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Old 26th February 2004, 09:27 PM   #1
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Default Power Supply and VR tube help!

Ok... I need to have 150v for my pre-amp at 40mA. Planning to use 1 or 2 VR150 reg tubes.
should I use one at 20mA or parallel 2 for 40mA..

so if I understand... I need at least 180v for strike... say 200v.. so 200-150 = 50v / 80mA (40mA for VR tubes and 40mA for pre-amp) is 625 ohm dropping resistor. will this work?

how do I equalize the current in the 2 tubes? and should I parallel them with a RC network to shunt the inductance ( I have heard 200 ohm and 0.3uf per VR tube).

power supply will be (per channe) 83 tube rect, 20H low DCR choke, 40uf oil cap, 625 resistor, 2 VR tubes, the RC filter network then my pre-amp.

my pre-amp is a u-stage so more PSRR there.

am i heading the "right" way???
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Old 26th February 2004, 09:39 PM   #2
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If I understand correctly the VR150/0D3 is capable of 40mA. The strike voltage is usually around 185v give or take. If you have a 40mA load I don't see a problem with one tube. This is what I have used in the past without any problems.

Joe
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Old 26th February 2004, 09:44 PM   #3
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Default hmm...

but aren't you supposed to run the VR tubes at middle of operating point... i.e. the 20mA.


otherwise the tube could swing 30mA to 50mA instead of 10mA to 30mA... as an example.
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Old 26th February 2004, 11:11 PM   #4
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Hi,

Quote:
Ok... I need to have 150v for my pre-amp at 40mA. Planning to use 1 or 2 VR150 reg tubes.
Never // VR tubes, this doesn't work.

Do you need to regulate a tube drawing 40mA?
If so you'll need more than one VR tube in series set at about half their max operating current.
So a single OA2 (VR150) won't cut it, 2 VR75s in series might but check the datasheet for Imax.

Other alternatives are series regs or shuntregs, the latter not using VR tubes but a penthode or triode in shunt with the load.

Never use USED VR tubes unless you know exactly how they were used and intend to use them in that exact same way.

Unless of course you know how to condtion/recondition these tubes for a new service.

Cheers,
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Old 26th February 2004, 11:41 PM   #5
EC8010 is offline EC8010  United Kingdom
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Default Frank the tease.

Quote:
Originally posted by fdegrove
Unless of course you know how to condtion/recondition these tubes for a new service.
OK, I'm hooked. How do you condition/recondition them?
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Old 26th February 2004, 11:42 PM   #6
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Quote:
but aren't you supposed to run the VR tubes at middle of operating point... i.e. the 20mA.
Where did you got that from?, current trough the VR tube should be more then specified min, (usually 5mA) and less then max, (usually 30 or 40mA depending on type). Regulation is almost the same inside the specified current range.

I dont see any problem in your application. Your preamp draw 40mA continous current so if the voltage drop resistor is calculated for 60mA current the VR tube will draw 20mA and your preamp the rest.

An example:

Raw DC 200V, dropping resistor value = (200-150)/0.06 = 833 ohm, 820 ohm is OK.

Problem with using VR tubes comes when the load is changing like for instance in a class AB amp or when using them for screen voltage regulation, in class A circuits they are easy to use.

Regards Hans
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Old 26th February 2004, 11:52 PM   #7
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Quote:
Never use USED VR tubes unless you know exactly how they were used and intend to use them in that exact same way.

Unless of course you know how to condtion/recondition these tubes for a new service.
hi frank, i'm just about to use 0D3 and 0C3 and i'm not sure if these are used or not. you're scaring me can you tell us more please.
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Old 26th February 2004, 11:53 PM   #8
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Hi,

Quote:
OK, I'm hooked. How do you condition/recondition them?
Pretty much the same way one regenerates CRTs or big kW broadcast valves actually.

Just like capacitors have a memory effect so do valves; they can be trained for a certain service which can be quite beyond believe.

That's the "jesuit" answer...

Whether it's worth the time and energy put into it depends on what you want and how desperate you are but most of the time it works.

Cheers,
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Old 27th February 2004, 12:06 AM   #9
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Hi,

Quote:
hi frank, i'm just about to use 0D3 and 0C3 and i'm not sure if these are used or not. you're scaring me can you tell us more please.
No need to be scared, worst case scenario: the VR tube won't ignite when it should or worse it will oscillate no matter what you do even when it was fine in the previous application.

Cheers,
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Old 27th February 2004, 12:15 AM   #10
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Hi,

Quote:
I dont see any problem in your application. Your preamp draw 40mA continous current so if the voltage drop resistor is calculated for 60mA current the VR tube will draw 20mA and your preamp the rest.
That will always do the job provided the B+ delivers the required voltage, i.e. more than 150V (180 something or thereabouts)

However if a non-regulated B+ is used the overvoltage at cold start can be used to ignite the VR as well, this is however a little trickier to get right.

Quote:
but aren't you supposed to run the VR tubes at middle of operating point... i.e. the 20mA.
I'm guessing but I think what was meant here is that the VR tubes regulate best when set to half their max current capability.
As you put it yourself it's almost the same within the operating window, however for Classes outside Class A this aspect should be taken into consideration to keep the VR tube well within it operating region.

Cheers,
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