Mark 1 Volume Dropping? Find a tech?

[kdove]

I have a '78 original Mark 1. Over the past couple of years I'm having a recurring problem that I think I'm fixing ... it's back.

Current problem: Occasionally, the volume on the amp drops about 30% then comes and goes. The amp might play for a while without issues ... then the volume coming and going starts. I played a jam last week and had no issues, but this week it's happening regularly.

In the past: I've had the problem ... but rarely. Here's some of the things I've done in the last year or so. I've thought that I've solved the problem ... but since it's been rare ... I can't tell for sure. I have already retubed (power tubes & preamp tubes) and replaced the 5 large capacitors (only time they were ever replaced).

One thing that has happened recently ... there is no output from the two 4 ohm outputs ... only the 8 ohm output is live. Earlier posts suggested that my power transformer may have a lead disconnected. That was intermittent once or twice but now is permanently not working.

I love the amp ... is the next move locating a tech? Anything else I could try to narrow this down?

 

[Boogiebabies]

Hey Ken,

It sounds like you may having issues with the OT instead of the PT. It may be time to send her back home so they could put it on a scope.

The only ideas I can think of are to check your primary solder joints to the tube pins and to check your solder joints and the buss wire on the green secondary tap to the two 4 ohm connections.

 

[disassembled]

If you are ok with it you might have some luck opening the amp up and tapping around inside with a plastic stick or a chopstick. It may be a bad solder joint as suggested but unless you know what you're looking for it's going to be very hard to just find through guessing.

If you don't feel comfy with the method i described (it certainly isn't the safest) a return trip home wouldn't be a bad idea especially if you use the amp a lot.


Greg

 

[kdove]

Played twice today ... two long sessions ... nothing appears to be wrong ... sounded great. Kinda frustrating with this intermitent problem. Not sure what's going on.