Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Nathan on January 27, 2018, 06:40:29 pm

Title: Volume Drop Problem
Post by: Nathan on January 27, 2018, 06:40:29 pm

Hey all,

I have a Mesa Blue Angel that is plaguing me with the most annoying problem: volume will drop out after about 15 minutes of playing. I can get it back to normal by flipping the standby switch off then on again, sometimes it take s a few tries but invariably it drops out later. Any clue what could be causing this?

Pretty sure I have tried changing every tube at one point or another and haven't been able to solve this. All my preamp tubes were tested by a buddy recently and they check out fine. Took the amp to a tech who could not reproduce the problem of course... There almost seems to be a phase issue when the volume drops too. FWIW I use the 6V6 side almost exclusively. Cheers if you can help!

Regards

Title: Re: Volume Drop Problem
Post by: shooter on January 27, 2018, 08:40:18 pm

Quote

Any clue what could be causing this?

run it with the 6V6 til it quits, power down then switch to the '84s till it quits, or not.  That should eliminate 1/2 the PA.

I'd monitor the "A" tap on the ps and see if it starts drifting down with volume (VDC)

Title: Re: Volume Drop Problem
Post by: jjasilli on January 28, 2018, 05:44:50 pm

Checklist:  geofex.com > tube amp debug page > Low Power or Loss of Volume


Also use tubenit's posted checklists & flowcharts.

Title: Re: Volume Drop Problem
Post by: tonepumpamps on January 30, 2018, 08:12:19 am

I've seen filter caps do some pretty strange things.  It could possibly be that.