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Voltage Regulator Tubes
Voltage Regulator Tubes
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Old 27th March 2007, 06:51 AM   #1
dsavitsk is offline dsavitsk  United States
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Default Voltage Regulator Tubes

I have been given a bunch of voltage regulators -- 0D3, 0A3, 0B2, maybe a few others -- and have no real sense of how to use them or whether they are worth the effort. Anyone have any good links or suggested reading?
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Old 27th March 2007, 07:51 AM   #2
showdown is offline showdown  Norway
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This is the PSU for my line stage, with 0D3s:
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Old 27th March 2007, 11:08 AM   #3
AndreasS is offline AndreasS  Germany
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Helpful applications are in the data sheets:


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Old 27th March 2007, 08:07 PM   #4
Sheldon is offline Sheldon  United States
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They are actually pretty easy to use - only a few considerations:

1. Need a little extra voltage above the operating point to light them off (depends on the type).

2. Use a current limiting resistor or current regulator to stay under the maximum current limit (the short term limit is well above the steady state limit) when the downstream stuff is not yet drawing current.

3. The general load recommendation I've seen, is that the load current should be within about half of the steady state limit, and the steady state current through the tube should be around half of the continuous maximum.

4. With series regs., you'll often see a high value resistor (200k or so) from the supply to the series connection between tubes. This helps light off the lower tube.

5. Keep the capacitance across each tube less than 100nF (even less to be on the safe side).

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Old 27th March 2007, 08:19 PM   #5
Wavebourn is offline Wavebourn  United States
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Voltage Regulator Tubes
Default Re: Voltage Regulator Tubes

Originally posted by dsavitsk
I have been given a bunch of voltage regulators -- 0D3, 0A3, 0B2, maybe a few others -- and have no real sense of how to use them or whether they are worth the effort. Anyone have any good links or suggested reading?
However, main functionality is not so significant (Zeners are available) as their nice look, when they indicate presence of a plate voltage and it's variations:


Click the image to open in full size.
Nothing in the universe is perfect. The ideal things are the ones that are most optimal. Optimization criteria, what matters. When I hear "No Compromise Design", I want to take a sledgehammer and test how impact-proof it is.
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Old 27th March 2007, 10:01 PM   #6
Eusebius is offline Eusebius  United Kingdom
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http://www.tpub.com/content/neets/14.../14178_148.htm theory and calcs


I've archived the following from the Net - not sure who the original authors were.

There is no "maxiumum input" as such. The tubes act like a zener, so whatever voltage you put into it, 150V will be dropped across the tube. That's why you need a dropper resistor, the rest of the voltage is dropped across is and this sets the current thorugh the tube. Without the resistor, even if you put 170V into it, without a resistor, it would blow up. You need to calculate the dropper resistor to drop the remaining voltage and give you a sensible current (5mA - 30mA for 0A2) through the tube. You also need to leave room for the current swing of the circuit you're powering. In theory, you could run them of kilovolts if you like, you would just need a *very* big resistor.Cheers, Pete P.S. The resistor can be replaced by a CCS.

Voltage Regulator (or VR) valves are ingenious devices designed to maintain a constant voltage across their terminals over a range of currents.Such valves have a cold cathode and contain gases at low pressure rather than the conventional high vacuum normally used in amplifying valves. The internal gasses are deliberately chosen to ionise (conduct) at a particular predefined voltage.
They work very well just like a zener.And they glow. Unlike mercury tubes they don't need to wait for the filament to light up, since they ain't got no filament. No mercury, either, just harmless argon. There's *neon* ones, too, which glow a cute pinkish or orange, like 0A3. Just don't force them to draw too much current (they only need a few ma to light up). Colour is entirely due to gas composition. Voltage drop is due to a combination of gas composition and cathode material. The level of intensity of glow is proportional to discharge current.
OD3 and 0A2(150V) are pink / lilac.
0C3 and 0B2 (105V) are also pink as far as I can tell (my 0C3s are almost entirely gettered)
I understand that 0B3 (90V) is a purple/indigo. Prettiest of the bunch IMO. thought ususally gettered into near invisibility.
0A3 and 0C2 (75V) are orange.
The confusion over colours possibly comes from the change in coding between the 0*3 (octal)and 0*2 (7-pin) series, where one went A to D with later letter higher voltage and the other went the other way. In addition there is the confusion added by the 85 Volt reference (low current high stability) 0E3 (octal) and 0G3 (7 pin).
Type OpV StrikeV min/max mA regV Pinout
0C2 75 115 (105) 5-30 4.5 7pin
0A3 75 105 5-40 6.5 Octal
0B3 90 110 Octal
0B2 105 133 (115) 5-30 4 7pin
0C3 105 133 (115) 5-40 4 Octal
0C3A " 127 " "
0A2 150 185 5-30 6 7pin
0D3 150 185 (160) 5-40 5.5
0D3A " 180 " "
0A4 Octal
0A5 7pin
Voltage Regulator 0A2 7 pin small
Maximum Supply Voltage ........................ 185 V
Regulated Voltage ............................. 150 V
Maximum Current ............................... 30 mA
Minimum Current ............................... 5 mA
Regulation (Min to Max Current) ............... 2 V
Voltage Regulator 0D3 octal
Maximum Supply Voltage ........................ 185 V
Regulated Voltage ............................. 150 V
Maximum Current ............................... 40 mA
Minimum Current ............................... 5 mA
Regulation (Min to Max Current) ............... 4 V

The 0A2, OB2, 0C2 tubes are all 7 pin minature base. The cathode of each is connected to pins 2,4,7. The plate is connected to 1 and 5. Pins 3 and 6 are listed as "internally connected" so don't connect anything to those pins.
The 0A3(a), 0C3(a) and 0D3(a) are all 8 pin octal bases, with a jumper between 3 and 7, often used to protect downstream electronics in case the regulator wasn't inserted, pin 5 as the plate, and pin 2 as cathode. The diagram snows pins 1 and 8 not connected.
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Old 26th August 2017, 02:51 PM   #7
Blitz is offline Blitz  Germany
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I have read through all of this incl. the links and manuals.

I do have some questions still:

- Lynn used an OD3 here: http://www.nutshellhifi.com/IT-Triode-Amp.gif ...but why did he use the 330Ohm Resistor in this position ? He uses a CCS to feed the stage. The CCS allows only 60mA. So, even in warm up he would not need any resistor at all. It is notthe series resistor, it is between Anode of the OD3 and reg HV+ ?

- where is the OD3 allowed to be positioned in a PSU ? Always as last element of a passive filterchain or could as well between a pair of LC- legs ? Example: My current line amp has One 5u4g feeding into one LC, so choke input. For channelseperation, two LC in parallel are following, so we have LC-(LC*2).

Can i just have one OD3 after the first LC feeding into the two chokes following, so LC-OD3-(LC*2)? Or must it be two OD3, one per channel after the last LC of each channel feeding directly into the tubes, so LC-(LC-OD3)*2 ?

- in the discussion linked above, people talk about a start voltage of the OD3 of 180V. This confuses me. Looking at the data sheet I find as well 160V as starting voltage... https://frank.pocnet.net/sheets/137/0/0B3.pdf ...Currently I have only 172V on my PSU...
Can I interpret it like: New OD3 will start with 160V, but need more and more voltage once they age (up to 185V) ? Or will even a new one not start below 180/185V ? AND : For how long do we need the starting voltage ? Fractions of seconds ? I guess any transformer will deliver much more voltage as long as there is no real load as the main tubes need to heat up first...?

Thx for your help.

Last edited by Blitz; 26th August 2017 at 02:55 PM.
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Old 27th August 2017, 02:00 PM   #8
DF96 is offline DF96  England
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I am going to guess that he added the 330R resistor to swamp the negative slope resistance of the regulator valve. This avoids forming a relaxation oscillator with the decoupling capacitor. In this respect voltage regulator valves are different from zener diodes: zeners have a small positive slope resistance but VR valves have a negative resistance so cannot have too much capacitance placed across them.

- where is the OD3 allowed to be positioned in a PSU ?
Where it does whatever you want it to do. If you know what you want to do then put it there. If you don't know what you want it to do then why do you think you need one?

Almost all valve audio circuits do not need voltage regulation. When present it is often there to impress journalists and customers by giving a superficial impression of precision. Personally I think it is quite silly to feed a valve stage via a series CCS and a shunt voltage regulator.

Starting voltage is a matter of age, sample variation, light level, local radiation sources, cosmic rays etc. Some military versions have a little radioactive gas inside to give a quick ignition under all conditions.
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Old 27th August 2017, 02:31 PM   #9
Blitz is offline Blitz  Germany
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Thx...so I can position an LC-Leg behind thenm ? I understand that any capacitance bigger than 0.1uF will destroy the Reg tube...the question is, if the Choke is isolating the following C or if this is already to much for such a tube...never used them before...
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Old 27th August 2017, 08:16 PM   #10
audiowize is offline audiowize  United States
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Originally Posted by DF96 View Post
Personally I think it is quite silly to feed a valve stage via a series CCS and a shunt voltage regulator.
Objectively you can reject quite a bit of power supply noise by doing this. Subjectively I believe it sounds better.
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