VARIAC: Procedure??? 2 old 30 wpc tube amps, unused for 4 years

out of curiosity:

what if I had used a floor lamp type in-line dimmer and just juiced it up bit by bit?

I’m still perseverating on your basement with “zero” humidity. One important  bit of advice that I and some others failed to convey is to always use a load resistance on the amplifier outputs. If you don’t have a suitable power resistor, you can use an old speaker or a single driver from an old speaker. But it sounds like you’re already up and running without any mishaps.

One simple solution is to use an inrush current limiter.  You just plug your amplifier into it and flip the switch.  Maximum voltage is applied in about 15 seconds.  I purchased mine at sigtomics.com, however I see that website is no longer active. The email address on my unit is tsiglin@sigtomics.com.

hope this helps.

thanks everyone, a good mix of input as always. and great sounding results!

What I did: the 5v4 only: Variac 50V for 30m; 75v for 30m; 90v for 30m. then all tubes in, repeat.
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I tested the tubes, they are all good. They had quad matched EL34 (RCA’s made in Great Brittan), they are still matched in strength on the meter. They had original Mullard EL37’s when I inherited them, but eventually they got weak, and EL37’s cost too much way back then. I don’t need the extra power, many options exist.

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Before they were fed from my McIntosh SS C28 Preamp (or source direct). Now everything goes thru my McIntosh mx110z Tube Tuner/Preamp recently overhauled by Audio Classics. They are dead quiet together up to my max volume setting (as I hoped they would be/used to be with C28).

One of the reasons I love the Cayin is because it sounds like these Fisher’s do (with added features and remote volume). Now, the Fisher’s sound like the Cayin. Hah.

They are Hard Lookers. Donna says they look ’interesting’.

they look like this pair of 80-AZ:  I never had the metal cages, they were concealed in the console.

https://reverb.com/item/40173234-pair-vintage-the-fisher-model-80-az-tube-amplifier-rare-military-ve...

my Cayin looks one day old.

https://6moons.com/audioreviews/cayin/a88t.html
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thanks as always, you are a great bunch hear,

Elliott

Ideally, a power meter, or at least an ammeter would be used with a variac, but the bulb is a passable workaround.  Also as mentioned before, you should keep well below the recommended bias reading until the amp is fully powered, and has been on for some time. And yes, dummy resistors or speakers must be connected.  Bad idea to run a tube amp with no load.  

Agreed on the dim bulb tester.  That said, I use an isolation transformer feeding a variance feeding a dim bulb tester for all tube equipment under test.  But for a 4 year old device, I’d start with the variance at 100 percent but the dim bulb tester at say 30%. Assumes a multi-bulb unit. Any problems will be obvious in a minute or two.   Good luck!

This is the procedure for an H-K Citation 2,
a 60 W/channel power amplifier.You can adapt the steps for your own amp:
Powering up a long unused Citation II

1. Check continuity of all the grounds. Check there
are no shorts to ground from the B+, bias, or heater
supplies. Turn the bias pots fully clockwise. Center
the AC balance pots. Put a load resistor on each
channel's output (8 ohms or 16 ohms is fine, just
connect it to the corresponding terminal.).

2. Install the 12BY7A's - (line level tubes) DO NOT install
the power tubes yet. Bring the amp up on the variac 30
volts at a time. Be sure the bias voltage at pin 5 increases
along with the line voltage from the variac. Run the variac
up to 110 volts or so and you'll see 60+ volts at each pin 5.
Be sure all the tube heaters are lit once you get up to 90
volts or so.

3. Shut the amp down, let the charge bleed off the caps
(you may have to wait a while or carefully use a bleeder
to speed it up). Don't get bit by those caps - they'll knock
you on your ass!!

4. Install the remaining tubes (the power tubes). Bring
the variac up 30 volts at a time, watch for the bias voltage
to climb as it should and check the B+. Be sure all the tube
heaters are lit once you get up to 90 volts or so.

5. Once you get to normal line voltage on the variac,
then start biasing the power tubes. Start slow, set the bias
for each tube at the mid point of the meter (or about 50 ma).
Let it run there, watch for any problems, check voltages, etc.
Let it run 10 minutes, keep checking all the tubes. Then run it
to just below spec (a couple widths of the needle below
the mark on the meter). Do the same thing as before - give
it 10 minutes. Finally, run the bias to spec, and monitor/
readjust as needed for about 1/2 hour.

Once that's all done the AC balance can be set, and you're
ready to listen! But do check the balance often in the first
10 hours of use, then again around 25 and 100. After that it's
just once every 3-6 months.

Never used one. Use a dim bulb tester on all new / old purchases.

So far, so good. 
Easy to build, easy to use.

I agree with jea48 and totem395. Four years isn't very long really for new caps, I doubt you will have any problems. I have a variac and use it often on old equipment. For me, I wouldn't even use it for these Fishers if what you're saying is accurate. A slow voltage increase could create problems.

moisture is not an issue, they are in climate controlled basement, thus no humidity, never too hot or too cold.

no diodes in the parts list.

It has one 5V4G Rectifier Tube.

so, others out, 5V4G in, do the variac thing,

then other tubes in (one 12AU7; one 12AT7; Two EL34 (originals were EL-37) and repeat the variac thing.

I'll go test the tubes now.

4 years isn't all that long ago but along with a Variac you
may want to look into adding a dim bulb tester.

 http://www.geek-tips.com/2015/11/22/dim-bulb-tester/

Unless the amps were modified there are not any regulators in the amps. A schematic wiring diagram can be found in the instruction manual.

Just a guess the power supply caps were replaced as well as any coupling capacitors.

I would probably pull all the tubes except the 5V4 full wave rectifier tube and bring the amps up slowly using the VARIAC. That will, should, reform the electrolytic caps in the power supply, if needed. If no smoke reinstall the tubes and bring the amps up on Line again with the VARIAC .

If in doubt though you might try sending a PM to @atmasphere.
Or if you are lucky he might read this thread and respond.

Slow start rectifier tubes (like 5ar4) can also mess with reforming caps using a Variac.

A local guy pieced together a simple SS plug in rectifier to reform the caps in my Pilot 232.

I was in a hurry once and subbed a 5Y3 for a 5ar4 when reforming the caps in Dynaco IV's.

Anyway, if it's tube rectified research the rectifier tube.

DeKay

In some tube amplifiers Zenor diodes are used to provide voltages to key elements of the circuit, for example the bias voltage on the grids of the output tubes. Diodes don’t conduct until a certain threshold voltage has been reached.Other kinds of regulatory tubes also are often employed. In such a circuit, it can actually be momentarily dangerous to the circuit when it is not supplied enough AC input voltage in order to activate these regulatory elements.Therefore, without seeing the schematic of your amplifiers, it is hard to give a yes or no kind of answer to your very specific question about the algorithm you outline. I personally would spend less time at the very low voltage settings. I would bring it up to 80 or 90 V within a few minutes, for example. Then go slow up to 120 V but that’s completely off the top of my head. If it was really overhauled within the last several years, you’re probably going to be OK anyway.

I found this,

I consider it prudent but I think it is extremely correct