Fixed bias cathodyne grid stopper

[Dingleberry]

Hi.

I have a princeton reverb-a-like scratch build on my bench at the moment and I decided to fixed bias the cathodyne phase inverter aka. do the "Paul C-mod".
Which is the correct way to include the grid stopper?
Picture 1 or picture 2?
Thanks in advance.

[jjasilli]

It does not appear that either the Princeton schematic nor the Paul C mod call for a grid stopper.  However the correct position for any grid stopper is your drawing # 1.  Preferably a grid stopper stopper should be soldered directly to the tube socket lug with a short lead.  Your drawing #2 is a voltage divider, not a grid stopper. 

[Dingleberry]

Hi.

Thanks for the reply jjasilli. Yeah I know that neither the regular princeton, nor in the "Paul C mod" does not incorporate grid stopper.
I just want to try it and see do I hear a difference. Will the distortion sound "sweeter" or is the effect noticeable at all.

Didn't realize that it indeed forms a voltage divider. Thank you for pointing that out. It's been almost like an half an year since my last tube build.
Day job, gigging, etc...
I was just trying to figure out will the bias point change if the resistor is installed.
Then I also realized that it will definitely not, because there should not be (at least in the "perfect world" conditions)) current flow in the bias voltage.
And yes straight to the tube socket the grid stopper goes. It's really an old school style point-to-point scratch build. Just few tag strips and nearly all of the components goes straight to the tube socket anyway. I can send send some pics if you are interested.

[jjasilli]

 

[Dingleberry]

Hi. Did the mods during weekend and it definitely improved the behaviour of the amp. The transition from clean to mean is very gradual now and the distortion sounds very smooth and articulate with no signs of nastiness.
I'm going to build a 2 x 10" can for it, I bet it will suit perfectly with that amp.
Here are some pics.
I will tidy up the wiring when I'm finally done and completely happy with the sound, mostly for aesthetic reasons  (no hums or noises or whatsoever) and to make it more road worthy as it's going to be my gigging amp. Also new pilot lamps will be installed. There were two holes for pilot lights already in the chassis so I decided to go with two pilot lamps. Lower, (red) will illuminate when in stand by-mode and upper (green), when switched to on-position. Nice little extra feature and it fills the existing holes in the chassis.
I have a shorter reverb tank (MOD 8AB2A1B) in order and will fine tune the reverb circuit for that tank. Tried it with long tank and it was way too overwhelming, instant surf at 3 on the dial. And that belton/accutronics tank was not particularly great sounding to be fair. And that shorter MOD tank will fit inside the cage, so it's a win-win situation. Hope to get the tank soon so I can get this baby on the road.

[sluckey]

instant surf at 3 on the dial.

Many people like to replace the 100K linear reverb pot with a 100K audio taper pot. This makes it much easier to dial in a low level on the reverb.

[Dingleberry]

Many people like to replace the 100K linear reverb pot with a 100K audio taper pot. This makes it much easier to dial in a low level on the reverb.
[/quote]

That's right, thanks! I'll probably have 100k linear there at the moment. Didn't put too much attention on that pot taper when I put it together.
I'm gonna add a "dwell" trimmer and maybe simple lpf-tone control to the wet signal (depends on how bright / dark the new unit sounds) in the spirit of 6G15 so I can tailor the reverb sound to what suits me best.