Sunday, June 8, 2008

Amplifier Tweaks: Final Lama Kazu 8SE

The tweaks to a simple single-ended amp could be endless. I think this will be the last adjustment to the Lama Kazu 8SE, however. (Note: It wasn't! Some edits to this post were made in October.)

I decided to try a 12BZ7 in the second gain stage/cathode follower. Of course the bias had to be adjusted for that. Not knowing how exactly the 12BZ7 would act at clipping, I decided to add a small (3.9kΩ) grid stopper on the socket.

After using the amp for a couple months with the 12BZ7 installed, I ended up switching back to a 12AX7, but kept the hotter bias caused by the 1.5kΩ cathode resistor I put in for the 12BZ7.

I added a 560kΩ resistor in parallel with the drive potentiometer. This serves to cut the bass response as the drive is increased, and really reduces the muddiness at high gains.

I also decided to go over the whole thing and check my original calculations; it appears I chose the wrong tap on the output transformer when I built the thing. I changed it over from the 2.5kΩ to the 5kΩ tap. It's now actually capable of producing the 8-or-so watts of power I originally expected!

Now with the 'BZ7 there's not a "normal" tube in the whole setup!

Coming soon: Sound samples of everything...