The AM Forum

I am looking to buy a tube type linear amp to be used on AM, 500 watts or so, recommendations?

500W carrier or PEP?  500W carrier is over the legal limit when modulated.

I use a AL-80B (single 3-500ZG).  Good for about 800W PEP, 200W carrier. (1KW SSB)  An amp that would do AM legal limit from Ameritron is over twice the price of the AL-80B

A pair of 3-500z's with a robust power supply will do 300 watts I think, at the limit, for 500 watts, you need a BIG amp I think.

I thought the rule of thumb was 4x the carrier power for plate disapation, you would need tube/tubes with 2000 watts of plate disapation and a heavy power supply.

Brett
N2DTS

Burt,

 As I understand you to be a pretty thorough Fellow just from on here, you've left the Field pretty open on choice/Price.

 There is Alpha Amps that will do quite well for your needs but at a large sum of money an I like them alot... But.

 Ya might give these guys a Look See here they will build what you want.

http://www.qrotec.com/ an they open up here shortly.

73
Jack.

Amp Supply made an amplifier with three 3-500z's...  (1500 watts dis. !)

LK-550ZC was the version with QSK built in.  It will sustain a 500 watt
carrier all day with enough head room to make big AM.

Expect to put out better than 1000 bux if you find one.  

The unit without the QSK addition should be a bit less.

That amp has the power transformer external in a seperate case.

Drake L4B is still a nice commerical amp.

The 1960's Henry 2K 10-80M amps are built like tanks and run a pair of 3-500Z's with about 3KV. Good looking amp too.  I have one and admire the quality work inside from time to time. No comparison to the ham amps built in the  1980's and beyond. (Except for maybe the Alphas)   They even use air chimneys installed correctly ... that's rare these days vs: the common homo-fan blowing air across the tubes.

You can pick up a 2K for about $600, or so, the last I checked.  It can be modified to cover 160 meters with some work.

T

Burt,

Here is a nice amp for sale for AM. 

http://swap.qth.com/view_ad.php?counter=730855

Not necessarily 

For 500W carrier under continuous duty, the tube(s) must have at least 1500W plate dissipation, maybe 2000W.
Consider the linear amp is at worst 25% efficient at carrier level (sometimes more like 33%, but nothing is perfect)
2000W in, 1500W burns in the tube, 500W out.
Be sure the power supply can deliver 2000 watts continuously.
At peak, the amp might be only 50% efficient (it should be better like 65% but what's perfect?).
The power supply will have to therefore deliver 4000 watts at the peak of the modulation envelope.
The average DC power required at 100% modulation by a sinewave would be about 3000W.

All of it scales down for lower power levels such as the often-stated 375 watts of carrier.

For it to never blow up {famous last words / marketing babble}:
(plate dissipation)
= (4 * carrier power)
= (1.33 * carrier DC input)
= (0.5 * peak DC input)
= (1.5 * 100% modulation average DC input - the suitable power supply CCS rating)

That's why the big amp boys on there, and they know who they are, have 250LB transformers and more than one 4-1000.

The purpose of overbuilding is for proper and safe operation within the rules consistent with hopefully endless component life, not for breaking the rules. Ham brands of amps are mostly no good for legal limit AM, except the very few and costliest, then then they prescribe a "duty cycle" so the power supply does not boil. The power supply is a weak link.

If you want to know the true AM average power capacity of an amplifier, see the RTTY rating and duty cycle in the manual. That gives a good idea what the amp will do without burning up either the tube or the power supply.

The cost of replacing tubes is the most expensive periodic maintenance on an amplifier, as long as the power supply does not cook.

Find an amp with two 3-1000's or two 4-1000's, or a 3CX3000.
The amp should have a proper cooling system as called for in the tube manuals, not some cheap fan.
If the power supply can be lifted by two sissies, forget it.
If it takes three men to barely lift it, that is the PSU you want.

I really do beleive all this stuff. That is why I am working to repair an amp with a 4000V supply and a 3CX3000. I have the new rectifiers now!! It will idle and coast and keep the lab as warm as toast.

One thing also to mention - the difference, at the other end, between a 500W carrier and a 350W carrier does not translate to very much in the grand scheme. The point is to get a well designed and well built amp and know its limits.

(Note: Patrick hit the "Post" button a little quicker than I did, so we said a few of the same things)

I think Burt knows what the legal limit is. No need to tell him the obvious, he took a license exam too. That 350W number that people like to throw around is not cast in stone anywhere.

In my opinion, no brand-name linear amplifier built in the last 30 years is worth squat. When the good-buddies started putting ham amps on channel 19, the FCC put ridiculously overprotective limits on stage gain in commercially built amps. They've relaxed a bit in the last few years, but all the manufacturers are still building panty-waist grounded-grid amplifiers that only serve to humiliate the tubes you put in them.

I'd keep an eye out for a homebrew grid-driven linear built by somebody who knew what the tube(s) was/were capable of. A good pair of grid-driven 4x1s (not some whimpy triode-connected grounded-grid 4x1s) will give you a good comfortable half-kilowatt of snot with ample headroom with modest drive.

Outside that, Tom mentioned the Henry 2k, which is probably your only real choice for a suitable commercially-built amp.

You're far better off with a non-linear amp. A single 304TL with about 2000 volts modulated and 50 watts of drive will put you well over the 500W level with only about 1/4 of the power supply needed for a linear.

Whoops... I see Patrick was posting at the same time, and even did most of the math.

If a linear or grid modulated tube amplifier is set up to run 100% modulation on positive peaks, the tube should dissipate approximately twice the carrier power.

When properly set up, the efficiency is about 33% when running unmodulated carrier, or about 1/3.  That means that 2/3 the input power is dissipated as heat.  So if the amp is designed to run 500 watts carrier power out, 1000 watts will be dissipated in the plates of the tubes, for 1500 watts DC input.

When modulation is applied, the plate of the tube should run cooler.  The DC input should not vary under modulation, so at 100% modulation, you still have 1500 watts DC input, but 750 watts output (500 watts carrier power plus 250 watts sideband power).  Now, the tube is dissipating only 750 watts.  The tube runs most efficiently at the 100% positive modulation peak, about 67%, or 2/3 efficiency.

This is plate efficiency, and does not take into account tank circuit efficiency, feedline losses, losses in the tuner (if used), etc, so if the tube is running 500 watts output off the plate, you will be lucky to get 400 watts into the antenna, so the real efficiency of the amplifier will be less than what the tube charts say.

I never heard of a rule of thumb that the plate dissipation should be 4 X the carrier output power, but with tubes getting  scarcer by the day, it wouldn't hurt to run them conservatively.  Theoretically, the plate dissipation should be twice the carrier output, but again that doesn't take into account losses that occur between the plate of the tube and the antenna, so the tubes will need to be rated for substantially more than 2X the carrier output for continuous service.

A linear is just as efficient when running AM as it is when running SSB.  The difference is that the 100% duty cycle of the carrier combined with the intermittent nature (short duty cycle) of the modulation peaks makes the overall average efficiency just a little higher than the carrier efficiency, but the peak output efficiency is still the same if the pep output is equal.


 

My post was from experience with dissecting military RF amplifiers, they are built not to fail and so use about twice the tubeage as is called for. The GRC-106's amp for example uses two 4CX350's, but does only a 100W carrier and 400W PEP on AM {carrier+USB}. The RT246 uses a 100W triode to make 35 watts FM.

To use the tubes to their maximum book ratings, sure it is more like (plate dissipation) = (2 * carrier power) =(0.5 * "SSB single tone" power). That's the way storebought linears generally run.

About the plate current variations, maybe I have to go back to the books about the DC input not changing. I could swear it does change with increased drive and power output, but maybe that math was for a CW signal at comparative levels of 25% power and 100% power, and not related to the average readings taken with a modulated signal.

The Henry 2K was mentioned, and it is a fine amp -most models anyway. Even the Henry 2K fully utilizes its tubes.
Out of my own curiosity I checked through the models since it is legion.
One positive note is there was no duty cycle mentioned except on one model, and only one model actually warns against AM use.
That is a big plus.

I decided to make these notes here for Burt since he is asking.

2K, 2KD, 2KR - 2*3-400Z - 1KW input on AM/CW. No warning against continuous duty. It is tuned & loaded at 2500V/800mA (which is a slight overload of the 3B28 rectifiers due to the PIV rating-vs-average current rating), then reduced to 400mA for the 1KW input on AM. Plate transformer originally rated 2800-0-2800V, Peter Dahl replacement is 3000-0-3000@500mA CCS - that is 1500W - quite good if the Dahl iron is there! There was a note from Dahl in the posted manual that his transformer would "last longer" than the original. Unknown if this signals a problem. The 2KR does not come with a power supply. The 2KD is a desk model with remote power supply. The 2K is a floor model

2K3 - 2* 3-500Z- looks like the same deal otherwise, solid state power supply and combined plate/fil transformer. Floor console.

2K Ultra - 2KW PEP inout on SSB, 1KW CW and RTTY, AM operation "not reccommended" (If AM used, DC input reduced to 600W). "cooling system is not designed for AM..", HV=2200V@400mA Uses 2 * 8873 400W conduction cooled triodes and large heatsink operating at up to 210 deg F on rear panel. This is not really an "Ultra" amp in any respect except that the conduction cooling was considered high tech in the days. Yet it still has a fan. Fine for SSB. Tubes might be scarce or costly. Self Contained desktop unit.

Classic series:
AM is claimed, but no tuning instructions are given for it. It is not clear whether the HV is to be set to "SSB" (high) or "CW" (low) for AM. All use a pair of 3-500Z's. The manual uses the word "barefoot". Maybe this is not a CB term after all.

2K Classic - 1200W PEP output, HV=3KV, 10M band an option, average speech input power 1000 watts, Continuous duty, 125 LBs shipping weight. Floor console.

2KD Classic - 1200W PEP output, HV=3KV, 10M band an option,  average speech input power 1000 watts, Desktop version (self contained power) Intermittent Amateur service, the ugly duty cycle has arrived with a warning that the desktop amplifier can be damaged by extended.. (use). 80 LBs  shipping weight

2K Clasic X (domestic) - 1200W PEP output, HV=3KV, 10M band an option,  average speech input power 1000 watts, Continuous duty, same RF deck as export version, 140 LBs shipping weight. Floor console.

2K Classic X (export) - 1800W PEP output, HV=3.7KV, average speech input power 1500 watts, Continuous duty, Larger power supply, 160LBs shipping weight. Floor console.

There are also the 3K (3CX1500 tube) and 8K (5KW), others.. but not likely to find easily, and might not be as inexpensive to own. edebris.com has all those manuals.

So the plain 2K is a real bargain. Can it be refitted with inexpensive 3-500Z's? They are a little taller than the 3-400's IIRC. If so, I think it would be my first choice, but in the 2KD variant since the power supply is remote.

The Warrior.. Hmm. four 811's will get you some watts, but they will burn at 100W carrier and 500W PEP unless you talk fast. I'd have to say, and I hope it does not piss anyone off, four 811's are good for a 65W carrier CCS. Put 572B's in and throw a 125W carrier/500W PEP till the power supply gets warm, which would take a while - that is a well made amp.

The QRO stuff looks real good. On the HF-2000 I'd ask about duty cycle first. Still, 800W input for RTTY would do for AM, if the 100% duty is there. It would be interesting to find a way to buy the HF-2500DX Mark III export version, and just not worry about it. 2000 watts continuous output - there is your 500W carrier capability Burt!

4CX800's     .... GU74 ...has the supply situation for these Ruskie toobs gotten any better ? 

most of the guys I know with Alphas are nervous about this ..73 ...John

Patrick said:

A lot of them did and can most of the power supplies have been beefed up to 3200 VDC. I have one, (albeit in parts, different story), and it will accomodat the 3-500Z's. With a little effort, you can also modify it for 160 Meters.

Don.  The AL80 claims 65% efficiency for SSB & CW due to their "dynamic bias"  circuit.  Would older commercial or homebrew linears have this feature? (Of course this is useless for AM.)

Thanks for clearing that up. I stand corrected. :D

Well, I can't run the 500 watt carrier but my Henry 2K(X) will run 350 watt carrier all day long... Works out to 600 watts of Plate dissipation +/- and the RF deck was hooked up with a Blower that mounts in stock configuration with no altering that moves about twice the CFM of air keeping the Pins of the 3-500's cool and saving from melt down.

Seems if you wanna go bigger... Next step for me would be dependant on the size of my wallet.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=160324772175 (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=160324772175)

http://www.alpharadioproducts.com/8410.asp (http://www.alpharadioproducts.com/8410.asp)

Or.... Build something BIG.... I am sure you have already looked at all this, but I couldn't resist throwing the Commander in there.. Desktop amplifier with a pair of 8877's... Kinda interesting too see what they were using for a xmfr. in that thing since there were only a handful of them built.

Wouldn't carrier be 750 watts if PEP limit is 1500 watts, with 100% modulation, pos peak is 1500, neg peak 0W?

I tried HRO and AES, who sells it?

For AM, instaneous plate voltage doubles at 100% mod.. Thus
PEP is four times carrier.

Pete

I am using a Gonset GSB-101, four 811's, rectifiers replaced with diodes.    I run it continuously 175W carrier output on AM.   You have run the loading heavy so you get 600-8ooW PEP.    The amp is rated for this AM power, probably due to its hefty power supply.   I use new Russian 811A's.

And for the same money, you can find an SB220...  2 500Zs, a slightly bigger power supply, and it doesn't weigh much more.

Its only good for about 200 to 300 watts AM carrier, though :/


--Shane

What are you going to be driving it with? How about a plate modulated amp?
N8QPC

Assuming you're going to be driving this with your Flex 5000A, it is just a matter of how much carrier power you are looking for and how much money you want to spend.  (I'm assuming here that you don't want to volunteer for cafeteria duty again to fund this...)

I am another Ameritron AL-80B user (single 3-500ZG) and it handles up to 200 watts of carrier output during AM operation without any sweat. Typically, I run it at around 150 watts of AM carrier and it swings up to 500-600 watts PEP without complaining. I have run it at 500 watts (output) with RTTY and it has no issues with that either. The specs say it will do a kilowatt of SSB but I never push it that hard and typically see 750 - 800 watts PEP output. The simplicity of running a single big transmitting tube rather than multiple 811's or 572's was a determining factor for me when I picked up my amp. The AL80B has a very rugged power supply and one nice big transmitting tube in an easy to handle package. Another nice feature is that 160 meters is covered as well as the standard 80-10. The driving power to output power ratio is about 1:10 so 15 watts of AM drive produces roughly 150 watts of AM output. I believe it is the best bang for the buck at this time.

One other thing to consider is whether or not you are going to be feeding your new amplifier with a 240 volt line. If you are going to be running it from a 120 volt outlet, that seriously limits your choices.

73,

Rob W1AEX

No.

At 100% modulation, PEP = carrier power * 4, not 2.

Just like doubling your AC voltage cuts your I²R losses to 1/4.

Amp Supply has been gone for almost 20 years but they sold a lot of amps. The LK-800 will do the job 24/7 but even now they bring big pesos.

The Ameritron AL-1200 and AL-1500 will also rumble along and both are in production. The AL-82 is a few watts down in dissipation but also good.

Various models of the Ten Tec Titan, Dentron DTR-2000L (needs mods for reliability), B&W or Viewstar PT2500/2500A also come to mind.

In some cases you may want to either drop power down a bit or use an external fan to provide a bit of air on the xfmr.

Carl
KM1H

I thought I knew something. After all I was chief engineer at two small stations, one a 1KW AM with 13KW FM. Clearly I am way below many of you as the responses seem to have come from geniuses. Let me clarify. I would like a tube amp that would loaf at 200 watts AM. I cannot build or modify (unless it is an old broadcast transmitter). I can fix as long as I have a schematic. I am not going to buy an Alpha. They are overpriced.

I had an SB220 years ago, not going there again

I have to drive it?
No I am not that stupid.
A Flex 5000A

I do not have 220V. I thought if you had a 100w carrier, 100w of plate modulation modulates it 100% for 200W pos peak, 0 neg peak

..ain't saying a word anymore.....Excuse Us...

I didn't realize I was dealing with a genius. If you are a broadcast engineer I am surprised you don’t build your own. But who am I to question greatness.
73 N8QPC

That attitude will get you nowhere. It was you who asked us for guidance, not the other way around.

We are trying to answer your questions. You'll find there are quite a few BC engineers (current and former) on this board, several of whom are participating in this thread and trying to give you the help you're asking for.

As a BC engineer, you never needed to know that your 1kW AM's PEP output was 4kW instead of 2kW. AM broadcast stations are licensed to a specific carrier power level, not PEP. The fact that you were once a chief engineer somewhere doesn't make your assumptions any more accurate, or impress any of us.

PEP @ 100% modulation = unmodulated carrier power * 4. That's a fact, whether you choose to accept it or not.

Now that you've revised your criteria to 200W, the answer is much more simple: pretty much any amplifier on the market can do that. You've found a reason to scoff at just about every linear suggested, so at this point I'd say you're on your own, pal. Just pick one and run it.

One last piece of advice: next time you ask for help, try to avoid getting all indignant because people are trying to help you.

Toodles.

--Thom
Kilowatt Amplifier One Zero Grid Current
p.s. You're welcome.

     




     Geez, shades of Johnie, W3EGC who is still in the cucunest...

I am NOT the genius, the respondents are

Whoa, whoa. I appreciate the help. I was not being sarcastic, most of you are far smarter than I, FAR smarter. I highly respect the answers. They have been VERY educational. How is it that you and others misinterpeted what I meant? I lean to the AL-80 AS RECOMMENDED. The reason I came to this forum is I suspected I would get help, but the respondents EXCEEDED my expectations

The written word is far inferior to spoken language and without the inflections, intonations, emphasis and de-emphasis it can be grossly misunderstood.  Nevertheless, I understood your humble attitude as just such probably because I feel humbled by the vast knowledge here as well.  I certainly and thoughoughly enjoy this thread and others that are so very educational.  I made a simple suggestion on an old Heathkit Warrior amplifier that claimed to be able to do 400 watts AM carrier (which I believe to be somewhere in the area of legal limit) more to find out what others thought about it too.  It certainly comes from the era before all the limitations were imposed upon amp makers because of the 11 meter chaos.  Its price seemed reasonable too.  Of course now that I know you are wanting to match it up with a Flex-5000 I understand your need for complete coverage of all the bands and maybe the money isn't that much of an issue.  (One day I hope that to be my case!)

At anyrate, I always enjoy your videos Burt and whenever you do obtain whichever amplifier you choose, I look forward to another youtube video highlighting the Flex-5000 with it on AM.

 8)  This is Kay Ecks Five Jay Tee

warrior cant do 400 watt carrier - maybe 175 with 572's. But it's a good low cost am amp. Unless you're dealing with modern crap like hypersil transformers, weight = scrotefulness.  I would not mind getting one myself

the Commanche would be pretty killin on am with more cooling i would think, but I dont know much about them. almost made of unobtainium.

The one I did see was MASSIVE in both size and weight. some fester many many years ago. I do remember thinking how scroteless a SB 220 looked compared to it.


http://www.heathkit-museum.com/ham/hvmkl-1.shtml (http://www.heathkit-museum.com/ham/hvmkl-1.shtml)

One would have to know the person that placed the ad to understand its meaning Derb.

yeh. true. I would not make good ad writer using words like " THE DERB 1000" - On AM IT'S SCROTEFUL!!!!!!!!!

they'd be like, WTF??!!!!  ??? :P


it occurs to me I have not a clue what you meant Jim. Excuse me, I've been rather rough as of late.  :P

----and I'm tripping on my 10 pm pills at the moment, which also does not help.  :-[

Derb,

I have a Chippewa (KL-1) and it does make the SB-220 look pretty wimpy by comparison.  I have run mine at 300 watts carrier on AM and it does that with no problem and could probably do a bit more but it would be pushing the finals pretty hard.  The only major problem with the Chippewa is having the plate current meter sitting at full plate voltage above ground.  I can easily imagine drawing an arc from the pointer to your finger (and no, I don't touch this meter while power is applied).  It also has a noisy blower but it does provide plenty of cooling to keep the 4-400's happy. 

Mine came with a homebrew version of the power supply which tips the scales at just over 140 pounds.  The original owner's son-in-law was the body shop manager at a Lexus dealership and he had the HP instrument case which contains the power supply painted and baked to exactly match the amp itself. 

Rodger WQ9E

you mean the pointer set screw is at full B+ or the whole meter? I believe I'd be putting some lexan over that zero set.  ;D

Well,
The set screw is theoretically insulated but again I keep my distance from it.  I seldom use this amp when visitors are in the shack just to make sure someone doesn't get fried. 

My Hallicrafters HT-19 (NBFM and CW rig) brings the plate (~1,800 volt) and screen supplies out to pairs of binding posts on the rear panel (for hookup to an external modulator).  When I got it these had no protective cover and no indication of how a cover could be installed so I made a Plexiglas cover for it.  The cosmetically matched SX-42 receiver has a cover to avoid shocks from the high impedance audio output.  I guess the assumption was the SX-42 was a consumer product but only hams would buy the HT-19 and should know not to touch the binding posts.  I don't believe the HT-19 went into full production as the manual sheets I got with it were stamped PRELIMINARY and every manual copy I have seen for it has the same stamp.  Mine came from a silent key estate-it might have been the root cause for the estate sale.

Rodger WQ9E

well, yeah. It killed everyone that bought one. Sure way to hold down those sales. whutta deathtrap. ::)

Finally got around to reading this thread.  Been way too busy trashin' and addin' to others.  ;D

Derb, Roger,  that Chippewa is one neat beast!  The Indian series has to be the all time greatest design. The Chippewa is the pinnacle. Rates right up there with Art Deco stuff in the '20's as far as looks.  Chromed knobs and all that stuff is way to costly for commercial rigs these days.

Roger, really nice P.Supply painted to match. Derb, I'm Curious, what did the original supply use to regulate the screen voltage on the 4-100's in linear service, a string of VR tubes?
If so, I guess they're hidden under the covers in the pix you sent.  Rog, VR tubes in yours?

Ralphie, every time I see your icon pix, I get a chuckle.  Were that I so kuhl as a JN, heh, heh.

burt i would definately look for one of the old henry consoles.  My amp of choice with my flex 1000 is a henry 2k classic x.  It is the export model.  the specs published a little earlier are what henry claimed but what i observe is 4.1 kv on the plates and under full load 2kw cw dead key the voltage only drops to about 3.9 kv  It truly loafs at 200 watts at 500 carrier i have had the hammer down with about  120% mod and the tubes didnt overheat or change color.  I also have a 5k and recently sold an 8k..  the was just too much and i was offered about 1100 more than they were new and a lot more than  i paid for it.   originally about a $9500 amp.  It would loaf at 1k of carrier.  the only warning i will give about the henrys is that they are louuuuuuuuuuuuud...  fan sounds like i jet turbin with the afterburners on.  the 5k and 8k are coll becuase the have a remote controll pannel that can be used on the end of a 100 ft cord.  My 5k is in the basement and the shack is on the 3rd floor.  oh and one thing about the floor consoles unlike the modern amps these amps have a hv filter choke that is about 3/4 the weight of the main transformer.  in my opinion these were the last of the real amps.

Rick,

Heath put the VR tubes in the RF deck portion, 4 0C-3's and 2 0D-3's.  The external supply provides 3,000 volts and all other voltages are either created or derived in the RF deck.  The power supply I got with mine is a fairly close copy of the original KS-1 and installs using the same plug-in connectors.  The builder used a heftier plate transformer controlled through a 240V Variac and it provides up to 4,000 volts DC.  The rectifier is a solid state bridge feeding a hefty choke and filtering is via a 20 uf oil filled cap.  He also included a plug in control box so that the supply could be used with other amplifiers or transmitters.  The builder/owner did a very nice job and he became a Silent Key a couple of years ago.

The Apache/Mohawk/Chippewa are on the bottom row and the power supply is just out of frame to the right, one of the PS handles is visible.  On the third shelf is probably Heath's lowest power linear, the HA-20, which is the matching 6 meter amp for the HX-30 SSB transmitter.  It only weighs 30 pounds and uses a pair of 6146's to produce 70 watts PEP output.

Rodger WQ9E

Out of curiousity:

How's does the old Hallicrafters HT-33 (with the 4CX PAs)
handle itself on AM duty?  I have one torn down for
restoration... 

Pete

I forgot to mention...The AL-80B is very quiet IMHO.  The 12V Icom supply for the Pro II actually make more noise then the AL-80B.

One has to be cautious and careful about the old Henry 2K series amplifiers.

A few things to look out for - none of which can not be overcome, but will require some effort to get right. I own two of the vintage units - a 2KD-3 and a 2K-3 (floor console)

- the power transformers can fry ( the one in the KD desktop unit is fried)
- there is no separate filament transformer in either, so you can't just throw in a random HV xfmr and go
- the TR switch is a relay that probably isn't really up to the task long term, ought to be replaced with something better
- it's not QSK, if you need QSK ur looking at one of those nice DIY PCBs for amplifier control as a retrofit
- the FRONT PANEL METERS - if they are the "heart" shaped ones are almost unobtainium (about $80 a pop if you can find them) are known to be blown for the Plate meter often. Since the are surface mounting you can't just throw in a random meter, you need surface mounting (stupid design, imho)
- the SWR adjust pot and switch is prone to failure (if it has been used a lot)
- the resistor at the end of the B+ supply is known to fail
- the "ballast" resistors on the B+ supply (big ceramic resistors) are known to crack, sizzle and fry (they get hot)
- the RF deck is designed for 3-400z tubes, if you try to use 4-400 or 3-500 you have to find shorty plate caps (or make 'em) and/or lower the sockets in the "well" as far as you can go (about 3/8") to find clearance
- imho the entire deck is max'd out at 3kv, if the B+ gets up there things tend to arc to ground a whole bunch (you may get different results than I did) stock B+ is 2.8kv and it will run forever at that voltage
- the tubes need to be biased slightly, and earlier models did not have the zener (it looks like a transistor on the back panel) so you have to add a diode string for bias - a small rotary switch on the back with taps on the string is not a bad idea
- the two 3-400z use a common filament choke and series fils, so you can not ever use just one tube. This can be a PIA in the event of a crap out or if you want to test one tube.
- the small resistors (i think on the grid?) that are on the bottom of the socket can be open or cracked - replace 'em.
- oh, replace the HV wire, it's shot - too old now.
- I added a heavy bottom plate, casters and a Hubbel twist lock AC connector on the rear of the PS...

If you go to QRZ.com and look me up, I think I still have a link to the work in progress on my Henry 2K... it's still not done. I need to put in the bias diodes and repair the meters, etc. etc...

So unless you buy one that has been gone through, or is of newer vintage than mine there will likely be some work involved in getting it fully operational.

                     _-_-WBear2GCR

Thanks Bear. Now I KNOW I will never get one of those.  ;D

Yeah, but otoh, if you buy one that is working ok, ur good to go.
Or, if you fix one up, it will stay working.
And it has pretty good snot for a pair of 3-500z...

Not a bad amp at all.

Price & condition is everything...

 ;D

                _-_-bear

Yep, the items you listed are the things I found wrong in my Henry 2K also. Though, I usually go through any commercial amp I buy and heavily modify it, so they didn't seem like a big issue. But, someone who wants a plug and play unit might not be happy... ;D

I ended up using just the RF deck with the common 0-4000v HV supply from the shack I use for all the amps.  I also stripped out all socket wiring and used copper strap for the grid connections to ground.  I added a quiet squirrel cage blower on the rear w/ a variac for air for the 3-500Z's.   I also added a string of diodes for the bias.  The ant relay hasn't failed yet, but I thought the same thing when I looked at it.

I raised the top inside cage about 1/4" so I could run 3500V w/o arcing.

All in all, I just love the stability,  mechanical and RF design of the unit.

In hindsight, I guess there WAS some work to be done on it, but it's all in a day's modifications to me... ;)
The time I spent modifying could have been spent building an amp, I suppose. Then again, I have seven homebrew linears in the shack for many different power levels and bands. It's nice to have at least ONE commercial amp to play with.


T

I'd have no objection to one with those problems, just be fun to mod and fix, and if it has those issues when examining it, you can point them out and bargain the price fairly (although the seller might be shocked to have any of those things pointed out!). Thanks for the tips on it!

Oh, I might add that there are a number of chassis layout variations in the early 2K series amps. The first ones (had a single red pilot light on the front) had a very different layout than the later ones, and the later ones have some variants too...

I suspect that the later versions mid 70s and after had many of these problems and issues resolved at the factory. Not sure though.

Tom, you can run 3500vdc on yours?
Mine arc'd a lot when the ballast resistors got open and the B+ rose above ~3kv...

Did you consider a shortie style plate cap instead of raising the covers?

               _-_-bear

Burt,
If you have a little cash, buy the biggest thing out there and run 375 watts carrier.
You'll have plenty of headroom and it will sound wonderful. The headroom is the limiting factor for linear amp in A.M. mode
Joe, W3GMS is very happy with his Ameritron AL-82. Very scrotful power supply and he runs legal limit.

I run a Ten-Tec Titan 425. Nice big amplifier with 2500watts out so, there's a lot of headroom. But expensive to repair and then you have those ceramic pubes.
Fred

Hi Bear,

Sounds like you could be the resident expert on Henry 2K's for sure... ;)

I can run 3500v on 80M, but on 40 and higher, I occassionally get arcing in the pi network cap plates. It doesn't do any damage, but it can't be run like that, of course.  I can get out an easy 1500w using 3kv with full pep drive on 80M - a little more with 3500v.

If I had the low profile  plate caps I wuda used them, but I just put some washers under the inside cover - that stopped the plate-cap-to-cover arcing.

BTW, I also have a 1979 Sigma XR-3000. Remember those?   I got the Henry and Sigma (pair of 3-500Z's also) in an even swap for a couple of older ssb transceivers I had lying around.  Anyway, when doing IMD tests between the Sigma and Henry, the Henry was much cleaner by maybe 5-6 db of side-trash.  Just a rough estimate listening to a local receiver with programmed material. Not sure why that wud be, other than maybe the tubes were softer in the Sigma. I used the same basic circuit except for the stock tanks in both. Both have input L/C.  So, I really like using the Henry in situations where IMD is important, like the DX window, etc.

All in all, if I was in the situation of needing a good pair of commercial 3-500Z's and didn't mind a little work, I'd put out a "wanted" ad - try to find a cheap Henry that had a blown out power supply for $200 or so. That wud be the perfect platform to work from for me.


Later -

T

The newer, Classic series of Henry amps are a better bet. (Yea, I know, they're newer but they are called Classic - makes no sense). These usually don't have the problems of the older 2k, 3k series. They also run higher plate voltage which means the 3-500s need less drive and put out more power. If you can find a 2K Classic-X like Mikey has, you'll be good for close to 2 kW PEP. That means you can run 300-400 watts carrier with plenty of headroom for audio munky swing.

That Henry 8K sure has a pretty mouth. A 3CX-3000A7 - and costing 5 figures new.  Export only, of course. Like Cuban cigars.

T

Thank goodness I got a good one, a little work, a larger blower, a couple minor changes and 350 watts of carrier all day long... I'll stand behind my Henry any day...

So many amps, so little time.  Pay attention to the cost of the tubes.  I had a Ten-Tec Titan I, 2 3CX800A7's, small desktop unit, separate power supply, big hypersil transformer, loafed at 375W carrier 125% peaks.

But I inadvertently hooked the output of the class E rig to the input of the Titan and discovered just how much 3CX800A7's fetch now.  Other big tubes have gotten expensive too.

I have a couple of TransWorld sand state commercial leenyars, a TW500 (500W) and TW-1000 (1KW).  The TW500 easily does 250W 125%+ mudulated AM whereas the TW-1000 will do 400W 125% easily.  I can old buzzard for 10 minutes on the -1000 before the fans even kick in.  Strapping amps indeed.  They're around on the surplus market; Uncle Sam used them paired up with the TransWorld TW-100 transceiver.

CTR Surplus has a pile of 3cx800s on ebay. Good dealer.
Solid state amps are cool. I'm having very good luck with my MRF150 amp and plan to mount two of them in an enclosure for 500 Watts PEP. Warm up project for the pair of 1200 watt modules I plan to shot gun marry. No tune just give it a load and drive it. Hoping to make it go from 160 to 6 meters.

Thanks for the heads-up Frank,
I found out that I can also use 3CPX800A7'a in my Titan, if the need arises.
CTR prices are better than buying new.

I think these tubes can last a long time, if they're not overdriven :o

Fred

And now to stir the pot!
20 Buck and a hand full of fets.....Build an E rig and you will strap CHEAP! ;D

I couldn't resist!

Brent(Tina)

20 bucks for a class E rig?  Tell you what, Brent.  I'll send you $40 for one and that's 100% profit.

YUP Brent
I'll send you $200 and you can build it for me.
Just kidding............I'm not a builder. I don't have a junque box and I don't have the patience to search for the parts on the cheap and build something to show others.
I graduated from Heathkit-101, that's it :P
Fred

Class E isn't linear, no matter how expensive. And they are expensive, what with all the crap outs they have.

Quite a few of the more strapping amps have been mentioned but for the price, a SB-220 is hard to beat.

I attempted to run My SB220 on AM with my Ranger and my FT1000D.  I think best case is 200 watts AM with a Good running SB220. They are simply not up to the task of AM use at higher levels.  If I talked for an hour, I had to back that down to 150 watts max. The amp got VERY hot. Its abuse for sure. The power supply is to small and the stock cooling fan is not enough. I know lots of people use them and I do as well. But its not really up to more then a couple hundred watts.  I think you need something MUCH larger to run full legal limit AM with out any time limits. I have watched friends with QROs and Alphas flat out burn them up on AM trying to run 400 watt of carrier. No time limit? Yeah right. The biggest problem is the Cooling.  The amps can take the power but they cant take the heat of an hour of AM let along a night of AM! The QRO 2500 is really maxing out at 300 watts AM use. Even with an external fan pulling through the amp it will overtemp in an hour of good use.

I kick myself for selling my 4-1000 amp.  I had a two piece amp that was built out of California. Cant remember the name builders call sign. 4-1000 pulse tube. BIG Dahl Trans on in a box on the ground. Vac caps and crank handles. 6600 volts on the plate at well over an amp. Nice BIG band switch that required two hands to turn. I never used it.. Now that I am on AM just about full time I wish I had it back! I am sure it would run full legal all night.


Clark

200W is not so bad.  The difference between 200W and 350W db-wise is not that great.  That's one reason I ended up with the AL80.

What a shit-stirrer!   ;D ;D

True dat. But everyone I've ever heard on the air crapped out. Even Karl's recent bit the big one. Unreliable it seems.

I dont think the wimpy phonograph motor fan in the Gonsets is going to be good enough for AM.  I am going to take the cabs to a local machine shop and have em cut round holes on the back cab for a Rotron fan set I got.  2 chrome guards, 2 air guides, the fans.  I mocked it up and it looks like Gonset put it in at the factory. mount em on rubber. will be pulling hot air out the back of the amp. Old buzzard transmission protection.

The class e guys are just a bunch of DAVEMADE wannabees talkin bout how many pills they be runnin..

cauwmawn

Seriously the class e stuff sounds great. and as far as the crapouts  it all goes back to the builder.  the only real difference is that the tube stuff is a lot more forgiving.  Those who have built the E stuff and engineered their layout better than a commercial rig seem to have no problems.  (err how the hell does the QIX cliplead speacial stay on the air.)

Boy!...you guys are easy!
I have never had a crap out on the H modulated 10 fet stuff. All the crap outs were from my big rig which was a prototype. Now days they are rock solid.

Besides there fun to build! Yup the reality is it cost about 200-500 bucks depending on your stash of parts.

The Tina

What Clark found is pretty much true for amateur linear amplifiers.  They were not really designed for use with high level full carrier AM and by the time SSB had caught on well enough to create a boom in external amplifiers most of the gear that would run AM did it as some form of controlled carrier which is much easier on the amplifier.

The SB-220 will probably do pretty well longevity wise if run in the 1 KW position in which is was also rated for RTTY service.  But in this case you are only going to be able to run about 250 watts carrier input which might be helpful with some of the modern transceivers but will be a waste of time and energy for most vintage AM gear.  The SB-220 runs pretty warm anyway (in the 2KW position the 3-500z's will start glowing pretty quickly just from the resting current).  It was pretty common for contesters to run the SB-220 with the external case removed and with an extra fan aimed at the power supply just to keep it happy in the old 2KW pep input limit days.

My Drake L-4B is pretty happy running AM with any of my 4 lines but that is with controlled carrier AM.  I have used my L-7 with my TR-7A on AM on 160 but I limit it to 200 watts carrier out and it definitely heats up.  The TR-7A is not controlled carrier and the L-7 doesn't have a blower and chimneys like the L-4B and instead uses a fan like the SB-220 and others.

I have several vintage amps but the only amplifier I feel comfortable running constant carrier AM at the legal limit is with a homebrew amp I specifically built for contesting and AM use.  The P. Dahl plate transformer alone costs and weighs more than a complete SB-220 and the RF deck uses 3 4CX800A tubes in parallel cooled by a large blower; the power supply section has its own small fan.  I built this amplifier for reliability and fun and not to hit some competitive price point or fit in a small space (it is in a 4 foot floor rack).  I was actually planning to buy an Alpha in time for the fall contest season but when I called Alpha to place the order (this was 8 years ago) it would be at least 8 weeks and probably 12 to 14 before it would be built and delivered. I am now glad the Alpha wasn't available because the HB was fun to build.  I do need to go back and spray a nice black wrinkle over the rack panels and relabel the controls; when I built it I wanted it finished in time for a couple of DX tests and it worked so well I never got back to the cosmetics.

Rodger WQ9E

Nice amp. No crap outs with that setup, unlike those JS Class E outfits.

Gee, I remember my last crap out of the class e rig. it was about 5 years ago when the antenna was yanked down by a tree and I kept keying the rig trying to find the problem. It was about the tenth time when I glanced over at the reflected power meter pegged. lost one FET. I think that is the third one since 1996.
Class e rigs crap out because of poor layout. As guys learn they improve and rigs get better.
Fred, I've had good luck with CTR.   I find parts from MRI systems lived an easy life.

Poor layout? Hmmm. Lot's of poor layout going on then. All that repair work for a single band amp. Seems a shame.

I went through the learning curve in the '80s with TO3 FETS.
Low Z is not easy.
I have to tell you the FQA11N90 is one kick butt FET.
You have a ground loop or a layout problem if you are blowing up these things.
A 365 pf broadcast variable is begging for mercey at 1 KW.
I think that is not the part to use in a big FET or tube final.

Thanks Steve!

The closest I have come to a crap out was 2 years ago when the ice built up on the horizontal portion of the 160 meter inverted L that lets my Hy Tower work on 160.   The weight of the ice and the heavy winds caused it to intermittently contact one of the guy wires on the Rohn 55 tower that supports the far end of the wire.  I reset the amp and a few minutes later it tripped again and after repeating a few times I went out into the storm to find the trouble.  I used the G3SEK tetrode board in this amp which provides a number of sensor inputs to take the amp offline in case of fault and it clicked into the standby position with no drama.  I used the line pickup part of a defunct wattmeter to provide RF output metering and high SWR protection for the amp and it did just as it should.

I have also accidentally activated the protection circuit when forgetting to change to the proper antenna during band changes.  I probably should make use of the band data from my FT-1000MP to interface with an antenna switch but I also use my Drake C line with this amp quite a bit so I am sticking with manual antenna selection for now.  The wrong antenna causes the screen current to soar which again trips the amp offline before anything bad happens.

Rodger WQ9E

 

Yep. Good stuff. All rigs crap out. Most crap out less over time/with improvements.

I thinking of taking a crapped out SB-200 (the powersupply is still okay and it makes 2400 volts) and revamping stuff in a new chassis but for 160 meters.  My working sb-200 does not cover 160 so I have no strap at all for that band.  I run my present sb-200 with 15 watts of drive for 100-120 watts carrier out and so far it doesn't seem to complain too much.  It does have a harbach pw-200 (powersupply board upgrade) and softstart and new fan. 

I have a pair of Svetlana 572B's that may have too much interelectrode capacitance for high bands but should be FB on 160 meters.  So there are the reasons.  Now my question.  What components should I beef up for running such a gg linear on 160 meters in the 100 watt AM level?   Cost dictates that I use the transformer out of the old SB-200.  (this thing was dropped and the chassis is beat up bad, I want to try my hand at chassis work anyway and mount the pair of tubes vertically) 

Another thought is eventually modulating this baby in Class C somehow.  If I can find an appropriate mod xfrmer, plate modulation would be my first choice.  I'm also flirting with the idea of other modulation (can triodes be cathode modulated?).

This will be my first homebrew tube project so I'm trying to keep things as simple as possible for the most success.  Would adding in a seperate filament xformer be a good idea for the pair of tubes?  I'm thinking that would free up some strap-power from the HV (even if it is just a little). 

Any thoughts would be appreciated.

KX5JT

A fellow named Chuck, WA0ZHH designed a modulator for an SB 200 some years back.  I forget the particulars, but he drove it with low power and built some sort of modulator for the SB 200. 

The last time I saw the diagram and description was on KC3OL's website.  I don't know if it is still there or not, but you might email Ted to see if he has that article in his archives.  It was an interesting proposition.

A fellow named Chuck, WA0ZHH designed a modulator for an SB 200 some years back.  I forget the particulars, but he drove it with low power and built some sort of modulator for the SB 200. 

The last time I saw the diagram and description was on KC3OL's website.  I don't know if it is still there or not, but you might email Ted to see if he has that article in his archives.  It was an interesting proposition.

Thanks Jim, I do recall seeing that a while back and that would be a great resource for me... I am having a difficult time locating the article now.  I'll email Ted but if anyone has this handy or a link that would be great too.

KX5JT John

A bit of googling turned this up:

http://s88932719.onlinehome.us/Boatanchors_Directory/Amplitude_Modulation.htm

See the 7th bullet down:

http://www.kc3ol.dynip.com/downloads/wa0zhh.jpg

John,

The stock SB-200 should do fine at 100-125 watts carrier output without stressing any of the components.  I imagine the stock HV transformer would be the first weak link if you start trying to run it at higher levels.  Depending upon what components you use for the output network heating might become a problem there also at higher power levels and the next step would be more air for the tubes.

If you are thinking about plate modulating the SB-200 in a class C setup the existing tune capacitor isn't going to have wide enough spacing.  If you stay with running it as AM linear you can just used fixed capacitance in parallel with the existing tune cap but if you plan on high level modulation you will need to replace it.  You will probably need to increase the value of the DC blocking cap; putting another 1000 pf in parallel is probably about right and again watch the voltage ratings if you plan to plate modulate it.

Generally, if money is no object you can modify just about anything to accomplish something far different than the original design intent.   However, if your ultimate goal is a plate modulated final for 160 you might be better off starting from scratch instead of trying to build one around an SB-200 or maybe see if there is a retired broadcast rig in your area available cheaply that can easily be moved up to 160.  Modifying can be fun but you often end up with an expensive compromise if you move something to far from what it was originally.  One of my colleagues spent several thousand dollars turning his minivan into a mediocre towing rig; for less money he could have bought something designed for the task which could actually stop and control a trailer and pull it up a mountain without leaving a trail of steam behind.

Good luck with your project whatever direction you take!
Rodger WQ9E

Hi Rodger,

Thanks for all the good advice!  I use my current SB-200 in AM service in fact for 80 through 10.  I do run about 15 watts from my TS-570 into it for 100-120 watts carrier out.  In fact I have replaced the power supply board with the Harbach.  That seems to be working out just fine.  The idea for my 160 is first to make a linear and do so with the idea of modulating it later. 

I'm realizing that modulating a couple of 572B's in class C will result in higher efficiency.  I know I'll need more strappable components in the tank circuit.  What about the power supply?  Higher efficiency would mean higher output at the same power input right?  If I'm thinking correctly, then going with the higher rated tank circuit components will certainly be needed... but will I have to really upgrade the transformer too?  The whole idea of this is that I'm pretty familiar with the SB-200, it'll be a "cut my teeth with homebrew toob stuff" kinda project where I will work a new chassis and learn as much as possible as well as "run what ya brung" as much as possible.  I have the 572B's and the sb-200 powersupply.  For that matter I have the sockets and some chokes, etc.  The tank components are pretty mottled and corroded, so getting beefier stuff for that makes sense anyway.  Staying with the mono-band 160 meter eliminates the band-switching headaches for such a newbie as myself.    So, first for ab2 linear but with the future in mind is what I'm thinking here (class c cathode modulated or possibly plate modulated).

Hi John,

You are welcome!

Probably the best information on power supply capability is that Heath rated the SB-200 for up to 5 minutes key down time on CW with a 50% duty cycle so the existing power supply should be good for around 1 KW DC average if you keep the transmission length reasonable.  The corresponding rating was 10 minutes on the SB-220 which was also stated as suitable for RTTY use.  I imagine the power supply, rather than the tubes and their cooling, was the reason for the more restrictive rating on the SB-200 since the tube temperature would likely reach peak value before 5 minutes is reached.

If you use a separate power supply for the modulator, that will be far less stressful to the supply in the SB-200.  This would also make your modulator stand alone for use with other rigs for future expansion and building.

If you are planning to plate modulate the SB-200 later, then plan on upgrading the tune capacitor to one with more voltage capability since you will have voltage peaks of at least twice the DC plate voltage under modulation.  I vaguely recall that some of the Svetlana 572B variants are not very tolerant of higher voltages so you may want to research that a bit to see if your tubes will stand up to plate modulation.

You will need to go to one of the handbooks (or there is probably an online calculator) and figure out the capacitance needed for 160 with a reasonable Q.  In any case, it will probably be less expensive to use a bit of fixed capacitance in parallel with a smaller tune capacitor rather than finding a proper spaced unit that will fit.  Just remember there is a lot of RF current so the fixed padding capacitors need to be able to carry the RF without heating and changing values.  I remember one of the earlier Ten Tec amps would suffer an output drop even with long dashes on 80 due to fixed capacitor heating-I believe they changed capacitors in later production.  For 160 only I would just strip out the existing tank coil and wind a new one dedicated for 160 use and save the bandswitch as a spare for your other SB-200.  The load capacitor should be fine, you will just need to add some additional capacitance in parallel for either linear or class C on 160.  The existing choke (in the HV lead) will also need to be larger for 160.

There was an article in CQ on converting the Heath "compact kilowatt" to 160 meters and I will try to find that and scan it for you.  The compact kilowatt is the SB-200's older/little brother with similar circuitry packaged for mobile use with no fan and an external power supply.  However, the modified component values for 160 will give you a good starting point.

Cathode modulation has low efficiency than conventional high level plate modulation but it certainly does cut the costs of building a modulator!

Sorry that this post is a bit disorganized.  My cold medicine doesn't seem to be doing what it should but it definitely is causing mental impairment :)

Rodger WQ9E

Yep, controlled carrier works well with a SB-220. I used a DX-60 for awhile with one and it held up just fine for an evening of chat. The hi speed Harbach fan helped. Ive also used the DX-60 into a NCL-2000, MLA-2500, Clipperton L, and a few others with PS or cooling limitations as an experiment. No problems when using a scope to set things up.

A T-150A with one 6146 pulled does well also.

Carl
KM1H

Carl is right on target and the controlled carrier rigs can sound very nice.  What is somewhat humorous is in many roundtables some of the DX-60 class rigs are easier to copy than some of the "big guns" running plenty of power but not enough modulation.  Controlled carrier lets you run most linear amps at their rated SSB input without beating them up too badly, in the case of sweep tube amps I would be a little more conservative.

I recently picked up a Galaxy 2000+ (the old WRL Galaxy, not the modern CB crap) that was missing all 10 of its 6HF5 tubes.  I am going to experiment to see if I can use 6GY5 tubes instead re-biased to work at around 800 to 1,000 watts input.  The 6GY5's are pin compatible and were less than $3 each.  If it works out it will become part of my Knight T-60/R-195 setup.

Rodger WQ9E

I think many/most of the Class E crapouts have to do with the fact that most/many are driving the finals with riceboxes, and transients are frying the gates.  A better approach, IMHO, is the holistic complete xmitter from VFO-->final.

Few things are absolutely bulletproof anyway  ;D

WOW Burt started quite a thread here  ::)

Fred

If you are looking for an AM linear, try building one of these (http://www.amforever.com/history/kfi_la_ca.pdf).

Curious to know what is hidden under the link, but could not open it:


Forbidden
You don't have permission to access /history/kfi_la_ca.pdf on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request

Quite true, and most things are also not very idiot proof.
In my case, I was working on my e-rig and reversed the polarity of the driver supply to one of the modules.   :-\  The result was a fried regulator circuit, and a blown driver.  The nice thing about homebrewing though is that building a new regulator circuit is small potatoes, but the driver will cost a few bucks...

Nothing to do with layouts, class e final designs, or construction.  Just a dummy (me) not being careful with the wiring.  Perhaps like having an expensive final tube slip from your fingers and hit the deck??

Waiting on a chip to finish the repair.
Nothing has 'bit the big one'.  ::)

Karl

Don
I'm forbidden too
Is this a secret NASA web site?

Fred

Karl,
Was that a DEIC420  ?

Already order it?

I have a used "spare".

I don't have any trouble opening it.  That's unusual. Most of the time I am the one who gets an error message while everyone else can open the link.  See if this works:

1. Go to http://www.amforever.com/

2. Click on the "Contents"  link to the left of the page

3. Scroll down to "Related History" near the bottom of the page.

4. Click on "The New KFI Los Angeles, CA 1932 - (2.53 pdf)" ,the last link on the list.
 

That works Don.  I think it's some sort of restriction from the AM Forever site.  I noticed from Internet Explorer, one cant right click and save most of those files on AM Forever, but I believe when I was using Firefox from my Linux machine I could.  A little silly because once it's loaded in the PDF viewer, I can save the file anyway.

Bruce,

Yes, a DEIC420, already ordered.  Crap!

But thanks very much for the offer!
Of course the new rig under construction will use IXDD414s

Thanks Bruce,
73, Karl

It is a typical amateur radio setup - let's see how much power we can get out of this thing. Not much different from the OBs dipping their 01's and 45's in oil so they could PB them.

Well, for a class E rig, this is an easy question, even for a guy like me that is light on 'theory'.

Each FQA11N90 MOSFET is good for 50W, so a two-module final with 4 MOSFETs each (8 MOSFETs total) can handle 400watts carrier. Bigger rigs scale accordingly, at 50W per FQA11N90.

Nothing complicated here.  Class E rigs can be built from QIX designs without much more builder-experience than a heathkit.  Anyone can sound great on AM by taking on the task of building one.  There is plenty of help available from other builders, just check out Steve's site: http://www.classeradio.com/

73, Karl

 

I never tried that, but back in 1959, my first plate modulator, the driver stage was a single 6AQ5.  After about a minute the tube would heat up and the audio would become all distorted.  I took the whole driver stage, which was built on a separate chassis about 6" X 6", and turned it upside down so that the 6AQ5 envelope was submerged into a glass of water.  That kept it cooled off enough to make an entire transmission before the audio started to go to crap.

Wow! And some guys are running 24 FETS.

There is a discussion on what to do with a 400Hz 15KVA diesel generator over on steelsoldiers.com . It made me think of those modulators in the class E rigs. Just beef up to the right strappage and feed a 60Hz signal. The genset could be rectified to +/-160VDC and the PWM would do the rest. I really like those designs, would be about impossible with hollow state. Very progressive engineering!