variac variable transformer

John Bessa · 13th October 2011, 10:44 PM

How many amps are necessary for trouble-shooting a tube set-up such as a fisher or sherwood amp? 10, 15, 20, more?

aardvarkash10 · 13th October 2011, 11:32 PM

with 10 or 20 amps you can arc weld...

Bigger is always better, but its generally more expensive too. A 500W variac should be ample, 350W would be ok. Less than that is likely a toy.

Pano · 13th October 2011, 11:37 PM

I use a 10A model and know a few other tube guys who do as well. No problems. Probably overkill.

VictoriaGuy · 13th October 2011, 11:39 PM

+1 on Aardvark's advice.
OT: I've got variac(s) but seldom use 'em for troubleshooting.
I find that the 'dim bulb tester' is more useful (and protects the 'test subject' better, too).

John Bessa · 13th October 2011, 11:57 PM

thanks

Dagwood · 14th October 2011, 12:04 AM

Hi John

Not sure on the rating of mine (about an amp) but it works fine
I agree with VictoriaGuy but have my Variac setup with a filament lamp in series. Almost covers all bases, just need to add a ammeter.

Cheers

Enzo · 14th October 2011, 12:21 AM

I use the variac in my shop all the time, an ammeter takes the place of a bulb. Either method works.

The variac is used mainly when things are wanting to bow fuses, I don't need it to be able to power the unit under test to its full output. Once we have established that the amp is stable and ready for high power testing, I no longer need what the variac does, and I power the UUT from the wall.

All that is the long way to say that I don;t ned a 1000 watt variac to service 1000 watt amplifiers. A smaller one will still be useful.

astouffer · 14th October 2011, 02:51 AM

I always wanted to make a variac test box that had meters for voltage and current and also switches to put in a 100 or 25 watt lamp. Maybe add a receptacle and also binding posts...

Dagwood · 14th October 2011, 03:16 AM

Like this?

I added a isolation transformer inside to protect the binding posts, would still like to add a ammeter.

Lamp can be switched on or off and I just swap the lamps from 40, 60 and 100 watts

TheGimp · 14th October 2011, 03:29 AM

I tried using a 2A variac once, and proceeded to blow the windings.

Best to use an over-rated one in case something shorts out.

13th October 2011, 10:44 PM	#1
John Bessa diyAudio Member Join Date: Jan 2011 Location: New Brunswick	variac variable transformer How many amps are necessary for trouble-shooting a tube set-up such as a fisher or sherwood amp? 10, 15, 20, more?

13th October 2011, 11:32 PM	#2
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	with 10 or 20 amps you can arc weld... Bigger is always better, but its generally more expensive too. A 500W variac should be ample, 350W would be ok. Less than that is likely a toy. __________________ Yes, conservatism thrives on low intelligence and poor information. But the liberals in politics... continue to back off, yielding to the supremacy of the stupid. It's turkeys all the way down. - George Monbiot, guardian.co.uk, 6 Feb 2012

14th October 2011, 12:04 AM	#6
Dagwood diyAudio Member Join Date: Feb 2010 Location: North of Auckland	Hi John Not sure on the rating of mine (about an amp) but it works fine I agree with VictoriaGuy but have my Variac setup with a filament lamp in series. Almost covers all bases, just need to add a ammeter. Cheers __________________ If you keep digging in the garden of failure you will eventually find success

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13th October 2011, 11:37 PM	#3
Pano diyAudio Moderator Join Date: Oct 2004 Location: North Carolina Blog Entries: 4	I use a 10A model and know a few other tube guys who do as well. No problems. Probably overkill.

13th October 2011, 11:39 PM	#4
VictoriaGuy diyAudio Member Join Date: Dec 2008 Location: Victoria, BC	+1 on Aardvark's advice. OT: I've got variac(s) but seldom use 'em for troubleshooting. I find that the 'dim bulb tester' is more useful (and protects the 'test subject' better, too).

13th October 2011, 11:57 PM	#5
John Bessa diyAudio Member Join Date: Jan 2011 Location: New Brunswick	thanks

14th October 2011, 12:21 AM	#7
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	I use the variac in my shop all the time, an ammeter takes the place of a bulb. Either method works. The variac is used mainly when things are wanting to bow fuses, I don't need it to be able to power the unit under test to its full output. Once we have established that the amp is stable and ready for high power testing, I no longer need what the variac does, and I power the UUT from the wall. All that is the long way to say that I don;t ned a 1000 watt variac to service 1000 watt amplifiers. A smaller one will still be useful.

14th October 2011, 02:51 AM	#8
astouffer diyAudio Member Join Date: Jun 2004 Location: Pittsburgh, crumbling wasteland	I always wanted to make a variac test box that had meters for voltage and current and also switches to put in a 100 or 25 watt lamp. Maybe add a receptacle and also binding posts...

14th October 2011, 03:29 AM	#10
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	I tried using a 2A variac once, and proceeded to blow the windings. Best to use an over-rated one in case something shorts out.

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