JCM800 Mini Saga Continues Hum

[boostedsuby]

I received some help with voicing and oscillation issues and how I am trying to tackle hum. I started with the EL34 power tubes and all was quiet. I added the 12AX7 phase inverter and the noise came back. Lifting the NFB stopped the hum, so I switched OT leads and reconnected NFB. Now I had hum plus squeal. Now I have put the OT leads back to the former position and I am trying to isolate the hum. I have swapped out the JJEL34s for a set of Rubys and swapped preamp tubes with fresh one to eliminate that variable. The hum persists regardless of knob positions, although there is a mild increase in the intensity of it as presence is rolled off. Does anyone have any thoughts or a troubleshooting strategy?

[xtian]

Grounding. Show where everything is grounded, and I’ll help.

[boostedsuby]

I feel terrible to lean on you so much. Thank you. I'm late for bed, but I will get them tomorrow after work if you are still interested.

[xtian]

In your other thread, you mentioned you were using this:

https://robrobinette.com/RR2104_Master_ ... JCM800_6V6

If you've done all your grounding based on this layout, I'd expect a good, quiet amp. Notice that the output jacks and the Presence pot must make good connections to the chassis. Use your multimeter to confirm this.

[boostedsuby]

Hmmnn, I am using Cliff jacks for the outputs, so they are isolated from ground Ill bet. I wish work could wait.

[luix]

What kind of hum do you have?

I've spent 5 month attempting anything possible and at last I discoverd that there was some strange unbalance in the heater and the humdinger, a trimmer between heater and a common voltage, solved at all!

I'm carrying on my humdinger evangelization opus

[boostedsuby]

I jumpered the jacks to chassis ground and all is quiet. I think that I overthink cliff jacks because I keep revisiting that very issue over and over when I deal with them. Thanks all.

[xtian]

I jumpered the jacks to chassis ground and all is quiet. I think that I overthink cliff jacks because I keep revisiting that very issue over and over when I deal with them. Thanks all.

OTOH, I used Switchcraft jacks for inputs (instead of Cliff)--Switchcraft do not have the switch on the ground connection, so you can't have a grounded input when nothing is plugged in.