Seeburg MR A5-L6 Amp cuts in and out

[Eric]

The short story is that my HF100R was fine until I took it apart to work on the cabinet. When I put it back together the sound now cuts in and out about every second. I’ve switched out the tubes with no luck. it was rebuilt almost 40 years ago. Any thoughts on what is going on?

[jukenorman]

The first thing to probably check would be the muting contacts on the mechanism switch stacks!

Norman.

[Eric]

I’ve checked them and they all look pretty good. It’s more of a pulsing. I can hear the amp turn on once it pulls a record and it maintains volume for a second or so and then it starts to pulsate.

[jukenorman]

It's quite difficult to say where to go next! What happens with the amp muting is that the signal is gounded part way through the amp circuit. That your problem occurs after the amp is made active probably means that the problem is in the early stages. If after the amp becomes active, you remove J4 (the muting plug) and the pulsing stops, that would definitely show the problem in the early stages. If that's the case,  I'm not sure what you can do that's easy, maybe try some freezer spray on components around the 5879 and 6SN7? It's not something I use much so hard to say how successful that might be. Is your AVC active? If so you could try disabling that by removing one of the tubes (see if that makes a difference?) - I think it's the 6SK7, although off the top of my head, I'm not certain (Edit - it is the 6SK7, I searched the forum lol!).

Norman.

[Eric]

Thanks for your responses, Norman! I really appreciate it. I’m ok with mechanical issues but not so good when it comes to the amp. It was going to be a routine tear down so that I could repair the cabinet, then this started up.