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Old 21st September 2006, 01:42 PM   #1
Sherman is offline Sherman  United States
diyAudio Member
Join Date: Feb 2004
Location: Chicago area
Question Pseudo dual mono PS?

I'm closing in on my winter project- a 30-50 WPC KT88 PP power amp. Though I'm still waffling a bit on the schematic, Citation, MKIII and a couple more. However my question is about the power supply.

Whichever schematic I choose I'll need significant current- 300 to 450 mA. I'd like to make a stereo amp rather than monoblocks. The Hammond 278CX seems to be an off-the-shelf PTX that can deliver the voltage (450-470 cap input) and current (465mA).

Assuming I use the Hammond I'd like opinions on whether to make two separate filters for the B+ lines ( I'm thinking CLCRC)versus one honkin' big filter for the whole shebang.

Issues with one big filter- finding (and paying for) a choke that can handle 400mA, giant (and HOT ) resistor.

Issues with two filters- chassis space, double the number of caps etc.

Whaddya think?
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Old 21st September 2006, 04:04 PM   #2
diyAudio Member
Join Date: Feb 2006
Location: you tell me
I tried both, in a way. My amp doesn't need as much current or voltage but still it's not that much different. I used JJ double caps (correct term?) to save space. I only used one rectifier and one half of the first cap and both sides of the two 47uF+47uF caps. Nothing wrong with this as such, but my power tranny just was running too hot as it was also powering all the filaments. For this reason only I converted it to two separate power supplies. Sonically I can't tell the difference but the trannies run a lot cooler. Would it be out of the question to build a separate PSU unit and a stereo amp? This would sort of solve the space problem. That's what I'm doing since I just can't get PTX -> OTX interference under control otherwise. Actually, I'm not building a separate PSU but rather a separate box for the power trannies. Rectification (2 separate tubes) is still done in the same box with the amps. Worth a thought, I suppose.
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Old 22nd September 2006, 10:38 PM   #3
Sherman is offline Sherman  United States
diyAudio Member
Join Date: Feb 2004
Location: Chicago area
Thanks for the feedback! I've done a bit more digging around and I think I've found just the choke I need to do the single big, honkin' supply at a reasonable price.

I was most interested in you not hearing a difference. That is good news. Bottom line is the sound, if I can measure something on my scope but I don't hear it I try not to get too worked up over it.
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