CBT-70 Bass amp

[rfgordon]

Here are some pics of the bass amp I'm building. First, sorry for the poor quality. They are from my phone. I was keeping the client updated.

Second, the gut shot is of V 1.0, which is cathode bias. He wanted to try it first that way, but I have since rebuilt it as fixed bias. He currently has it for a couple of weeks.

When he brings it back for me to finish off I'll take nicer pictures and post those. Gotta love them big ol' Edcor trannies!

[M Fowler]

Rich nice amp.

What circuit did you go with? I want to build a bass amp for my nephew.

I really like Edcor transformers they put out some power and good tight low end bass response.

Need to know more

Mark

[LeftyStrat]

Rich nice amp.

What circuit did you go with? I want to build a bass amp for my nephew.

I really like Edcor transformers they put out some power and good tight low end bass response.

Need to know more

Mark

Another thing to look for is the old Dynaco iron used in Sunn bass amps. Sometimes you can find it on the cheap, though shipping can be a killer. I managed to score one for $60 including shipping.

Good for a couple of KT-88's. I'm saving it for a clean guitar/bass amp, maybe sort of a mini-SSS/Winterland. Whenever I can get a round tuit.

[M Fowler]

What about those potted transformers on Ebay are they worth using for a Ampeg B15N type of build.

[LeftyStrat]

What about those potted transformers on Ebay are they worth using for a Ampeg B15N type of build.

Never really looked at them. The Dynaco model number is A-431. Just about everyone I have talked to that owned the Sunn 200s loved them.

[bb5000]

What about those potted transformers on Ebay are they worth using for a Ampeg B15N type of build.

Never really looked at them. The Dynaco model number is A-431. Just about everyone I have talked to that owned the Sunn 200s loved them.

I use the Dynaco Mk III transformers (new from Triode Electronics) in my Weber 6S100, great for bass ! That's the P782S PT and A-431 OT.

[M Fowler]

Those transformers would provide plenty of power and the Triode Dynclones I have used sounded great.

[rfgordon]

This design borrows heavily from Fender/Dumble circuits, though it runs 6550s for power. The first two gain stages are sort of Fendery, though I used 150k RN65 resistors on the plates, a la Dumble. The bass and treble pots are 1MA with a 100k mid pot. The PI is pretty close to a Fender Twin, though with a slightly larger cathode resistor. My goal was to keep it fairly simple.

When I get the amp back I'll install a fan power supply in the chassis and finish wiring the balanced line out. I got the wee tiny line out transformer from Weber. I used the rectifier board kit from Turretboards, since it seems to be quiet and reliable for high power amps. I used Ken's chassis, too.

One quirk of mine is that I like to put at least one vintage part in every amp. In this amp it is the circuit board for the bias supply (you don't see it in the pic posted, since that's of the cathode bias version.) The billboard-style circuit card came out of a Leslie 125 amp. The eyelets on it lent themselves perfectly to a bias supply layout.