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. __________________ "It may not be easy for some to not hear differences, even if they are not there." - Vacuphile,

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: SW Florida	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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