Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Solid State => Topic started by: TerryD on February 18, 2011, 01:56:56 pm
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What is a Thermalloy? I'm assuming I have the right number. One is on the back of the amp the other had been knocked off. Can they be replaced? Are they expensive? Where can I get the part? Thanks.
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Such as this:
http://www.newark.com/aavid-thermalloy/8909nbg/insulating-cover/dp/18M8294?in_merch=true&MER=ALT_N_L5_FansHeatSinksAndThermalManagement_None
?
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Thats exactly it. what are they? How important? If one is knocked off how difficult to replace? Thanks, Terry
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> What is a Thermalloy?
They make a LOT of different heatsink products.
Thanks to thermion for looking it up.
> Thats exactly it. what are they? How important? If one is knocked off how difficult to replace?
They cover the power transistors. The power transistor case is LIVE. Probably 50 Volts, not horribly fatal, but if you short the transistor case to the chassis you will melt the amp; if you short it with a ring it can burn your finger to the bone.
IF the transistor has not been damaged or loosened, you can use the amp if you DO NOT have an accident.
Accidents happen.
So you really should fix it.
With amp OFF!, see if you can loosen the two screws. What you want to do is get the screws out but do NOT loosen the transistor from its mounting surface. It's stuck on with white goo, if it gets loose you really should take it off, clean it, and re-goo it (it's the same goo we use on PC CPUs). If the screws come out and the goo is undisturbed, just put the insulator on and tighten well.
EDIT: it appears the 8909 is supposed to snap-on. This depends on an exact fit to the transistor. If you have the old one, snap it on. Or get a fresh one and snap it. If it won't stay snapped-on, think what else you can use to cover the transistor against electric contact yet allow full flow of air over the heatsink.
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I'm thinking maybe the whole transister is knocked off. It looks like the piece I would screw it into on the inside is still there. How do I figure out what part to replace it with...which transister I need. Would the transister be on the outside of the amp just under the thermalloy? There are two on the amp. I'm hesitant to pop the other thermalloy off. Thanks
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http://www.musicparts.com/products.asp?Company=Crate
However you should probably turn to a tranny-amp guru. And that may cost more than a IIR is worth.
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I'm thinking maybe the whole transister is knocked off. It looks like the piece I would screw it into on the inside is still there. How do I figure out what part to replace it with...which transister I need. Would the transister be on the outside of the amp just under the thermalloy? There are two on the amp. I'm hesitant to pop the other thermalloy off. Thanks
If you want to do the work yourself, a schematic would be keen. Discrete transistor outputs from this age amp would most likely a PNP/NPN pair.
It is unlikely the output transistor has been knocked off. TO-3s would be bolted to the chassis for good heat conduction out of the device. Can you post some pix?
cheers,
rob
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Here are pics. As I said the remaining one on the back has written on the piece "Thermalloy 8909NB" I included a picture of what it was connected to inside. That seems in good shape except for the screws being ripped out....it looks like the one remaining without the connecter screws through it.
Please, if you could, explain what to do in laymans terms. I like to know whats going on, but am handy with my hands and could do it, if possible, without knowing Thermalloydynamics.
Do you think the amp could be fried already??
People have given me several places I could get part 8909NB, if that was what I needed, so these seem easy to get.
Whats under that plastic cover. This, to me is a nice amp to waste. Thanks a lot!
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Forget about the thermalloy. It's just a proctective insulating cover for the transistor. The transistor is gone too. You can't even start to fix this without knowing what polarity the missing transistor is. Then you need to know what type. Then you need to check the driver transistors too. You need a schematic and a layout with parts locator. And you need to understand transistor amps. You can't just shotgun fix most ss amps. And just simply replacing the missing transistor probably won't fix it. It's likely that there is also another problem that caused the transistor to fail or maybe it took out some drivers when it died. Either way, if you just replace the transistor, the new one may fail as soon as you apply power.
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Thanks guys for the help.
I did get the schematic which they sent from crate to make sure both transisters were the same one.
Called Digitech and the guy cross referenced an obsolete part number for the transisiter. No special knowldge needed otherwise...the part went where the other got knocked off and it was engineered so you can't put it in wrong.
What was to lose? Now this is a great amp for someone.