PT, OT, Choke Placement

[chrisw67]

So, I figured I'd start getting the chassis planned out for the amp I'm building. It's going to be based on a 50w JCM800 / Plexi, but with two switchable EQ/drive sections after the cathode follower. SS rectifier, 2xEL34 and 3x12AX7.

I did a version of the headphone trick to get the OT and PT placed relative to each other, and this is the quietest location without pushing the OT to the far side of the chassis:

I connected a lead to the Common and 16Ω terminals of the OT, and plugged it in to my sound card, loaded up my DAW and set the input gain so that 0dB on the meter was when the PT and OT were next to each other in the same orientation. Then rotated and moved them around until I couldn't get the signal to go any quieter. As it is, it's -50dB. I couldn't hear any induced hum over the normal background noise. Does that sound about right? Or am I being too fussy?

Also, will that leave enough space to the left of the OT for the preamp tubes, and will it really matter where the choke goes? Or should I repeat the same procedure for the choke as I did for the OT?

Thanks in advance! 🙂

 

[jeff5may]

I would place the choke close to the PT, and in the same orientation. You can measure crosstalk if you feel the need, but the PT and the choke aren't going to cause noise problems if they talk to each other.

 

[chrisw67]

Thanks very much, Jeff - I had a play after reading your comment and have gt it sorted now! Time to get the drill out, I reckon!