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Old 12th June 2013, 10:00 AM   #11
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You definitely will spend less, if the bulk of your power trafo needs are provided by a toroid. At $57 each, the AnTek AS-4T320 easily takes care of the B+ need and seems to have enough 6.3 VAC current too. A Hammond 166R5 would take care of 5 VAC needs and happens to have a CT, from which the B+ can be taken.

On the subject of the rectifier bottles themselves, use current production ElectroHarmonix (EH) 5U4GBs. The Russian tube is quite decent and it's priced favorably.
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Old 12th June 2013, 01:12 PM   #12
Einric is offline Einric  United States
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The stock Traffo has 780VCT I was thinking more along the lines of the AS-4T400 to handle the B+ and 6.3V.
I will check out that hammond for the 5V.
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Old 13th June 2013, 08:14 AM   #13
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The AS-4T400 is out of stock, but the AS-4T360 is in stock. I think the AS-4T360 will be OK, if you switch to low forward drop 5AR4s for B+ rectification. Use a 100 μF./450 WVDC 'lytic in the 1st PSU filter position. The fact that a 5AR4 draws but 2 A. of heater current allows us to be "creative" and come up with an excellent match for the job. Wire the 5AR4 heaters in series (pin 8 to pin 8) and energize the string with a 3 A. rated Hammond 166M10. Connect the 166M10's secondary CT to the pin 8/pin 8 junction. Take the B+ from that point too.

NOS 5AR4s are OUTRAGEOUSLY expensive, but the current production Sovtek 5AR4 is affordable. In all aspects except PIV capability, the Russian tube is quite good. Deal with the PIV weakness by employing the series SS diode tweak, along the lines shown in the uploaded graphic. A single, 1 A. rated, UF4007 in series with each rectifier's paralleled plates will be fine.

BTW, the graphic does not originate with me. Good ideas get saved for future use.
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Old 13th June 2013, 01:24 PM   #14
Einric is offline Einric  United States
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GREAT IDEA!!!
I really can"t wait to get ahold of these.
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Old 13th June 2013, 02:22 PM   #15
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In the meanwhile, you can read about a modification of the similar AP-55... The Shrine of the Ancient and Most Excellent Stromberg-Carlson AP-55 / AP-56 Power Amplifier
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Old 14th June 2013, 12:21 AM   #16
Einric is offline Einric  United States
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I have been reading that, the guy that sold these to me pointed me that way.
I also have the matching rack mount preamp for these, it has 6 inputs with modular construction.
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Old 14th June 2013, 11:20 AM   #17
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Time out please! I hope nothing has been ordered from AnTek. Reviewing the info. given earlier in the thread reveals a conflict.

The chart of voltages on the schematic graphic shows 340 VAC on the rectifier plates, which means the OEM power trafo is 680 VCT. However, the OP has stated, "The stock Traffo has 780VCT". If, as I suspect, the graphic is correct, the "correct" toroid to order is the AS-4T320. The 5AR4 rectifier scheme previously mentioned would be retained.

BTW, 450 WVDC PSU caps. should be OK, if the AS-4T320 is employed. OTOH, series connected 'lytic pairs, along with voltage equalizing resistors, seem indicated for use in combination with the previously discussed AS-4T360.
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Old 14th June 2013, 01:37 PM   #18
Einric is offline Einric  United States
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Default Parts List

Here are the scans of the parts lists off of the web.
I'm still waiting on the originals to come in the mail.

The parts list does show a 780VCT power transformer.
However, I don't have possession of these yet so I won't be placing any orders until I have had a chance to inspect these parts.
I bought them sight unseen from a coworker 300 Miles away.
He is an old time tube technician so I do trust him and his judgement but I always "trust but verify".

Hopefully I have them in a few weeks, unfortunately it may be months.
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Old 15th June 2013, 10:13 AM   #19
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The 500 WVDC rating of C1 is a clue. Dividing 500 by 21/2 yields approx. 354. Allowing for the forward drop in 5U4s makes 390-0-390 seem reasonable.
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Old 6th July 2013, 04:01 AM   #20
Einric is offline Einric  United States
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Thank you all for the help, but it turns out these are SC AP-55's.
I will start a new thread.
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