How hot is too hot?

[Diplomat383]

Good morning, back on the B52 AT-100. After playing it for a while, I decided to check the bias. It was WAY hot, got a reading of 218 MA. Instruction calls for 120. I backed the trim pot down allll the way and it is now at 167 ish.

That is the sum for all 4 power tubes, if I understand the instructions. It sounds just fine, seems to operate normal. It is hot, but it always was super hot when running.

This amp, I tell ya.

 

[Lake Placid Blues]

Re: How hot is too hot?

With the lights out do you see any red glow on any of the plates?

 

[Diplomat383]

Re: How hot is too hot?

Nope, only part that is lit up is above and below the plates.

 

[Erlend_G]

Re: How hot is too hot?

I had a Fender Pro Jr,

and when I put in new tubes, that had labels on it;
it would fry the labels off the tubes...

Always heard the Pro Jr, and also Blues Jr ran very high voltages :/.

sorry, I don't know enough about amps to help you. But wish you the best!

-Erl

 

[Lake Placid Blues]

Re: How hot is too hot?

What is the plate voltage? And what tubes? You could have brought into a safe range if they are EL34s and the plate voltage is 450. (167/4 = ~41 ma) 41 ma being 70% of 55 ma.

If the amp was designed for EL34s and your running a 6L6 or 6550 that would explain the initial extra high reading.

 

[Diplomat383]

Re: How hot is too hot?

This has 6L6GC tubes. Sounds fine, operates just as hot as it always did and never failed at our band practice the other night and I was cranked fairly loud. The amp really doesn't owe me anything, and I would be sad if it fried but I would understand. These aren't the most reliable amplifier lol

 

[Lake Placid Blues]

Re: How hot is too hot?

Ah 6L6s. Assuming the plate voltage is about 450 your good at 167 for four tubes. It would only be around 62 % max plate dissipation. If the PV is less than 450 your probably a lil cold. I don't know where they came up with a 120 ma recommendation, though, unless it has like 500 volts on the plates, in which case it has no business running 6L6s in the first place.

 

[Lake Placid Blues]

Re: How hot is too hot?

Okay the plate voltage is reportedly only about 430. Just be sure that your measuring for 4 tubes and not for two. If it is for 4 tubes then your a little cold right now.