Paralleled SE, cathode biased questions.

[dobbhill]

Now that's what a Fender Champ should be!
Great work!
D

[xtian]

About the hum, did you listen to your transformer placement? That's what I'm fighting on this stupid Fargen.

Please say how you implemented your Presence control. My client wants one on his SE build.

[alvarezh]

Yes Martin, here is a picture with a 12AX7 in front of it for comparison. It's very unique!

Dobbhill, I concur with you 100%. Fender engineers should lurk around here, I am sure they could learn a thing or two from you guys. Thanks for the kind words!

Xtian, regarding the hum, yes, I should try all possible causes including the grounding scheme which I will post later on whether I find the cure or not.

Here is where I got the idea for the presence control, it's on page 16 of the PDF:

http://courses.physics.illinois.edu/phy ... Report.pdf

The way I implemented it is on the attached schematic.

I played with a guitar today. I think it's loud enough for gigging even through a crappy Jensen C12K. The reverb works, it's weak but I haven't checked the reverb tank specs, could have the wrong input impedance. There is certainly a strong throaty sound to the chords with good note definition.

The amp sustains notes forever, but at medium volume, I would like a little more headroom before it starts to flare. I have to work on lowering the feedback loop's resistor value to tame it.

It's been on for about four hours (no signal). PT is running somewhat on the hot side while the OT is warm. The heat emanating from the KT120 not helping even though it's 3 inches away from the PT. It's 1 inch away from the OT and you can tell the difference in temperature from the side facing the tube to the opposite side.

A few issues still to resolve but at least we have a working specimen that just needs to be refined.

Thanks a lot for your help!

All the best.

Note: The forum app will not place the tube's picture vertically, you need to rotate it 90° CCW.