Bringing up old tube equipment on a Variac

[HarryO]

I was wondering what are your methods of bringing up old tube gear on a variac. How fast, safeguards, hook ups, etc.

HarryO

[JBryan]

Hey Harry,

Most of this is common sense and I'm by no means an authority but in case you just want a primer, here goes. First, make sure that the variac is working and grounded properly. It'd also be a good idea to test the tubes and check the component for loose or bare wires, scorched parts, dried out or bleeding caps, etc before hooking anything up. If you suspect the component may be damaged, use resistors or shorted plugs on the outputs, otherwise just hook up a pair of speakers you wouldn't feel too bad throwing away. Now you're ready to plug it into the variac and slowly bring it up to 20v. You most likely won't see anything light up but if you smell something burning or see a flash, turn the variac down and inspect the component for scorched parts - especially resistors and wires. If everything smells OK, leave the component at 20v for 30 minutes or so (depending on its condition and age). Some folks would suggest letting it idle for at least an hour but I don't have that kind of patience. Next, increase the voltage to 50v and if you smell or see anything, shut it down. Wait about an hour and increase the voltage to 80 and observe for damage. At this point you should see the tubes and lights begin to glow dimly. After another hour, bump the variac up to 100v and finally 120v an hour after that. You could probably bring the component up faster but this procedure will also reform the caps which you'll want to do anyway.

If at this point, nothing smells or has blown up and the component appears to be operating properly, you can hook it up to your test speakers and give it a listen. Once again, I'm not an electrician or tech so maybe one of the gurus will check in with corrections and tips but I think you'll get by without burning down the house. Have fun -Bryan

[HarryO]

Bryan,

I actually bring mine up much slower starting at 5V for a half hour, 10V/half hour, 20V/half hour and in 10V incriments for a half hour each to about 50 and then about an hour between incriments up to 80V. I guess I've just gotten 2 old pieces in a row with hums. I wanted to check to see if I was pushing them too hard too fast. I've gone quite a while without any problems and the last 2 were extremely nice and I didn't figure on both having problems. The tubes all tested good and if not were replaced before heating up the units. I"ll just have to go through them earlier than anticipated. Any info is helpful.

Thanks,

Harry

[NOSValves]

It all depends on the recitification method the gear uses. SS rectified I start at about 20V for a few minutes. While doing this I monitor the voltage drop across the first dropping resistor or choke. When this drop stabalizez your power supply caps have charged and are not showing any signs of servere leakage. I then bump it up and repeat until I reach a problem or full voltage.

If the gear is tube rectified starting at anything below 50V is a waste of time since most likely the rectifier will make zero DC voltage until you get some heat in them especially with a slow start design like a 5AR4.

I rarely do a complete variac job on gear anymore except in special collector situations since its become my policy to quit wasting time since I will not do the fix what is broke type work when your talking amplifiers. Most of my customers are going to use the gear and don't collect it. I rebuild the gear 100% or I don't touch it for the most part so any parts save by a super slow start are going to be replaced anyway. I do variac up tuners and preamps since they often can live a happy life with original power supply filter cans since they often have much lower operating voltages and heat issues.

By the way bringing up on variacs has proven to be a PITA. It really does not magically reform the caps in the end they often end up failing if placed back in regular use after a few months anyway.

Craig

[HarryO]

Thank you Craig,

It's great you take the time to pass along good info. I love listening to the older gear I haven't had a chance to listen to before. It gives me a different flavor of what's been available and the sound as it's evolved over the years. I'm just a "parts changer" in the field and have no design or manufacturing experience. Your shared practical experience and knowledge is most appreciated.

HarryO

BTW, Keep the name and Logo.