squealing gain channel..

JackBootedThug

JackBootedThug

MURDERATOR
new used amp...egnater vengeance. Clean channel is fine but get lots of squealing on the gain channel. With the boost switch off and gain at 50% it's gone. Tube probably? Just an initial fire up after receiving the amp yesterday.
 
This is what I have to pick from.
IMG_1815.jpeg
 
I think I’m going to load the mesa str 420’s and do a hg in v1. I also have an at7 as well. Two ruby hg’s to mesa 12ax7’s and a mesa at7….
 
JackBootedThug said:
I think I’m going to load the mesa str 420’s and do a hg in v1. I also have an at7 as well. Two ruby hg’s to mesa 12ax7’s and a mesa at7….
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I would figure out if you have a tube problem before changing all the tubes.
Isolate the problem first.
That way you don't use the bad tube in a other amp.
 
I threw the mesa 6l6 gc’s in and swapped the pi out with one of those hg’s. I also noticed it has a switch inside for I assume the first gain stage. Silicone or tube. After I bias it I will play around with it some more.
 
Question….can’t get a reading on the inner pair of tubes. The outer was reading 65 mv but the inner pair wouldn’t read on my multimeter. Noise is gone now though.
 
stephen sawall said:
Does the inner pair take 6L6 ?
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You can run almost any combination of tubes as long as you keep them paired correctly. It had 6550’s outside and whatever on the inside. I changed them to all 6l6’s because that’s what I happened to have. For some reason it just won’t read the bias on the inner set. I’m getting an O L reading from my meter…they are performing identical to the other set which is reading 65. Odd…no readplating or anything odd.
 
Change the meter to the next highest setting while unplugged and then plug the meter in and try to measure the inner set.

Problems like this can be tube related but it can also be due to faulty or failed components not related to tubes. Try to get it biased but if it doesn’t work then I’d say tubes failed on the inner pair/circuit causing damage that needs repair by a professional.
 
glpg80 said:
Change the meter to the next highest setting while unplugged and then plug the meter in and try to measure the inner set.

Problems like this can be tube related but it can also be due to faulty or failed components not related to tubes. Try to get it biased but if it doesn’t work then I’d say tubes failed on the inner pair/circuit causing damage that needs repair by a professional.
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It’s working. I have a cheapo Walmart special meter but it’s fine. It’s working great in full power or half power mode. Inner tubes are lit up identical to the outer ones. I think I will probably just run it on half power for now anyway. That way there’s no issue and I’m not burning up a good pair of tubes.
 
"The bias point for 6L6GC tubes is a matter of personal taste and tube life. Fender recommends 60mv for safety and tube longevity, but some say 68.3mv is the sweet spot for 6L6GCs. Others recommend 50-55%, and Leo idled his 6L6GC amps at 50-55%."

I just read the above quote. I'm at 62mv...so what exactly would 50-55% be? The Eggie manual says to bias 6l6's at 60mv-70mv....I'm fine with how it is now but was just curious. Oh yeah-the pair I could not get a reading on were biased so high that it was causing an error. I started lowering the bias pot and the first reading I got was over 120. Once I lowered the bias the background noise decreased some.
 
Tube wattage divided by plate voltage x the percentage you want to run the tubes at = your mA per tube

if you were running el34's ... and your plate voltage was say 400 and you wanted to run at 70 % .... it would be 25 / 400 x .70 = .043 or 43mA

One of the best BIAS vids out there IMO .... been going back to this for reference for years now

https://www.eurotubes.com/store/pc/generic bias video.htm
 
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