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Old 19th November 2013, 10:00 AM   #1
UJF is offline UJF  United States
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Default P. Millett Engineers Amplifier

Hello Everyone, I am increasing the power output of the designed WPC from 17 to around 40. The power transformer recommended was a "700VCT (350-0-350) to get 450VDC" B+ input. However no current level was ever discussed, so I choose 400 mA and Edcor part number XPWR029-120. Now I find Edcor no longer makes that transformer with that high a current rating. Was I correct in choosing that current level or can I get by with a lesser amount? Can anyone recommend an alternative power transformer. The Edcor was priced right at about $90. Other transformers I looked at with similar specs are quite a bit more.
Thank you for the help.

Millett DCPP
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Old 19th November 2013, 12:02 PM   #2
tomlang is offline tomlang  United States
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The voltage is a little less but the current is good. Double check your filament draw though, depending on tubes used may require an auxiliary filament transformer.

Transformer - Hammond, Power, Replacement for Fender, 120 V | Antique Electronic Supply

Pete full wave rectifies his bias, with this one you'll need to half wave it but should work fine.
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Old 20th November 2013, 01:25 AM   #3
AJT is offline AJT  Philippines
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in my case what i do to get the power capacity of the power transformer is:

1. compute filament power of all tubes used in watts
2. compute plate power requirements, e.g. 40 watts is 80 watts stereo,
160 watts for plate,including those of drivers and preamps,
3. add total for 1 and 2
4. divide that by a factor of say 0.6 to get primary power capacity.

then you can shop around for for suitable power traffo...
getting a bigger power traffo can mean cooler operating temperature...
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Old 20th November 2013, 09:55 AM   #4
UJF is offline UJF  United States
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Thumbs up P. Millett Engineers Amplifier

Thank you Tom & AJT for the info. I will look up the data for the tubes and work thru the calculations. I have never done this so it should be interesting. I'll post how it works out. I also have a note into Hammond asking for their recommendations. In the mean time, any other weigh ins will be a learning experience for me. Thanks guys.
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Old 20th November 2013, 10:50 AM   #5
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there is an entire thread where they discuss increasing the power output from this amp

Posted new P-P power amp design
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Old 21st November 2013, 01:28 PM   #6
UJF is offline UJF  United States
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I like the size and mounting configuration of the 290FX Tfxr. Can I assume the 320-320 VDC will result in a lesser wattage output than the 350-350. And Yes, the circuit has a full wave rectifier on the PC board. Can I try that with the Tfxr before I start ripping the rectifier in half?
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