Amp repair help

[Wingman0121 10+ year member]

You guys know all amps use some sort of metal clamps to hold the transistors firm against the heatsink, well after getting an amp back from repair some of the transistors are just very slightly different in thickness so some of them are not sitting against the heatsink as tight as they should be. What backing material can I add to the black plastic side of the transistors so all of them can sit flush against the metal clamps? Thermal adhesives? High temperature rubber? It is not the side that gets really hot but I don't want things to melt either.

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[nateberrier 10+ year member]

if you have some busted amps you could take the sil pads out and put them in between

 

[Wingman0121 10+ year member]

if you have some busted amps you could take the sil pads out and put them in between

I thought about that but I don't have any broken amps laying around nor any other non-working electronics to recycle through.

 

[Spooney 10+ year member]

It bothers me that not all the transistors match in thickness. Makes me wonder if perhaps somebody did a hackjob on your amp. Now if the parts that vary in thickness do different jobs(ie. rectifiers,ps fets,outputs ,etc) it may not be a big deal but if say some of your outputs and or power supply fets are mismatched in thickness from each other then there is a good bet that they are not the same part. All parts in parallel with a component that failed like a fet or output bjt should be changed out with matched date coded parts when doing amp repairs. By that I mean if one and only one power supply fet blows then even if only that one is reading shorted or blown open all of the ps fets should be changed as all of the fets that are connected in parallel with it saw the same abuse,they just didn't fail yet but believe me eventually they will. Same goes for the outputs. If one in a channel fails its best to replace the whole channel to increase reliability. Using fets or outputs that all came from the same batch goes a long way towards making an amp more reliable. There are a lot of techs out there however that do not observe this practice.Why do some techs do repairs like this? Simple really,money. Much cheaper to charge you full price and only do a half *** job knowing the amp may just make it past their short warranty periods. If it doesn't they still probably pocketed enough profit to make the repair again and still come out on top. Anyways for your original question the old school orion amps used to use a simple two sided foam tape on the backside of their clampdown bars. 3M makes some that you should be able to find at most hardware stores. Its about 1/2" wide and white in color . Just take the backer off of one side of the tape and stick it to the clamp down bar and leave the backer on the side that will touch the transistors so it doesn't stick to them should you ever need to remove the clamps downs again(this tape will pull transistors apart if you aren't careful). Should help even out some of the irregularities while applying proper pressure.