Should she be hot?

Benscotz

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Hi everyone, newbie here, I just picked up an old technics ah-eh760 on gumtree. Wired it all up miles of speaker cable, never had these tri wiring speakers before. Anyway it all seems to work nicely the cd player jumps pretty easily if you knock it but my concern is the amplifier seems pretty warm on the top which I think is fine but I lifted it up to move it a bit and underneath in one corner it seems very very hot. I can leave my finger on it for a while but it's damn hot. Is this normal?
Many thanks ben
 
If you can keep your finger on it,it is not to hot. .. But what level of ventilation have you around it.
 
I've just got it out on a table at the moment so should have plenty of ventilation, it's now getting to hot to touch in that area, I'm probably going to take the top off and have a look at what components are in that area
 
Amps can have hot spots, depending on where the transformers are positioned. As above ventilation is crucial. There is probably a safety cut off built in, I certainly had one in my old 1990s Technic amp.
 
Well popped the top off, and that little thing there is what is causing the very hot part, around the transformer is just warm
 

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Looks like a heatsink for the output transistors. The idea is the transistors are very firmly attached to a metal surface which will dissipate the heat away from the transistors. A paste and a thin plastic washer is normally electrically insulating the transistor from the heatsink. If the paste has broken down then the transistors will run very hot. This could be your problem. It's not a big job to put right by someone who knows what they are doing.

Hope this helps.
 
Thanks everyone for your comments, I've took the heatsink off and dosnt appear to be any sign of thermal paste ever being used, can see the dust around where the transistors sit.
So either there getting to hot for some worrying reason or they are actually in range when they are hot and I'm just paranoid
 

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Well had the stereo on all day so far, nothing bad seems to have happened, that area is still really damn hot ‍♂️
 
Personally I’d give the whole inside a good brush to get rid of all the dust.

Then I’d spray the offending item in contact cleaner and use it to thoroughly clean the chassis where it sits.

Then I’d suggest refitting it using heat paste. Even if there’s no evidence of it having been there before. A tiny bit just to make sure of a
Perfect seating.

It won’t take long and at least you’ll know it’s done as good as can be.
 
I agree with Paul or Blondie, in addition, there is nothing to be lost with a little metalwork. .. a bit of artistic licence with a Coke can and a sissors will provide a massively larger heat sink than provided on that circuit.. just make sure it doesn't short anything!. What is puzzling is that this looks like a output stage ..Two transistors and a diode, so I would expect to see the same elsewhere for the other channel
 
I've given it a clean out and had a good look about, not really sure what I'm looking for but everything looks in good shape and certainly can't hurt adding some thermal paste or even a better heatsink, I'm just puzzled if the thing is supposed to get that hot, I've looked up the transistors and I think I read they go up to 150 degrees, so guess I'm going to run with it and do some more research, it will either be fine or I'm guessing the worst thing to happen would the transistors break down
 
The service manual calls it a regulator transistor and how to change it, not much else though
 

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The service manual calls it a regulator transistor and how to change it, not much else though
Ok that makes sense and why there is only one.. like I suggest artistic aluminium cutting will enhance that little heatsink a lot.
 
Yeah the heatsink isn't very substantial, but that only adds to my worry it shouldn't get as hot as it does, I'm sure i can improve it.
Thanks again
 
You mentioned "Tri-wiring" your speakers. This could be affecting the impedance load presented to the amp, causing more power to be drawn than necessary, overloading the power regulator transistors. Try running with just normal single wired speakers and see how that goes.

IMHO, tri-wiring will not achieve any benefit, other than costing more in wiring and connectors!
 
I have never come across a stereo that needs 6 wires per speaker, it was a nightmare, the speakers are the ones for the stereo, the back of the stereo has high med and low for and so do the speakers, so had to wire up tweeter mid and bass.
I suppose I could just use the mid connection on the stereo to single wire speakers?
 
Wow! I've just looked up the user manual for this system and it does indeed have three separate connections (amplifiers) for each of the speaker's Low, Mid and High drivers and DOES require tri-wiring! In this case, you need to conform to the specified wiring protocol for the L/R speakers.
 
Yeah lol, was a bit of a faff, I'm pretty confident I've wired it up all correctly, one at a time so basically wiring up 6 speakers.
 

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