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Author Topic: King Conversion 6 meter SB-220 amp  (Read 3290 times)
K9FV
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Posts: 494




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« on: July 13, 2017, 11:36:56 AM »

Hello all, and maybe Lou if you're monitoring this board.  I buddy has got the amp and has been VERY happy with it for several years.  Just now the input has went caput.  With 10 watts input drive into dummy load, there is no output and the SWR on driver rig (756Pro) pegs to max input SWR. 

Is there a schematic available for the King Conversion?  I'd like to see how the input circuit works.  I didn't expect to see an external adjustment for input SWR.  When I built my 6 meter amp using a GS31b tube I didn't use an external adjustable capacitor, but if I remember, they're all fixed value capacitors.

Since these are a pair of 3-500 tubes, shouldn't I be able to solder a 115 (100?) ohm resistor from cathode to ground for each tube, giving an actual 50 ohm impedance?  Then use an MFJ 259B antenna analyzer to test input circuit (all with NO power applied of course)?

Any suggestions from anyone about possible causes of input SWR to be so high it's pegged meter?

I'd sure appreciate any guidance I can get - I follow directions pretty good.

73 de Ken H> K9FV
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W1QJ
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Posts: 2966




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« Reply #1 on: July 13, 2017, 01:43:36 PM »

Before you do anything make sure the input contact on the relay is making up.  Make sure nothing happened to the input wiring.  Make sure the plates on the input tune cap ate not shorting.  Go thru the input circuit checking for continuity and shorts   make sure the dial is turning the cap and that a shaft coupler didn't come loose.  It's a passive circuit and nothing can go wrong with it except z loss of continuity or shorts.  No need to do what you plan.
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K9FV
Member

Posts: 494




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« Reply #2 on: July 13, 2017, 02:15:04 PM »

Thanks for the comments Lou - I know you're really GREAT on these amps... heck, you built them {g}

You're right, the input problem seemed to be a wire broke on the open frame relay.  I soldered that back in place and now the SWR seems to be ok.  Something that interesting, with about 20 watts on key down CW, the SWR bumps up to 1.5 or so, then back to zero.  Not sure what the "bump up" on the meter indicates (756Pro meters).  With 20 watts input, power out on a LP100A watt meter there is only 160 watts with the "CW/Tune/SSB" selector switch in "CW/Tune" position for a 2,000 vdc plate supply.  Key down with 20 watt input gives a plate current around 450 mA with grid of about 80 mA or so 150 watt output.   This is with Input Tune tweaked for max, then - TUNE maxed, then LOAD maxed to get this readings.  Each of the knobs affects the output nicely so I think the knobs are all tight 'n working.

Increasing drive to 40 watts gives around 350 watt output, which still isn't very good.

What is the sensitivity knob located just to left of metering selector knob?  I see the "input tune", "TUNE", and "LOAD" knobs - these are pretty obvious use.

73 de Ken H> K9FV

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K9FV
Member

Posts: 494




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« Reply #3 on: July 13, 2017, 02:17:26 PM »

I should have mentioned these power readings are into a Cantenna dummy load.
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W1QJ
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Posts: 2966




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« Reply #4 on: July 13, 2017, 02:38:24 PM »

Let's not waste bandwidth here.  Contact me at gudguyham@aol.com. Lou
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K9FV
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Posts: 494




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« Reply #5 on: July 13, 2017, 03:14:43 PM »

email sent
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K9FV
Member

Posts: 494




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« Reply #6 on: July 13, 2017, 08:08:01 PM »

Please allow me to sing the praises of Lou (W1QJ) the builder of the King Conversion 6 meter amps.  He called me on phone and spent over an hour talking me thru the problems with the amp (after we touched on old black power cartridge rifles and custom knives).  It turned out it was the internal wiper wire that was broken on the relay - factory wiring from factory.  I soldered wire, Lou talked me thru proper tune up on the amp, and what each of the controls did.  Amp works GREAT.

Lou also provided some suggestions to pass on to owner of amp for using amp on AM..... go light with time in QSO to give tubes time to cool. 

Again Lou - THANK YOU!!! for all the help and guidance.

73 de Ken H> K9FV
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W1QJ
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Posts: 2966




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« Reply #7 on: July 13, 2017, 10:54:39 PM »

My pleasure Ken.  Enjoyed the chat about old black powder long guns, hot rods and custom knives.  Thanks, Lou
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KM1H
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Posts: 5253




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« Reply #8 on: July 14, 2017, 06:47:22 AM »

Quote
Lou also provided some suggestions to pass on to owner of amp for using amp on AM..... go light with time in QSO to give tubes time to cool. 

As a long time 6M amp converter plus a service shop for most other tube amps, plus an AM operator here is a little general advice.

Rarely are the tubes a problem as far as cooling is concerned unless they are being pushed well beyond their safe limits.

The metal anode 3-500Z Eimacs as shipped in most of the the SB-220 family can run a dull orange for 24/7 without damage as long as the seals are cooled.
The graphite versions are fine at a dull red.

The big problem with the SB-220 and many other older amps is that the PS is rated to barely survive at 2000W PEP INPUT which was the old FCC rule. This equates to about 1200W PEP output at a 20-30% duty cycle. When the FCC rule changed to 1500W out the first thing to fail in the SB-220's was the wimpy transformer especially during contests.

On AM the carrier is only about 30% efficient while the AM sidebands are about the same as SSB at 60-65% with a combined average in the 40-50% range. While the sidebands duty cycle is still the same as SSB it is the carrier that is a major heat generator.
 
Next comes the builders ability to do an efficient conversion which should run 1100-1200W out key down with 70-80W drive. With good tubes a 6M monoband amp is as efficient as a multiband HF one on say 20M.

A good rule of thumb in those cases is to run the AM carrier at 25% of the total plate dissipation. This equates to 250W in the above case for 1000W PEP....with a clean and well lubed fan PLUS clean tube glass. You would be surprised at how much nicotine staining affects cooling.

I still run the same NCL-2000 prototype I converted to 6 in 1964 and have converted many hundreds of all sorts of HF and industrial amps since then that are still in use all over the world.

Im also a long time black powder rifle owner plus have been into hot rods and customs since I was a kid. Most has been sold off but I still drive a 68 Impala SS 396 convertible in the good weather.

Carl
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K9FV
Member

Posts: 494




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« Reply #9 on: July 14, 2017, 08:20:35 AM »

I've got a couple of muzzle loaders - all reproductions, but fun to shoot.  My big fun thing these days are the old black powder cartridge rifles like 1874 Sharps (A Pedersoli in 45-70), the old Rolling blocks (got 3 of those, all made in 1870's to 1880's).  They are of the Swedish military rifle in 12.7X44R chambering.  I rechambered two of them to 50-70 which is almost the same thing.  One I ordered a E.R.Shaw barrel in 45-70 to put a new barrel on the action.  I also have an old original 1878 Trapdoor in 45-70.  Sure is fun to shoot those old rifles.  I mostly load with smokeless powder in light loads - my old shoulders can't handle the recoil of full power loads very much.  And hot rods - ahhh, those were the days.

Thanks for the input Carl, the comment Lou made on AM was in response to me telling him I'd had to resolder one (2?) of the pins on the 3-500 tube 3 or 4 yrs ago on this amp.  Due to the pins getting hot enough to melt the solder it just seemed the amp was being run well past it's ability to cool.  Back off on output and go easier on the amp seemed to be good advice to prevent overheating the tubes to cause pins to come unsoldered.

Now, when I say the solder melted in the pins, there is no way I know for sure the pin/wire wasn't making contact up inside the pin where I couldn't see.  I do NOT consider myself an expert at all on amps - I'm not worthy to carry water for folks like you Carl and Lou when it comes to knowledge of amps.   I could see the tip of the pin and it was certainly open and looked like the filament wasn't soldered.  That's been 3 or 4 yrs ago, and  my "forgetter" works a lot better than my "remember" works.   I wish I'd took photos of the pins at the time.  The socket connections with the melted solder pin were also discolored.

After cleaning the pin connections on tube socket, re-soldering the pin on tube, the amp then started working good.  Before my work, the amp acted like it was working on only one tube.  I don't remember which pin, just it was one of the bottom pins, but MUST have been pin 1 or 5 since those are the high current heater pins and the other 3 pins are grids to ground.

73 de Ken H> K9FV
« Last Edit: July 14, 2017, 08:34:51 AM by K9FV » Logged
HFCRUSR
Member

Posts: 356




Ignore
« Reply #10 on: July 14, 2017, 06:49:39 PM »

Quote
Lou also provided some suggestions to pass on to owner of amp for using amp on AM..... go light with time in QSO to give tubes time to cool. 

As a long time 6M amp converter plus a service shop for most other tube amps, plus an AM operator here is a little general advice.

Rarely are the tubes a problem as far as cooling is concerned unless they are being pushed well beyond their safe limits.

The metal anode 3-500Z Eimacs as shipped in most of the the SB-220 family can run a dull orange for 24/7 without damage as long as the seals are cooled.
The graphite versions are fine at a dull red.

The big problem with the SB-220 and many other older amps is that the PS is rated to barely survive at 2000W PEP INPUT which was the old FCC rule. This equates to about 1200W PEP output at a 20-30% duty cycle. When the FCC rule changed to 1500W out the first thing to fail in the SB-220's was the wimpy transformer especially during contests.

On AM the carrier is only about 30% efficient while the AM sidebands are about the same as SSB at 60-65% with a combined average in the 40-50% range. While the sidebands duty cycle is still the same as SSB it is the carrier that is a major heat generator.
 
Next comes the builders ability to do an efficient conversion which should run 1100-1200W out key down with 70-80W drive. With good tubes a 6M monoband amp is as efficient as a multiband HF one on say 20M.

A good rule of thumb in those cases is to run the AM carrier at 25% of the total plate dissipation. This equates to 250W in the above case for 1000W PEP....with a clean and well lubed fan PLUS clean tube glass. You would be surprised at how much nicotine staining affects cooling.

I still run the same NCL-2000 prototype I converted to 6 in 1964 and have converted many hundreds of all sorts of HF and industrial amps since then that are still in use all over the world.

Im also a long time black powder rifle owner plus have been into hot rods and customs since I was a kid. Most has been sold off but I still drive a 68 Impala SS 396 convertible in the good weather.

Carl
I envy you your Impala SS. IMO the '68 was the best body style of all Impalas-they got it right that year. Sorry for the OT.
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Not a ham, but an avid hobbyist in HF world. All things, short of transmit happen in this shack.
KM1H
Member

Posts: 5253




Ignore
« Reply #11 on: July 15, 2017, 07:58:44 AM »

Quote
I've got a couple of muzzle loaders - all reproductions, but fun to shoot.  My big fun thing these days are the old black powder cartridge rifles like 1874 Sharps (A Pedersoli in 45-70), the old Rolling blocks (got 3 of those, all made in 1870's to 1880's).

Mine are both Thompson Center versions,  a .50 for gun club competition and a .54 for the woods which I dont do much any more.

Still have my dads 1927 Stevens lever action .22 which keeps the larger pest population down.

Had a Winchester 44-40 saddle gun but somebody wanted it more than I Grin
Quote
Thanks for the input Carl, the comment Lou made on AM was in response to me telling him I'd had to resolder one (2?) of the pins on the 3-500 tube 3 or 4 yrs ago on this amp.  Due to the pins getting hot enough to melt the solder it just seemed the amp was being run well past it's ability to cool.  Back off on output and go easier on the amp seemed to be good advice to prevent overheating the tubes to cause pins to come unsoldered.

That has absolutely nothing to do with AM or any other mode. Typical reasons:

1. Never soldered properly when built as it takes a lot of heat do do it properly.

2. Little aluminum strip missing from the back of the perforated steel top, this is very important for directing air to the socket pins and is often missing.

3. Slow fan, dirty blades, very common

4. Fan blade not placed on shaft as per manual instructions. Also very common.

Quote
I envy you your Impala SS. IMO the '68 was the best body style of all Impalas-they got it right that year. Sorry for the OT.

I had many 63-64 Impalas when I was specializing in buy-fix-sell including a 409 4 speed wagon! The 68 caught my eye in 98 when I went down to Hendersonville NC to move my mother to live with us. With 55K original and no body or frame rust I was hooked. Went down a few weeks later to drive it back after the seller went thru it.

Far from the fastest Ive owned but the best long haul cruiser with family, the trunk space is huge!

Carl
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