Ampeg B15 build -- question about lead dress

[ldervish]

You should use Audio 10% taper. With those, flat response will be at half rotation of the Bass and Treble. I've been having a hard time finding any pots with a 10% Audio (log) taper. The PE pots are about 15%.

Actually it looks like there are some differences between the B-15NC and the SB-12 in that the tone stack and volume pot locations are reversed i.e the NC has it's tone stack between the two gain stages, where on the SB-12 it is after the gainstages. Also there is a cap bypassing the volume pot, as well as a 270k gridstopper (?) and another 270k from the bass wiper to ground, and the treble pot is 4M instead of the 1M in mine. Are these differences due to the 6SL7 architecture?

I must have been looking at some others when I said a lot of them were almost identical b/c this one certainly is not.

[hylaphone]

Wanted to follow up here...
Got the power section straightened out, changed the bias cap value from 10uF in the Piazza schematic to the correct 100uF and the amp is dead quiet! It sounds fantastic with guitar, I played around with NFL values until I found a good balance between articulate low end and a growl when pushed. May put in a pot there at some point for the new owner, who is a bass player.
Ended up using a giant white Motor Run Capacitor for the first filter, mounted like a can cap. It's like Moby Dick. This seemed the most elegant solution to an oversight in my layout. Looks pretty cool, and seems to be doing it's job! Here is a pic, awaiting thick wire handles and a metal cage:

Just wanted to thank you all for the help, this was an interesting project and I learned a lot from your insight.

[Randall]

Man, that looks so great. I just started populating mine. I really like the off angle trafos. I had mine plated recently, and I'm just getting into it.

Any chance of a gut shot?

[hylaphone]

Sure, here's a picture:


Only thing I'd change if building the amp again is to locate the preamp filter cap to the left side of the board.
Just a matter of neatness, it is very quiet as is.

[Randall]

Well done!

[Mick Bailey]

I've used quite a few motor run caps in tube HT supplies. Really like them and they ought to last a lot longer than electrolytics.

[pdf64]

'I've been having a hard time finding any pots with a 10% Audio (log) taper'
The regular CTS audio taper seems to check out at about 10%.
Pete