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Old 21st December 2010, 07:48 AM   #1
laksaja is offline laksaja  Estonia
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Default Tube rectifier


Since I know that here are many of talented persons in tube area, I would like to ask a little help. I ordered custom made toroidal power transformer to my EL84 tube amp, but when i received it it was obvious that there was misunderstanding between me and the transformer maker. I wanted centre tapped HV secondary and also 6.3 CT, but the transformer came as it on attachment picture (not 250v - CT - 250v, but 125v - CT -125V). Im using it now with 1N4007 diode bridge without CT, B+ voltage is 273 - 300v DC and total current draw is 137 mA)

My question is, would it be possible to use tube rectifier (5Z4S) with this transformer?

Thank you in advance!
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Last edited by laksaja; 21st December 2010 at 08:11 AM.
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Old 21st December 2010, 12:35 PM   #2
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you would have to play with PSUD to get the ballpark figures, but you're not going to get 300VDC using a 5Z4 rectifier (full wave) with a 250VCT transformer. You could try a hybrid bridge half-tube/half-SS, but the voltage drop of the rectifier would be too much. SS diodes are just that much more efficient than their glass brothers.

Try the UF4007 diode. I've found it to be rather good versus the ol' 1N4007.
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Old 21st December 2010, 02:23 PM   #3
DF96 is offline DF96  England
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You could try a temporary lash-up of half valve/half SS bridge, but it might drop too much voltage. In addition, you need to watch maximum cap value and minimum series resistance more carefully with a valve rectifier - this could mean more volts lost.

Given what you have, I would do the best I could with SS, as it is not quite as evil as some people pretend! Better diodes (to reduce minority carrier storage), a little series resistance (to broaden the charging pulse) and care about wire routeing and grounding arrangements should be sufficient.
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Old 21st December 2010, 02:23 PM   #4
laksaja is offline laksaja  Estonia
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Join Date: Sep 2010
Thank you for the info!
I just wanted to use tube rectifier to eliminate soft start circuit for HV, which could be essential for diode rectifier. I presume this is the only option I have right now or let the transformer rewound.
Since I never used tube rectifier before, what could be the proper AC voltage for transformer to get +300v DC out? I maybe misunderstood, but some tube rect have 70v drop

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Old 23rd December 2010, 03:07 PM   #5
k9swc is offline k9swc  United States
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Back to the original question of whether you could use a tube rectifer... previous answers are correct BUT... they missed the bigger picture. Since you got the "wrong" HV windings on your transformer, you're pretty much forced to use a full-wave bridge circuit to get the voltage you want... usually requiring two additional rectifier tubes and their separate filament transformers. Lots of extra parts, work, and cost - I'd recommend sticking with the SS rectifiers...

Btw, you probably now know you should have ordered a 500V CT (or 250v-0-250v ... I suspect the manufacturer saw your 250 - CT - and stopped there without considering your other 250v after the "CT"...which would require a 125 - 0 - 125 winding.)
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Old 23rd December 2010, 05:44 PM   #6
laksaja is offline laksaja  Estonia
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Thank you all for valuable info! I will stay on the SS rectifiers and Im currently working on the soft start circuit, which based on PIC10F206 ultratiny microcontroller. However, I ordered another massive transformer with 250v CT 250v , 5.2V @ 5A and 2x6.5V @5A. That should work

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