That inner grommet could well be the problem.  The pin should be in the center of the grommet.  That will allow the inner pan to "float" whereas right now it is hung up on the pin and can't move.
Fix it and see if it helps the issue.

Quote from: Don on November 06, 2014, 10:53:28 PM
The only temporary solution I noticed, which would only last for a few days or until I move my amp or something is to shimmy the reverb tank away from the speaker, but don't hold me on that one. When I did this a few days ago the hum was completely gone and I was able throw the reverb knob all the way over to twelve without a hum.

If this is the case then it's definitely a physical problem caused by the proximity of the speaker.  And I doubt you were able to shimmy it very far so it is operating right on the border of oscillation.  If it's such a critical location, then it could be that the grommet is making a difference, put a temporary support there, even cardboard, to raise that corner as much as the grommet would and see if it helps.

  The hot glue is there in addition to solder, not instead of it.  It helps keep heavy parts or cables secure so they don't move around and degrade the solder connections.
So you want to keep it in place.
Are the four corner springs in place inside the tank?  They keep the inner pan centered  and help reduce the physical vibration.
Are there any screws going through those grommet inserts?  If not, you don't really need the brass insert and can use any kind of similar rubber grommet for the missing one.
As far as the cardboard, keep it but you could try some thin foam between the cardboard and the bag.

As Phatt mentioned, if pulling the tank away from the speaker makes it quit, then it is a physical feedback issue, caused by the proximity of the tank to the speaker.  It is a fairly common issue.
Any chance you changed the speaker?  Otherwise, could the tank have moved in it's bag?  Sometimes it only takes 1/2 an inch.  Or it's possible the springs have stretched enough to cause the problem, in which case a new tank should solve it.

The part I don't get is that the footswitch will kill the feedback, but the reverb pot will not.  The only thing I can think is that the pot does not go completely to zero.
Does the level of the feedback change as you turn down the pot?

 The point about the eq was to try and narrow down the area.  If the eq can affect it, then it is happening before the eq.

  You posted 2 schematics, look at the other one for masters and reverb.
I guess there is a FX level pot also on the back of unit?

Quote from: Stormlord1736 on October 24, 2014, 05:10:49 PM
Tnx, for the answare. I have a few more questions.

Quote from: g1
The belton tank is the equivalent of an accutronics model 8EA1C1B.

On the accutronics website I only found the 8EA2C1B, it's the same?

The fourth digit denotes the delay length.  The 1 is short delay, 2 is medium.
Otherwise the specs are the same.
The codes are explained on this page:
https://www.amplifiedparts.com/tech_corner/spring_reverb_tanks_explained_and_compared

  The 270V is the RMS value of the AC voltage coming out of the power transformer.
If you have not simulated the whole circuit, you will not see the proper voltages.
With no loads on the various points in the power supply, they will all show the same voltage when simulated, as you have found.
The belton tank is the equivalent of an accutronics model 8EA1C1B.
The colors shown for the output transformer are the wires connected to it.
You may find a model number on the output transformer itself, but that will probably not get you anywhere.
For proper simulation of the OT you will probably need some spec like the turns ratio or input and output impedance.
Others here that use spice may have better ideas, I have never used it.

  Those are SR-2873 diodes, rated for 2000V.  Probably no longer available except through peavey.
  Some people use 3 1N4007's in series instead.

 The dim bulb indicates the short is not present right now.
It's possible one of your power tubes has an intermittent short/failure.

Here you go, the grids are in fact paralleled.

  Did you take out the power tubes yet?

  Is there a switch or a footswitch jack?  Some require the footswitch to work.
So maybe your friend had a way of turning it on.
Otherwise, weak tubes and caps (especially the cathode caps) can make the trem weak.
Maybe he had some work done later that mucked up the grid wiring and forgot?
Anyway, try to find the real schematic.

For 120V use, the jumper from 3 to 4 is removed.  A jumper is placed between the two 0 tabs, and another jumper between the two 120 tabs.  Hot goes to the 120's, neutral goes to the 0's.

The various points of the primary side are reading correct, so it does not seem there are any shorts in there.  Plus it is not blowing the fuse, which would be expected with a primary short.

  Looking again at the schematic, the thermal fuse goes between the 7th tab and one of the 0 taps.  So it can easily be bypassed and the transformer rewired for 120V operation.