How to restart tube amp and pre in boxes for 2yrs

i read a caution that tube amps need to be hooked up to a speaker load at all times when turned on. can anybody verify this?

Most tube amps are supposed to be operated only w a load (speaker or resistor across outputs) but I have no idea if this applies to the momentary on-off approach Elizabeth advocates. Best approach is to use a variac and bring the voltage up very, very slowly to allow the capacitors to "re-form" (whatever that means). 2 years is not that long, you might want to ask Chris @ Parts Express who does a lot of modification work on SF gear and I think used to be involved with that company (maybe co-owner??).

Swampwalker, great idea! A variac is the way I do it with equipment that's been off for a few years or more. I will usually pull the output tubes, and monitor the voltages from the tube sockets. Contact the manufacturer just to make sure it's safe to pull the output tubes. With the output tubes pulled I only run the variac up to 110Vac. Internal voltages will be higher because you have the output tubes pulled and you don't want to over voltage the caps. Or let a tech do it for you. I'm on the west coast.

Two years is not a long time to be sitting idle. The electrolytic caps should be okay (assuming they were okay going into storage).

You should not have a problem with speakers not attached if you don't put a signal into the amp.

Elizabeth's approach would be a not to difficult to implement safety measure. Be sure to have a reasonably long time between turning on the amp again. Some tubes hate being turned on again immediately after being turned off. If I do that with my power amps, I sometimes get a tiny flash from the rectifier.

Larryi..You're actually at an advantage having a tube rectifier. The tubes running off that rectifier (high voltage) have a nice soft start. No tube will conduct until the rectifier starts conducting and turns on, minimizing the inrush current. Tube units with solid state rectification are a different story. Voltage appears at the tubes before they have a chance to conduct. The inrush current is not minimized and there is no soft start. That makes it much harder for old capacitors to form up, and puts a strain on the power transformer. The flash you see on the rectifier is because there is no soft start for the rectifier. It provides a soft start for everything in the circuit it feeds.

Important that you bring the amps to room temperature of 72 degrees for at least a day. Never start them otherwise. Second the load comment.

Hifigeel1,

Yes, the rectifier does act as soft start for other tubes and for the power supply caps.

Perhaps you can help with the issue of using a variac for tube gear that use solid state rectification. A friend had such an amp that had problems with diodes in the bridge rectifier blowing up. The manufacturer stated that both over-voltage and under-voltage could be responsible for that happening. Since the use of a variac would create such under-voltage situation, I am wondering if that claim is really correct.

wow the last 2 comments are way over my head. But tonight after i come back from my dance class i will do what Elizabeth told me. tks to all and i hope to enjoy my records soon Daniel

For those of you with Plinius amps(the old one's anyway), a load is needed. Don't ask how I know.

Larryi..That sounds hard to believe. I would think the line fuse would blow before the diodes short out. Most manufacturers use rectifier diodes that are at least two times higher in current than are needed. That being said, as AC line voltage goes up current draw goes down and vice versa. So running your tube amp for a while at half voltage is not a good idea. This is partly the reason why I pull the output tubes before running an amp up on a variac and never exceed 110Vac on my variac and always on the advise of the manufacturer. I always set the voltage on my variac using an accurate DVM, note where that is on the variac dial as it varies with line voltage fluctuations, and then shut the variac off, and set the variac back to zero before I plug the amp into it. I carefully monitor the plate voltage at the output tube socket and compare it to the circuit diagram to make sure I'm not exceeding that voltage. I don't recommend doing this if you don't have expertise in measuring high voltage equipment. These voltages can be lethal. One other thing...If the amp has a start up relay and/or ramp up circuit at start up, that's a whole different kettle of fish and I would suggest contacting the manufacturer before attempting to power it up using a variac. Always make sure the amp is fused with the proper value. Apologies to anyone I may have bored.

"as AC line voltage goes up current draw goes down and vice versa"

This is most definately wrong - read up on ohm's law and do the math.

Ya sorry bout that..I shouldn't post on pain meds...I do stand corrected..

What I was meaning to say was that at low AC voltage when using a variac, when the circuit initially gets energized, current can peak. That varies depending on circuit topology, solid state vs. tubes etc. That is all.

TKS you all i listen to music last night for the first time in a long time. Now getting my turntable put together but i wont expect anyone here to walk me through it......lol Happy listening Daniel

Running a tube amp for any length of time without output tubes installed, as Hifigeek suggests, can be very dangerous. The reduced current draw in the power supply will cause the B+ voltage to shoot up considerably, and may exceed the capacitor maximum voltage rating. On an older amp with marginal capacitors, this greatly increases the risk of capacitor failure. The Variac idea is a good one, but leave the tubes in place, or monitor the voltage on the capacitors to make sure it stays below their rated voltage.

Indeed Selectric, I even monitor AC ripple as I'm bringing the voltage up and carefully touch the caps to make sure they're not heating up!

Hifigeek1,

You are far braver than anyone I know when charging up questionable caps. A friend had a cap blow up when he turned on an old amp and he said the explosion was unbelievably powerful. He is a gun person so he knows what loud is, and he said the cap going up was louder than any gun he has fired.

Larryi I've been doing that kind of work for 25 yrs. Actually a cap will give you warning signs. At low voltage they can heat up and/or sizzle or tic from arcing. That's why you run the amp up slowly. Never bring an amp with caps that make noises up to full voltage. Also if the cap is leaking from the vent.

I'm too much of a chicken to be close by looking for warning signs. I lend my stuff to a friend who can power it up on a variac for me.

Well that works. lol

It’s always a good idea to use a Kill-A-Watt energy monitor (available on eBay or Amazon for $20-$30) in series with the Variac to monitor the current draw of the amp as the voltage is slowly brought up.  If everything seems fine at first, I always leave the Kill-A-Watt hooked up for a few hours while running the amp to make sure current draw doesn’t start creeping up which usually indicates a power supply cap about to give it up.

Yes, a device to monitor voltage and current draw of the amp is the best approach.  I've seen situations where even at a low voltage setting when powering up, the current draw appears too high so one knows there is a problem somewhere when well below when full voltage is applied.  Measuring current and voltage together is the best approach.  Interestingly, a very young tech I know said that he actually prefers a dim bulb to relying on the ammeter.  He said that the bulb reacts faster than a readout of current.

That's all good to know.  In '17 I powered up a tube amp of mine that had been dormant for nearly ten years and in '20 I powered up another tube amp I owned that had been in hibernation for well over ten years and i wasn't aware of this stuff so I basically plugged them in and turned them on. 

I guess I was lucky.

That second amp I alluded to has been asleep again for about four years so I guess I should look for a variac on ebay.  The second amp, the one that woke up in '20 and then went to sleep again, does use a tube rectifier though.