Peavey Classic 20 MH - Tube or Bias issue?

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teleguy234234
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Peavey Classic 20 MH - Tube or Bias issue?

Post by teleguy234234 » Sun Sep 24, 2017 8:15 pm

Hey all - first post here.

I bought the above mentioned amp used on reverb for a great price back in spring. It just got new power tubes a few months ago and tonight the darn thing is already acting like they're dying. The signal keeps going down and the power tube indicators on the front are changing from green to red with my signal dying. Now I bought this amp last summer used on reverb so when this happened a few months ago I thought ok it's probably had old tubes but seriously after only a few months of maybe 30mins to hour practice every few days my tubes are dying?

From what I read this amp has a bias feature but was told it wasn't necessary- should I be biasing these tubes? Did I get a bad tube set? I don't have much tube amp experience so I would really love some help here.

Edit: I use the amp in with headphones MDSI 100% of the time and also run my amp at the point of breakup but that shouldn't be an issue.
Edit 2: Are there any good tutorials/can anyone tell me how to bias this amp...Im trying to save money by not taking it to the amp tech...

ScottMarlowe
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Re: Peavey Classic 20 MH - Tube or Bias issue?

Post by ScottMarlowe » Mon Sep 25, 2017 11:49 am

The common method for adjusting bias on these is to turn it on, let it warm up, and then adjust the bias pot one way until the TSI starts to turn red, then the other way til they start to turn red, then put it halfway in between.

Or you can take it to a tech and let them do it with a bias probe etc. But apparently the halfway between red method works pretty well.

teleguy234234
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Re: Peavey Classic 20 MH - Tube or Bias issue?

Post by teleguy234234 » Mon Sep 25, 2017 3:15 pm

ScottMarlowe wrote:
Mon Sep 25, 2017 11:49 am
The common method for adjusting bias on these is to turn it on, let it warm up, and then adjust the bias pot one way until the TSI starts to turn red, then the other way til they start to turn red, then put it halfway in between.

Or you can take it to a tech and let them do it with a bias probe etc. But apparently the halfway between red method works pretty well.
Thanks man! Actually already got another response in a diff forum saying the same. Ordered a new set of jj's from eurotubes for $25. Hopefully these will last longer with the bias adjustment. I'm guessing since the MDSI is a dummy load I can just leave my headphones plugged in as well. Pretty nifty!

teleguy234234
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Re: Peavey Classic 20 MH - Tube or Bias issue?

Post by teleguy234234 » Mon Sep 25, 2017 9:56 pm

Does anyone else find when using the MDSI that the clean channel doesn't get quite into that edge of breakup tone and the overdrive channel is WAY quieter than the clean channel? I run my clean channel on 7 which gets a tad dirty but not quite edge of breakup. Using a boost on my JHS Ruby Red I can drive it into over drive but I'd rather get it from the amp. The second channel I can't ever get the levels right but it has great sounds. It's always quieter than the clean and that's with the post volume maxed and pre volume as a gain control.

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