Superscope 1240 Question

[Jeff Knight]

Hi Everybody,

I am doing a recap on a Superscope 1240 that I bought recently. I am relatively knew at this so I was hoping someone could help me out.

When I was recapping the amp board I noticed a wire loose on the back of the board. It was connected to something that said 65C on it. I thought it might be a thermal fuse, but I can't see to find anything to confirm.

Does anyone know what this is and if there is a compatible replacement?

Thanks!
-Jeff

 

[fromnowon]

It was probably screwed to the heat sink . . . the leads break off very easily. General advise is to be really careful and not move those around much.

https://audiokarma.org/forums/index.php?threads/replacing-the-stv-3h-and-4h-diodes.279530/

There are some STV3H-Y's available on ebay but my understanding is the 4Hs are really tough to come by.

Have you been able to find a service manual for your 1240? Hopefully that 65C is a 3H.

 

[AE Bob]

Those bias diode stacks can be repaired, although it is tedious. You need to CAREFULLY grind away enough of the plastic body to expose a small amount of the wire that is broken off. You then solder a piece of 20 AWG or so wire to the exposed stub, then imbed the connection in epoxy glue. I have done several (don't ask why {;>(

 

[Jeff Knight]

It was probably screwed to the heat sink . . . the leads break off very easily. General advise is to be really careful and not move those around much.

https://audiokarma.org/forums/index.php?threads/replacing-the-stv-3h-and-4h-diodes.279530/

There are some STV3H-Y's available on ebay but my understanding is the 4Hs are really tough to come by.

Have you been able to find a service manual for your 1240? Hopefully that 65C is a 3H.

Thank you very much for your help! I found a service manual on ebay. My problem was there was no code on the back of the board, so I really wasn't sure what to look for in the manual. Now, that I know it is a bias diode, hopefully I can find it in the parts list. Hopefully it is the 3H. If not, I will try Bob's approach.

 

[Lavane]

Those bias diode stacks can be repaired, although it is tedious. You need to CAREFULLY grind away enough of the plastic body to expose a small amount of the wire that is broken off. You then solder a piece of 20 AWG or so wire to the exposed stub, then imbed the connection in epoxy glue. I have done several (don't ask why {;>(

I had to do the same. I bought a Literal basket case on the cheap all in pieces, cut wiring, bodged repairs, etc. When I removed the amp board from the box a lead got knocked off one of the bias diodes.

 

[Jeff Knight]

Well, I finished re-capping this. I plugged it in and there was a loud hum coming from my speakers and the amp board started to smoke. Looks like I am back to the drawing board lol. *sighs*

 

[AE Bob]

You need a Variac or Dim Bulb Tester!!!!!!!!!!

Did you repair or replace the bias diode? Without the diode in place, the output stage will draw tremendous current and burn up.