Author Topic: 0-350V 0.2A Bench Power Supply  (Read 9267 times)

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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #100 on: November 23, 2017, 07:18:48 AM »
The most common TV set tube here is PL509 ($3 NOS) but new and imported EL34 etc is WERY costly here
I can use also NOS Generator tubes with 12 and 27 heaters

@oldway
too many inesencial words (who don`t know what he can use?) too small practic schematics&figures  :-//
« Last Edit: November 23, 2017, 07:21:11 AM by 001 »
 

Online Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #101 on: November 23, 2017, 07:30:23 AM »
The only problems with using PL509 (or PL519) is its 40V heater and the need for >50V negative grid bias to cut it off.   As I discussed earlier, one should handle the required power with a tapped transformer and a tap changer circuit, or three in parallel (with cathode current sharing resistors) if you don't want to go the tapped transformer route.   You'll probably need three transformers as tapped transformers with isolated 40V (20-0-20) heater windings are rare like hens teeth.   You've got to balance the cost of the (possibly imported) parallel tubes for the simpler circuit against the cost of the extra transformers and relays for the tap changer.

« Last Edit: November 23, 2017, 08:18:57 AM by Ian.M »
 

Offline richard.cs

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Re: 0-350V 0.2A Bench Power Supply
« Reply #102 on: November 23, 2017, 07:48:20 AM »
There are vast stocks of new and unused P-series TV line output valves making them very cheap (at least in Europe), and the 300 mA heater can be run easily enough from a suitable transformer, in some ways more conveniently than the several amps needed for the E series version of the same device. Yes they have a 7 kV peak anode rating but they were designed to be used in what is essentially a flyback converter running straight off rectified 240 Volt mains (so about 350 V d.c.) with a peak current of up to 1.5 Amps, they are relatively high-current, low-voltage devices compared to what their peak anode voltage rating might otherwise suggest. They are also ridiculously tough so long as you don't exceed the heater-cathode voltage spec.

I am sure 3x EL34 as Oldway suggests will work fine, but I see no reason 2x PL509s or similar wouldn't work as well at a significantly reduced cost.

 
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #103 on: November 23, 2017, 08:06:00 AM »
There are vast stocks of new and unused P-series TV line output valves making them very cheap (at least in Europe), and the 300 mA heater can be run easily enough from a suitable transformer, in some ways more conveniently than the several amps needed for the E series version of the same device. Yes they have a 7 kV peak anode rating but they were designed to be used in what is essentially a flyback converter running straight off rectified 240 Volt mains (so about 350 V d.c.) with a peak current of up to 1.5 Amps, they are relatively high-current, low-voltage devices compared to what their peak anode voltage rating might otherwise suggest. They are also ridiculously tough so long as you don't exceed the heater-cathode voltage spec.

I am sure 3x EL34 as Oldway suggests will work fine, but I see no reason 2x PL509s or similar wouldn't work as well at a significantly reduced cost.
Yes, You understand me
 

Offline David Hess

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Re: 0-350V 0.2A Bench Power Supply
« Reply #104 on: November 23, 2017, 08:07:11 AM »
Current Siliconix datasheet probably doesn't specify DC SOA because of laziness or CYA.

I did an informal search of DC safe operating area specifications a couple days ago and I would be very cagey about them.  Except in power MOSFETs intended and designed for linear operation, they strike me as grossly optimistic based on my understanding of how vertical power MOSFETs optimized for switching service behave.

My tentative conclusion was that with the right design, an indestructible linear high voltage power supply for power vacuum tube applications using power MOSFETs is very feasible.  I have been considering something like this but for much higher voltages and much lower currents where the design considerations are too different to apply.
 

Offline oldway

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Re: 0-350V 0.2A Bench Power Supply
« Reply #105 on: November 23, 2017, 08:11:21 AM »
I think you are really so old to learn .... :-DD

NB: see your topic
http://www.eevblog.com/forum/projects/so-old-to-learn-serious-problem/

Before you do a project, you have to understand what you're doing, that's what I'm trying to do.

This topic does not belong to you, there are certainly other people who are interested in this subject .... I answer you as well as to all the other interested persons.

You write that you find cheap PL509 tubes where you are, but you have not even indicated in which country you live ....

On ebay.de, PL509 are not cheap at all.....(cheap price 25 euros - only 37 hits)
EL34 tubes, you find hundreds on ebay.de (cheap price 15 euros - 493 hits), and not at exorbitant prices.

But I never forced you to use EL34, you do what you want, I do not care.

If you follow the indications and my explanations, you will be able to modify the diagram of IP17 Heathkit to make it correspond to your needs ....

You do not have patience and you make the topic go in all directions, you will not get anything like this.

I am a logical way in explaining you little by little how should be a HV power supply using what is currently available, whether one lives in the USA, Europe, Asia or Russia.

I will stop here with my participation in this topic....By By...
 

Online Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #106 on: November 23, 2017, 08:21:00 AM »
@David Hess,
Did you look at SiC HV power JFETs? 
 

Offline T3sl4co1l

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Re: 0-350V 0.2A Bench Power Supply
« Reply #107 on: November 23, 2017, 08:23:00 AM »
I did an informal search of DC safe operating area specifications a couple days ago and I would be very cagey about them.  Except in power MOSFETs intended and designed for linear operation, they strike me as grossly optimistic based on my understanding of how vertical power MOSFETs optimized for switching service behave.

Old designs -- I don't think any HEXFETs had 2nd breakdown.  They weren't much more space-efficient than lateral MOS (nor any better on Qg), so weren't capable of operating at high enough current density to reach 2nd breakdown.  ST example:
https://www.seventransistorlabs.com/Images/ST_IRFP460.pdf
IRF740 is a smaller transistor so it would be even less likely to encounter problems.

Intermediate generation VDMOS exhibits 2nd breakdown.  Some of the most interesting SOA curves I've seen were from IXYS (hmm, I wonder if I can find an example).

Bizarrely, current gen SuperJunction MOS is apparently DC stable again, despite having higher power density than ever!  Maybe it's been designed for lower tempco and better current sharing?  There are some quirks in transconductance, too; who knows what else is different?

I don't have a problem with using classic MOS like these for one-offs, even for small production.  I would not do it for full production, not without a receiving inspection/qualification process in place ($$), and anyway, full DC SOA parts are available among new parts.

Tim
Seven Transistor Labs, LLC
Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!
 
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Online Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #108 on: November 23, 2017, 10:15:06 AM »
Why not combine the design I posted, using LM317 & the BJT cascode, with the one posted by David, using the valve?

how to do it?
EDIT:
Bad circuit attached, see the link below for the corrected one:
http://www.eevblog.com/forum/projects/looking-for-yours-opinions!-hv-stabilized-power-supply/msg1359532/#msg1359532
« Last Edit: November 27, 2017, 10:20:37 AM by Hero999 »
 
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Offline David Hess

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Re: 0-350V 0.2A Bench Power Supply
« Reply #109 on: November 23, 2017, 10:34:13 AM »
@David Hess,
Did you look at SiC HV power JFETs?

I did not because they cost significantly more for a given power and this is exasperated if multiple packages are used to lower case to heat sink thermal resistance.
 

Online Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #110 on: November 23, 2017, 10:41:17 AM »
@Hero999,
That looks pretty dodgy - TR2 clamps the grid no more than 0.7V negative of the cathode so the valve cant cut off and the LM317 lets out its magic smoke.  Also even if you rework the current limiter so it doesn't FUBAR the cascode,  TR2 sees the whole output voltage and high voltage PNPs suitable for linear region operation are not so common.
 
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Offline chris_leyson

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Re: 0-350V 0.2A Bench Power Supply
« Reply #111 on: November 23, 2017, 10:58:12 AM »
Chinese EL34 are £9.44 from RS components.
Quote
how to do it?
And exactly how is the EL34 current limit going to work, Tr3 isn't going to do anything ?? Been spicing the T-reg regulator https://linearaudio.nl/t-reg-tube-voltage-regulator well a simplified version of it. Got my current limit set to 100mA and at 350V HT tube dissipation is 31.5W Anode and 3.5W screen grid. You might need to consider running at least two tubes in parallel and foldback current limit. I'm aiming for maybe 350V HT, 0-250V output @ 100mA foldback current limit with a single tube. It depends on the transformer I have available, I think it was for a Maplin valve amp a long time ago.
« Last Edit: November 23, 2017, 11:01:15 AM by chris_leyson »
 
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #112 on: November 23, 2017, 05:10:35 PM »
Chinese EL34 are £9.44 from RS components.
Quote
how to do it?
And exactly how is the EL34 current limit going to work, Tr3 isn't going to do anything ?? Been spicing the T-reg regulator https://linearaudio.nl/t-reg-tube-voltage-regulator well a simplified version of it. Got my current limit set to 100mA and at 350V HT tube dissipation is 31.5W Anode and 3.5W screen grid. You might need to consider running at least two tubes in parallel and foldback current limit. I'm aiming for maybe 350V HT, 0-250V output @ 100mA foldback current limit with a single tube. It depends on the transformer I have available, I think it was for a Maplin valve amp a long time ago.


Wow!
Interesting project! What is main benefit of this circuit? It can't go below pass tube bias voltage so regulation range is too small, isnt it? Do You recomend this circuit as a preregulator?
« Last Edit: November 23, 2017, 05:57:02 PM by 001 »
 

Online Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #113 on: November 23, 2017, 08:08:49 PM »
@Hero999,
That looks pretty dodgy - TR2 clamps the grid no more than 0.7V negative of the cathode so the valve cant cut off and the LM317 lets out its magic smoke.  Also even if you rework the current limiter so it doesn't FUBAR the cascode,  TR2 sees the whole output voltage and high voltage PNPs suitable for linear region operation are not so common.
I'll be honest. That circuit was a bit of a guess. I don't know much about valves. They're long before my time!

So the grid voltage needs to be negative, in order for to cut-off, therefore breaking the current limiter? That's a pain. Something to drop more voltage, such as a resistor or even a zener, would need to go in between the cathode and TR3's base to drop enough volts, to cut it off enough to limit the current.

EDIT:
Bad circuit attached, see the link below for the corrected one:
http://www.eevblog.com/forum/projects/looking-for-yours-opinions!-hv-stabilized-power-supply/msg1359532/#msg1359532

I think a MOSFET is probably an easier solution, although it's not as abuse tolerant.
« Last Edit: November 27, 2017, 10:20:58 AM by Hero999 »
 

Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #114 on: November 23, 2017, 10:27:15 PM »
The Tube at Yours circuit is  strange biased  :o
 

Online Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #115 on: November 24, 2017, 01:27:21 AM »
@Hero999,
That looks pretty dodgy - TR2 clamps the grid no more than 0.7V negative of the cathode so the valve cant cut off and the LM317 lets out its magic smoke.  Also even if you rework the current limiter so it doesn't FUBAR the cascode,  TR2 sees the whole output voltage and high voltage PNPs suitable for linear region operation are not so common.
I'll be honest. That circuit was a bit of a guess. I don't know much about valves. They're long before my time!

So the grid voltage needs to be negative, in order for to cut-off, therefore breaking the current limiter? That's a pain. Something to drop more voltage, such as a resistor or even a zener, would need to go in between the cathode and TR3's base to drop enough volts, to cut it off enough to limit the current.



I think a MOSFET is probably an easier solution, although it's not as abuse tolerant.

To see what you are up against here's a LTspice test jig for a PL509.   N.B. it does *NOT* fully model the valve - although  Norman Koren's Tube SPICE models are well respected, they are only approximate.

Things to note:
If you don't use fixed bias for the screen grid G1(relative to the cathode), you will need *MUCH* more negative drive to the control grid (G1) to reach cutoff.  Try the effect of tying G2 to A via a 10K resistor and you will see the issue.     

If you use the valve in cascode with a LM317 with a high screen grid voltage, you are in for a world of grief as the cathode potential at cutoff will significantly exceed the LM317's maximum input-output voltage differential even if you use a LM317HV.  Practical experiments with a reduced screen grid supply floating on the output voltage will be needed to determine if this configuration is possible.   A negative grid bias supply will also be needed - possibly derive both from capacitively coupled bridge rectifiers driven from the 40V heater transformer.

Note instructions in the SIM to enable download of model file on first run.


« Last Edit: November 24, 2017, 01:30:11 AM by Ian.M »
 
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Online Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #116 on: November 24, 2017, 04:07:56 AM »
Sounds like a nightmare. I'll look at the zip in a bit. Meanwhile, here's the MOSFET version, which should be fine, as long as the safe operating area, isn't exceeded.
 

Online Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #117 on: November 24, 2017, 09:05:30 PM »
I've just simulated the original valve based LM317 current limiter circuit, using the models posted by Ian and it works perfectly. I connected both grids together, as the circuit was designed for a triode, not tetrode. With the current limit of just over 200mA, the valve would dissipate 80W, so it needs to be fairly chunky, possibly requiring a fan.

EDIT:
Bad circuit attached, see the link below for the corrected one:
http://www.eevblog.com/forum/projects/looking-for-yours-opinions!-hv-stabilized-power-supply/msg1359532/#msg1359532
« Last Edit: November 27, 2017, 10:21:23 AM by Hero999 »
 

Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #118 on: November 24, 2017, 09:14:12 PM »
Why You connect grids together? :palm: if You prefer triode mode, connect second grid to anode
For normal operation tube must be properly biased so voltage across 317 must be about 40-60v i.e. 12w on this IC in standby  :-//
« Last Edit: November 24, 2017, 09:18:47 PM by 001 »
 

Online Hero999

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Re: 0-350V 0.2A Bench Power Supply
« Reply #119 on: November 24, 2017, 09:49:28 PM »
Why You connect grids together? :palm:
Why not? What's wrong with tying the grids together?

Quote
if You prefer triode mode, connect second grid to anode
That doesn't work, according to the simulation. With one grid connected to the anode, the valve won't cut-off, until the other grid is biased negative, which is possibly what Ian was concerned about.

It works perfectly with both grids connected together. I don't know if this works with all tetrodes or if it's specific to the simulation model. I suppose the data sheet is the best place to start.

Quote
For normal operation tube must be properly biased so voltage across 317 must be about 40-60v i.e. 12w on this IC in standby  :-//
No, for proper operation, the voltage across the LM317 should be between 3V and 40V. Anything greater than 40V could damage it. Anything under 3V and it might not regulate properly. In standby (no load) the only current through the LM317 will be 1.25/R1 = 1.25/240 = 5.2mA, so the power dissipation will be low.

EDIT:
I had R3 set too high, which resulted in poor current limiting. Change it to 10k and it's much better. A current source would be best, as mentioned by T3sl4co1l.
« Last Edit: November 24, 2017, 10:08:09 PM by Hero999 »
 
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #120 on: November 24, 2017, 10:15:54 PM »
You cant connect grids of power tube together due different electric durability and geometric issues. The screen grid in fact not a grid but spring. Real tube will not work this way. It is si!ulator mistake :palm:

Connection 2d grid to anode directly or with limiting resistor is a common practice for decades. Why simulator dont know it?

At 1.5v bias voltage tube blow itself
 
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Online Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #121 on: November 24, 2017, 10:25:02 PM »
I'd take the biassing for Hero999's proposed grid configuration of strapping G1 to G2 with a *LARGE* pinch of salt as its *far* *far* away from the operating region Noman Koren's tube models are written for.  They are the product of careful curve fitting to published data sheets, and aren't based on a physics model so if you are designing outside of the datasheet limits (and zero accelerating potential between G1 and G2 is about as far outside as you can get), the model's less trustworthy than a timeshare salesman!  :popcorn:

As the PL509 (or EL509) is a beam tube, the G1 and G2 wires are supposed to be precisely aligned so strapping G1 to G2 should work, and I cant see any way it could cause damage, unless you are dumb enough to exceed 5mA pass significant G1 current under positive biass, however you'd need a whole set of experimental characteristic curves to model the resulting triode.  I strongly suspect that it will pass *FAR* less current at zero grid bias than the Koren tetrode model indicates. 

http://www.oestex.com/tubes/triode.htm is worth a read.

If anyone has suitable equipment for power tube curve tracing, and can spare the time, it would be interesting to see how the curve families for different methods of strapping a beam tetrode as a triode compare (including the proposed G1-G2 strapping) , with the datasheet screen grid biassing for tetrode operation as a control.
« Last Edit: November 24, 2017, 10:54:47 PM by Ian.M »
 
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Offline richard.cs

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Re: 0-350V 0.2A Bench Power Supply
« Reply #122 on: November 24, 2017, 10:33:12 PM »
Why not? What's wrong with tying the grids together?

...

It works perfectly with both grids connected together. I don't know if this works with all tetrodes or if it's specific to the simulation model. I suppose the data sheet is the best place to start.

Needing to bias the grid negative to cutoff is expected behaviour. Connecting the grids together is an unusual thing to do (as in, almost never done) and I suspect that the simulation model is simply not representative in that configuration. I have no idea what the valve would do in the real world. What range of grid-cathode voltage does your simulation regulate with?

Usual valve operation is that it is "on" with the grid at 0 volts relative to the cathode, and you progressively reduce the current as you bring the grid more negative with respect to the cathode. This behaviour  is like an N-channel JFET or depletion-mode MOESFET. If you make the grid positive with respect to the cathode then you can on some types turn it slightly harder on but too positive and it will start to collect electrons, and current will flow into the grid. This is generally bad because the grid is not able to dissipate much power. Grid 1 current / power limits tend to be very low (but I can't actually find it in the datasheet). Sorry if some of this is obvious but you said you don't have much experience with valves. Hopefully it's helpful to someone anyway.

PL509 datasheet is here: http://www.r-type.org/pdfs/pl509.pdf

Page 7 shows current as a function of grid 1 voltage with the valve "triode-strapped", i.e. grid 2 connected to the anode and a fixed anode voltage of 160 V. Note that the range of Vg1 is 0 to -50 V.

Pages 8 and 9 show pentode operation with grid 2 held at a fixed +160 V, 175 V and 190 V relative to the cathode but the anode voltage varied with constant Vg1. The Vg1 range is 0 to -40 V.

edit: Ian.M has posted whilst I was typing. He makes a good point about the alignment of G1 and G2, but we're in agreement that the simulation model is probably junk for this configuration.
 
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Offline 001

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Re: 0-350V 0.2A Bench Power Supply
« Reply #123 on: November 24, 2017, 11:58:16 PM »
Well
As oldtimer I see what Hero999 circuit is not proper. Real tubes is tubes.  :-//

So the main dilemma for me is to use pass mosfet or pass tube
Ok. Few days ago I wanted eliminate all tubes from my gear
But now I uncertain
I desided to use disctrete transistor regulator circuit anyway
But what about pass element?


This circuit looks good http://www.audioxpress.com/article/t-reg-a-high-voltage-regulator-for-tube-amps
but can I strip reference and sense resistors to additional negative source to add regulation from zero insted actual minimum limited by bias voltage?
« Last Edit: November 25, 2017, 12:00:44 AM by 001 »
 

Online Ian.M

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Re: 0-350V 0.2A Bench Power Supply
« Reply #124 on: November 25, 2017, 01:50:23 AM »
I suggest you take a PL509 (or PL519 or EL509 etc.) and set it up on your bench and characterise it. You need to know how much voltage swing you need on the control grid before you start designing circuits.

 As you've sold off your HT variable supply, for the DC supply, feed an isolating transformer from a Variac, into a bridge rectifier followed by two banks of reservoir caps and a large choke (one built like a transformer) between them with a power bleeder resistor calculated to have a time constant with the total capacitance of no more than 2s so it will totally discharge in no more than 10 seconds.    For the PL5xx filaments, you need 40V at 300mA, and hopefully you have a bench supply that can do that.  Otherwise use a transformer and a rheostat, and adjust to 300mA RMS when hot. 

You need to know the minimum anode voltage with zero grid bias to get your maximum output current, and should also test at 400mA to have some margin for loss of emission with ageing and to allow for differences in individual valves.   Put an ammeter that will read up to 1A and down to <1mA between the cathode and ground for this test.  Let the valve warm up at a moderate cathode current - say 100mA for ten minutes before making any measurements.

You also need to know the negative grid bias required for cutoff, at the maximum anode voltage you valve could ever see e.g with the PSU unloaded and the mains input 10% above nominal.  You'll need to decide what minimum current you'll accept at cutoff, and will need to make sure your final design can always sink that much current right down to your minimum output voltage.      If in doubt, measurements at 1mA and 0.1mA would probably be useful.   Measure the current as voltage drop across a 10K resistor.

You may need over -250V on G1 to get full cutoff, but you only need a few mA current so to get the negative grid bias supply, capacitively couple another bridge rectifier to the transformer secondary, feeding a decoupling capacitor then a resistor  (47K 5W wirewound would be good) and another decoupling cap, then use a physically large 500K pot rated at least 1/2W between the negative supply and ground.   Decouple the pot wiper with 0.1uF to ground, and feed G1 from it.  Start with maximum negative bias and crank up the Variac slowly till the anode voltage reaches the maximum design voltage (allowing for 10% mains over-voltage) while watching the voltage across the 10K cathode resistor.   If it rises over 10V, your negative bias supply cant supply enough voltage.    Then reduce the bias until you get 1V (100uA) and 10V (1mA), measuring the G1 voltage for each.  The voltage drop across the cathode resistor adds to the G1 negative bias, so if you have -100V for 10V across the cathode resistor, your actual Vg1k bias voltage is -110V.
 
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