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X force 2 pill troubles

Myst-hic

New Member
Mar 5, 2021
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Hello all, I have searched, watched, and read as much info on this amp that is out there for weeks, and i am more confused than when I started. Quick story, I bought the amp as parts on order to steal the pills for a Texas star, that was a successful swap, it's initial problem as seen in 1st photo is that it burned the rf chokes off the relay..before pulling pills I used a 10uh Texas star choke across hot side of relay to bias terminal, immediately would sizzle when I turn the amp on..no rf..so i disconnected bias, preamp, output trans wire one at a time with the same results, so then I gave up and stole the pills. Since then I've rebuilt the key circuit, new relay, put a nice pair of hg's in there, I don't plan on hooking up the preamp...i also put a diode across the coil, it keys well...but where and what rf choke should I place across? What might blow the choke? The ab bias circuit maybe shorted somewhere? What should the bias cap at relay be in value? It has a .1 poly at moment, is that correct? Anyone out there with a clear pic of their black label base relay with this setup? I thank you all in advance for any input, 73's from 2 OP 095
 

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X-Force never made a class AB amplifier. The vast majority were class C with a small number of silver case amps being class B if a customer ordered it that way. They also had a redish colored case line called MagnaForce that were all class B. Then the black case TNT line were also all class B.
 
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Thank you, this must be class b silver box..black label. It has the 20w sandbar with a mess of components going to ground, hi low switch for power, not variable like the bigger 2x4's and such.
 
Two things come to mind here, it appears that the circuit is injecting the 12V bias through the keying relay. In order for this to function properly there must be a DC blocking cap inline to keep the DC from directly shorting. I can't really tell if there's one from the picture. I usually use one at the antenna side as well as the input. The other thought would be the voltage dropping diode, if it were to short out you'd see the same result. The choke value isn't critical as it's just blocking AC, I'd use something around 2.5uH - 5uH.
 
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X-Force never made a class AB amplifier. The vast majority were class C with a small number of silver case amps being class B if a customer ordered it that way. They also had a redish colored case line called MagnaForce that were all class B. Then the black case TNT line were also all class B.
Did any 11m amps ever come with proper Class AB circuitry? Not being RF engineers, is there a truly substantial functional difference? Most buyers don't care as long as it works well for SSB.
 
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Bias reduces efficiency especially at incredibly high drive levels. Class C will always be more efficient than class A,B, or AB.

Plus side, you can run ridiculous power and not push it over the thermal cliff as fast.

Drawback, it will sound like dirt on sideband.

Just a choice. "Competition" AM? Or sideband?

73
 
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Bias reduces efficiency especially at incredibly high drive levels. Class C will always be more efficient than class A,B, or AB.

Plus side, you can run ridiculous power and not push it over the thermal cliff as fast.

Drawback, it will sound like dirt on sideband.

Just a choice. "Competition" AM? Or sideband?

73
I'm sure something made by Kenwood or Icom would be labeled accurately, but in the 11m amp game, it's a crapshoot.

It seems as there's typically two options when ordering a new amp, with or without a side band circuit. Highly unlikely it's full class A, so we'll say it's Class B or Class AB.
I'm curious as if there's any functional difference in SSB usage or even power between AB or B.

Further, it appears most 11m SSB amps are Class B. Were class AB ever produced in substantial numbers?
 
Years ago Peakaboo built a line of amplifiers called Joker. He came up with his own regulated class AB design which worked very well. I think Texas Star is a passive AB but when they get warm they slide into class B. Bulletproof made several small 2 pill amps that were sold as class AB and there were some small blue face Palomars as well.

When it came to X-Force, Fatboy, Davemade, AM Power, No-Name, Sno-Cap, Donkey Stomper and all the other hand built amps most were class C. They would just add a SSB delay of the customer ordered it that way. Some would add the delay and change it to class B, very few did a true AB. The good old days when Toshiba finals were cheap and plentiful.
 
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Bias reduces efficiency especially at incredibly high drive levels. Class C will always be more efficient than class A,B, or AB.

Plus side, you can run ridiculous power and not push it over the thermal cliff as fast.

Drawback, it will sound like dirt on sideband.

The exact reason that class c amps became popular with the keydowns because the object was to produce the most amount of power for each amp of draw by the devices.
They only needed to key a short amount of time to win a belt.
As people started hearing about keydowns boxes, everyone wanted one, not understanding that the whole point was to win a 30 second shootout.
Not a daily driver.
The rest is history.

73
Jeff
 
Two things come to mind here, it appears that the circuit is injecting the 12V bias through the keying relay. In order for this to function properly there must be a DC blocking cap inline to keep the DC from directly shorting. I can't really tell if there's one from the picture. I usually use one at the antenna side as well as the input. The other thought would be the voltage dropping diode, if it were to short out you'd see the same result. The choke value isn't critical as it's just blocking AC, I'd use something around 2.5uH - 5uH.
Thank you Rick! That's the info I was looking for, oddly enough I finally found a useable pic online, wired it correctly, and boom!! Surprisingly with the awesome hg's I put in from eighteen electronics this baby fell right in tune with slight reduction of output tuning cap, awesome swr's!. I have a feeling the preamp was causing the burning choke, I did not rebuild that, I don't need it, it's only a.c. blocking cap is in the bias, not on input or output, I may put some in in the future, I will guess the same values as an Texas star? I may throw a choke across the relay in time, thanks for that info.. I am very pleased with my 450 watts peak with 60w drive, I don't think the screwdrivers will be back in there for a bit
 
Two things come to mind here, it appears that the circuit is injecting the 12V bias through the keying relay. In order for this to function properly there must be a DC blocking cap inline to keep the DC from directly shorting. I can't really tell if there's one from the picture. I usually use one at the antenna side as well as the input. The other thought would be the voltage dropping diode, if it were to short out you'd see the same result. The choke value isn't critical as it's just blocking AC, I'd use something around 2.5uH - 5uH.
Two more quick points, if I were to place a new choke, which terminals of the relay would I cross? It originally was hot 12v input to coil to somewhere else, would I span to output tuning cap/post on relay? Also, it never had a reverse diode, so i put one across the coil...
 

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