Peavey Classic 50/50 - Eating Valves (very bright red!)

[stokes]

Nick,are you now using the old tubes?

[NickH]

Nick,are you now using the old tubes?

No, I am not using anything at the moment... It sat on the testbed tube free until Tuesday when a fresh set of tubes will arrive from Peavey...

I only put some old tubes in it just long enough to test it..

Cheers

N

[stokes]

Good luck,then.It sounds,from your last test,that you will be okay with the Peavey tubes,hopefully.

[Enzo]

Yeah, I can;t imagine anything other than a failed tube that would burn up 10k grid stoppers. B+ got on the grids somehow inside the tube.

Stokes, I agree we should always check the bias, and if you have a set of tubes you just must use and they won't fall into reasonable bias, then modifying the amp is about all that is left. My beef with the world is that considering how cold the amp is for the vast majority of tubes, it would take EXTREMELY hot tubes to fall into the red plating zone... unless they are just bad. With that in mind, when I hear about a set of tubes all red plating in an amp like this, and then people go first to redesigning the bias circuit instead of solving the problem, I cannot help but think the effort is misdirected, at least in terms of troubleshooting. SO that is where my bad attitude comes from. How many times around here have we seen someone whose first reaction is "design flaw" rather than "I'm missing something." I have been training techs to troubleshoot for decades now, and I can't help but look at things from that perspective. I am not against modifying the bias circuits, just not as a response to a failure symptom.

[stokes]

Enzo,if you read the earlier posts,that is exactly what I said early on,find the cause of the burnt resistor before checking OT etc.As a player as well as a tech,I do appreciate a well biased set of tubes and am rarely satisfied with my tone without tweaking the bias to find the "sweet spot".So I am a big fan of adjustable bias.All my amps have it,even the couple of Boogie amps I own.I dont like using current production tubes,so for me it is a must.Hell,I have a half dozen cathode biased amps that all have an adjustable cathode resistor.It may not be absolutely necessary,but unless I know they are idling at a specific current....like I've said before,old habits die hard.