Concert Bass with a Concert Lead PowerAmp Circuit board

[tinman948]

A friend just wanted me to look at his Concert bass amp that he smoked, but when I went trace down the bad resistors it seem that this is a different circuit board than the Concert Bass. The board says Concert Power and seems the have the correct components. My question is, are the Concert Bass and Concert Lead Power Amp circuit-board interchangeable. There are no wires left out and it mount up perfectly.

[tinman948]

I forgot to mention that this is a red knob amp

Ok a little more looking on the board I found a part number 20-0111D.
That makes it a Concert Lead.
So I got a Concert Bass amp with a Concert Lead circuit board in it.
It fits like it was built that way.
Makes yea wonder!

[tinman948]

I got a question though. Does this make it a Concert Lead or a Concert Bass?

[tinman948]

Ok I'm gonna put this question out there to see if I get any response to see if I should be in a different forum.
With this being a Concert Bass amp with a Concert lead circuit board in it, is this something Sunn did or was it modified after it was bought? It was bought used.

[george]

Okay - the Concert Lead had a channel with reverb and a dry channel - marketed for guitar players

Concert bass no reverb channel and marketed for bass players.

Both designs could share the same output board.

If your amp says Concert Bass on the front panel that's what it is. Someone may have "repaired" it and replaced the output board ?

Sunn marketed this model/series (red knob - post balck and silver face - whatever) as capable of driving a 2 ohm load. You usually end up with a power amp board failure when you try driving anything under 4 ohms.

[tinman948]

Thanks,
    I replaced the 4, 24ohm-2w resistors. 1, 22ohm-5w resistor and the 5, 2N3055 power transistors. Seems to be working ok.

    All I had were these resistors laying around. What do you guys think?

[loudthud]

Do you see on the circuit board where is says "COMMON ______" ? That means parts with a solid outline are common to all versions of the board. Where is says "SLAVE ONLY_.._.._.." that means on a Concert Slave amp you add the parts with that outline like R134 and R135. Where is says "L, B, KYBRD ONLY _  _  _  _" that means that you add parts with that outline for the Concert Lead, Concert Bass and Concert Keyboard amps like CR107.

The Concert series went through several major design changes over the years. Even if you have the correct schematic, it's not uncommon to find some little difference between the schematic and the amp you are trying to repair. You are looking at a power amp board that was the same for the Concert Bass, Lead and Keyboard amps.