Kris Mach 3+3 weak/muddied audio

[BigLion]

Just got through recapping this beast, it puts out 200+ watts fine, but the audio is weak and muddied (as reported by contacts). anyone know what the issue is? I have the schematic as attached. The difference in my model (must be a new mod by Kris) is the 6BQ5 is removed, and a 2 transistor trigger board is in its place. This is an official Kris mod as the PC board has Kris stamped on it. Unfortunately, I don't have the schematic on it, but could draw one up it that would help. Anyone help?

[Bluerunner]

Sounds like you are over driving the amp. 200 watts is probably all it will do.
If it is maxed out on a dead key, there is no room for positive modulation (adds power when you speak). All you will get then is distorted, negative modulation (loss of power when you speak) from over driving the tubes. Typically 2-2.5 watts or even less is all you need to drive that amp.

[BigLion]

yes,my exciter is dropped to 2 watts input. I have it tuned right, dropped the load down to 100w output on my Bird, yet still audio is weak and muddied. Could the 6JG6 tube be flakey? I have no tester to see if it is the issue. The 3 6LQ6's are good as I can drive to 200+W.

[MDYoungblood]

What radio are you using, you might have a 2w DK but if it is swinging "boo-coo" modulated watts then that is the problem. I believe the 6JG6 tube (driver tube for that amp) should only be driven with up to 15w. My suggestion then would be to try a different radio.

3's

Greg

[BigLion]

OK I tried 3 different radios, all w/o a power mike, and on my Bird meter, with screaming in the mike I get 3.5 watts output. I ordered a NOS 6JG6 tube to see if that is the issue. There is not much more I can replace, and it was working fine for months on the same radio. I don't use a power mic when warming my feet with the amp, so overmodulation isn't the issue; more of lack of it.

[BigLion]

Think I found the problem! I borrowed a friend's Sencore Mini-Mite, plugged in my 6JG6 tube, and it was in the "?" section nearest to "BAD". guess the driver burned itself out after who knows how many years. Still waiting from ePay for my NOS tube, hopefully that will knit this issue up.

[MDYoungblood]

Yep, probably the cause. Swing amps like yours are made for the driver tube to take all the abuse so as not to fry the final tubes. Hope you found 2 on that auction site just in case one is bad.

3's

Greg

[BigLion]

Got the replacement tube; checked it on the Mitey-Mite V and it swings all the way to 100 Green. Popped the tube in, tuned it up, and as long as I keep the load down to 150-200ua the audio is loud and clear (along with the 200+w punch). Will be sending it back to my friend now with a warning to keep the load down on AM -- I suppose I can increase to 300ua on SSB as no carrier to deal with.