how hot is too hot :)

norburybrook · Post by **norburybrook** » Mon Apr 06, 2020 6:12 pm

greetings , hope you're all keeping well and safe in these strange times.

I've been working in the studio the last few days and using my 100w Bluesmaster. A lovely amp, however I've noticed at the end of the day when switching it off it's really hot, the on off/standby switches would burn your fingers if you held on to them.

The amp is sounding great and showing no signs of any stress etc but none of my other amps get that hot.

Is this a problem waiting to happen somewhere down the line?

and what causes this?

M

YouTube · Post by **xtian** » Mon Apr 06, 2020 8:42 pm

What's your idle dissipation set at? EL34s or 6L6s?

martin manning · Post by **martin manning** » Mon Apr 06, 2020 9:13 pm

With 6L6's you have four tubes dissipating say 18W from the plates, and another 5.7W from the filaments, so nearly 100W, heating the power end of the chassis from below. No doubt the heat will age some components more quickly. If you are going to have it running for many hours at a stretch, maybe consider a small fan, if you can fine something that's quiet enough.

donvan · Post by **donvan** » Mon Apr 06, 2020 9:39 pm

I agree that 100 watts of heating from below the power side of the chassis sounds like it could get warm. But I think Marcus is saying that he has other amps (presumably 100 watts also) and they are not getting that hot.

Mr. dB · Post by **Mr. dB** » Mon Apr 06, 2020 9:44 pm

martin manning wrote: ↑Mon Apr 06, 2020 9:13 pm With 6L6's you have four tubes dissipating say 18W from the plates, and another 5.7W from the filaments, so nearly 100W, heating the power end of the chassis from below. No doubt the heat will age some components more quickly. If you are going to have it running for many hours at a stretch, maybe consider a small fan, if you can fine something that's quiet enough.

There will also be some heat contributed by the power transformer, no?

martin manning · Post by **martin manning** » Mon Apr 06, 2020 9:57 pm

Sure, both transformers, the choke, the preamp tubes, and the resistors.

Charlie Wilson · Post by **Charlie Wilson** » Mon Apr 06, 2020 10:33 pm

My amp gets pretty warm from power tube proximity heat but it seems to level off at some point. I have a Mercury Twin power transformer in my amp and I know those things run pretty cool. What power transformer do you have in the Bluesmaster?
CW

talbany · Post by **talbany** » Tue Apr 07, 2020 3:07 am

My Low plate classic w/ STR Fender/Sylvania 7581 runs around 124.40 watts at idle it gets warm

The Music Man w/JJ EL-34's pulls 134.13 watts at idle and if left on long enough gets hot!

Install a fan. It does not have to be huge just something to blow out the heat

BTW. Don't hold on to the switches.

Tony

nworbetan · Post by **nworbetan** » Tue Apr 07, 2020 3:17 am

When I was a dishwasher back in high school I learned that my personal threshold for "this feels hot enough to burn my hands and my reflexes are telling me to let go, but my brain knows it isn't going to cause any damage" is in the ballpark of 140 degrees F. (The industrial sized dishwhashing machine had an internal thermometer and that was roughly the temp the dishes were at when they exited.)

A lot of common electrical components are rated to tolerate 85 degrees C, but need to be derated as you approach that temp, and their lifespans are probably going to be shorter as you approach their limit also.

Those are my 2 cents.

nworbetan · Post by **nworbetan** » Tue Apr 07, 2020 5:21 am

I guess one more tidbit is that sometimes you'll hear about an amp that "opens up" or "comes to life" after it's been on and running for a while. What's happening (or at least one thing that's happening) is that as the iron cores of the transformers slowly absorb heat, the resistance of the copper changes slightly, which changes the voltages by a small but audibly noticeable amount, even if you only have silver ears and haven't upgraded to gold yet.

http://www.resistorguide.com/temperatur ... esistance/

norburybrook · Post by **norburybrook** » Tue Apr 07, 2020 9:45 am

thanks guys.

The amp is this one

https://ampgarage.com/forum/viewtopic.p ... luesmaster

the transformers are from an old peavey amp. I think I have Russian tubes the 5PS 5881 type ones and left the bias voltage at 6L6 values meaning they're running at 70% rather than 60%, does that will mean they're physically running slightly hotter? . Might try knocking that back, they're not red plating or anything and sound good.

A fan is obviously the quicker fix. I think I have some computer fans kicking around that will be perfect, would it be safe to power them from the relay PS? I Might make the front panel vented too like a 2 rock, the dumble ones are solid and don't kelp with air flow. In fact you could fit a fan in the front baffle that would pull or push air though

The amp is running great, quet, consistent, and sounds great so it's just the heat issue that worried me slightly as I've used 'old' transformers and therefore they could be on they're way out perhaps after all this time. I presume they just work until they don't

martin manning · Post by **martin manning** » Tue Apr 07, 2020 10:21 am

The original Tung Sol 5881 is a 23W tube, where the 6L6GC is 30W, so you probably should dial the idle down a bit, unless you know the rating of the Russian tube. And yes, that will help, a Watt is a Watt. A computer fan mounted on the front panel and pushing air out through the grille on the power tube side would be a good solution. The Vox cloth has an open weave, so I think the flow would be adequate. I'm not sure your relay supply will have enough power to drive it, though. What are the specs on the fan motor?

norburybrook · Post by **norburybrook** » Tue Apr 07, 2020 10:37 am

martin manning wrote: ↑Tue Apr 07, 2020 10:21 am The original Tung Sol 5881 is a 23W tube, where the 6L6GC is 30W, so you probably should dial the idle down a bit, unless you know the rating of the Russian tube. And yes, that will help, a Watt is a Watt. A computer fan mounted on the front panel and pushing air out through the grille on the power tube side would be a good solution. The Vox cloth has an open weave, so I think the flow would be adequate. I'm not sure your relay supply will have enough power to drive it, though. What are the specs on the fan motor?

IIRC computer fans run on 5vDC possibly 7vDC.

I suppose Dumble never had issues with this, and my other two 100w amps are out in the field and have had no issues. The dumble head cab isn't the best design for ventilation though with a solid top and front panel.

I'll have a look over the next day or so see how things are inside and take a few voltages and knock back the bias on the tubes.

Funny, the other amp of mine that runs noticeably hot is my Princeton reverb, I've noticed that has distorted the rear face plate due to heat

M

martin manning · Post by **martin manning** » Tue Apr 07, 2020 10:39 am

Are you sure you don't have 6∏3C (6P3S) or 6∏3C-E (6P3S-E)? They are only 20 and 25W rated respectively.

norburybrook · Post by **norburybrook** » Tue Apr 07, 2020 10:39 am

martin manning wrote: ↑Tue Apr 07, 2020 10:39 am Are you sure you don't have 6∏3S or 6∏3S-E? They are only 20 and 25W rated respectively.

yes they are the tubes. which ever are the military spec ones.

M

Tube Amp Archive

how hot is too hot :)

how hot is too hot :)

Re: how hot is too hot :)

Re: how hot is too hot :)

Re: how hot is too hot :)

Re: how hot is too hot :)

Re: how hot is too hot :)

Re: how hot is too hot :)

Re: how hot is too hot :)

Re: how hot is too hot :)

Re: how hot is too hot :)

Re: how hot is too hot :)

Re: how hot is too hot :)

Re: how hot is too hot :)

Re: how hot is too hot :)

Re: how hot is too hot :)