Hey All,
I've got a variac I got as a gift many years ago. Typical chinese one rated 500VA. How can I determine what amp is safe to use with this? My least powerful amp is a Bassman 50 and my most is an Eico ST-70 and a Traynor Mark II. Hard to tell which of the last two would suck more power.
Any definitive answer to this one?
I've got a variac I got as a gift many years ago. Typical chinese one rated 500VA. How can I determine what amp is safe to use with this? My least powerful amp is a Bassman 50 and my most is an Eico ST-70 and a Traynor Mark II. Hard to tell which of the last two would suck more power.
Any definitive answer to this one?
A 500VA variac made for 120 volts AC is good for about 4 amps. This will suffice as a servicing tool for any or your amplifiers. I see no reason to otherwise use a variac with these.
Large tube amps suck about 3X more from the wall than they will deliver as audio output. So a 500VA ought to power a 150 Watt tube amp.
Variacs typically heat very slowly. I would not worry too much bringing-up a 200W tube amp on a 500VA variac. A 300W SVT at FULL roar may heat the variac quite quickly.
Variacs typically heat very slowly. I would not worry too much bringing-up a 200W tube amp on a 500VA variac. A 300W SVT at FULL roar may heat the variac quite quickly.
Note that maximum power you can load variac depends on the transformation ratio. If you use a variac to reduce voltage from say 230V to 115V the variac can only support 50% of maximum power and at lower output voltage even less. Check the maximum allowed current, it should not be exceeded.
See example here http://docs-europe.electrocomponents.com/webdocs/144b/0900766b8144b7b7.pdf
The 2A version is specified at maximum 480VA but it is not applicable except for a 1:1 ratio, at 50% setting max power is half
See example here http://docs-europe.electrocomponents.com/webdocs/144b/0900766b8144b7b7.pdf
The 2A version is specified at maximum 480VA but it is not applicable except for a 1:1 ratio, at 50% setting max power is half
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Get a Kill A Watt meter. Put it between the wall outlet and the Variac. Set the Kill A Watt to read VA. Keep the reading below 500 VA. A short burst above 500 is OK, but the average should be kept below 500.
https://www.amazon.com/P3-P4400-Ele...id=1483189380&sr=1-1&keywords=killawatt+meter
Amazon puts these on sale from time to time. I got mine for $14 but it was a few years ago. They are good to have to figure out just what different things use, and how much power they waste (difference between watts and VA).
https://www.amazon.com/P3-P4400-Ele...id=1483189380&sr=1-1&keywords=killawatt+meter
Amazon puts these on sale from time to time. I got mine for $14 but it was a few years ago. They are good to have to figure out just what different things use, and how much power they waste (difference between watts and VA).
It strongly depends on the quality and manufacturing date of your watts 😛
PS: The Lepai 2 doesn't bring more than 3W +/- cleanly into 8Ohms. "700W"
This is a great suggestion, and I'm an idiot! I've already got one! A HA HA HA!!! I originally got one for my coffee roaster. I found I needed a minimum of 120vac to properly roast a batch, then I forgot it could be used for anything else. You can't make this stuff up!
I'll probably use this for my guitar amps, but I'm getting the sense no one uses these on a permanent basis for their old tube stereos, etc. So what do ya'll do with your vintage amps to get the proper voltage on your heaters? Hey, even doing a cap job runs into problems when you realize you now need to rate your caps over 500v because of the increased wall voltage.
For example, you have a 60's Fender Bassman and would like to keep the B+ down under 450v as it was intended. With today's wall voltage, that's not going to happen.
1. Put a resistor in the heater circuit to bring it down to 6.3vac at your most typical wall voltage and call it good.
2. Use the low voltage transformer trick that R.G Keen describes on his website.
3. Something else I don't know about?
Thanks everyone for all the info.
For example, you have a 60's Fender Bassman and would like to keep the B+ down under 450v as it was intended. With today's wall voltage, that's not going to happen.
1. Put a resistor in the heater circuit to bring it down to 6.3vac at your most typical wall voltage and call it good.
2. Use the low voltage transformer trick that R.G Keen describes on his website.
3. Something else I don't know about?
Thanks everyone for all the info.
The limiting factor at lower output voltages is going to be the current handling ability of the xfmr wire and the carbon brush. The 500VA rating is at full output voltage only. So you really want an Amp meter on the output. 4 Amps apparently. Or could put a circuit breaker there. Usually they have a fuse already.
2) low voltage xfmr used as a buck autoformer.
2) low voltage xfmr used as a buck autoformer.
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