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Looking for power transformer of about 250 to 275VAC 400VA

Discussion in 'Tube Audio' started by Alan0354, Jan 2, 2018.

  1. Alan0354

    Alan0354 Super Member

    Messages:
    2,735
    Location:
    Bay Area
    Hi

    I am looking for a cheaper power transformer with secondary of about 240V to 275VAC 400VA. I want the +B to be about +350V or so. It would be nice to have 6.3VAC for filament also.

    I am even open to use a 120V to 240V isolation transformer and buy a separate 6.3V transformer. Both Edcor and Hammond are either not enough power or very expensive. Someone might know cheaper ones out there.

    Thanks
     

     

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  2. mike567

    mike567 Member

    Messages:
    62
  3. soundmotor

    soundmotor super modified Subscriber

    What is the actual B+ current you are looking for?
     
  4. Alan0354

    Alan0354 Super Member

    Messages:
    2,735
    Location:
    Bay Area
    I am using this for 2 pairs of 6L6GC running about 80mA per tube. So the idle current is 160mA total per channel and 320mA for the whole amp. But this is a class AB design, so I need more than 320mA + the current for the rest of the tubes.

    thanks
     
  5. Tom Bavis

    Tom Bavis Audiophool Subscriber

    Messages:
    9,000
    Location:
    Macedon NY
    300VA is enough - over an amp at 275. If screen voltage is 400, max current is about 210 mA per pair (RCA data sheet), lower if screen voltage is lower. The transformer is good for 1A @ 275V, about 700 mA from a full-wave bridge. Would handle both channels driven to full power, If you want more margin use two of these: http://www.antekinc.com/as-2t230-200va-230v-transformer/ (but it's only 230V - power will be lower)

    The 120-240V 500VA transformers are available for $75 or so (much less surplus) BUT the output voltage will be 220V or less when reversed. They have about a 10% step-up ratio to counteract the perhaps 10% voltage drop at half-load. So output it is 10% high unloaded, correct at half-load, 10% low at full load. Reverse it and it's 10% low at no load, 20% at half load, 30% low at full load. IF you can find one tapped for 105V or 110V, it MIGHT be OK.
     
    Alan0354 likes this.

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