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Old April 9th, 2012, 10:21 PM   #1 (permalink)
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Troubleshooting Heat in a 5E3

I was planning on installing a new set of pickups in my tele tonight but there was a "problem" with the order which will prevent me from doing that.

Fortunately I have a list of other things that i can spend some time on. I recently rebuilt my 5E3 (thread here)

The amp sounds fantastic and plays great but one thing i noticed is an extreme amount of heat coming from the power-tubes. they're probably 200+ degrees. They're so hot i almost burned myself the other night when trying to get my hand close to sense the temperature.

I've been reading around the last week or so and it sounds like i'm not the only person who's had an issue like this and that it may be, or may not be an problem.

Could you help me troubleshoot it and see if i have an actual problem or not? I'm not certain what i should check to start?

Here are some pictures and voltages, i'd be happy to check anything else or share any other detailed pictures if that would be helpful.

My filtering section is 16/16/16. Each capacitor respectively is reading:
- 329VDC
- 281VDC
- 208VDC

The large cement resistor (6V6 cathode) w/ 25v capacitor (far left of the board) is reading 18.3VDC

I also grabbed my IR thermometer to check temperatures. After 5 minutes or so of being powered up (nothing in the input jacks and the volume/volume/tone knobs at the mid-point) the power and rectifier tubes are reading off the chart of the thermometer, it maxes out at 230-250F (i'm not sure where, if i move it around a little i can get some reading around 230 but it immediately reverts to, "Hi." Alternatively the preamp tubes are both just over 100F and within a few degrees of each other, which from my limited experience i would consider, "normal."

Here are a couple of pictures:

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Old April 9th, 2012, 11:07 PM   #2 (permalink)
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I have the same concerns myself in a recent 5f1 build. After fixing several self-infected injuries the amp sounds wonderful. I have a Champ 600 chassis which I used and put a 5f1 kit on it which added a rec tube to what was designed to be a two tube chassis. This is my rational for why my chassis is hot, and I do mean hot. I haven't measured the temp but after an hour of playing full tilt the chassis is too hot to keep your hand on more that a second or two.
So I have done several observations and it seems to be tube heat raditation. the tubes after an hour are hot, the rec tube seems to be more hot than the others, but that could be that it's heaters are just more visable.
I'll follow this thread for sure, maybe we'll learn something.
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Old April 9th, 2012, 11:16 PM   #3 (permalink)
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Damn, after taking a closer look at your chassis, it's got several second degree burns, you defiantly need to figure this out before you do some serious damage, good luck.
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Old April 9th, 2012, 11:20 PM   #4 (permalink)
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If you think they're hot on the outside, imagine how hot they are on the inside.

If your plates aren't glowing red, you're fine.
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Old April 9th, 2012, 11:31 PM   #5 (permalink)
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Before we go any further, ask yourself - have you ever played any similar amps where the tubes did not also get hot to the touch under use?

Now, stop and consider that, from the heaters alone, a 5y3GT is consuming 10 watts of power (2 amps @ 5 volts) and each power tube is consuming almost three watts (0.45 amps @ 6.3 volts.)

Then consider that the power tube's (6v6GT) plates are rated for a maximum safe power dissipation of 14 watts for each. So conceivably each power tube could be dissipating around 17 watts.

Ever put your hand on a 10 watt light bulb? That sucker was hot wasn't it?

What makes you think "sound" watts are any cooler than "light" watts?
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Old April 9th, 2012, 11:33 PM   #6 (permalink)
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that's kind of what i was thinking. just not knowing enough about what acceptable temperatures are and the fact that this amp definitely runs hotter than my others i thought it best to get a second opinion (so to speak ; ) )

also, i recently got a new set of tubes and i didn't want to ruin them
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Old April 9th, 2012, 11:50 PM   #7 (permalink)
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IR thermometers are not all that accurate especially home ones. Took some temperatures on a Bassman with contact thermocouples and though I can not recall the exact temperatures but 250 degrees on the glass sounds on the low side to me.
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Old April 10th, 2012, 12:47 AM   #8 (permalink)
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I agree with everything said as the the heat of the tubes. I can also see where that confirms my suspicions about my amp. However the second and third pic you posted appears that the chassis has burn marks above the pilot lamp and the pots. If this is a shadow or reflection then fine, but if those are burn marks and this is a new amp, I'd look a little deeper. Assume nothing.
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Old April 10th, 2012, 01:07 AM   #9 (permalink)
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thanks guys.

boredguy - those are reflections for sure, the heat i'm getting is definitely from the rectifier and power tubes.

i guess with the IR thermometer i wasn't really looking to the actual readings to be super-accurate, more that the difference between the pre-amp and power tubes is probably representative of the temperature difference between them.

is there a list any of you guys know of regarding acceptable voltage (ranges?) per-socket. i feel like it's been covered here and on other forums many many times, especially for the 5E3, but i haven't been able to dig anything up.
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Old April 10th, 2012, 11:22 AM   #10 (permalink)
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I know how you feel about the heat those power tubes are putting off and I initially was just as concerned as you yet after getting confirmation from others here, I quit worrying about it and accepted it as normal but man they do run Hot !! .....i did install a few rows of peel and stick aluminum duct wrapping tape to help keep direct heat off the rear top panel
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