HEC B500E amp

[zinger827]

I just picked up a HEC B500E amp person said it needed a the keying circuit rebuilt. Any ideas what parts are needed? Also is there a way I could jump the relay to see if amp will key up and has power out? No way I'm sticking my fingers in there to get zapped. Also noticed it has 3 6lb6 tubes on top row and 3 6lf6 tubes on bottom row is that normal? Thanks.

 

[Shockwave]

If you look at the 5 lug terminal strip mounted to the left of the relay and behind the transformer, you're likely to find that small black transistor on top is burnt out. From the picture it looks like one of the 3 wires on this part could also be shorted or broken.

The final tubes were probably all 6LF6 tubes when it was new. Someone probably replaced 3 with the 6LB6 tubes because that's what was available. While it would be nice if all 6 were matched, I've seen these two types of tubes play nice together in the same stage because they are close. I'd be more concerned about the condition of the tubes than the type here. Because if one set is stronger than the other it will do the majority of the work.

 

[zinger827]

Ok that transistor is a 2n3643 in schematic. Is there another that will cross with it like a 2n2222a?
Holden Electronics Company B-500E

 

[Shockwave]

The old 2N2222A should work well here. You may want to check D4 also to be sure it's not shorted from too much drive.

 

[zinger827]

Yes I will replace d4 and check d5 also while replacing the transistor. Will post results in a day or 2 when I get to work on it. Thanks.