Acoustic Model120 Part identification

[Tilman]

Hi,

I am going to repair that amplifier. There is a small transistor like component mounted on the heat sink between the two output transistors. It measures a short between the two outer legs.
I am not sure if this might be a temperature switch. I tested it with a heat gun but it remains in the short status.

Can someone identify this components ?
Thanks!
Tilman

[MarkusBass]

I don't have schematic of this amp (Enzo may have it). But I would look at similar amps, e.g. this one: http://www.ampix.org/albums/userpics...c_215B-120.pdf
or this one: http://www.ampix.org/albums/userpics...ice_manual.pdf (page 10). This is a npn transistor. You may have to register to see the schematics on ampix.org.
If the transistor is shorted, I would also look at the output transistors (at least).

Mark

[Tilman]

Hi Mark,

both outputs and several resistors are burned. I was able to identify all dead parts....except the one on the picture.
How do you know it is a NPN ? I did no find any part with the printed numbers on the casing.
Tilman

BTW: Still working on the Kustom.....

[Sock Puppet]

This has come up before in this thread:

http://music-electronics-forum.com/t16021/

[Tilman]

Great! Thank you Sock Puppet!
I did not find that thread because I did not know the companies name was "acoustic control". I searched for Acoustic Model 120......

[Tilman]

HA! Just found a schematic for this thing! You know what it says for the bias transistor ?

"NPN TO220 (bias)" ... great....

Tilman

[Tilman]

Replaced the mystery TO-220 with a TIP31C along with new output transistors and several burned resisters....the thing works again.
Sound very good to me too. Almost like a tube amp...it has a very nice bass overdrive sound.
Tilman