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Old 27th December 2012, 11:32 PM   #1
jervill is offline jervill  United Kingdom
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Default Single Transformer, two valve rectifiers

Hi guys,

I've seen power supplies with the filter stage split after the rectifier valve for each channel. I was wondering wether it would be possible to split this at the transformer secondary. That is, use a separate rectifier and filter stage for each channel drawing from one transformer.

I have a hammond 373ex that is rated at 345ma with a 5V 6A tap. I've recently been given a pair of matched rectifiers so was looking at conducting some experiments with the PS. I'm expecting about 40-60ma draw each channel. I know it's a bit OTT but its more for learning than anything else.

Hope everyone had a nice Christmas and all the best for the new year!
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Old 28th December 2012, 12:24 AM   #2
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Separate rectification from same HT winding works just fine, but if you are using 5V rectifiers like 5U4 or 5AR4, you'll need a separate 5V filament winding for each rectifier- remember that the filament is the cathode (B+ out) in a directly heated 5U4, and in case of indirect heated 5AR4, the cathode sleeve is internally connected to filament. I used this topology (2 rectifiers, one HT winding) in a preamp power supply with 6AX5GT rectifiers (cathode isolated from filament).
You could also look at using TV damper diodes if you have a suitable heater winding available - they are robust, cheap, and have excellent heater-cathode insulation, allowing use of common heater supply, BUT, they are half-wave - you'll need 4 individual tubes to get two separately rectified supplies from one centre-tapped HT winding.
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Old 28th December 2012, 02:19 AM   #3
jervill is offline jervill  United Kingdom
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Quote:
Originally Posted by radiotron View Post
Separate rectification from same HT winding works just fine, but if you are using 5V rectifiers like 5U4 or 5AR4, you'll need a separate 5V filament winding for each rectifier- remember that the filament is the cathode (B+ out) in a directly heated 5U4, and in case of indirect heated 5AR4, the cathode sleeve is internally connected to filament. I used this topology (2 rectifiers, one HT winding) in a preamp power supply with 6AX5GT rectifiers (cathode isolated from filament).
You could also look at using TV damper diodes if you have a suitable heater winding available - they are robust, cheap, and have excellent heater-cathode insulation, allowing use of common heater supply, BUT, they are half-wave - you'll need 4 individual tubes to get two separately rectified supplies from one centre-tapped HT winding.
Hi,

Thanks for the response. Would you say then that it would defeat the purpose if I paralleled the 5v 6A tap (not the valves) to heat two GZ37? I'm looking to be able to use just what I have and I don't have any other 5v transformers. Thanks.
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Old 28th December 2012, 02:44 AM   #4
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If you're stuck with only one winding, but it is capable of powering 2 x 3A rectifier filament (the GZ37 has a 3A heater), then your option is to simply parallel the two rectifiers, adding a small value of resistance in series with each anode (22-47 ohms) to ensure equal current sharing. You'll not be able to obtain separate HT from each rectifier, because as previously described, the filaments are internally connected to cathodes, so they're commoned together by the 5V winding (of which you only have one). I hope this makes sense, rgds
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Old 28th December 2012, 07:51 AM   #5
jervill is offline jervill  United Kingdom
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Quote:
Originally Posted by radiotron View Post
If you're stuck with only one winding, but it is capable of powering 2 x 3A rectifier filament (the GZ37 has a 3A heater), then your option is to simply parallel the two rectifiers, adding a small value of resistance in series with each anode (22-47 ohms) to ensure equal current sharing. You'll not be able to obtain separate HT from each rectifier, because as previously described, the filaments are internally connected to cathodes, so they're commoned together by the 5V winding (of which you only have one). I hope this makes sense, rgds
That makes sense. Finally (hopefully), if I implemented paralleled rectifiers I could then split the filter stage of each channel. Would there be any theoretical advantage in doing all of this to power a low powered SET amp?
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Old 28th December 2012, 07:40 PM   #6
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Default series connected rectifer filaments

I have a 10V CT winding on my PT.

I've read that you are not suppose to connect directly heated rectifier filaments in series. Maybe this only holds true if you are taking the B+ from one side of the filament?

What about two 5V4GA with filaments in series? The cathode is connected internally to the heater, but I would take my B+ from the 10V center tap.

Would it matter how it is series connected? 10V to pin 2, jumper from pin 8 to pin 2 of the second filament, then the other side of the 10V winding to pin 8 of the second rectifier filament?
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Old 29th December 2012, 01:40 AM   #7
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Nobody? Really?

Quote:
Originally Posted by scott17 View Post
I have a 10V CT winding on my PT.

I've read that you are not suppose to connect directly heated rectifier filaments in series. Maybe this only holds true if you are taking the B+ from one side of the filament?

What about two 5V4GA with filaments in series? The cathode is connected internally to the heater, but I would take my B+ from the 10V center tap.

Would it matter how it is series connected? 10V to pin 2, jumper from pin 8 to pin 2 of the second filament, then the other side of the 10V winding to pin 8 of the second rectifier filament?
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Old 29th December 2012, 01:46 AM   #8
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Bring your B+ out from the cathodes and you're golden.

All good fortune,
Chris
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Old 29th December 2012, 02:00 AM   #9
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Thanks much Chris.

Does that mean I should not use the center tap of my 10V winding for the B+?

If that is the case, should I series wire so that the cathode side of the filaments are connected?
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Old 29th December 2012, 02:03 AM   #10
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Quote:
Originally Posted by scott17 View Post
Does that mean I should not use the center tap of my 10V winding for the B+?

If that is the case, should I series wire so that the cathode side of the filaments are connected?
You want to connect the cathodes to the center tap and take your B+ from there. Piece of cake.

All good fortune,
Chris
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