Roland cube 60 keyboard help!

[pontiacpete]

yes

[pontiacpete]

It took a few years but I finally got back to this amp. I got it working, but it’s creating a lot of heat. The back panel is getting to about 195° where the output transistors are attached.
I’ve used it for a quiet rehearsal for 2 hours and it sounded very good but very hot.
Is this the way these amps run? Or is this something I should be concerned about?

[sugeda]

Check bias current and adjust with R58 if necessary.
Oscillation generating an inaudible frequency would cause heating.

[pontiacpete]

I measured .48 and .45vdc across the .33r which is about 1.4A. Seems like a lot.

Thanks for the schematic, I don’t think I’ve seen this one anywhere and it seems to be the right one for this amp. Amazing.

[sugeda]

Normally 10mA ... 20mA

[pontiacpete]

Do you think I should be looking for an oscillation with a scope or just lower the bias?

[sugeda]

First reduce the bias current.

[pontiacpete]

I raised r58 from 6.8K to 15k and I get about 18mA across the .33rs. It’s running much cooler and still sounds good. If there’s nothing else then thanks again for the help.

pete