West Grande mod

[flintrock]

Found two 20v 5w zeners in the shop, can I use those in the center tap or since I got the KT's just not worry about it? Thanks

[martin manning]

I think I'd try it with the voltage as is but I would reduce the bias feed resistors to 120-150k for KT88's.

[flintrock]

I dropped them down to 150k's now just in case. My customer will be using this in a punk band, so reliability is one of the biggest concerns.

[flintrock]

Recieved my KT88'S from CE today, matched within 5ma, but pulling around 76-80ma. What is a comfortable ma to be at 60 or 70%, since these are higher output tube?

[martin manning]

JJ says their KT88's are 42W max plate dissipation, 42W*0.7/565V would be 52mA. I'd start there.

[flintrock]

I finished the amp and got it biased up at 52ma on the nose. Sounds really good, LOUD, and a nice full bass. Ready to rock. Thanks all, esp. Martin and Leo for getting me in the right direction.

[martin manning]

Great! The Grande is all but gone, but this amp lives on!

BTW, did you add screen resistors? Small ones (100 or 470 ohm) might help to prevent oscillation.

[flintrock]

Yep, I put in some 1K's.