Guitar amp regulator too hot

Thread Starter

robismod

Joined Sep 22, 2015
111
I have a guitar amplifier (tube) that has a 7815 regulator that’s supposedly getting too hot, (according to other users). The solution is to put a heat sink on it I read. However after getting into it I find the part has an “isolated tab”. I had to make a very small sink to fit in the tiny space but not sure how to mount it, since it looks to me like both sides are a plastic-like material. Which side does it mount? Does it need a thermal paste?
Thanks
 

SamR

Joined Mar 19, 2019
1,806
I assume this is in the TO-220 package? The metal "Backplate" is the GND as is the center pin. It should go to the heatsink with paste between. Be careful snugging the retention screw that it doesn't kick the xstr up as it needs to sit flat on the heatsink.
 

DickCappels

Joined Aug 21, 2008
6,185
Either side should be fine. A thin layer of thermal compound may help with the thermal coupling. Before you modify your amp, you might want to measure the case temperature to find out whether the 7815 is actually too hot. Those regulators are nearly bullet-proof having built-in circuitry to prevent damage from over current and overheating and will shut down if too hot or if the input-to-ouput voltage and current curve exceed the maximum safe amount.

If it is not broken, it might not be a good idea to fix it.
 

bertus

Joined Apr 5, 2008
20,318
Hello,

Are the decoupling capacitors on the in and output of the regulator mounted?

3-pin_low_power_regulators_with_capacitors.png

For Isolated mounting material have a look at the following picture:

TO220_isolated_mounting_material.jpg

I have taken a TO220 transistor for example.

Bertus
 

Thread Starter

robismod

Joined Sep 22, 2015
111
This Bugera two channel amplifier is one of the earlier models from a company that had some known issues in the beginning, from all I have read. (New power tubes, running at 4 ohms into a 4 ohm cabinet) Last week while using at a rehearsal, it would take spells of suddenly the guitar audio would quit, and a whine/fizzing sound would start and rise in pitch for about 7 seconds. During this period the used channel LED would not be lit as well. After the whine stopped, the channel LED would come back on and the guitar audio would resume. This happened about 4 or 5 times in a couple of hours. Getting back home I started studying and found some info about this particular regulator being an issue that supposedly was cured by adding a sink. (Couldn’t find one locally so I made a small aluminum piece to attach...it’s a very limited space so it’s L-shaped so that part of it will stick out over top of the part)
I went ahead and replaced the 3 caps nearest it—66,67,68 and found one of them bulged badly at the end that was against the board.
Thanks so much for the ideas/help.
 

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Thread Starter

robismod

Joined Sep 22, 2015
111
It appears I may have fixed it...so far so good for the last couple hours with a few playing sessions within. I notice a little hum when the amp is first turned on but seems to disappear in a couple minutes . Thanks again for the help.
 
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