Variac Vs Attenuator?

[jamme61]

I've used the Variac and attenuators (many attenuators) I like the Variac best but have always backed off from using it because of the warnings on the internet. Who really knows? I just read this Variac warning--

shortens heater life and can lead to cathode stripping. Lowering voltage, depending on the circuit, will often lead to increased current, possibly causing early transformer burnout.

To me I think the attenuator has be stresing my amp and tubes out too, right? would love to hear what you think about using the Variac.





http://www.thegearpage.net/board/showth ... 1&page=2[u][/u]

[John_P_WI]

Do some research into cathode stripping / poisoning at voltages under 500 volts. Doubt you'll find conclusive evidence that it is an issue.

Additionally, search on TAG for ampdoc, he built a volume scaling set-up by lowering the power tube heater voltages without ill effect.

Yes, the variac does darken the tone some with lower voltages. Yes, attenuators prematurely wear tubes. There are other ways to achieve Eddie's studio mojo that are simpler and safer.

[Reeltarded]

I attenuate only to get a tap off the signal there and provide a load, otherwise it would be all variac.

Been running them until the lights go out since forever. It's super easy on the tubes. They are light bulbs; they can run forever at half the rated voltage.

[Leo_Gnardo]

I've used the Variac and attenuators (many attenuators) I like the Variac best but have always backed off from using it because of the warnings on the internet. Who really knows? I just read this Variac warning--

shortens heater life and can lead to cathode stripping. Lowering voltage, depending on the circuit, will often lead to increased current, possibly causing early transformer burnout.

To me I think the attenuator has be stresing my amp and tubes out too, right? would love to hear what you think about using the Variac.

A couple variac cautions:

0.) Select a variac that gives you zero to 100% line voltage, not one that goes to 115-125%, then you can't make a misteak.

1.) turn it down not up, regardless of what EVH said in his first Guitar Player interview. See 0.) above ^^^

2.) Simple amps only please, not ones with extra power supplies to enable channel switching, op amp/transistor circuits etc.

3.) dial variac up to 100% line voltage to let your amp warm up. Then dial it down to the level you like. An amp run at say 50-60% line voltage could take "all day" to warm up. (Got this advice from Mark Hitt now on tour with Robin Zander band, after I fixed up his 100W Hiwatt. Credit where credit is due!)

In fixed-bias amps I find the bias tracks line voltage pretty well, never have seen one go bazerko. If you take an amp that's on, running from reduced line voltage from variac, and decide to dial that variac up, do it slowly over the course of 5 to 10 seconds so bias voltage can keep up. I can imagine a situation with a heavily filtered bias supply where you'd be drawing excess plate current if you made that transition quickly or instantly, because it takes time for the bias supply to charge.

[jamme61]

thanks for all the info - I have a plexi and 18 watt clone and this will be perfect for the variac.

[jamme61]

any sugestions on a good model to buy? I have an old general radio W5mt only 5 amp and no meter.

would this be ok? http://www.circuitspecialists.com/variac-tdgc2-2.html

[WRC34]

I just obtained an old variac for use in builds and testing. This info is great in regards to how to use it safely and properly. I am curious to see how certain amps/circuits will act when the intended line voltage of 115 and sometimes 117 is applied as opposed to the loosey-goosey variation of 118-125 that I get depending on the time of day!

[C Moore]

any sugestions on a good model to buy? I have an old general radio W5mt only 5 amp and no meter.

would this be ok? http://www.circuitspecialists.com/variac-tdgc2-2.html

I have been looking at the same unit.....but it SAYS it is rated for an input of 110 VAC.
Does that worry any of you guys.?
Or does that just get the 0-130 VAC output.?
Thanks

[John_P_WI]

any sugestions on a good model to buy? I have an old general radio W5mt only 5 amp and no meter.

would this be ok? http://www.circuitspecialists.com/variac-tdgc2-2.html

I didn't fully read the specs but am guessing that the meter is an ammeter not a voltmeter. 20 amps is by far and above anything needed.

[C Moore]

any sugestions on a good model to buy? I have an old general radio W5mt only 5 amp and no meter.

would this be ok? http://www.circuitspecialists.com/variac-tdgc2-2.html

I didn't fully read the specs but am guessing that the meter is an ammeter not a voltmeter. 20 amps is by far and above anything needed.

I guess I am the one that does not understand.?
Typically, wall voltage in the USA is closer to 125. This unit says it is "rated" at 110.
Does that just effect their number of 0-130, or does it reflect the limits of the input voltage for this device.?
Thanks

[jamme61]

any sugestions on a good model to buy? I have an old general radio W5mt only 5 amp and no meter.

would this be ok? http://www.circuitspecialists.com/variac-tdgc2-2.html

I didn't fully read the specs but am guessing that the meter is an ammeter not a voltmeter. 20 amps is by far and above anything needed.

I guess I am the one that does not understand.?
Typically, wall voltage in the USA is closer to 125. This unit says it is "rated" at 110.
Does that just effect their number of 0-130, or does it reflect the limits of the input voltage for this device.?
Thanks

found this video review https://www.youtube.com/watch?v=D1jaTevZGWs