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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 29th Nov 2020, 10:38 pm   #1
AdrianH
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Default What value caps for 3 to 5 mA off a voltage multiplier?

Is there a calculator anywhere that would give the value of capacitors to use when building a voltage multiplier, I am after between 3 to 5 mA to use with a typical small electrostatic CRT.

I would like to provide from a 250 -0- 250 normal HT for valves plus a HT of around 1000 plus Volts.
I am thinking of using this circuit construct: -
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I have in the past done a -ve voltage doubler to give 1000 ish volts between -670 and plus HT, but this time I need +HT and +1000 Volts with respect to Gnd. It was all trial and error last time and would like to work a bit cleverer this time around!

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Old 30th Nov 2020, 12:55 am   #2
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Default Re: What value caps for 3 to 5 mA off a voltage multiplier?

Calculators exist for common basic rectifier styles. Nobody bothers to do them for the more adventurous types.

It's time to dip your toe into the world of LTspice.

Don't be put off by some of the comments flying around from people who find it intimidating. It's a step into heavier stuff than most people are comfortable with, but it's actually quite friendly and helpful once you get going a little. You then have a very powerful tool indeed and you can go as far as you need on future things, recycling the effort it took to get going. There are plenty of users on here to give you a steer.

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Old 30th Nov 2020, 2:10 am   #3
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Default Re: What value caps for 3 to 5 mA off a voltage multiplier?

The multiplier circuit shown only gives about 400V but adding a couple of diodes and a capacitor to parallel up the phase inverted tripler stacks instead of just shorting them together works OK.

1µF caps get you around 1100V HT with about 75 V ripple at around 5mA.

You might just get away with 630V caps but 1000V would be better.

Sim circuit attached- I used an early (V3.0) version of Simetrix but LT Spice or any of the other free Spice packages would do just as well!
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Old 30th Nov 2020, 7:45 am   #4
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Default Re: What value caps for 3 to 5 mA off a voltage multiplier?

I thought the cap has nothing to do with it, it's the winding, could be wrong though.There's a free doodad over on Duncan amps, PSU 2, here you go - http://www.duncanamps.com/psud2/index.html it says it does doublers.

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Old 30th Nov 2020, 9:04 am   #5
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Default Re: What value caps for 3 to 5 mA off a voltage multiplier?

But that's more than a doubler and things go sour very quickly with higher order multipliers.

David
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Old 30th Nov 2020, 9:29 am   #6
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Default Re: What value caps for 3 to 5 mA off a voltage multiplier?

It's a full wave tripler, or I hope it is!

I do find LT spice intimidating, it is bad enough understanding the old tech of valves and trying to learn KiCad, which seems to have simulation as well although never looked at it as there is little sim stuff for valves (I think.) so spice will be a way off yet.

Adrian
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Old 30th Nov 2020, 10:34 am   #7
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Default Re: What value caps for 3 to 5 mA off a voltage multiplier?

It took me a while to try LT spice, but I am really glad I bit the bullet.
Valve models are available, I have modelled a complete multi stage valve preamp with tone controls. I modelled the pots as two resistors and got ltspice to run the simulation as a series of passes so I got a single plot showing the response with pots at mid point and at their ends.
What I am saying is that while Lt spice seems intimidating at first its possible to get quite advanced in a fairly short time, even this old dog managed to learn new tricks.

Peter
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Old 30th Nov 2020, 11:34 am   #8
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Default Re: What value caps for 3 to 5 mA off a voltage multiplier?

Thanks Chris I had not seen your reply for some reason, put it down to old age. Having to look at Farnell with the £40 min value order or get a handling charge. They have some metallised film 2uF caps:-
https://uk.farnell.com/epcos/b32774x...ial/dp/3254528
that I could get a batch off if suitable, not really sure if they are suitable for the ripple, I could go to 5uF
https://uk.farnell.com/vishay/mkp184...-pp/dp/2133987
and would appreciate comments about using these caps, they seem to say pulse use which I guess would be a high ripple content?

Adrian

p.s. I will try simulations when I get the nerve up.
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Old 30th Nov 2020, 12:45 pm   #9
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Default Re: What value caps for 3 to 5 mA off a voltage multiplier?

Parts ordered closing thread.

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Old 30th Nov 2020, 12:58 pm   #10
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Default Re: What value caps for 3 to 5 mA off a voltage multiplier?

Thread closed at OP's request

Cheers

Mike T
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