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Recommend AM linear




 
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ab3al
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« Reply #75 on: April 12, 2009, 08:11:00 AM »

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.)
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« Reply #76 on: April 12, 2009, 09:26:26 AM »

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
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« Reply #77 on: April 12, 2009, 11:55:04 AM »

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

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.
Clark


* HB amp.JPG (246.57 KB, 573x1000 - viewed 1078 times.)
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Steve - WB3HUZ
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« Reply #78 on: April 12, 2009, 09:38:21 PM »

Nice amp. No crap outs with that setup, unlike those JS Class E outfits.
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WA1GFZ
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« Reply #79 on: April 12, 2009, 10:08:29 PM »

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.
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Steve - WB3HUZ
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« Reply #80 on: April 12, 2009, 10:13:54 PM »

Poor layout? Hmmm. Lot's of poor layout going on then. All that repair work for a single band amp. Seems a shame.
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« Reply #81 on: April 12, 2009, 10:40:58 PM »

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.
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« Reply #82 on: April 12, 2009, 10:59:43 PM »

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

 
Nice amp. No crap outs with that setup, unlike those JS Class E outfits.
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Rodger WQ9E
Steve - WB3HUZ
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« Reply #83 on: April 12, 2009, 11:08:52 PM »

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


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.
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KX5JT
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John-O-Phonic


« Reply #84 on: April 13, 2009, 01:51:15 PM »

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
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« Reply #85 on: April 13, 2009, 05:43:46 PM »

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.
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John-O-Phonic


« Reply #86 on: April 13, 2009, 06:24:47 PM »

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
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« Reply #87 on: April 13, 2009, 07:40:21 PM »

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
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« Reply #88 on: April 13, 2009, 07:55:15 PM »

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


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« Reply #89 on: April 13, 2009, 08:42:43 PM »

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).
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« Reply #90 on: April 13, 2009, 09:51:04 PM »

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 Smiley

Rodger WQ9E
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« Reply #91 on: April 14, 2009, 08:57:56 AM »

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
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« Reply #92 on: April 14, 2009, 09:33:47 AM »

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

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
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« Reply #93 on: April 14, 2009, 11:32:20 AM »

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  Grin
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« Reply #94 on: April 14, 2009, 12:47:41 PM »

WOW Burt started quite a thread here  Roll Eyes

Fred
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« Reply #95 on: April 14, 2009, 01:29:06 PM »

If you are looking for an AM linear, try building one of these.

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« Reply #96 on: April 14, 2009, 01:34:32 PM »

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
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« Reply #97 on: April 14, 2009, 02:48:37 PM »


Quote
Few things are absolutely bulletproof anyway 

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.   Undecided  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'.  Roll Eyes

Karl
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« Reply #98 on: April 14, 2009, 02:56:24 PM »

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

Fred
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Are FETs supposed to glow like that?


« Reply #99 on: April 14, 2009, 03:07:45 PM »

Karl,
Was that a DEIC420  ?

Already order it?

I have a used "spare".

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