I would not recommend? using a BIG? 240 vac variac to run the entire amplifier.? You will end up with poorer V regulation.? ?The peak current on the 240 line, every 8.3 msecs will make you gag.? W8JI measured 60 amps every 8.3 msecs on an AL-1500 running 1.5 kw? CCS? CXR.? ?However, I have seen? BIG variacs used on 1-2 kw output amps.? But they gotta be big, in order to not get sag on peaks.?
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I have seen? constant V xfmrs? (Sola and other brands)? that were as high as 10-50 kva.? ?To run just the 5V @ 10 amp fil on the 8877, a small, OUTBOARD? 125 va? ?sola could be used.?
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The alpha 9500? only has taps for 220 vac...and also 240 vac.? ?They say not to use > 250 vac.? Below is from their manual.
"High: >250 V Lifetime of the tubes may be reduced. Ask your utility company if they can reduce your line voltage. If this is not possible, consider placing your own step-down transformer in line between the AC outlet and the amplifier. A transformer with at least 4-kVA rating is required, due to the nature of the current waveform in the primary. Another choice for voltage control, a ferro resonant voltage regulator, is an expensive solution, but is a good way to stabilize primary voltage."
250 vac is probably not going to damage anything.... except for perhaps the higher than normal fil V.? ?Sure, the B+ will be on the high side of normal, but that's really a non issue.?
Myself, I would be inclined to use a 5 vdc outboard supply..... and modify the rear apron, to? feed the external 5 vdc into the amp.? But that's just me.? ? I doubt you will get anywhere with the local power company.....you might, would not hurt to ask.?
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Another possible option (instead of using an external 4 kva rated 250 to 240 xfmr)..... is to use a buck - boost xfmr.....in buck mode.? ? IE:? 240-250 vac primary, and a 10 vac (@ 50 amp)? secondary.? ?The 10 vac sec is wired in? series with one leg of the incoming 250 vac.? ?Then you end up with 240 vac? going into the amplifier.? This method has been used before with excellent results.? BUT,? you have to know when to use it, and when to remove it from the line.?
IE: keep track of seasonal? ?incoming V changes.?
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I know several folks? who have 253 vac....and in some cases, even a bit higher..... in summertime.? ? (? AZ, Ga? etc).?
Jim? VE7RF
