ADA Microtube

[Valvehead]

Hey guys--i have a Microtube 100 poweer amp here. If powered on it blows the 4 amp fuse .

It has a big short somewhere--my light bulb limiter lights up very bright when amp is on--but still in standby. If i pull the 2 main power wires from the power trans to main pcb , the light goes out. So the trans is ok .

I actually had the output transistors for this , so i started there. The pcb comes out very easy..so why not ...2 new 9530 and 2 530 . No change after that.

I cant see anything burnt etc...

Im attaching a pic of 1 part. It looks like 2 tiny , long ceramic resistors ?? 1 wire goes from that to the 4 amp fuse , and other wire to the 1/2 a fuse. So..what is this piece ?? there is an arrow pointing to it .

So , i dont think Ive worked on an ADA power amp before , any suggestions where to start ?

does anyone have a scem for this thing ?

[g1]

That part is a thermal breaker. It will open if the unit overheats.
The schematic should be available at elektrotanya. Please post it here.

[Tom Phillips]

...any suggestions where to start ?...

You did a good job of ruling out the PT as the problem but then you jumped right to the output transistors. Work your way down the path through the power supply circuit right after the PT next. Isolate / check rectifier & filter caps next.

[mozwell]

microtube 100 in case they are not available elsewhere anymore

[Enzo]

So , i dont think Ive worked on an ADA power amp before , any suggestions where to start ?

Same place you start on any amp that blows fuses. Are the output devices shorted? Are any of the rectifiers shorted? Are any of the power rails shorted to ground or to each other?

[Valvehead]

sorry guys---life got in the way--and i own this amp so its on the back burner. I will post back when i can work on it

[Valvehead]

well-- i finally worked on this one .

it was a shorted diode. replaced it and the unit works great