Tube rectifier

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.

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!


  • Trafo_tube.JPG
    43.7 KB · Views: 302
  • IMAG0063.jpg
    184.9 KB · Views: 300
  • Trafo_config.JPG
    49.6 KB · Views: 295
Last edited:
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.
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.
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

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.)
Thank you all for valuable info! I will stay on the SS rectifiers and I´m 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 :)

It´s nothing better than have some hot wine next to the christmas tree and listening "warm" sound :)

Wonderful Xmas time to everyone and successful new!


  • IMG_1740.jpg
    137.5 KB · Views: 256
So current draw I is between 0mA and 5mA (i.e. unknown), and the voltage drop V is unknown. All you have to do is calculate V/I to get the resistance. This assumes, of course, that it is DC you want to drop. For charging pulses you may need a smaller resistance.

It might help if you give us some context. Is this related to your other questions about 1626 in another thread?
mcgyver2822 said:
The output of the tube is 150 volts..current unknown. I would like a ballpark figure of the dropping resistor to use to equate the tube.
If the current is truly unknown then the resistor value must remain unknown too. R=V/I. If you don't know I then you cannot calculate R. Nobody can calculate R.

You might guess that the voltage drop is 10V and the current is 1mA DC - then you need 10k.
Or you might guess that the drop is 5V, current is 5mA in charging pulses - then you might want 1k divided by 2 or 3 - maybe 330R.

Allow a factor of 2 either way, so start with something between 150R and 20k.
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.