[R-390] Fwd: R390a Navy

[K7iou1]

Hello, I'm new to the group. 
I bought a r390a (63) Imperial that doesn't receive. There is a low level motor boat sound in the speaker. Bad capacitor? With the Line Level at 0 and Switch +10 the LL meter is almost pegged. The carrier level adjustment on top of receiver is backed off almost full counter clockwise and carrier level meter is high also and fluctuates slightly. I've checked all the tubes and replaced as necessary. I used Camoline on the PS connector as it was intermittent with no display lights. 
A ham well known for his audio mods reworked the audio module and as his schematic indicates it will now accept a 4-8 ohm speaker.
So today I was checking it out per the Y2K and was checking the rear connections, jumpers etc. On the back there is a bell shaped plastic filled with epoxy above the terminal strip with rigid bare leads connected to #9 and #13 and a red wire to a Dow Key relay and black wire to ground mounted on the back. Looks commercially made.
If I disconnect it the carrier meter drops from indicated to 0.
Anyone know what this is?
I also have a Howard Mills restored Collins and I hate to swap modules to find the culprit. I do have another audio module and could clean, fill the tube sockets and try it.
His modification was done in 1981 & I picked it up from his shed. So I suspect it's been sitting 30+ years in a dry desert environment. The unit looks pretty clean and no seen corrosion.
He also disconnected the diode load in front and per schematic it was to have a 500k pot to adjust tone. I temp installed a 1/2 Meg pot and it seems to work. I can turn AF up & down & hear it change. I can adjust tone pot and hear it change.
Regards de k7iou