Strange amplifier problem

I've been working on a Seeburg VL200 amplifier. It has the correct HFMA1-L6 and TSR-3 that was in the jukebox. I recapped the amplifier and changed any out of tolerance resistors.
It plays great on the bench with plenty of volume and good, clear sound. All voltages are correct. Here's the problem.

When the amplifier is put into the jukebox it doesn't work. It has very low volume and when shut off a faint crackling noise is heard. I first suspected the speaker system
so I tried the plug and speaker used on the bench. No change. I then checked the 4 pin plug between the selection receiver and amplifier. All voltages were correct on the amplifier
side of the plug (6VAC and 120VAC) and all tubes are lit and the amp has correct B+ voltage. I even tried using jumpers between the two just to be sure. Here's the strange part.

If I remove the amp, laying it close by and use jumpers from the 4 prong selection receiver plug to the amp plug the jukebox plays and sounds great through either speaker system.
I can't figure out why the amp won't work when in the jukebox? The only thing I can think of is some kind of strange ground problem when the two touch each other. Has anyone ever
had this problem before?

To begin dealing with these sorts of problems we first look for variables.

-Is the input source the same for both in, and outside the cabinet tests?

-Is the amp laying down when it works well and not when vertical? Loose octal tube sockets are common on these old amps.

-Has the output tran been changed or it's wiring tampered with? Unlikely cause.

- Examine the condition of the pickup and mute cables. These often land on the 6L6's and deteriorate. My V and VL had this problem. On one the pickup cable was so badly burned it had measurable resistance and actually varied the level as i flexed it.

-Slightly tap/wiggle the tubes when the amp is vertical and malfunctioning.

-Look for a difference in main B+ in the two conditions. Parasitic oscillation -can- cause this but the sag in B+ will show it. I doubt that is your problem here.

On VL I have on location would vary in level as I closed the back door. The reasons are resistance in both speaker and volumes jumper plugs. A little cleaning fixed this problem You would not think that the chassis would flex enough to aggravate something like this, but it did.

Rob/NYC

I have seen this before on phono's that have the green colored, audio input/mute cables. These cables either open, or short out, when flexed--which is what happens when you move the rear door--You might also check that the squelch wire is "making a good connection" with the door closed--- Good luck--let us know what you find--Ron Rich

Thank you both for your help! It gave me things to check out. I did find and repaired the problem.

I had noticed that if the two were apart, but still mounted in the jukebox and attached with jumpers it would work great.
I took a look at the two guide pins that are mounted on the selection receiver and go through the amplifier. The pin on top, when together, was coming into the amplifier and rubbing against
one wire of a capacitor! It was shorting the output to ground. This was well hidden and I had to look at an angle and close to see it. Moving the wire and covering it with insulation took care of the problem.

Who wooda thunked THAT--I guess you lucky that the darn thing did not 'blow up" !!
Thanks for posting it--
Ron Rich

Ron,

Somebody on the German Jukebox Forum had recently exactly the same problem with the same amp in a TSR1-L6 V200. .
Quite a coincidence! Watch those pins!!.

Regards,

Martin

Yes watch those pins! I just helped a friend with his VL200 a week ago and the top pin was within 1/8" of a cap wire!