It would be helpful to find out where the hum is originating.  Pull the 7199s leaving only the output stages active.  If you still hear hum, it suggests that the problem is in the power supply.  It's very unlikely that the hum is originating in the output stages  as the push-pull operation should cancel it, and particularly since the the midpoint of the heater supply has +20 volts DC strapped to it (and be sure that R61 and R62 are measuring very closely in value.)  If the hum disappears with this experiment, plug the 7199 of one channel back in and see if the hum returns.  If it does, you now have a place to start looking for potential causes.  If not, plug in the other 7199 and the hum should then return.  Email if you want to discuss the troubleshooting process in more detail.  I didn't have time to read everything posted, so apologies if I've restated anything mentioned before.   Maynard    

 OK, I just got in and tried there ideas.

1) I swapped one of the ouput tubes from each of the two channels to see if the pairings might make a difference. No change.

2) I pulled the 7199s to see if I still had the hum and it's still there without the 7199s. Power supply? Maybe reroute or shield the AC lines in the chassis?

 1) I swapped one of the ouput tubes from each of the two channels to see if the pairings might make a difference. No change.

if you swap out unmatched power tubes it won't change.....matched power tubes will cancel hum....swapping around mis matched tubes will not change that they are not matched.  So basically, matched tubes cancel hum better.....or..root cause it and clean up the power supply....more caps...chokes...etc.  In your last thread during your rebuild...you said the amp sounded good....if now you have hum....the wires did not move around....the tubes however do decay and change over time.

 Right, I had the amp hooked up to some AR4 speakers after the rebuild and it seemed pretty quiet with them. I'm now using the amp with Belles which are, of course, much more revealing. Mind you even with the Belles I only notice the hum when no music is being produced. Maybe I'm being too picky. I can certainly try choking with the old trannies as you suggested but if that did work I don't know how I would wedge those things in the chassis.  

JL Sargent:

 OK, I just got in and tried there ideas.

 

1) I swapped one of the ouput tubes from each of the two channels to see if the pairings might make a difference. No change.

2) I pulled the 7199s to see if I still had the hum and it's still there without the 7199s. Power supply? Maybe reroute or shield the AC lines in the chassis?

In your picture of the underside it looks like you installed a toggle switch at the lower left corner to serve as the on/off switch. Leaving the switch wired in, take it out from its location and fold it back so that the wiring is nowhere near the output tube sockets (fold it over the side of the chassis) and see if the hum persists (with the 7199s removed also.)

 OK, with the 7199s out and the toggle switch pulled out and away the amp is 90% better. So I put the 7199s back in and tried it with the toggle switch still out and away and most of the noise is back? 

Note: My "on" indicator lamp is 120v too. Maybe I should go with a DC lamp and move the switch to the back reducing the AC wires all together?  

JL Sargent:

 OK, with the 7199s out and the toggle switch pulled out and away the amp is 90% better. So I put the 7199s back in and tried it with the toggle switch still out and away and most of the noise is back? 

Note: My "on" indicator lamp is 120v too. Maybe I should go with a DC lamp and move the switch to the back reducing the AC wires all together?  

I'm with tube fanatic and JJKIZAK on this one. I think the physical location of the wiring ("lead dress") is at the root of the problem.

Does the hum occur if nothing is connected to the amp inputs? How about if  RCA shorting plugs are connected to the inputs?

Once it is certain that the amp (not the interconnection of the amp with other equipment) is humming, try this:

1. Connect amp to speakers. Connect shorting plugs to amp inputs.
2. With amp upside down, move wires around with a non-conductive tool (plastic ballpoint pen barrel?) and see if you can change the loudness of the hum.

The lead dress as it stands now does not appear to be optimized for minimum hum, so it could be coming from any number of sources and pickups. The power switch wiring and the filament wiring, as mentioned by others are likely culprits.

JL Sargent:

 OK, with the 7199s out and the toggle switch pulled out and away the amp is 90% better. So I put the 7199s back in and tried it with the toggle switch still out and away and most of the noise is back? 

Note: My "on" indicator lamp is 120v too. Maybe I should go with a DC lamp and move the switch to the back reducing the AC wires all together?  

Try just a plain old switch with no indicator light and see what happens. Keep the switch and AC lines as far away as possible from any signal parts of the circuit.

 Some great suggestions guys! I will be able to get after it this weekend. I'll go by the electronic supply and pick up those caps and I'll reduce my AC wiring to the bare minimum and see what we have then. Thanks a lot!

JL Sargent:

 Some great suggestions guys! I will be able to get after it this weekend. I'll go by the electronic supply and pick up those caps and I'll reduce my AC wiring to the bare minimum and see what we have then. Thanks a lot!

 

 

The coaxial leads from the input jacks to the 7199 (g1) grids could be configured so they don't snake around the JJ capacitor and run in parallel with a output transformer primary lead. The line signal input wires need to be as far away from AC and HV DC as much as possible. It may or may not help with noise.

The best approach with line signal leads is to mount the input jacks as close to the tube's input (g1) grid as possible. However, it's not the most esoteric and practrical procedure over having the input jacks at the back of the amplifier.