This is the P/P EL34 type tube amp.
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Electrolytic capacitors deform over time when not exposed to voltage. The oxide layer that forms the dielectric slowly dissolves. Capacitors that wee rated at 450 working volts when new might only be able to handle a fraction of that after 15 years unused.
It is also possible for the electrolytic capacitors to dry out over time.
Best advice is to inspect them for bulges or leaks, then use a variac to raise the voltage slowly and give the capacitors time to re-form.
How about pulling the signal and power tubes.
If the rectifier is a tube you will need to leave it in.
If you are worried about powering them directly off the mains put some kind of load in series with an amp first.
The wife's toaster or maybe an iron. Something with around 500 watts resistive load.
Fire it up, sorry couldn't resist, and check power supply dc output voltage. Leave it on for a minute or two.
If no smoke plug the amp directly into the wall recept.
Check power supply DC voltage.
If everything looks OK unplug amp install tubes.
A couple of cheap speakers might not be a bad idea for the ultimate test.
The amp should NOT be powered up unless you monitor voltage while running the amp up on a variac. Either buy a variac, or bring it to a tech who can do that for you. If you value the amp, start it up that way especially if the company is no longer in business and replacement parts may not be available. I do that with equipment that hasn't been run in 5 years as well...
Thanks for all your input. I'm running the left channel right now on a cheapo computer speaker. Seems fine, no weird popping noises or buzzing at start up. I think I'm in the clear on this one. I'm going to run it for about 15 minutes, shut it down and then do the same to the right monoblock.
I did. They're monoblocks, so I had the speaker connected to the one I turned on.
Really pleased and surprised at how quiet these amps are after sitting so long. Was expecting some hums or buzzes. Really a nice warm sound with a good amount of punch.
This was a World Audio Design KEL-80 kit amp that I built back in the late 90's. Not even sure if they're still around.
Just take the equipment out in the driveway, put it up on cinder blocks, connect to the oldest and funkiest speakers you have, wear safety glasses, and have a non-liquid CO2 fire extinguisher ready to hand. No worries...
If you wait until the 4th of July to do this, you get extra credit for any sparks which may be produced during the process.
For a bit of a preview, go to YouTube and run a search for *4000W Tesla coil test" or "Vanguard (Flopnik)."