'86 Mark III Combo - strange noises after turning off

[AR]

Once again - 1986 Mark III Purple stripe, simulclass & EQ, no verb

There's a small issue I'm having with this amp. Doesn't seem to affect performance that I know of, but after turning off the amp (turn to standby for 60-90 seconds or so, then turn off power) there is some crackling coming from the back.

Not crackling like electricity, or like speaker noise -- kind of like the idle "clicks" your car makes after you shut it off. I associate that sound with heat and things cooling or something of the sort.

Is that all it probably is, or is it a sign of something else?

I've checked the tubes (tapped with eraser-end of pencil), and did not hear anything -- they all look to be in good condition also. Now, I bought them with these tubes installed, so they probably need to be replaced, but the amp sounds find so they're not too bad off.

Any ideas?



Here are some pics so you can tell me if something looks obviously wrong. I'm fairly new to amp diagnostics.

http://agoodstart.com/areed67/markiii/ (more pics)

(back)

 

[Boogiebabies]

I have had tubes crackle whn they start to cool down. It's a few seconds of a series of pings and then it stops.

Just a note, the tubes in your outer sockets are STR-415 NOS Phillips 6L6's. I would have them tested before you throw them out. They sell for $ 150.00 a set.

 

[AR]

I have had tubes crackle whn they start to cool down. It's a few seconds of a series of pings and then it stops.

Just a note, the tubes in your outer sockets are STR-415 NOS Phillips 6L6's. I would have them tested before you throw them out. They sell for $ 150.00 a set.

Thanks for the tip! I have the original Mesa stock tubes as well - the original owner said he removed them before they needed to be replaced and stored them all these years. Any idea what those would be like, or what they're worth?

 

[Boogiebabies]

The outer tubes are the stock Mesa tube back in the day.
Depending on what you have, they may be Chinese junk or American gold. The tubes you have in the inner sockets are Sovtek 5881's rebranded by Mesa as the STR-425.