Tube rectifier connections

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Tube rectifier connections

Postby Core32 » Tue Jan 27, 2015 10:34 am

I'm a complete newby to tube design, so watch out for smoke! :$
I've been researching designs for a tube PSU and I have a question regarding the connection between the transformer secondary(s) and the rectifier.
I will be using a 5U4GB tube.
I would like to know the effect/advantage of using the 5V secondary of the transformer like the second picture, versus not using it, in the first picture.
Does using the 5V secondary make the filter input inductive or would the filter input still be considered capacitive?
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Re: Tube rectifier connections

Postby SteveH » Tue Jan 27, 2015 10:53 am

The first circuit is not a valid design - You need the 5v transformer to heat the tube.
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Re: Tube rectifier connections

Postby Core32 » Tue Jan 27, 2015 12:11 pm

That makes perfect sense.
I have seen that bad example a few places on the web and I actually copied that one from a site and removed all the text with MSPaint before posting.
Are some rectifiers "self-heating", or some such terminology, that do not require the extra 5V windings?
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Re: Tube rectifier connections

Postby DeathRex » Tue Jan 27, 2015 5:32 pm

The 0Z4 and the BH, and maybe some more. I don't have a 0Z4, but the BH is a very old rectifier, used in the earliest power supplies for radios, back in the 20s. It and the 0Z4 have gas inside to help with emission.
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Re: Tube rectifier connections

Postby Core32 » Wed Jan 28, 2015 5:49 am

Thanks for the answers.
I also see some designs where the 5V winding has a center tap and the input to the filter is taken from there.
Are there any advantages/disadvantages to that arrangement?
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Re: Tube rectifier connections

Postby Shannon Parks » Wed Jan 28, 2015 8:06 am

Definitely have fun with this if you don't have it already:
http://www.duncanamps.com/psud2/

Image

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Re: Tube rectifier connections

Postby EWBrown » Wed Jan 28, 2015 8:08 am

The usual connections for rectifier tubes such as 5U4, 5AR4/GZ34, etc, the two anodes are pins 4 and 6, and the filament is pins 2 and 8, take the rectified DC off pin 8, that makes it compatible with the 5AR4/GZ34 (and some others) which also have a cathode, which is connected to pin 8. A 5V winding center tap isn't really necessary, and may add +/-2.5VAC more ripple.

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Re: Tube rectifier connections

Postby Core32 » Wed Jan 28, 2015 9:15 am

Yes, I have been running simulations using the PSU Designer II for about a week now.
From what I have seen it does not have a transformer model using the extra 5V winding connections,
but I have found a couple of violations using the tool I would not have otherwise, until I smelled them. =:o
And good advice about using the "compatible" pin for rectified DC.
Thanks again.
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Re: Tube rectifier connections

Postby Impmon » Sun Feb 01, 2015 9:52 pm

Core32 wrote:I'm a complete newby to tube design, so watch out for smoke! :$
I've been researching designs for a tube PSU and I have a question regarding the connection between the transformer secondary(s) and the rectifier.
I will be using a 5U4GB tube.
I would like to know the effect/advantage of using the 5V secondary of the transformer like the second picture, versus not using it, in the first picture.
Does using the 5V secondary make the filter input inductive or would the filter input still be considered capacitive?


The 5U4GB doesn't have indirectly heated cathodes, but rather filament/cathodes. Not using the built in 5.0V secondaries can have the advantage of keeping switching glitches from being coupled into the HV secondary, as these will be isolated with a separate heater PTX. It probably doesn't make much of a difference to be worth it since it's almost never done. The exceptions would be Hg diodes that're used with very high voltages, and you need the secondary well insulated from the core, and you'd rather not have any extra secondaries in there that could see a flash-over. The other is hollow state bridges where you have the 5U4-types as the positive rail, and indirectly heated singleton diodes like TV damper diodes as the negative rail. These run off 6.3V, and a separate heater PTX is s good idea since the heaters can float to avoid Vhk stresses.

The only input inductance the heater secondary contributes is leakage inductance, and that's so small as to be irrelevant as to ripple filter operation. The second schemo is still a C-input type, and will behave as such.

Running a 5U4GB with a cold cathode is only done if you connect it to an induction coil to make X-rays.

Core32 wrote:Thanks for the answers.
I also see some designs where the 5V winding has a center tap and the input to the filter is taken from there.
Are there any advantages/disadvantages to that arrangement?


Taking the raw DC off a center tap has an advantage of nulling out switching glitches so's they aren't coupled as noise into other secondaries that share the same core.
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Re: Tube rectifier connections

Postby Geek » Mon Feb 02, 2015 8:33 am

Impmon wrote:Running a 5U4GB with a cold cathode is only done if you connect it to an induction coil to make X-rays.


And 1B3GT's are better for that, anyway ;) (666)
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Re: Tube rectifier connections

Postby Core32 » Mon Feb 02, 2015 7:52 pm

Imp,
I didn't grasp it all of course, but I think I have the general idea.
If you have the extra 5V secondary, use it or you have to use an external PTX for it.
The 5U4GB will not be very happy without it.
And, if the 5V secondary has a center tap it might be worth experimenting with to see if the rail noise is any better.
Thanks.
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Re: Tube rectifier connections

Postby kheper » Tue Feb 03, 2015 7:31 pm

Core32 wrote:Imp,
I didn't grasp it all of course, but I think I have the general idea.
If you have the extra 5V secondary, use it or you have to use an external PTX for it.
The 5U4GB will not be very happy without it.
And, if the 5V secondary has a center tap it might be worth experimenting with to see if the rail noise is any better.
Thanks.


You could simplify matters and go with a solid state FW rectifier. No 5V heater necessary and cheaper (unless you already have the 5U4GB).
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Re: Tube rectifier connections

Postby Core32 » Tue Feb 03, 2015 8:23 pm

Yes, I already have a matched pair of 5U4GB tubes and I really want to do an all-tube design. (A pair of mono-blocks.)
Probably because of the challenge as much as anything. (y)
My first two quarters of EE classes I had tube theory and design along with DC analysis.
That was the last year any tube courses were taught there.
I've been SS and digital ever since and always wanted to go back and revisit.
With my eyesight getting weaker and my ears beginning to sing all by themselves I figured it was now or never.
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Re: Tube rectifier connections

Postby Impmon » Tue Feb 10, 2015 3:16 pm

Core32 wrote:Yes, I already have a matched pair of 5U4GB tubes and I really want to do an all-tube design. (A pair of mono-blocks.)
Probably because of the challenge as much as anything. (y)
My first two quarters of EE classes I had tube theory and design along with DC analysis.


If you're gonna go that route, you have to remember that the biggest differences between PS design with hollow state diodes like the 5U4 is this: much larger forward voltage, much smaller Isurge ratings. You can get the spec sheet for the 5U4 from Frank's with the plate characteristics.

Even though specced for an Isurge= 1.0A/plate, that isn't as large as it seems at first, and can easily be busted, especially with a C-in filter. You can also be looking at a Vf= ~100V -- whereas a Si diode drops a volt or less.

That was one problem I had with one of my designs: a PTX with an ideal current rating, but it overvolted badly with Si diodes (458Vdc, whereas I needed 350Vdc design nominal). I had to lose 100V, and considered a MOSFET dropper in the negative rail. Since this PTX also had a 5.0V/3.0A secondary, that pretty much said "5U4GB". Running the calcs with Isurge= 0.8A, gave a Vf= 100V. It was pretty obvious this PTX was designed to produce 350Vdc with a 5U4GB. That's what I needed, and that's what I got.

The other problem is excessive reservoir capacitance. A 47uF capacitor busted the Isurge spec, and needed to be dropped to 34uF (two 68uF/300V in series with voltage balancing resistors). That'll cost a few more volts due to averaging. All problems you can avoid by going solid state, and including a really big capacitor.
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Re: Tube rectifier connections

Postby Geek » Tue Feb 10, 2015 3:32 pm

I've been using PIV relief diodes in series with the AC side of the tube rectifiers as of late. This seems to work and you still get that tube rect. sound while the rect. survival rate being much, much higher than without them.

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