Strange loop hum

[Guitarxtc]

I tried in one of my builds Merlin/Engl 12ax7 fx loop and i have loud hum only if i just plug guitar direct in return jack ,guitar volume at 0= zero hum ,from 1-9 loud hum ,on 10 hum is half loud. with delay,chorus,reverb in loop... no hum.
I changed tubes,tried new cable,guitars,new loop jacks,solder... Never heard this on other amps,i have no idea any more what to try.

[maxkracht]

Sounds like you have a grounding problem. Do you have a schematic or pictures of the loop?

[pdf64]

Have you checked for oscillation?

[Stevem]

Are you ever actually going to play the amp like that, I would think not.

If you jump between the send and receive with a cable and there's no hum issue then call it good.

[Guitarxtc]

Have you checked for oscillation?

Is a 194HZ hum, i will try to use other tube position and rewire for fx loop ,that tube was for clean channel

[Guitarxtc]

Are you ever actually going to play the amp like that, I would think not.

If you jump between the send and receive with a cable and there's no hum issue then call it good.

Probably i will not play like that, but i can't sleep if i don't resolve this

[bepone]

I tried in one of my builds Merlin/Engl 12ax7 fx loop and i have loud hum only if i just plug guitar direct in return jack ,guitar volume at 0= zero hum ,from 1-9 loud hum ,on 10 hum is half loud. with delay,chorus,reverb in loop... no hum.
I changed tubes,tried new cable,guitars,new loop jacks,solder... Never heard this on other amps,i have no idea any more what to try.

You are not posting any valuable info.. schematic, what did you connect and where , voltages.. which amp. Very basic description of the problem.
What i can see, 100% this is not normal