Variac?

[rwagoner]

I have a few project tube radios I want to start working on. I am not sure the last time they were energized ... and am under the impression that I should use a variac. Does anyone know ... are the various like those sold on Amazon any good? How high an amperage would I need? And is it true they should only be used with tube equipment and not solid state?

As always, thank you!

[Notimetolooz]

Do you know how to use the Search function on this forum?
Actually I just did an advanced search and didn't find as many threads as I thought I would.
Anyway, first step is to try to predict what the largest current draw will be on anything you are likely to work on in the near future. Most radios and TV in the later years have a wattage rating number on them. Divide the wattage by 120V and that will give you a rough idea of the amperage draw.
Most home radios would draw less than 2 amps. Most TVs, jukeboxes and large stereos would draw less than 5 amp. Some HAM radio transmitters might draw 15 amp or more.
I my opinion a ammeter or watt meter should be used with a variac.
In use the voltage is slowly increased from zero, if the current or wattage climbs too high or too fast that means there is a problem.
There are a few tubed based TVs that have what could be called a "soft start" circuit where a relay does not activate until the voltage climbs to a certain point. Those can be a problem, the increase in voltage should not be increased too slowly or there will be problems.
Powering up a solid state unit may cause problems, so it may not be a good idea.
A low cost alternative would be to use a "Dim-bulb" tester.
https://www.antiqueradio.org/dimbulb.htm

[dewickt]

The essentials for the work bench are a good VOM, scope, and a metered variac. The variac has saved me many times by showing high current draw a low input voltage !! Most of what I work on, TVs included, draw less than 1.5A to 2A at 120V, I bring them up slow and watch the current.

[zeno]

There are 2 things you need.
1) a variac with amp & volt metering
2) an isolation transformer
If money is no object get one of these.
https://www.ebay.com/itm/Sencore-PR5...AAAOSwjwJgLTmT
That will do almost anything. B&K also made one. I have used the Sencore
since abt 1974 & only replaced the socket on it once. Great for tube
& solid state. In fact indisposable for solid state work.

73 Zeno
LFOD !

[Chip Chester]

Just a note: forum search engines occasionally vary in their effectiveness. If you're not finding what you think you should find, one sure-fire solution is to use Google site search, thusly:

site:videokarma.org variac

Cut and paste that whole thing into a Google search box, and hopefully you'll find some more in-depth remarks. You can add more specific search terms after variac as well.

[Electronic M]

Variacs are nice for powering up unrestored equipment and if you aren't %100 percent confident a recap job has been done right.
You can get by with a dim bulb tester.
If you never power up an unrestored item and are meticulous or (over?)confident in your recap work you could do without both, but it is nice to have one.

If you work on any hot chassis sets an isolation transformer is usually a must....If you never power up the set disassembled (which prevents a LOT of troubleshooting methods) you usually can get away without one but some non-UL sets and older sets can be dangerous to opperate without a variac even fully assembled....For instance I've got a 40's Sonora radio phono combo where the tone arm, mode and motor switches which are all metal are electrically hot if the unit is plugged in the wrong way.

[Notimetolooz]

Originally Posted by Electronic M

If you work on any hot chassis sets an isolation transformer is usually a must....If you never power up the set disassembled (which prevents a LOT of troubleshooting methods) you usually can get away without one but some non-UL sets and older sets can be dangerous to opperate without a variac even fully assembled....For instance I've got a 40's Sonora radio phono combo where the tone arm, mode and motor switches which are all metal are electrically hot if the unit is plugged in the wrong way.

I think you meant to say "isolation transformer" instead of "variac" in that last part.

[kf4rca]

Build your own variac. You really don't need a voltmeter. You want to keep your eye on the amps.

[rwagoner]

I guess in part what I was wondering was if that specific model was any good, but a lot of good points were made here (especially as to the safety of the chassis!). As always, thanks.

[Notimetolooz]

As was said, you could assemble one yourself if you find a panel mount variac without a case. I think Powerstat was another brand name.
https://www.antiqueradio.org/Variacs.htm

If you buy a modern unit pre-assembled unit I don't think you should have many problems as long as the current is enough. Be aware that Chinese units might not be up to its rating, a 5 amp should give you some extra cushion.

There actually are some that also combine a variac and an isolation transformer. Check carefully.