70's Ampeg SVT crackling, popping, fan problem

[jaseandwave]

I took my old SVT (mid 70s i reckon) to rehearsal yesterday and although it sounded fantastic there were a few loud 'pops' here and there, also i noticed the sound level dropping from time to time and then coming back again. Also after a couple of hours the fan stopped working and there was a kind of burning smell. So I turned it off.

Booted it back up this morning to see what happened and the fan is working again! Still some pops though.

All the tubes bar one were replaced about 12 years ago but the amp has been sitting doing nothing for the last 7 years so they've done very little work.

Any ideas as to what the problem might be would be appreciated.

Also anyone know when this model was built?

[mac1amps]

It's quite likely that the amp is in dire need of general maintenance (cleaning all controls, switches, sockets, tube pins, etc.), as well as replacing any faulty tubes. Actually, it's rare to see an older SVT come in my shop that DOESN'T need maintenance attention. With an SVT it's absolutely ESSENTIAL that the fan be working AT ALL TIMES! Otherwise it's a potential time bomb for your output network. Amps are like cars, in that it's not at all good for them to go long periods of time without being used. I always advise my vintage amp collector clients to power up their amps at least once a month (if not even more), even if you don't play out of it, just let it warm up for a while. When it comes to sevicing an SVT (especially an older one), I strongly reccomend taking it to a pro who know's what he(/she?) is doing. It would be overwhelming, and potentially disastrous for a newbie. One more thing, MANY people (especially novices) will automatically start with buying all new tubes, assuming that will "fix everything", whereas if the maintenance hasn't been done (the aforementioned cleaning, checking soldering throughout the preamp AND the power amp/ power supply chassis, checking for loose hardware, etc., etc.), it's likely that it will still have alot of crackeling/ static. Not to mention the fact that it's quite likely that [at least] most of your preamp tubes are still fine (even though their sockets & pins may be oxidized, resulting in static, etc.), and replacing them ALL would be a waste of $$ ($$ that you're more than likely going to need for power tubes).