Fender M80 runs hot

[Luthin You]

Hi i'm a tube amp tech but s/s is weird to me. Why does an M80 (non chorus)run a hot output stage?Thanks in advance.

[Enzo]

Try these

[Luthin You]

thanks Enzo , Im an old dude and dont know how to open those pages . Sorry to be a pain, any hints ?

[52 Bill]

thanks Enzo , Im an old dude and dont know how to open those pages . Sorry to be a pain, any hints ?

They are pdf's, you need Acrobat Reader to open them.

Basically the first one suggests changing two bias resistors R74 and R76 from the original value of 1K to 2.2K.

The second one suggests changing the Sil Pad insulators (grey rubber sheets) for mica washers with heat sink grease.

Another thing to check is for broken off caps that can cause the amp to oscillate at a very high frequency. Look at the output Zobel network and see if it shows signs of overheating.

[Enzo]

Move your mouse to put the cursor on one of the images in my post. Click on it. it should open all by itself then or put up a box asking you to pick an option.


And there are other measures. Those bulletins cover general situations, but specific amps have specific needs, so we can usually chill amps by messing with the bias string.