DC30 Type Build Issue

General discussion area for tube amps.

Moderators: pompeiisneaks, Colossal

Post Reply
GregNey
Posts: 2
Joined: Tue Apr 03, 2012 2:33 pm

DC30 Type Build Issue

Post by GregNey »

Hello,

I am currently wrapping up a DC30 type build. I am currently in the testing phase and have one (hopefully small) issue on the 12ax7 channel. Everything is fine on the EF86 channel- better than fine actually :-o

On the 12ax7 channel, when I start my volume at 0 and work my way, everything seems to be fine for the first 5% of the rotation. The pot tapers very quickly (too quickly? definitely more so than the EF86 channel) to a steady volume, (I'm going to call it a clean sweet spot) and then there is no more gain available. For about 90% of the pot range, it sounds the same. Then, close to the maximum setting, I lose all sound on the channel- similar to when my pot was at 0. I've already replaced the pot with a new, verified one. The original tested fine when I pulled it out. I've also replaced the 180pf cap between pin 1 and the pot wiper... Not sure where to go from here.

Any help is greatly appreciated.

Thank you!! Greg
beasleybodyshop
Posts: 1089
Joined: Tue Jul 02, 2013 12:51 am
Location: East Texas (Yee Yee!)

Re: DC30 Type Build Issue

Post by beasleybodyshop »

Sounds like you have some oscillation somewhere in your circuit. Check your lead dress on all your signal wires in respect to your plate wires.

Hope that helps.
"It's like what Lenin said... you look for the person who will benefit, and, uh, uh..."
GregNey
Posts: 2
Joined: Tue Apr 03, 2012 2:33 pm

SOLVED

Post by GregNey »

Solved it. It was the 500pf coupling cap. Replaced it and all is right!

Thank you!
Post Reply