Tube temperature

[tonezoneonline]

I just fixed a Ampeg fliptop for an electronics engineer.The amp works fine and all the voltages check but he is an engineer and so measured the temperature of the tubes.He says the're to high of a temperature.I say everything is fine.
Just out of curiousity ,does anyone know how hot in degrees tubes usually run at.
TIA

[Tom Phillips]

Sounds like a bit of a hit and run statement that engineer made to you.
I don’t have an answer but it would be interesting to ask the EE a couple of questions such as:
1) What was the method used to measure the temperature of the tubes?
2) If you say the tubes are too hot then what is an acceptable temperature?
3) If you can answer #2 then please point us to the supporting reference literature. I'd really like to read it.

If you want to get nasty you could ask him why he didn’t fix the amp himself if he knows so much about tube circuits.


BTW I'm an EE too.
Tom

[markbul]

I've seen 200 degrees somewhere. Tubes certainly could be too hot - try running EL34s in a sealed box. I seriously doubt temperature is a problem in your case. As long as there's space to dissipate heat around the tubes, they can take care of themselves.

[Tom Phillips]

Max tube temp info found

I scanned through the RCA receiving tube manual and found that some tubes have a "bulb temperature (at hottest point)" listing in the maximum ratings section. The max temp ranged from 180C to 225C. (Agrees with Markbul's post) I didn't go through the whole book so there may be some specifications out of that range. I noted that 6BQ5/EL-84, 6L6GC, 6V6GC, 6K6 and 6CA7/EL-34 did not have a max bulb temp listed.
A few other comments:
* By "bulb temperature" I figure they mean the glass bottle outside surface. That means you would need to use a contact measuring instrument not an infrared temp sensor that would probably see through the glass and read the temp of an internal element.
* Of course all this does not take into consideration the musical instrument amp tradition of ignoring the maximum ratings of tubes.
* I think the tube temperature is something to be concerned about in a new design but there isn’t much we can do about existing designs without modifying the cabinet, adding a fan etc. I’m not going to worry about it on an amp that has already lasted for 30 or 40 or more years.
* First time I ever heard of a customer saying that he measured the tube temperature and they wee too hot. WTF? Always something new coming up.
Cheers,
Tom

[tonezoneonline]

Thanks for the replys.This guy is a friend and someone I play with somtimes so it's not a big deal.Just got me curious.I figured the RCA manual might have something but had not had a chance to look thru it.He did use an infrared temp sensor and you make a good point about that.This is a flip top so the tubes are in a cage and completely open.
BTW Tom,I went back to school at the age of 40 and recieved a ET degree.
I was planning on going on but ran out of time,money and desire.I have a lot of respect for the EE's.I do poke a little fun now and then at you guys because a few of you are just way to anal
Thanks for the help.

[Tom Phillips]

Cool. Seems like this just turned out to be an interesting exercise. We learned something and your EE customer is not really giving you a problem.
Have a good day,
Tom

[Steve Conner]

Hey, gotta stick up for EEs here! I'm happy as long as I can't see the plates glowing red