How did tune a varmint XL 600

[88_bandit]

Yes I was wondering the proper way to tune my amplifier I have a varmint XL 600 tube type 2 driving 4 it has a trimmer on the back and one inside the box also.

 

[nomadradio]

The Load and Plate get peaked for max modulated power.

Modulated.

If the peak on the "Plate" knob is broad and hard to see, it's okay to peak that one on carrier alone, but the Load must always be peaked for modulated power.

The Driver Tune usually peaks at the same spot whether you modulate the radio or just use a dead carrier.

The trimmer on the back was just plain wired wrong in a lot of these at the factory.

Best way to set it is with a second SWR meter and coax jumper placed BETWEEN the radio and the amplifier's radio socket. This permits you to see the SWR that the radio is feeding into when the amplifier is keyed. In a perfect world, the amplifier's input will be a perfect 50 ohms, showing the radio a perfect one-to-one SWR.

Ideally, that trimmer should be set for minimum SWR reading with the radio and the ampllifier keyed, and the amplifier tuned for max modulated power.

In real life, that trimmer may or may not appear to help much at all.

Like I said, many of these left the factory with that circuit just wired wrong.

Anyway, hooking that second SWR meter between the radio and amplifier allows you to see how much SWR the radio is keying into when the amplifier is keyed and active.

That way if the radio pops a final transistor down the line, you'll know what to blame.

With any luck, the contacts in the amplifier's relays have been cleaned some time in the last 40 years, and you won't be having on-again, off-again problems with the relay contacts dropping in and out.

73

 

[88_bandit]

The Load and Plate get peaked for max modulated power.

Modulated.

If the peak on the "Plate" knob is broad and hard to see, it's okay to peak that one on carrier alone, but the Load must always be peaked for modulated power.

The Driver Tune usually peaks at the same spot whether you modulate the radio or just use a dead carrier.

The trimmer on the back was just plain wired wrong in a lot of these at the factory.

Best way to set it is with a second SWR meter and coax jumper placed BETWEEN the radio and the amplifier's radio socket. This permits you to see the SWR that the radio is feeding into when the amplifier is keyed. In a perfect world, the amplifier's input will be a perfect 50 ohms, showing the radio a perfect one-to-one SWR.

Ideally, that trimmer should be set for minimum SWR reading with the radio and the ampllifier keyed, and the amplifier tuned for max modulated power.

In real life, that trimmer may or may not appear to help much at all.

Like I said, many of these left the factory with that circuit just wired wrong.

Anyway, hooking that second SWR meter between the radio and amplifier allows you to see how much SWR the radio is keying into when the amplifier is keyed and active.

That way if the radio pops a final transistor down the line, you'll know what to blame.

With any luck, the contacts in the amplifier's relays have been cleaned some time in the last 40 years, and you won't be having on-again, off-again problems with the relay contacts dropping in and out.

73

What about the trimmer inside the top cover?

 

[nomadradio]

Oh, yeah..

That's the driver "Load" control.

Max modulated power. It usually doesn't need to be tweaked when you change frequencies, like the ones on the front.

73

 

[Dmans]

88_bandit,
I'm pretty sure (99.5%) this will apply to your XL600. Might be worth printing out and having handy.

http://www.cbtricks.com/Amp/brewer_labs/graphics/xl150-xl450_tune.jpg

73's
David

 

[Timothy Scott Nichol]

Yes I was wondering the proper way to tune my amplifier I have a varmint XL 600 tube type 2 driving 4 it has a trimmer on the back and one inside the box also.

Start with turning your mic gain off. Tune amp for Max output using Tune and Load. Then adjust the trimmer on rear for peak then tune interior pot for peak. This i what I did on my XL 600 I just retubed the entire amp. It idles at 800 watts no pain no strain.
415
Muledriver on the sand pile.

 

[Shockwave]

Start with turning your mic gain off. Tune amp for Max output using Tune and Load. Then adjust the trimmer on rear for peak then tune interior pot for peak. This i what I did on my XL 600 I just retubed the entire amp. It idles at 800 watts no pain no strain.
415
Muledriver on the sand pile.

That tuning procedure will not allow for proper peak power output when modulated and will allow too much carrier. Tune with a constant audio tone for maximum and then back the carrier down to 200 watts and it might swing to the needed 800 watts for 100% modulation. Run the carrier hundreds of watts higher and the audio as well as tube life will greatly suffer. Your radio (not the amplifier) should be adjusted to key the amp at around 200 in the normal mode. "Super mod" is just a filthy class C signal from these amps.

 

[Timo714]

That tuning procedure will not allow for proper peak power output when modulated and will allow too much carrier. Tune with a constant audio tone for maximum and then back the carrier down to 200 watts and it might swing to the needed 800 watts for 100% modulation. Run the carrier hundreds of watts higher and the audio as well as tube life will greatly suffer. Your radio (not the amplifier) should be adjusted to key the amp at around 200 in the normal mode. "Super mod" is just a filthy class C signal from these amps.[/QUOTE

sounds good, on mine the dead key would be right at 200, I pull mic gain off tune for peak then I adjust my driver and tune for voice. I hear you on the supermod position, why does the amp run/tune better With it on.

 

[Timo714]

The Load and Plate get peaked for max modulated power.

Modulated.

If the peak on the "Plate" knob is broad and hard to see, it's okay to peak that one on carrier alone, but the Load must always be peaked for modulated power.

The Driver Tune usually peaks at the same spot whether you modulate the radio or just use a dead carrier.

The trimmer on the back was just plain wired wrong in a lot of these at the factory.

Best way to set it is with a second SWR meter and coax jumper placed BETWEEN the radio and the amplifier's radio socket. This permits you to see the SWR that the radio is feeding into when the amplifier is keyed. In a perfect world, the amplifier's input will be a perfect 50 ohms, showing the radio a perfect one-to-one SWR.

Ideally, that trimmer should be set for minimum SWR reading with the radio and the ampllifier keyed, and the amplifier tuned for max modulated power.

In real life, that trimmer may or may not appear to help much at all.

Like I said, many of these left the factory with that circuit just wired wrong.

Anyway, hooking that second SWR meter between the radio and amplifier allows you to see how much SWR the radio is keying into when the amplifier is keyed and active.

That way if the radio pops a final transistor down the line, you'll know what to blame.

With any luck, the contacts in the amplifier's relays have been cleaned some time in the last 40 years, and you won't be having on-again, off-again problems with the relay contacts dropping in and out.

73

Nomad knows best