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Old 31st October 2011, 07:35 PM   #1341
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Default PSU for tube 26 preamp

Hey guys,

Finally started my first 26 PSU only for B+, hybrid rectifier AZ1, Bartolucci one power transformer Model CF125 125VAC 100W rendering 90% regulation 0,5% 4 Kg & Bartolucci one choke MR8L 10H 100mA VDC 200 DC resist 10 ohms 3 Kg, inside box only 2 schottky diodes 4A 600V Cree Z-Rec Sic + one MKP, next box 26 PSU heaters & yes I will go for 4 boxes (two PSU B+ + one PSU Heaters + one 26 tube preamp), a pic just for fun.
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Old 31st October 2011, 10:33 PM   #1342
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I must have missed something - why two B+ supplies?

Andy
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Old 1st November 2011, 10:12 AM   #1343
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Because I have two power transformers & two chokes or isn't better to have two B+ supplies?
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Old 1st November 2011, 10:27 AM   #1344
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I don't see any point in two power supplies. It would be better to put the two chokes in one supply.

andy
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Old 1st November 2011, 10:32 AM   #1345
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Thanks Andy, about PSU heaters also sharing the same box like PSU B+ so go only for two boxes?
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Old 1st November 2011, 12:00 PM   #1346
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I'd use 3 boxes. I would put the filament supply in a metal box for screening if you have chokes in it - you need a 1 metre umbilical at least because if you have chokes they can hum. You may build without chokes first of all, but you may want to change the filament supply to a larger box if you do decide to add chokes.

A further option I'm exploring is putting two stages in the preamp box, since an AZ1 will comfortably feed four tubes. You'd have the option of direct coupling stage 1 and 2 and finishing with an output transformer. You'd then only need the output stage in the amp box, and you could experiment with a few different options including PP 2a3s or even a hybrid ss stage which could produce 20+ watts. If you put the PSU in the amp box you'd eliminate the preamp PSU and just have 3 boxes in total, with a larger choke input PSU that would power the whole amp.

andy

Last edited by andyjevans; 1st November 2011 at 12:09 PM.
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Old 1st November 2011, 12:11 PM   #1347
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I support Andy's recommendation.

The filament transformer [and wiring] will spill Large B-field [magnetic] for C-in supplies, and E-field for choke input. Either way, they are best kept at some distance for the B+ supply, to minimise the coupling.
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Old 1st November 2011, 01:42 PM   #1348
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Rod & Andy,

3 boxes it's only necessary for filament bias not for cathode bias? so If I want to start with cathode bias I only need 2 boxes?
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Old 1st November 2011, 01:50 PM   #1349
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It is possible to have the filament transformer in the same box as the B+ trafo - BUT, a separate box is probably better.

In any case, please keep the filament trafo and B+ trafo apart, as much as you can.
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Old 1st November 2011, 02:00 PM   #1350
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OK I will go for 3 boxes so at least I can try filament bias also.
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