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+150V DC Vacuum Tube Regulated Power Supply?
+150V DC Vacuum Tube Regulated Power Supply?
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Old 24th May 2018, 06:14 PM   #1
rongon is offline rongon  United States
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+150V DC Vacuum Tube Regulated Power Supply?
Default +150V DC Vacuum Tube Regulated Power Supply?

I'm laying out a stereo headphone 'spud' amp in a salvaged mono amp chassis that needs a 150VDC 120mA B+ supply. My design goals are:

1) Use the salvaged chassis' mounting holes with minimal modifications. I suck at metal work.

2) Use parts I have on hand. That's not much of a limitation, as I have too many parts in storage. I need to use 'em.

3) Use a vacuum tube based regulated or stabilized power supply. I just want some pretty tubes sticking up out of this chassis.

So...

My power transformer choices are an Allied N51X (115V:115V), an Allied N68X (115V:230V if wired backwards), or a salvaged 600VCT at about 150mA power transformer that also has 5V and 6.3V windings.

I have some vintage Radio Shack 12VCT 1.2A transformers if I need to make a separate heater supply.

I also have a couple of one-off chokes, 6H with DCR of 98 ohms and 10H with DCR of 141 ohms. I figure both of those are good for >110mA.

I was thinking of using an 0D3 VR tube, and I have a promising looking circuit simulated. However it will require a lot of high wattage power resistors to drop the volts necessary to feed the 0D3 its 20mA. I'm afraid the heat will be horrible. But having two pretty 0D3s sitting on the amp is an attractive idea.

Being that this chassis has three holes for octal sockets, I was thinking it could fit a tube series regulated B+ supply. I have some 6AS7G and I have way too many 12AX7s. I even have a few 6SL7 and 6AC7. The problem I'm running into is that I can't get anything I've designed to provide as low as +150V at the 110mA load I'll need, even though a 6AS7G with paralleled triodes should do this easily.

While I'm okay with taking a basic circuit and altering it to suit, it seems I am not competent to design a tube series regulator from scratch. I've tried; I've failed. So I'm asking for help.

Can anyone recommend a simple series regulator topology (using tubes, not a Maida) that can deliver +150V at 110mA?

Many thanks.
--

PS - I have a simple series regulator schematic using 6AS7G, 12AX7, and 0D3 that I was trying to modify to deliver 150V. I can post it this evening.
--

Last edited by rongon; 24th May 2018 at 06:16 PM.
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Old 24th May 2018, 06:48 PM   #2
Miles Prower is offline Miles Prower  United States
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Quote:
Originally Posted by rongon View Post
So...

My power transformer choices are an Allied N51X (115V:115V), an Allied N68X (115V:230V if wired backwards), or a salvaged 600VCT at about 150mA power transformer that also has 5V and 6.3V windings.
Are you going hollow state or solid state for the power supply? The Allied PTXs will work with a full wave doubler if solid state. For hollow state, the 600VCT is your only viable option.

Quote:
I also have a couple of one-off chokes, 6H with DCR of 98 ohms and 10H with DCR of 141 ohms. I figure both of those are good for >110mA.
Go with the lower DCR here.

Quote:
Being that this chassis has three holes for octal sockets, I was thinking it could fit a tube series regulated B+ supply. I have some 6AS7G and I have way too many 12AX7s. I even have a few 6SL7 and 6AC7. The problem I'm running into is that I can't get anything I've designed to provide as low as +150V at the 110mA load I'll need, even though a 6AS7G with paralleled triodes should do this easily.
Lots of possibilities for the series pass device. 6AS7s are good, and you can also try pseudotriodes as well. 6L6-oids work quite well for this.

Quote:
Can anyone recommend a simple series regulator topology (using tubes, not a Maida) that can deliver +150V at 110mA?

Many thanks.
--

PS - I have a simple series regulator schematic using 6AS7G, 12AX7, and 0D3 that I was trying to modify to deliver 150V. I can post it this evening.
--
Yep. This was designed as a screen voltage active regulator. The 6AQ5 here is operating as a pseudotriode series pass element. It runs well below its PD rating for this application. Will need to be something else for this project. The reference voltage is from a 0A3 regulator (Octal type -- 75V) that doesn't need to draw much more than 7.0mA, as there is no current demand in parallel here. No need for hot, high wattage ballast resistors.

The error amp is an unbalanced LTP that makes good use of the otherwise hard to use 6X8 with its shared cathode. The pentode half is a high gain device which is what you want here, as it allows for enough NFB to stabilize the voltage and correct for ripple hum.
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File Type: jpg AltScreenReg.jpg (29.7 KB, 641 views)
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Old 24th May 2018, 07:27 PM   #3
rongon is offline rongon  United States
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+150V DC Vacuum Tube Regulated Power Supply?
I'd totally use that 6X8 based regulator. I think I can make a noval tube socket fit in one of the holes for octal sockets. I'd have to buy a 6X8 or two, as I don't have any.

Would it be possible to use a 6AC7 and a 6J5 (or similar) so I can use up metal octals I already have lying around?

Quote:
Are you going hollow state or solid state for the power supply? The Allied PTXs will work with a full wave doubler if solid state. For hollow state, the 600VCT is your only viable option.
I have nothing against UF4007 diodes and their like. The only reason I'd use a tube rectifier would be to get another glowing tube up on top of the chassis.
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Last edited by rongon; 24th May 2018 at 07:45 PM.
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Old 24th May 2018, 09:58 PM   #4
Sodacose is offline Sodacose  United States
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This is similar to what Miles posted, but uses 12AX7, 0C3, and 6AS7. You might get something out of the included write up as well:

La Luciernaga (Part 1, the PSU) – wauwatosa tube factory

This wouldn't do 150V output, but using a 0A3 voltage reference might get you close.
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Old 24th May 2018, 11:15 PM   #5
Hearinspace is offline Hearinspace  Canada
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+150V DC Vacuum Tube Regulated Power Supply?
What about Jan Didden's regulator here?
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Old 25th May 2018, 12:27 AM   #6
kward is offline kward  United States
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A Maida could certainly be made with a tube pre drop device instead of a mosfet or bipolar power transistor. I've done it. It is a bit more complicated (for one thing mine used a separate screen supply), and would still use the 317, which may be distasteful if you're looking for an all-tube solution.

The 115 VAC secondary doesn't have enough voltage to give you room to regulate. If your only other choice is the 230 VAC secondary, a standard series-pass regulator could be made to work, but at 150V output, the solution will spill out the excess voltage drop across the pass devices as heat, which could become excessive. At 150 mA output, you will probably need two pass tubes paralleled together.

A solution I can see working would be to locate a transformer that had say 160 VAC secondary. I'd use silicon rectification, a pair of 6550's or 6L6's or whatever for pass devices, and a 12AX7 error amplifier. If you had a 100V voltage reference tube, could even throw that into the mix. Seems like that should work without too much trouble.

Morgan Jones' book Valve Amplifiers has a chapter devoted to power supplies, and the topology I described above is discussed in that chapter.
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Old 25th May 2018, 01:50 AM   #7
rongon is offline rongon  United States
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+150V DC Vacuum Tube Regulated Power Supply?
Quote:
Originally Posted by Sodacose View Post
This is similar to what Miles posted, but uses 12AX7, 0C3, and 6AS7. You might get something out of the included write up as well:

La Luciernaga (Part 1, the PSU) wauwatosa tube factory

This wouldn't do 150V output, but using a 0A3 voltage reference might get you close.
Thanks, I'm trying it out in LTspice. I can supply a .asc if that would be helpful. This circuit is attractive because I have all the tubes necessary in storage.

I substituted an 0A3 model (courtesy Stephie Bench). Fed by a raw B+ of +400V, and with a 110mA load, I get +171V DC at the output with the 50k pot cranked all the way.

Question:
Now that the 75V reference is in there, the 12AX7 triode on the left is running with its grid positive to its cathode by about 0.5V. The 12AX7 triode on the right is running with about -0.8 grid bias (still likely to draw grid current). Is this a problem in this type of usage?

Wait... Thanks to kward for bringing up 6L6GC or 6550 as a pass tube. These are good for 30W plate dissipation, and will drop a lot more volts than paralleled 6AS7 pair. Usually you don't want to drop that many volts, but here I do. I'm working on it...

OK, here's what I got.

400VDC in, 160VDC out. Its efficiency is ghastly.

Uses a 6550A-triode for the pass tube, a 6SL7 for the error diff-amp, and a 0A3 for the voltage reference. Those were chosen because I have 'em.

LTspice says the ripple rejection is really good. It also says the 6SL7 sections are both biased with a negative voltage on their grids, which I figure is a good thing. The 6550A is dissipating 25 watts. The 0A3 is drawing almost 6mA.

How's it look?
--
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File Type: png 400V-in_160V-out_TubeVoltageRegulator.png (24.6 KB, 586 views)
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Old 25th May 2018, 01:20 PM   #8
Sodacose is offline Sodacose  United States
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The 6550 looks like a much better pass tube choice here due to the very low VDC target output.

With the 6AS7, you must set the grid well below the cathode in order to drop enough voltage. The 6AS7 cathode is your output, so you're being asked to set the grid a good deal below the target output of 150V. The 0A3 sets the 12AX7 cathode to about 75V, so you have less than 150v-75v=75v to work with across the 12AX7. It just does not have the perveance to set the anode low enough. In fact, with a 400V input it doesn't look to me like you have any available voltage across the 12AX7 (just judging from plate curves here).

By contrast, the 6550 looks much better. To drop ~250V across it, the grid only needs to be 10-20V lower than the cathode. You still do not have much voltage room across a 6SL7 or 12AX7, but it's a much better situation than the 6AS7.

* A lower voltage reference would help, but I definitely understand the desire to add some glass for the fun/aesthetics of it.

* Although the gain of the error amp would be lower, you could also try simming other higher perveance dual triodes like 6DJ8, 5687, etc. That may give you more room to vary the output.

* A lower B+ than 400V will require you to drop less voltage across the pass device, both lowering dissipation and decreasing the negative bias required.

Cool parts bin project though!
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Old 25th May 2018, 03:01 PM   #9
Alan4411 is offline Alan4411  Wales
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I would go for a more simple solution.

Buy a cheap 24 or 25 volt 1 amp transformer and 'stack' the 115 volt transformer on top so you get 140 v ac or so. Then with silicon rectification you will have close to 200v HT which should be enough headroom for losses and proper regulation without the extra heat of another 150v at 110ma or so.

A VR150 /0D3 needs about 185v to work properly and 8 to 10 ma through it so it will need to go before the pass element. A 75 volt or 90 volt regulator might be better suited?
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Old 25th May 2018, 03:13 PM   #10
Sodacose is offline Sodacose  United States
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Here's a simple hybrid that I did recently with 0D3 and a MOSFET:

0DCAE9C6-0EE2-4AA7-BCE4-A3FC8AE85CFE.png

You'd still have sockets left over. Maybe use a tube rectifier or a couple damper diodes to use them up. Or build the above for each channel?

edit: IRF820 was what I used, I think. Ignore the transistor symbol.
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