2. amps-preamps
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Audiophile quality variacs to decrease voltage?

I have an older 30 w.p.c. tube amp that should be run with 110-115 Volts coming into the unit. The average voltage coming from my AC lines is 124 volts, which puts the operating voltages inside the amp well above what it should be, and will cut short the life expectancy of various components and tubes in the amp. I purchased a newer model 10 amp variac to reduce the incoming voltage to the amp, but quickly found that the sound quality was noticeably reduced with the variac in line, at any voltage set between 100 and 124 volts when in use. Are there any "audiophile quality" variacs available, or some that "sound" better than others? I researched power conditioners that might have the feature of reducing output voltage, but the only solution I found were the new PS Audio Premier power plants that can do this. Unfortunately, they retail for $2,000, and my budget does not allow for such a purchase. Even at used prices, their reliability seems to be an issue from posts I have read on them. Any suggestions from others who have suceeded at reducing voltages without ill effects? Thanks for your help!
bigshutterbug

Showing 6 responses by eldartford

eldartford
4,262 posts
 
How sure are you about the 124 volts? I would doublecheck this before buying anything. Also check the other leg of the 220 volt input to your house. Maybe the other leg is 8 percent low which means you have a neutral grounding problem. It is not unusual to see a volt difference, but 18 volts (+9 to -9) would be bad. (Does anyone know what spec the power company is obligated to maintain?)

If the 124 volts is correct that's just less than 8 percent high. Don't worry about filiaments. (Has anyone ever had a filiament burn out?) Your plate voltages will be 8 percent high but different amps run the same tubes at different plate voltages so I doubt this will be a problem.

Look at the bright side. You have a 32.4 watt amp :-)
eldartford
4,262 posts
 
Even better...it's a 35 watt amp! (E^2/R not E/R).
eldartford
4,262 posts
 
Albertporter...Of course I understood his question. He measured 124 volts but it makes sense to be a bit skeptical of such a measurement. If it were my measurement I would double check my reading, (even I have been known to make a wrong reading)and if it still looked like 124 volts I would somehow check the meter (or try a different meter).
By the way, the two sides of my power measure 115.6 and 114.5, which I believe is typical.

My suggestion to measure the other leg of his power was related to troubleshooting the reason for a 124 volt reading. I never suggested running another line.

If he absolutely must drop his voltage your transformer suggestion is clearly the best way to do it. Patching in a nine volt 3 amp booster transformer scares me.

My main point was that I think his amp will do fine on 8 percent high voltage, and he really doesn't need to do anything.

To repeat my question...what voltage regulation is the power company supposed to supply? Maybe you can get the power company to fix your "problem".
eldartford
4,262 posts
 
Another thought...I seem to remember that the distribution transformers that step down the voltage for your house have taps that are supposed to be connected so as to give you the correct voltage. Go after your power company.
eldartford
4,262 posts
 
Bigshutterbug...Hey...did you contact your power utility? Or are you determined to spend some money?
eldartford
4,262 posts
 
Bigshutterbug...Assuming that they acknowledge that 124 volts is too high, they CAN definitely solve the problem. Distribution transformers (the ones up on poles that feed into houses) have taps that can be selected so as to output the proper voltage. This is necessary because the voltage input to these transformers drops as you go further away from the substation (which has larger transformers).

While I don't think your amp would suffer at 124 volts, the lifetime of incandescent light bulbs is strongly dependent on voltage. A five percent voltage reduction will double the life, with 20 percent less light output.
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