Variacs (off Amazon)

Seal

Supporting Member
Messages
548
I'm thinking of buying my first Variac. I see there are some on Amazon with varying prices. Any suggestions? (I'm in the USA).
 

Rod

Tone is Paramount
Silver Supporting Member
Messages
20,932
It seems you want the ones with a digital readout. The analog meter versions have very inaccurate readings, so running it at 117 volts could actually be sending your amp 150 volts Or something close to that...
 

glpg80

Member
Messages
68
For my workbench, I rarely work on anything that needs more than 5A rms current so I run a fairly small Chinese variac.

If you need precision, it’s likely even the integrated digital displays will be off slightly and I recommend an RMS voltmeter combined with a plug in power meter to measure the RMS voltage and average power. Plug-in power meters can tell you how much power is being consumed if needed which will give you an idea of RMS current.

If it’s just being used to variac down an amplifier, be sure to adjust the bias of the power tubes at the reduced voltage.
 

Troglite

Supporting Member
Messages
136
Agree. Those are nice AND cheaper than the AmpRX Brownbox.

But neither of those are actually Variacs. So they are really only relevant if your only intended use to lower the voltage while playing your amp. If you want to actually do recaps or other repairs/mods, you still need a Variac.

Sorry, I don't have advice for the OP. I am in a similar position and still learning.

Pricey, but made in the USA and it's a quality built unit.
https://vintagesoundworkbench.com/amp-maniac
 

CJReaper

Member
Messages
1,843
Dave Friedman seems to think the Chinese ones on Amazon are fine, don't know if he has a preference for anyone in particular other than it should have a digital readout.
 

jnovac1

Supporting Member
Messages
6,119
I'm thinking of buying my first Variac. I see there are some on Amazon with varying prices. Any suggestions? (I'm in the USA).
i got a “vintage” genrad variac on craigslist, 40 bucks. superb quality. can’t imagine that a modern import would be as reliable.
 

Troglite

Supporting Member
Messages
136
Assume that is the uncased, uncorded, unmetetered salvage variety. The cased, cabled, and metered ones are getting a lot more expensive!!

Also... I would welcome feedback from the TPG experts on my understanding that if you are using a variac to RUN an amp... a 10 amp model might be warranted... and in fact, a bucking transformer like the brownbox or amp maniac would be better.

Conversely, if your using a variac on your workbench... a 5 or even 2.5 amp model is probably adequate b/c you won’t bring the amp up to full power under those conditions anyway.... it’s just warming the amp up for testing purposes. And this is really the intended/ideal use of a variac.

have I interpreted what I have been reading accurately? What did I miss?

i got a “vintage” genrad variac on craigslist, 40 bucks. superb quality. can’t imagine that a modern import would be as reliable.
 

jnovac1

Supporting Member
Messages
6,119
Assume that is the uncased, uncorded, unmetetered salvage variety. The cased, cabled, and metered ones are getting a lot more expensive!!

Also... I would welcome feedback from the TPG experts on my understanding that if you are using a variac to RUN an amp... a 10 amp model might be warranted... and in fact, a bucking transformer like the brownbox or amp maniac would be better.

Conversely, if your using a variac on your workbench... a 5 or even 2.5 amp model is probably adequate b/c you won’t bring the amp up to full power under those conditions anyway.... it’s just warming the amp up for testing purposes. And this is really the intended/ideal use of a variac.

have I interpreted what I have been reading accurately? What did I miss?
nope. fully functional finished unit. built like a tank. my understanding is that if the variac is rated for more than the mains fuse on your amp, you are safe. example, 3 amp fuse on amp, 5 amp variac is adequate.
 

71strat

Member
Messages
8,976
One still needs to stabilize the voltage for best results when using a Variac/BrownBox.

I asked the people at AMPRx years ago, and they told me that was the optimum way to use the device.

Most large venues that pros play already do have the voltage stabilized by huge, super expensive regulators, and noise filtration.

I use either a Furman P1800AR, or the Furman SPR 20i, and the BrownBox. I stabilize the volts at 120v, and I run amps/BrownBox at 110v. They run much cooler, and sound better. My wall voltage is often as high as 129v, and was burning $$$ NOS tubes up. Specifically NOS 50s M/O KT66s. Havent burned 1 tube in 6 years since stabilizing/and lowering my voltage, though I never really had a problem with my 69 Dual Showman Rvb, my Metropoulos GMP45 head would run extremely hot vs now. It did make the DSRVB less harsh, and warmer.
 
Last edited:

HotBluePlates

Member
Messages
9,409
i got a “vintage” genrad variac ... can’t imagine that a modern import would be as reliable.
nope. fully functional finished unit. built like a tank. ...
Genrad = General Radio = the company that coined the trade name "Variac" now used in the same way as "Kleenex" or "Xerox."

General Radio was known for over-built equipment. Anything from General Radio/Genrad will probably last 100+ years.
 

Seal

Supporting Member
Messages
548
This would be mainly for working on amps and safely bringing up the voltage.

I guess I could try for playing amps too.
 

glpg80

Member
Messages
68
For such applications, I find my light bulb limiter far superior to my variac.
+1

Having a high wattage tungsten incandescent light bulb as a ballast is a good tool to have for a repair bench. If a component fails, it will limit inrush current to a minimum and help save power transformers. They‘re a must have for benches and I prefer them in addition to variacs for repair work.
 

ironman28

Silver Supporting Member
Messages
578
For such applications, I find my light bulb limiter far superior to my variac.
I rarely use the variac except to correct for low/ high line voltages or to simulate "vintage" power. Get a line meter that displays V and A to adjust the line and also monitor the current. Pretty soon you get a feel for a correctly operating amp by watching the current during power on-standby-idle.
 




Trending Topics

Top