my SB-102 and Drake C-line with a center "neutral" position.

Rodger WQ9E

Yes.. The cooling is the big issue. Thats why I dont like using them on AM.  I did with a ranger and yes it worked. I also used my FT1000D with outboard audio with it. But I would rather fined something that wont cook itself.  Us left coasters tend to key for 5 to 10 minutes a time here on AM.  At Five minutes in an SB 220 is really screaming for mercy.

The Drake is a big step up in my opinion. But it has its own issues.

I have used SB220s for 15 years.  I have used them on every band.  Mine spends most of its time on 40 or 80 as I mainly use the Low bands. No issues with IMD here.  I know, I plotted the amp. I dont have to worry about. Clean in, Clean out.

For years I have heard people bitch about arcing the cap over and how it needs to be changed and how to supress "harmonics".  BS.

Tune the antenna so its flat BEFORE you flip the amp on!  Tune the amp at low power input on the tune postion. Then when its tuned, go to high power and increase drive.. DUH.  I have never had an arc over on an SB220.

Its a neat little KW amp for SSB.  My main complaint really is the band switch is the same size as the tune and load. I have almost hot switched mine several times. I have to stare at the knob and check each time as I am worried about this. Most SB220s have been hot switched and the failed so called "weak" band switch takes the blame.. LOL

Clark

WOW!!! I didn't know that I would cause such a stir when I asked the question, LOL. As I said before, you guys have given me much to consider and I really do value all of what has been said. The first modification I will make to the amplifier is change the cooling as it appears that everyone agrees this is inadequate. The second will be adding the stand-by switch. 

This is the way we discuss. Nobody is mad at anyone.  At least I hope..  :)


Clark

LOL. We skipped school on the days they had sensitivity training.

I LOVE the people that can't tell the difference between a discussion and an argument.

My ex girlfriend being one of them.


--Shane

I never had an amplifier, and would not think of buying one, as it seems (to me) that you spend a lot of money in electricity in one for little power output.

Maybe if I had a flex radio, that would likely be cool, but to put a ranger or some such into a big amplifier and have it generate loads of heat to get 200 watts out seems kind of silly to me.

Brett


 

Yes...........It's fun!! Sometimes its fun to put one across someones bow and give them a good poke in the ribs. If they cry and run away it's no fun. When I give them a good poke in the ribs, I full well EXPECT one in return! thats half of the fun of it. One needs to be thick skinned and have a sense of humor.  ;D  ;D

Ifn you cant run with the big dogs, stay the hell on the porch :o :o Screw a bunch of sensitivity training, that stuff is for pansies! Besides, everyone enjoys watching a good fight.

you just gotta learn to disagree agreeably ;D

                                                     The Slab Bacon

Having been born and raised in Brooklyn, then LI and next into the Navy, sensitivity training would have been a recipe to disaster.

Go to any New England selectmans/city council or Town Meeting if you want to hear fireworks. Don Rickles would be proud ;D

The current crop of castrated males in this country makes me puke.

Carl
KM1H

At the risk of commenting on the actual subject, my experience with using older linear amps on AM has been they work fine as long as they are tuned to provide the peak power output on AM that matches their ratings on SSB.    If you don't load them heavily enough you can get a higher carrier power but the peaks will be clipped.    I find that the sweet spot for AM is to tune the amp for max power output then increase the loading until the power drops to about 175W to 200W of carrier on the output.   This should give you the best sounding audio peaking around 700-800 W PEP.

If you do the math, there is very little difference in the actual AC power input for given RF power output when comparing a plate modulated rig and a low level rig driving a linear. Sure the RF final is less efficient, but there is no high level modulator (nothing more than a linear amp that is now more efficient than an RF linear amp).

HUZ,
Also there is a lot less hardware to break down

( Bolded emphasis in quote mine)

Yup, Brett.  That's why I presently use a Courier on my present Flex setup and plan going to legal limit with an amplifier upgrade some day (soon).  But, that aside, the stuff you have built has inspired me to buy stock in the 4D32 and either go your route of 3 x 4D32s or an 813 OR a Russian GU-48.  Why put one's eggs in one basket. :)

Al

Yep, no big mod transformer, no power sucking audio driver circuitry, etc.  Avoiding the linear amp option made sense back in the day when there was a limit on power input. No longer.

Cherry plates on a 3-500Z is piss weak.
They ain't working till you get that orange near white!!!

Good point. I use a 1kc tone to tune the Viking 1 driving a pair of 8874s in AB2.
The scope tells the story. Nice round peaks at 1499 W PEP! And you're correct. The loading is the key.

And if I'm not gettin my 4CX250R's to pop, then I'm still on the LV tap, at 2Kv...

2800 volts makes them REALLY come alive, although you BETTER have the loading right :)

Hence the reason, I refer to the 250 as the "Popcorn" tube!

--Shane

Ok, well, how much power can you get out on 110 vac?
The pair of 813's runs 600 watts of carrier out, 2400 watts pep, on 110vac.

Ok, the modulator is on another 110vac circuit, but the lights dont dim or anything...

What amp could run 600 watts (or 700 watts) carrier out for 20 minute old buzard transmissions, and on 110vac?

Brett

All about tank Q Bud, so it is loaded properly

110VAC depends on the conductor and breaker size not to mention the plate iron.
Normal 20 amp circuit  would do 2 KW plate modulated or linear amplified.

On a 20A line anything with 800-1000W Pd tubes and a full flow air system. That might include the old Henry's, Heath Chippewa, Johnson T Bolt, Hallicrafters HT-33B and a few others. I think it was BTI that had a 3-1000Z amp in the 60's.

If building Id use 4-400A's as IMO they are a bit underated for Pd and cheap. Use 3-4 if you want to lock the mike and try to break the OB record.

If you got the money there are 8877 medical pulls (actually the pulse 3CPX1500A7 is used) or if you want a real loafer the YC-156 is a bargain in the pull market. Both are in the $300-400 range for very good ones.

Carl
KM1H

Four 4-400s sounds like a real nice amp..

I had a single 4-1000 amp with Vac variables, 2 amp PWD transformer. With 7000 volts on the plate it really put out power. The 4-1000 pulse tube I had was a screamer. I wish I still had it.. Like a dope, I sold it off thinking I would never need that much power.  I am sure It would have ran full legal AM all night.

Clark

I got a 4CX250B in the Viking 1, Shane.

Well, I did. Just last week I conduction cooled it with a 8560.
Same tube, different cooling. Works great.

Shane, I have some  serious questions for you:

What  fascinates these people about CB, and specifically the "Superbowl" channel?    One would naturally think that they might be attracted to amateur radio?   After their so-called  "competition",  what attracts them?   What fascinates them?

Why  does he refuse to opeate on amateur radio?   As above,  what attracts him to CB,   what is it that fascinates him?

Frankly, I just don't get it.   To me, CB/freeband, etc.  is  a dead end.

they like it better.  :o

OK, but why?  What's the attraction?   

1.  Generally, the people on 'the superbowl' are a lot less stringent about who they "accept".  If you pay the price of admission, your admitted into the "Club".  On amateur radio, it just isn't that way.  I'm looked down upon as being "no code".  So what, I passed novice through extra in one sitting, and gave shit about the code.  15 years or so later, soon as they dropped it, and I got HF equipment, I came back.

I enjoy both services.  So do a LOT of amateur operators!  I know of at least one top ten finisher of most contests that runs 27.025.  Discretion is the better part of valor, hence the reason I actually KNOW who the person is.  If they where known in the amateur ranks, they would be looked down upon.

Dennis let his call expire and gave up on amateur because of the same reasons.  WHY?  Why get a ticket to be part of some elitist club.

I ran in to the same problem asking for help here.  I put a name out, and all of a sudden, 3 people where jumping all over me, asking for call signs, etc.  I got news for you, YOU DON'T NEED  A CALLSIGN TO HAVE A WORKING TRANSMITTER, YOU DON'T NEED  A CALLSIGN TO GET HELP, NOR DO YOU NEED A CALLSIGN TO PURCHASE JUNK FROM A HAMFEST with the intention of fixing it up and putting it on a shelf.  BUT, I only got 1 (ONE) response that actually helped.  I did spend a week fighting off the (assholes) guys who wanted to trace down who I was talking about based upon clues I gave, etc., etc., etc.  Funny, the person I was helping actually IS ON THIS REFLECTOR NOW!  BUT, he wouldn't have been, had this reflector been the ONLY way he was introduced to amatuer radio.  Upon going to his house, his attitude was "those people suck!", since they wouldn't help out since he WOULDN'T provide a proper call.  What a bunch of crap, hiding behind the "I can't help someone I know is doing something illegal" lingo, when in actuality, it was because they didn't want to help someone who <<might>> be a CB operator.

CB radio has it's place.  I don't know of anywhere other than 2 meters that you can pretty much just buy your equipment and be accepted.  And that isn't even a given on 2 or 11 meters.

Just my take.  I enjoy all radio services, have radios for all services, and think that people that bash one radio service over another are nothing more than lids.  PERIOD.

As to what drives them to do what they do?  What drives ANY of the consistent top 10 contest finishers to do what they do?

Hope that didn't go over the top.

--Shane

I agree with most of that.  Ham Radio is actualy alot worse then CB in many respects. Especialy if you are young and on AM.


Clark

Who's young and on AM?

No crap. This is an amateur radio BB. Why would we want to help out CBers? They have their own BBs.

Define young!

There are some differences between services and even on ham bands but we all have something(s) in common.   And one thing is highly evident, we like to spew RF.  Isn't that good enough?

OK, but what is it about 27.025 that attracts him?   I can't quite get my head round  technically competant people  doing "keydowns" and yammering on the Superbowl channel.   

I can't quite get over this "elitist" idea.   Now maybe we don't act this way here in Canada?  I don't know.    You must have some real  snobs and  smug arrogant types where you are.    I think this "elitist"  claim is false.   I don't trust it, as I think the reasons are otherwise.

  Actually, in Canada you do.  One may not possess a functioning transmitter, as that constitutes  an illegal radio station.   But I digress...

Again, I have no interest in CB per se, though I do operate there occasionally.     

As long as the participant(s) obey the rules of the radio service they are operating in, I have no problem with that. If they're motivated to engage in activities which are in violation of the rules of their radio service, I have no desire to help them. In my opinion, if you can't follow the rules, then "hit the road"!

My point exactly.  Amateur radio, like most anything else, is what YOU make of it, no matter your age. I have just as much fun now as I did when I got into amateur radio via AM at age 14. If ya wanna piss and moan and point fingers at others, you can do that at any age. If you wanna have fun and learn, you can do that at any age. It's all about you and your choices.

I am glad you got it all figured out Steve. 

Clark

Pete,

My point is / was, I came and asked about the part value.  And as soon as I typed the name of someone, it turned into a fiasco.  A simple name.  A FIRST name.  But, I digress, this is getting to the point of being nowhere near topic.

And it's the same people that do it time after time, so no, it ISN'T the community as a whole (ham radio), but a select few elitists that believe for some reason, rose petals exit their backside.

I also agree with you on the legality issue, but I'm also a realist, and know that ALL radio services have outlaws.  I won't pass judgement on someone because of the way they choose to operate their radio.. Life is too short to alienate potential friends / information because they might run 100 watts on 11 meters!  OOooohh, call the CIA / FBI  / FCC / INS / blah blah blah.  Seriously.

Anyway, this is completely off thread now.

To the Canadian gentleman, who knows what makes them do it...  Why do people drag race?  It IS a thrill when you hit the PTT on the D104 or footswitch, and watch the line section meter edge to the 40-45 kw level, and pin when you give it any modulation.  I mean, when your running the same or greater PEP than a broadcast station is allowed, it WILL give you a woody.

I will say I've run across a LOT more tolerant amateurs in .ca than I have in the US.  In Canada, in general, people seem to be a lot more tolerant of personal freedoms, even though from what I've seen the country itself has less than we do.  I've never run across a canadian amateur that hasn't been willing to help, regardless of license class... Interesting, since you pointed out that is CLEARLY in violation of the law (as it is here, KNOWINGLY helping someone break or you know is going to break the law...  ALTHOUGH, we may own pretty much any transmitter (subject to export restrictions, etc) we can get our hands on, no laws there (generalization).

I enjoy all radio services.  Amateur radio is a WELCOME addition to my radio addiction.  I can always find DX, always find someone to talk to and have a civil conversation with.  Granted, since upgrade to general, I find myself on 11 meters a LOT less..... BUT, I still have my radios,  and they still are connected to antennas.  Just no DX, and THAT'S my forte... DX and technical sides.


--Shane



--Shane

Maybe because it WAS an amateur that asked, for another amateur.

The CB part of it came because I mentioned a first name.

It wasn't like I came on here and said "I have a CBer that has a johnson he runs into a pair of tetrodes, and he needs to know the value of XXX so he can get his 50 kilowatt hammer back"...  It was "Hey, anyone have the value of XXX on chassis YYY"....  Got the response, said "Thanks, and thanks from ......"... Which fired up a hornets nest of "CBer CBer CBer"... Culminating in me having to post a callsign to get some aholes off my back.

One must keep context in mind!

--Shane

Yes, one must keep the context in mind. You are new here and no nothing of the history of this forum. Yet you want to paint with a broad brush. There are almost 2900 members here. You can P&M about a few so called AHs or you can choose to have fun. It has nothing to do with CB versus amateur. It has to do with attitude. Your call.

LOL. Take all the cheap shots you want. I'll keep having fun and you can keep pissing and moaning about amateur radio and AM.

Remember the SB220?

I have listened there and it sounded like a bunch of people with distorted audio shouting rhyming hip hop slogans with fake accents. Not my cup of tea. But as long as they stay there and don't bother anybody, I say, to each his own.

I will!

Thank these guys for making sure BPL dies.

Why not put a legal broadcast or shortwave station on the air then? Can't run with the real big boys? Let's hear the excuses...

I dont think you can put a am BC station on.  Dont you have to buy a existing station and it's associated CP/license/call?

Wow, this thread sure had gone to the bottom feeders.  As an amateur radio operator, I take pride in being a legally authorized radio station operator.  Outlaw operation should never be glorified.  It's simply a ethics question for me. 

I operate an amateur radio chat room on IRC and we often get either illegal cb'ers or even pirates that come and ask questions about how to do something that is obviously illegal.  I always try to set the example not by deriding or degrading the individual but simply being an example and pointing out that what they are proposing is against the law.  I then refer them to The Amateur's Code http://kx5jt.net/amateurcode.html. 

Notice the last one is

PATRIOTIC...station and skill always ready for service to country and community.  

Does that not also mean to operate LEGALLY in accordance to the law of our country?
I believe it does.  It's the RIGHT thing to do.  Okay, that's my opinion.  Everyone has one.  Flame me if you want but it's correct and no one can argue it isn't.

Of course then I go on to tell them how great the Amateur Radio service is and how much fun I have in it, extolling the virtues, etc.  I actually have sparked interest in our wonderful service on more than one such occasion and may have even been responsible for *gasp* some new callsigns!  (One or Two even learned *gasp* MORSE CODE!!! )

/soapbox off

Anyway, I REALLY was enjoying the TECHNICAL discussion of the SB-220 on AM.  I hope you guys get back on that issue soon.

I for one and really tired of this whole "no code general" type of banter. Who the hell cares?  If a man is licensed, He is licensed.  He has done what is required of him by law. 

Clark

I actually tried, and the paperwork that was involved for a low power station was just insane.

Then, I asked a broadcast engineer for help in doing such (I had a community and more than a handful of people in a "small town" that had NO local station inquiring) by the name of John Bartal.  He informed me, in no uncertain terms, that as soon as I had the paperwork all done, the surveys, etc., it pretty much was a free-for-all, and the guy who could put the station up FIRST, would win... Meaning, one of the low power specialists, one of the religious broadcasters (for shortwave), etc.

So, I actually DID TRY to do just what your asking, I DID inquire to a licensed Broadcash Engineer (based out of the Santa Maria, Ca area... I was in central California at the time, and he was in charge of 2 AM stations and an FM station in the Bakersfield area), and it wasn't cost effective...

Just the cost of GETTING the license can cost more than building a 15 kilowatt station.  Period.  And, according to the ENGINEER I INQUIRED WITH, it's still no 'sure thing' for the little guy, I was told I would pretty much do the legwork for a small low powered specialist to come in and take me over.

As a reference, there are 4 or 5 licenses issued for the area I was looking in.  None of them have been worked on other than the initial surveys....  As soon as the surveys where done, the SW religious broadcasters started inquiring on the sites, and the BC stations specialing in satellite downlinks and unmanned "revenue generators" started inquiring....  Meaning, as soon as someone did the necessary work, they were sure to jump on it.

That's what I found, when trying to get a LEGITIMATE shortwave or low powered (not part 15) AM or FM radio station in operation.  I had the IDEAL location, 6500 feet ASL, with 100 watts, I had good reports from 200 miles north of Bakersfield to Disneyland!

Anyway, I'll answer more questions on the SB220.....  Otherwise, it's a pissing contests, and I'm perfectly comfortable with the size of my external dangler, thank you.


--Shane

bc radio is not glamourous at all. Once you get into radio for money, you become a prisoner of the business end of things. You wind up not doing what you love but becoming part of the commercial radio
culture.

When the dollar enters, the fun leaves. it becomes just another job. You're forced to conform or you wont last long. Forever a slave to ratings and $$$$$.

this is the only kind of bc radio thats fun, where it's so small the $$$ dont take over.

http://www.americanprofile.com/spotlights/article/1887.html

ok, back to the sb 220....

How about your internal dangler?


As far as the SB-220, as W2JBL has proven, the amp can be used successfully on AM. He's shown this in decades of use. And yea, he's been known to make a few old buzzard transmissions. So go ahead and put that SB-220 on and pin our S-meters!

I know it has been a while since anyone has posted on this thread, but I thought I might share a couple of things you can workover on the SB-220 to improve it's performance. One area most needing attention is the power supply tank circuit. I have increased mine from around 20mfd @ 3kv to around 55mfd @ 3kv by replacing the caps with 470mfd/450volt 30x55mm long life Panasonics with the original hardware, and using 100k-ohm Dale/Vishay 10 watt resistors replacing the 30k/7w originals. It makes the HV stiffer, and runs cooler with the bleeders load reduced.

The second area of attention was the parasitic suppressors on the 3-500z's. Using true ceramic composite resistors @ 47ohm/4.5w rated at well over 4Kv continuous stab voltage, (expensive and large....13 bucks each and 1/2" in diameter) and using them as formers for 100nH coils made with 12 guage solid copper. (2 turns 24mm round x 12mm wide) It's self-resonant frequency was around 500+ Mhz so it worked well even in the 10 meter band. The ceramic composite resistors are truly non-inductive and one of the best replacements for carbon composite. Also, removing the floating grids and firmly grounding them as Eimac suggests, removes much of the resonant problems from using the "super-cathode" driven design proposed by Collin's engineers, and adopted by Heath in this design.

Lastly, and most importantly, was the fan. Building from a fairly good design to start with, I did not go with Harbaugh's replacement, (since the motor in mine was just fine) I chose instead to replace the nylon fan blade (250~275 cfm @ 3000rpm original) with a nylon one from Grainger which was rated at 450cfm @ 3000 rpm. I then did some research on the way in which the fan was placed inside the amp, and it's open blade design. By utilizing a fan shroud, 30mm in width around the circumference of the opening including the bottom opening, it increased the overall performance by more than about 20%. (that doesn't include the increased cfm from using a higher cfm blade) Using a shroud over open blade design is a significant improvement. I used 16 guage aluminum, 30mm wide from the hardware store and formed it to the current opening inside the RF deck area, and made a separate section for under the chassis to completly shroud the fan blade itself.  I used the current screws holding the rf deck separator to attach these items to the chassis itself. It does a great job of now pulling air in from the transformer/capacitor area as well, aiding in the cooling of these components.

You can get a glimps of this rebuild over at http://www.k5dbx.com (http://www.k5dbx.com)  

I like the look of that Anniversary Series.

Very kind of you Steve...

Old amps should never die, they should be rebuilt and placed back into service....

VERY Beautiful!

I use an SB220 (not stock, either) on AM, and like it.  I've recently started using a bigger amp, but still love the SB220.

I'm interested in a couple things...  What is the drive level required now, and what is the PEP output...

Also, can you point me to the Eimac publication that talks about directly grounding grids?  I'm a FIRM believer in it myself, but have never run across it from Eimac...  I took it from Bill Orr talking about reducing drive requirements by directly grounding them....  To me it was a bonus the amplifier becoming more stable!


Thanks, in advance....  VERY beautiful construction.  Nice amplifier!


--Shane

It was Eimac who recommended the Heathkit method. Rumor has it they changed their mind but Ive been unable to find an official release. And Heath used it for 26 years; its pretty hard to argue with success of around 60K amps.

Carl
KM1H

Now there's a definitive test procedure!

Ya see Chris, ya did it all wrong. You probably used a spectrum analyzer and other lab equipment.... dummy!

There's 2900 members on the Forum now....wholly smokes...

Way Kool :)

73

Jack.

I wish to He!! I hadn't sold my SB 220 to someone who I considered a "friend."  I gave him a good price 'cause he expressed an interest in it during my last move.  He then proceeded to sell it to someone at a higher cost and my precious SB 220 is gone forever.  NEVER AGAIN!

That P&M said -- I still have my EFJ Courier and it's doing a FB job on AM with my Flex.

Al

Clark says "Tune the amp at low power input on the tune postion. Then when its tuned, go to high power and increase drive.."

I have always heard that this is not the proper way to tune.  I was schooled that the amp should be tuned at max power then loaded a touch more, then reduce the drive to the operating level you want.  Maybe you mean to get a "rough" tune at low power than fine tune at max?  This method is supposed to get the best linear peaks.

John KX5JT

KM1H, actually it was a the folks at Collins who started to promote the "super-cathode" driven grids. Initially introduced with attempts to tame the 30-L1, engineers at Collins were the ones who prompted those at Heath to use it. Eimac's technical documentation on their design specs for the 3-500z is here.. http://www.umich.edu/~umarc/station/docs/3-500z.pdf (http://www.umich.edu/~umarc/station/docs/3-500z.pdf)

KD6VXI, Shane, thanks for the kind words about the project! When I initially started the rebuild of this project, I began at the drawing board to think about what to do. There is ample documentation and engineering on using low, medium and high Mu triodes. I went back to Eimac’s engineering, and looked at various homebrews in the ARRL archives using various builds using triodes. I know there is a lot of controversy and sides to be drawn in this arena. I worked at Altec-Lansing throughout the 80’s and have years of experience with triodes in the AF range in class A and A/B designs, and know some of the shortcomings. Eimac’s documentation certainly shows that you should firmly ground the grids. When you begin to float the valve, and especially the grids, you have made yourself a "tuned-plate/tuned-grid" oscillator. That’s how you use a low Mu triode designed as an oscillator. That’s why this design can end up making you do all kinds of various voo-doo tricks to keep it from oscillating, when it should have started with the most elegant design, the “grounded grid.”

Working at Altec taught me some very important lessons when it comes to IMD/THD in triode amps. You could take the same parts and give them to the line, and watch the results. More times than not, if the circuit is of a solid design, poor IMD/THD was poor build quality. We know most "splatter" is from either over modulation, or simply running the PS tank circuit out of gas, not from the -40db ~ -50db 3rd and 5th order IMD which is where the 3-500z specs fall. (which is actually better than most transceivers)

To your question of power and drive, it will easily develop 1Kw @ 2.5kv with 100 watts of drive in key down CW, and around 1.35Kw @ 3.1kv at that same level of CW. I have seen on PEP peaks a little over 1.5Kw, but that was without ALC and peaks from the exciter @ 115w out.
 

You are correct John. The plate tuning can be set pretty close to where it needs to be at a lower power, but the load MUST be set at the peak power level you plan to run - at least for best linearity.

Not to belabor a point, but where did this originate?  I have been fooling with amplifiers for years and never have read it anywhere.  I have a series of technical articles from Eimac and have never read it there either.  What gives, can someone tell me who proposed this, does it work and the theory behind it with proper sources.  What effect does adding more loading have on linearity? 

From what I was taught, the tune cap, coil and load cap are for impedance matching and if you add capacitance to the load side you are just changing the matching impedance which does nothing for linearity.

That "friend" thing has happened to me also. Guys like that are pretty low. Thing is, they do not see anything wrong with it.

As for SB-220 on AM, I'd keep it much lower like 150W but then I tend to run things as in CCS mode because they last much longer. I never run my NCL-2000 over 100W carrier for any length of time.

Cooling is the key. Almost every ham-type amp at any power level sufers from inadequate cooling. It's driven by people demanding quiet operation.

That said, enough cooling air can make the difference. I did some experiments with the NCL-2000 at 200W carrier where I set the amp on the top of a bud rack that had a 300CFM rackmount dual squirrel cage blower inside. The amp fit well onto the top opening with the rack's access door opened and although it was noisy, everything in the amp ran only slightly warm to the touch for >1hour including the power transformer and the finals.

At least one person told me that too much air will just blow past the object to be cooled and not pick up any heat, but that was not true in this case. The 8122's might be a special case since the airflow is forced against the convoluted fins by turbulence but that does not explain the transformer's coolness. Maybe the wire was warm, but there is no doubt the core was kept very cool and that has to count for a lot. the NCL-2000 design accidentally lends itself to this technique having many perforated holes and for whatever reason lots of airflow space around the transformer.

I got to think that if the SB-220 (a hackable/non-collectible specimen?) were treated to some mods where 300CFM was forced through it from underneath, it could run reliably at high power for as long as you wished. It would be interesting to get a same-size cabinet, install a bower in it, put it under the SB-220, and push 300CFM up through the amp.

To me the most objectionable blower noise comes from the motor, then the intake, then after that, any "hissing" sound due to restrictions in the airflow.

OpCom, I agree with you concerning the SB220 cooling design. This was one area I chose to make mods that were fairly easy, yet overlooked by many. By replacing the fan blade with the highest CFM pitch design I could find, and shrouding it, made a tremendous difference. Airflow was much more directive, and the chassis design lent itself, once this was done, to draw considerably more air through the transformer side. Noise levels really didn't increase that much either. Certainly a squirrel cage design could deliver more airflow, it would lack the ability to draw air from the right side of the cabinet around the transformer/capacitor area.

Now, where was that plasma cutter I left over here next to the cabinet?! :o

Actually Collins had no involvement in the 3-500Z or the SB-220, that came directly from Eimac and the chokes were used by several amp manufacturers.  The Collins 30L1 had an obvious influence in the SB-200; different amp several years apart.

That 1980 3-500Z spec sheet has little in common with the original 1968 release which had several different specs and was quite a different tube. That resulted in the 1969 Eimac ads promoting the 3-500Z in the SB-220, Henry, and Swan amps.

Carl
KM1H

Been around since the 20's or 30's. This was standard tuning procedure for linears and grid-modulated rigs.

Carl, I think you may be confusing what is being said here. The Collins 30-S1 (which is a tetrode amp) used a floating grid, which is a proper application of this design, since there was zero grid control current. This idea carried over to the 30-L1, and was copied by Heath, as well as other manufacturers. I never said Collins designed the 3-500z or the SB220. I said the idea to float the grids came from Collins engineering. There was an Eimac engineer some years later (late 70's early 80's who was writing for some publications) who was promoting this design concept from the 30-L1, however, it is a bad idea. From an engineering viewpoint, why would you place a triode in a configuration of an oscillator when you don't want it to oscillate? I prefer mine "grounded grid." You can roll your own any way you want. It doesn't matter whether you look at Eimac's 1968 (graphite) or the 1980 3-500z triode specs, "grounded grid" has always meant "grounded grid."

From the 1968 specs..."Operation with zero grid bias simplifies associated circuitry by eliminating the bias supply. In addition, "grounded-grid" operation is attractive since power gain as high as twenty times can be obtained with the 3-500Z in a cathode-driven circuit." (which is what the SB-220 is) In the 1980 revision, they include a "Typical Cathode Driven (grounded-grid) Amplfier Circuit for use with 2 3-500Z Tubes." Please note grids are grounded, not floated.

I don't see any modern amplifier manufacturers adhering to this "good old days" procedure. Flipping through about 6 different amplifier manuals, most just say, set drive level of the exciter to some "X' value of initial plate current or some initial grid current, and then quickly adjust Tune and Load or Plate and Load controls for maximum RF output using either an on-board RF output indicator or an inline RF output indicator. None mention any last touch up of the Load control. As Jim points out, I don't see where changing the matching impedance with the Load control, beyond maximum RF output, does anything for linearity. Maybe it's a function of the type of RF output network you have between the final tube(s) and the antenna.

Actually the main point in my comment was to tune with max power.  The adding just a touch more on the loading comes from what I've heard from others.  But the using as much drive as the amp takes as a max when "dipping the plate current" is supposed to help to give the best linear peaks. 

Where did I hear this?  I heard this from other hams on the air.  In fact after hearing it I took notice that if I use my rice box (TS-570) at 100 watts CW to tune the Henry 2K4, then switch over to my DX-60 (which in CW will only put out 60 watts) I do typically see better peaks, about 1KW instead of 800W from the DX-60 on AM.  If I use the DX-60 in CW position I get about 800W and a more flat topped peak on AM.

So it does seem to work i my case.  I add just a scoatch more loading because I've heard doing that helps.  I can't really say I see that on the scope, but I only add enough to sacrifice maybe 10 watts peak.

John KX5JT

Evening Pete... found this on page 13 of a TL-922 operating manual...

Ott

I'm no wizard by any stretch so I'll chime in  ;D  First let us establish a few things.  We're talking about grounded grid, triode, cathode driven linear amplifiers right?  "Increase the loading":  We all understand we're talking about reducing the value of the load capacitor, correct?  There is confusion over this (in some parts; not here I expect) because a lot of amps have the load cap front panel numbers going  up clockwise, and internally a clockwise rotation of the cap shaft reduces the load cap's capacitance.  But, other amps have it right (in my opinion); you turn the big knob to a higher number and the capacitance goes up.  But not everyone knows or understands this, so "increase the loading" comes from "turn the knob to a higher number" but the guy with the oddball amp where that increases the capacitance is thinking, "huh?"   Or you can sort of think of it as increasing the participation of the actual load i.e. the feedline and antenna, doing more with the pi network inductor's stored energy and tangoing less with the load capacitor.    Okay, anyway now that we are past that, why reduce the load cap value?
It increases the average plate current, i.e. the output tank circuit is slightly off resonance but grid current is lowered (which is good) and (I'm pretty dim on this part) internal output tank circuit voltages are lowered slightly (this is good) but more important, with less loading, on peak envelope crests, you have reduced the possibility of breaking into non-linearity.

I'm still trying to figure some of this stuff out so please direct questions to a real expert hi hi  (many are on this board).

Rob

You can see it first hand at your station with a good scope.
Tune up with a tone (I use 1kHz) at 100% in the "low power" position. Then go to High power and you'll find the load needs tweeked. WHY?

Most hi/lo switched on amps cause an increase in plate voltage. You've just changed the plate impedence!

When you modulate you change the voltage and current. Peak values present a different impedence than nominal.

So yes, it's all about impedence.

Im not confused and Im fully aware of the timelines of Collins equipment. However the Super Cathode design concept preceeded the 30S1 with Bill Orr and others publishing about it.

The 30L1 grid bypasses came about in an attempt to tame four 30's design 811A's where it worked to some degree in a zero bias amp. In the SB-200 the idea was borrowed for tubes that required an operating and cut-off bias. While it works the amp is not fully neutralized on 15M and above.

Most engineers and some hams are fully aware of the SB-220 and other amps controversy over grid chokes that has been going on for decades. Two of the main protagonists have been at it for decades in forums and web pages. However the chokes in the SB-220 are not the source of instability as they simply act as 25 Ohm resistors at 80-10M and you are left with a resistive loaded capacitive divider that reduces tube gain a bit and promotes stability. The problem is that Heath initially copied the 200pf from the SB-200 and it took until late SB-221 and then the HL-2200 before they realized the error and reduced the values.  The true primary causes of SB-220 series instability is out of tolerance 47 Ohm suppressor resistors and the VHF choke, RFC-2 which just happens to be resonant in the range of the 3-500 parasitic. Replace the parasitic resistors and use a nichrome 10-20 Ohm real wire wound resistor (which does double duty as a HV surge current limiter) in place of RFC-2. No voodo science involved. The whole process can be observed with a GDO and spectrum analyzer and then the cure is simple. The oft arcing bandswitch and Tune cap is a tank circuit design flaw, parasitics are not involved.

The 3-500Z amps with directly grounded grids are no more stable than proper floaters. The AL-82 is a prime example of an IED when it lets loose. The AL-80 family is close behind. The B&W/Viewstar PT-2500 series also had IED problems at first.

Eimac reversed themselves in the late 70's simply because the now legal 1500W 160M rule complicated the design with 160-10M amps and they didnt want to get involved. The fact that they warranteed failed 3-500Z's in Heath and other floating grid amps pretty much says it all.

Carl
KM1H

My take on that TL-922 SSB tuning procedure is that, as you tune the amplifier's Plate and Load controls for maximum RF output, the "last" or "final" adjustment should be made only with Plate control. This is different then the earlier poster's description of dip the plate", increase loading, dip the plate, increase loading, until to get to the specified operating plate current recommended by the manufacturer and then as a final adjustment, increase loading just a hair or two.
If you go to the preceding page on the TL-922 manual, you'll should notice that for the CW tuning procedure, they use the dip the plate, increase loading procedure, and then no final "increase the loading just a hair".

Here's a web site I've visited many times.  Interesting guy.  Here's his version tuning up a linear amp.

http://www.w8ji.com/loading_amplifier.htm

This is the method I agree mostly with.  I like the idea of using a pulsing circuit to minimize overloading stuff tho'.

Drill up to his home page for some drool pictures of antennas and his workshop

Al

This is really good information here too:  http://www.cpii.com/library.cfm/9

Rob

That is what I was speaking about Buddly.  Changing the tune and load controls simply changes the impedance between the final and load.  If you tune for max power, you tune for max power plus matching the plate impedance to the load impedance and should you want to "Load lightly" then you can set the load control either side of peak power and accomplish the same thing.  Change the impedance and less power will be transferred resulting in less current in the plate and grid.  You simply have one impeadance at the load undercoupled and less power then the same thing but with a different impedance overcoupled.

Changing the plate voltage does affect the plate impedance but if you use lower plate voltage to tune then you should retune after changing the plate voltage (or for that matter the current) in any case.  Who was it, Pete that said the last adjustment should be the plate control for final dip, which is correct.  Most high power amplifiers have recommended settings for tuning or at least should.  Nothing I have ever built or used has a high/low siwtch.  I always just start with low drive and work up, but one thing for sure is if you aremismatched at the load, you will have heating in the final tank circuit, so I am not going to do that.

If there are any mistakes or mispellings in my answer it is because the dam reply panel keeps flopping up and down making proof reading impossible.  What is wrong with this thing?

Carl,

At least your logic is moving closer to exactly what I said in my first post. Like I said, I prefer to keep my triode in grounded-grid configuration, and I really don't need NiCr wire, 12 guage solid copper works just fine. When you begin to float the grids with a modest 50pf, a GDO and a SA will show you that the grid resonance at low VHF range increases from about -50db~-40db with grounded grid to close to 0db to +10db floated, and the farther up the band you move, the worse it gets. Add more capacitance, exacerbates it further (you are now creating a triode in a oscillator configuration) For the life of me, I cannot understand this die hard need to rationalize poor engineering practices, unless of course you DO want your triode to be an oscillator.

I would question however, the "double duty" assumption that using NiCr wire somehow provides protection to a catastrophic failure of a valve. I have seen numerous catastrophic failures of tube amplifiers for decades, and I can attest to one thing, using NiCr wire on the anode won't save anything if the anode goes to grid or cathode. At Altec, we saw hundreds of triode based amps come in for service after running 24/7 for decades. When a valve fails, NiCr wire will not respond fast enough to go open circuit, or provide enough "surge current limiting" to do a thing. All you have done is reduce available current to the anode for regular service, and provided a false sense of insurance.

I think it is your browser.  I had that happen to me on some PC I was using with Internet Explorer I think (but might have been something else) and there is something about the form for posting that made it go crazy.

I wonder if "tune for maximum power output" is what manufacturers tell folks now mainly because it is a no-brainer for consumer product hams.  The amp I have from Ten Tec even has a LED output voltage driven watt bar to make tuneup even easier.  All they have to tell people is tune for the maximum reading on the LED watt bar.

To be fair, it is also the case that with a class AB linear amp, the plate current dip is not as pronounced as it is with a class C PA in a plate modulated AM rig.  The Ip meter measures average Ip.   At resonance of the tank, in class C with the tube is conducting for a small part of each cycle the average Ip dips noticeably.  With class AB the conduction is much more of the cycle so there is not as much noticeable dip when the tank is matched the anode to the load.   So the dip and load instructions are harder for people to follow, and making things worse are newer amps that include 160 m. which seems to force some tank circuit compromises to get from 1.8 to 30 MHz.  

Manufacturers could get into what I just got into, but probably find it easier to tell people to just tune for max suds and design the RF deck so if you don't overdrive the amp you can do that and be linear.  

But, if you want to be kind to ur amp   :D you can also drop the load cap value a tad.

Rob

Hey Rob!

You know, over on YouTube Ameritron did a couple tune-up videos....

http://www.youtube.com/watch?v=OT1UaCrVvd4 (http://www.youtube.com/watch?v=OT1UaCrVvd4)

Rob it is probably my browser, but I am not sure so I can't say.  All I know is the board design parameters should be for compatibility with anything.  But that aside.

Tune for max is matching the tube plate impedance to the load impedance.  If you tune for a mismatch on the load side you have higher circulating current in the tank circuit.  I have seem many B&W 850 tank coils that are melted because of this kind of thing.  A pair of 4-1000s in parallel with 6 kv on the plate with as much current as the pole pig would develop into something that either was mismatched or broken.  That caused the coil supports to melt, I don't care who designed it or what frequency of operation.  Push the knot to the end of the rope and it disappears like parts in high power amplifiers.

You seriously insist on missing the point of the reasoning behind the floating grids. I really havent noticed your logic as it doesnt seem to follow any pattern. They do work when the proper values are used and the classic 2 tone static IMD test shows about a 2-3dB IMD improvement over direct grounding.

You also totally missed my point of insisting on using a real wire wound resistor. I said nothing about using nichrome as part of the anode circuit wiring. The proper use of a HV surge resistor is to limit fault current to a safe value until a fuse or other safety device trips. It is also supposed to survive. Since internal gas arcs are a lot more common than a grid falling into a plate it works rather well, Ive yet to see one blown open and many tubes have survived. Ive worked around, designed as a job, and repaired amps for all applications (not just ham) for close to 50 years and can say Ive about seen all possible failure modes.
A classic enameled wire wound fits the requirement, a cement resistor does not.

Complaining about the small voltage drop in normal operation is ludicrous at ham power levels.

Carl

Carl,

Believe me, I know how to use triodes as an oscillator. To try to squeeze 2db~3db improvement in IMD at the 3rd or 5th order region, when it is already -40db~-50db below the primary two-tone, in my opinion, doesn't justify elevating the grid resonance in the VHF range from -40db~-50db to 0db~+10db or more, and creating for yourself the issue of oscillation. +/-2db variance can be seen in assembly or wire routing or shielding. You more than likely, (with most common transceivers today) will be introducing IMD at the -30db 3rd order region from the exciter. For the medium Mu 3-500z, I'll leave the grids grounded.

I did however, misunderstand you when I thought you were advocating the use of NiCr wire as the anode lead material. I do understand you in using a current limiting resistor in the anode path, but if you want a protection circuit, I would prefer using an active HV crowbar circuit. Back in the 90's when AG6K wrote his article about the SB-220 in QST, there were engineers who spoke directly to this issue about using current limiting resistors in the anode path in their rebuttal to the article. From the Sept. 1994 issue of QST; "The addition of a 10 ohm resistor may only offer a negligible improvement in most circuits. (which I agree with) It is alarming to note (the article which proposes this method) recommends a resistor rated at 10 watts 500v. Any device rated at 500v is subject to several thousand volts. The manufacturer of such resistors absolutely do not endorse the use of this type of resistor in this application. The correct component would be an energy absorbing type of resistor such as the Carborundum SP type, or RDC PCN type. The PCN series resistor for this type of application should be rated at 80 watts or more dissipation to safely handle the stored energy of a 25uF capacitor circuit charged to 3kv."

I guess at the core, I have to ask myself, how many folks do you hear complaining about how horrible the IMD is on 3-500z based linears in a grounded grid configuration, and then ask, why do so many folks seem to have to address the issue of VHF stability in those amps who utilize a floating grid. I would prefer the most stable platform, especially when it's IMD is equal to or well below the exciter I'm driving it with.

I dont know where you are coming up with those resonance # as there isnt any reference mentioned.

The actual (high Mu as defined by Eimac) 3-500Z IMD 3rd in a SB-220 as biased is in the mid 30's at best and that is PEP. Adding another 2-3dB on a quiet band is certainly noticable. While this is better than many rice box rigs it falls far short of the Class A exciter options as well as the -40dB and better 6146 rigs of the past. If you really want excellent IMD, run zero bias in the CW position and stuff 560-680uF caps in the PS. Then you can use it as an IPA for a real tube.

With my primary SB-220 interest being 6M conversions, of which Ive done over 250 since the early 70's, Ive gone for stability and SSB signal quality. Customer feedback indicates long term stability with any brand of tube and the grid chokes doing their part during a gas arc. The FB also refutes any claim that the stability falls as the frequency goes up. In fact the amp works quite well on the European 4M band.

Since directly grounding the grids raises the gain it then holds that instability potential increases.  There is no benefit to be gained by trying for another 100W out other than stressing an already marginal PS and tank circuit in a stock amp. Many hams have reported going back to the chokes and later value caps after experiencing switch arcing. Adding a resistor to the input also works.

IMO it is a waste of time to modify a SB-220 grid circuit except for changing to 115pf caps (standard value 110 and 120pf also work). Instead concentrate on new suppressors and adding the surge resistor. Adding one little 10pf 1kv SM cap across the 40-20M switch lugs will act as a snubber to prevent contact arcing.

I could go on about tweaking the suppressor design to reduce heating but thats a whole different subject.

HV surge resistors have been around for many decades before the QST wars. RCA even included them in spec sheets of the 50's. The earliest ham amp use that Im aware of is in the 1963 National NCL-2000 of which I was on the design team as a fresh out of the Navy ET.

Carl

 

Carl,

There are a couple of sites out there that have mirrored what I have seen with my own testing of grid resonance...however my results are from the SB-221 w/Johnson socket.

http://www.w8ji.com/grid_resonance.htm (http://www.w8ji.com/grid_resonance.htm)

The SB-220 is a fine candidate for use in 6 meter operation. I've seen many at full legal limit. As far as a current limiting resistor in the HV path for catastrophic failure, my point was not unlike Tom Rauch's point, it's negligable, and won't help you in the least if the valve fails. And recommending or using a device not intended for the voltages incurred in the HV path is not good engineering. I prefer other methods to protect the HV area.

Rauch is one of the last people Id use as a reference. Your statements above confirm that you really arent that knowledgable about the subjects.

Im thru wasting my time.

Carl,

I wish you well then...have a great day. If you have a beef with Rauch that's your own issue. However, that doesn't address the issue to which I was speaking, nor does it justify poor engineering practices. I can only assume if you can't argue with results of the sweep, you need to discredit the source and dismiss it since it doesn't serve your agenda. Oh well. And BTW, Tom Sowden, (W6KAN) stated, "Warren Amfahr (W0WL), a top Collins engineer when the HK SB-220 was being designed, told me in a phone conversation that the "feedback" idea was originally driven by Mr. Collins. He felt the IMD products of the Eimac tubes were not low enough to meet Collin's standards and therefore he had his engineers draw up a feedback circuit that was later borrowed by Heathkit."

On the SB-221 I own, it's 3rd order IMD in a grounded-grid configuration is at worst -38db, and 5th order -46db on 2 tone in the 75 meter band. Move the bias current greater than 200mA and those numbers begin to vary. It's spectral 2nd harmonic is better than -50db and 3rd harmonic better than -68db. +/-2db of IMD at those levels won't be perceptable to the ear.

I said it before, and will again...I will stick with my grids firmly attached to ground and you can roll your own any way you wish...good luck...