Blown mje350 and led [REPAIR VID AT END] [resolved]

[Paul Joppa]

Yes , the 375 volt will be more reliable. The higher voltage is the primary reason for changing from the MJE350.

If there were an even higher-voltage PNP transistor available, I would probably want to switch again.

[Paul Birkeland]

Either one will work adequately in the Paramount.   The change is to buy a little extra tolerance to high voltage (the MJE350 is rated for 300V max) and to better handle the thermal requirements in that position.

[Rob Capizzi]

https://youtu.be/0LyUAwK985c?si=dsYMtSWcko1YbfEU
SUCCESS!  YOU GUYS ARE GREAT! THANK YOU!
4 out of 5 diodes fried.

[Paul Birkeland]

The presence of the MJE350 in the original circuit was likely the cause of the fried zener diodes. 

Don't hesitate to clip a little heatsink onto the 5731A down the road if you can.

[Rob Capizzi]

I will. I have mini ones that'll be perfect.  All of them I suppose could benefit, even the power supply board? What's the best way to attach? Thermal paste and maybe thin tie wire twisted.

[Rob Capizzi]

I'm going to pick up heatsink glue

[Paul Birkeland]

I would just get some small clip on heatsinks for TO-220s.  I wouldn't glue anything on or use thermal grease, that's pretty overkill for the application. 

[Rob Capizzi]

I got nte425. Thermal Interface pad self adhesive.

[Paul Birkeland]

Something like this is fine:
https://www.digikey.com/en/products/detail/assmann-wsw-components/V8508A/3476148

If you need to take the heatsink off for future work, it's pretty easily done.

[Rob Capizzi]

Do any of the repairs I've done have an effect on the audio at all? Sonics, volume?

[Paul Birkeland]

No, you're just replacing broken parts with new ones.

[Rob Capizzi]

Heat sinks

[Rob Capizzi]

Should I replace all four mje350 on both boards in both amps?

[Paul Birkeland]

I would take the heatsinks off the high voltage rectifier diodes, as they dissipate nearly no heat. Likewise on the remaining MJE350 in the Paramount. 

[Rob Capizzi]

I would take the heatsinks off the high voltage rectifier diodes, as they dissipate nearly no heat. Likewise on the remaining MJE350 in the Paramount.

Ok I will. I am also going to replace the old A side mje with mje5731AG on both amps. Also both on the center board in the foreplay. I will only heatsink the MJE5731ag  on the B side only? . I assuming the MJE5731ag  will work on both the A and B side. Any other prevention upgrades I should do?
Also, why in the manual ,A side calls for MJE5731a and B side mje350?  Thanks.