my amp went bang

[lightningfingers]

(The amp in quesion is a 30W Gorilla practice amp) I've been putting off a general amp service for a while now (so have its previous owners, its been in need of a service since 1989)

So today I replaced all the filter caps in the power supply, and every other electrolytic in there. I decided to replace the heatsink as well, as the old one was crappy. The poweamp wouldnt work with the new heatsink in place, it emitted a low humming noise ad no guitar could be heard. So i've been playing through it all day with no heatsink, and as you probably guessed it burnt out just now, getting a new one isnt really a problem, but I need it to work with a heatsink in place, any tips? Do you need one of those little insulator things? (It originally had one but I lost it.)

TIA

[Paul Marossy]

You may need that heat sink insulator that you lost...
Is it a solid state amp?

[lightningfingers]

Yeah, its a ss amp :oops: . I love it all the same though. Its sounds almost if not as good as my AX84, and at least twice as loud. I'll go to Maplin tomorrow and get another insulator.

[aron]

You should be able to get the insulator - I think you can even buy a sheet of it and cut it. Radio Shack?

[Paul Marossy]

Sometimes on power transistors, the collector is connected to the part that the heat sink connects to. If you connect that directly to ground, it shorts out the transistor. Just my thoughts...

[niftydog]

DOH!

You definately need the insulator. And, you'll probably need the little plastic grommet that goes in the semiconductors mounting hole. Basically, you want to prevent any electrical connection between the semiconductor and the heatsink.

[dolhop]

I'm curious as to what you mean by "general service".  Solid state amps usually don't require any service - they're like cars requiring an oil change.  Yes, the caps may lose their wits over time, and can be replaced if the hum gets to be too loud.  But if it isn't broken, don't try to fix it.  

As for the heatsink, unless you were going for something more aesthetically pleasing, there was probably no need to change that either.  There are strict calculations regarding heatsink requirements that would have been taken into account when the amp was designed.  And so, the heatsink that was on there would have been large enough to dissipate the heat generated by the amplifier - increasing the size would yield no benefit to the quality of your sound.  Now, if the amp was overheating and cutting out, then an increase in heatsink size would be justified.

It definitely sounds like you're missing the insulation.  But definitely do NOT use the amp without a heatsink.  Even just turning the amp without use can fry the transistors......

[Mike Burgundy]

The heatsink on these isn't  really comfortably large as it is. As stated, make sure there is absolutely no electrical contact between the poweramp and the heatsing, but please DO use heat-conducting paste - otherwise you're running the risk of installing a (smallish as it is) heatsink that doesn't work as it should.
hih

[RDV]

They got Radio Shack in England??

RDV

[Paul Marossy]

But definitely do NOT use the amp without a heatsink

Yep. Those power transistors only acheive their ratings by proper heat sinking. Without proper heat sinking, they can literally destroy themselves due to dissipation.

[lightningfingers]

I'm curious as to what you mean by "general service". Solid state amps usually don't require any service - they're like cars requiring an oil change. Yes, the caps may lose their wits over time, and can be replaced if the hum gets to be too loud. But if it isn't broken, don't try to fix it.

Thats all I did. Replaced the caps and the rusted old heat sink.

RDV: we don't have Radio Shack, but we have Maplin, which is just as bad, if not worse.

I have a new IC now (TDA2030AV), but the placement on the PCB (and the shape of the IC)makes it impossible to use a socket...if I attatch the heatsink (and the insulator) first, will it survive the soldering?

[petemoore]

I'm curious as to what you mean by "general service". Solid state amps usually don't require any service - they're like cars requiring an oil change. Yes, the caps may lose their wits over time, and can be replaced if the hum gets to be too loud. But if it isn't broken, don't try to fix it.

Thats all I did. Replaced the caps and the rusted old heat sink.

RDV: we don't have Radio Shack, but we have Maplin, which is just as bad, if not worse.

I have a new IC now (TDA2030AV), but the placement on the PCB (and the shape of the IC)makes it impossible to use a socket...if I attatch the heatsink (and the insulator) first, will it survive the soldering?

>>>Heat and IC's don't mix well, avoid anything that will heat your IC past warmer. Use heat sinks [I use alligator clips when in doubt...sometimes you can get away with a kwik touch of the iron on long leads...use a clip to be sure it doesn't see damage level temperatures/

[Nasse]

I think power chips are meant to be used without sockets. The legs might sometimes work as heat conductors, helping the chip keeping cool. I think some low power chips like 386 and 380 used to be like this in the old days.

Good practice is to use long flat nose tools and squeeze enough so it takes heat as much as possible. When a robot or some soldering machine is doing the job, I don´t know if they use any heat sinking in the component leads, it should tolerate quick soldering.

I made a mistake and did a reverse layout for a chip amp but just noticed I can solder the chip on copper side and the other components to other side :roll:  :oops:

[Paul Perry (Frostwave)]

they can literally destroy themselves due to dissipation.

...as can we all
one thing with heat sink insulators, you can get some kind of thin rubbery material now, instead of the fragile mica. Plus, wiht the silicone rubber ones, you don't need the heat conducting paste, because as you tighten the bolts up, the rubber deforms slightly so there are no air gaps under the transistor. But be careful no to overtighten. And check with a multimeter for shorts BEFORE turning the unit on.. you usually only get one chance with power transistors.

[Paul Marossy]

you usually only get one chance with power transistors

Yep, tubes are much more forgiving devices than transistors...
(generally speaking)