I don't know if this is a problem or not so I thought who better to ask?
I built a pre-amp with two VR-105 tubes in series to regulate my B+ at 210V. My voltage is stable at that point during testing and the unit sounds wonderful to my ears. However, one of the tubes (the one on the right) has a small flicker over about 1/8th of the circumference at times. By that I mean a darkening and not a flare up. Is this a problem or a sign I should worry about?
I've tried swapping tubes as well as replacing them and the issue remains.
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I built a pre-amp with two VR-105 tubes in series to regulate my B+ at 210V. My voltage is stable at that point during testing and the unit sounds wonderful to my ears. However, one of the tubes (the one on the right) has a small flicker over about 1/8th of the circumference at times. By that I mean a darkening and not a flare up. Is this a problem or a sign I should worry about?
I've tried swapping tubes as well as replacing them and the issue remains.
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The issue remains how? You get the flicker no matter which tube you put in that socket?
To better help you, also post the schematic.
To better help you, also post the schematic.
Well, last night there was a little flicker but currently no. Tube is slightly different in brightness but more noticeable in the picture than in real life. Will post schematic in a bit.
I'd like to check with the guy who designed the rest of the circuit before posting the whole thing. I'm using two #76 and two 2C22s.
you may have too little current through the regulators;
the VR105 requires between 5 and 40 mA current to work;
my experience is that the lower end is critical, the smaller the current the more likely they flicker; I would go for 20mA to be on the safe side;
as we don't know what the voltage is from the rectifier nor what the load current on the 210v line, I would measure the current which flows through the regulator tubes directly; current can then be adjusted by varying the 8000 ohm resistors
the VR105 requires between 5 and 40 mA current to work;
my experience is that the lower end is critical, the smaller the current the more likely they flicker; I would go for 20mA to be on the safe side;
as we don't know what the voltage is from the rectifier nor what the load current on the 210v line, I would measure the current which flows through the regulator tubes directly; current can then be adjusted by varying the 8000 ohm resistors
The choice of parallel resistors depends a LOT on the voltage presented to them, before the gas regulation tubes. Would do a lot for the precision of the discussion here, were you to measure the voltage.
I'm assuming it'll be around 285 V DC, in which case,
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I'm assuming it'll be around 285 V DC, in which case,
E = IR and
I = E/R so
I = (285 - 210) ÷ 4000 Ω
I = 0.0188 A → 18.8 mA
Those are the basics. Now, with the measured voltage, we can establish a nice 20 or 25 mA working point, and adjust the resistors. Might even only need change out one of them, too!I = E/R so
I = (285 - 210) ÷ 4000 Ω
I = 0.0188 A → 18.8 mA
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
It's suggested on data sheets that there should be a resistor in series with each regulator to limit current , otherwise problems develop. From GE. "If a current through the tube is increased beyond a certain point the tube will go into a so called arc discharge. Under these conditions, a cathode spot rather than a uniform cathode glow appears on the cathode . . . . ..
I don't use regulator tubes but I do remember there's also a general rule to put a large value resistor in parallel with the upper tube to insure the lower tube fires properly. I don't know how to determine the value though I believe it's high, Like 500K or 1 Meg or up there somewhere.
I don't use regulator tubes but I do remember there's also a general rule to put a large value resistor in parallel with the upper tube to insure the lower tube fires properly. I don't know how to determine the value though I believe it's high, Like 500K or 1 Meg or up there somewhere.
A series circuit is a series circuit.
Series: R, VR, R, VR, Ground
Is the same as:
Series: R, R, VR, VR, Ground.
An OD3 requires 180V to fire, and when fired is 150V (on).
I believe that two OD3 tubes in series will fire if you have a little bit of margin voltage: 180V + 180V + 20V = 380V.
Until one or more of the two OD3 fires, there will be 0Volts across the series resistor.
Two VR105 and a resistor all in series is similar (just a different firing voltage, a different fired voltage (on), and do not forget to have some margin voltage too).
If that power supply is also used to power other tubes (at the input connection to the 8000 Ohm resistors) until the other tubes warm up,
the B+ will go to secondary 1.414 x RMS Volts. A 275Vrms secondary, and B+ will rise to 389V before the other tubes warm up.
Did the simple version with no parallel resistor not work for anybody?
Perhaps you had to use a parallel resistor across the top tube, or a parallel resistor across the bottom tube (in either top or bottom position, the result would be the same).
Tell us of your experience.
Thanks!
Series: R, VR, R, VR, Ground
Is the same as:
Series: R, R, VR, VR, Ground.
An OD3 requires 180V to fire, and when fired is 150V (on).
I believe that two OD3 tubes in series will fire if you have a little bit of margin voltage: 180V + 180V + 20V = 380V.
Until one or more of the two OD3 fires, there will be 0Volts across the series resistor.
Two VR105 and a resistor all in series is similar (just a different firing voltage, a different fired voltage (on), and do not forget to have some margin voltage too).
If that power supply is also used to power other tubes (at the input connection to the 8000 Ohm resistors) until the other tubes warm up,
the B+ will go to secondary 1.414 x RMS Volts. A 275Vrms secondary, and B+ will rise to 389V before the other tubes warm up.
Did the simple version with no parallel resistor not work for anybody?
Perhaps you had to use a parallel resistor across the top tube, or a parallel resistor across the bottom tube (in either top or bottom position, the result would be the same).
Tell us of your experience.
Thanks!
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Flicker is normal in gas tubes. If voltage is stable within specs, I wouldn't worry about it.
If current is low, only a part of anode is engaged. Current heats the gas locally, gas conductance decreases, and then glow jumps to colder area. This is the reason of flicker.
If current is low, only a part of anode is engaged. Current heats the gas locally, gas conductance decreases, and then glow jumps to colder area. This is the reason of flicker.
Is the regulator tube circuit buffered or is it directly driving a load, like maybe a preamp? The VR's work best when used just as voltage references, sourced with constant current sources. The output then gets buffered, by, say, a cathode follower.
That's w/o load ... but
as I understand the OP the 210v power a pre-amp and we don't know how much current this draws ...
so the current through the regulators may very well be much lower ...
I still think that direct measurement of regulator current is what I would do ....
The OP says its a VR-105 (OC3) regulator, not (OD3), so 105v (on) 115v to fire (according to Tung-Sol DS).
Yes I am using two OC3s. My 4 tubes consume 27mA total.
2C22 @ 11mA X 2
#76 @ 2.5mA X 2
My voltage prior to the pair of 8K resistors is 348V.
thanks for all the information and help!
2C22 @ 11mA X 2
#76 @ 2.5mA X 2
My voltage prior to the pair of 8K resistors is 348V.
thanks for all the information and help!
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OK, 348 V DC before the pair of 8,000 Ω resistors.
To the poster that wanted to directly measure the amperage through the VR stack, I say "don't". Too much circuit fiddling. The proxiy value of 35 mA is “good enough”. The preamp circuits or sections will take a few mA each, Call it about 10 mA for both. Well, that's still 25 or so mA thru the VR tubes.
All in all I wouldn't change a thing. Just live with the fact that some VR tubes are flickery. From my half-century back experience, I can attest to that. VRs, especially the bluish variety, can flicker quite a bit. Argon. Likes to flicker.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
I = E/R
I = (348 - 210 → 138) / ( 8000 || 8000 → 4000 Ω )
I = 138 ÷ 4000
I = 0.0348 A … → 34.8 milliamps
Which is close to the 'high side' of what the voltage regulator-reference valves 'like' to have. But still within margin. I = (348 - 210 → 138) / ( 8000 || 8000 → 4000 Ω )
I = 138 ÷ 4000
I = 0.0348 A … → 34.8 milliamps
To the poster that wanted to directly measure the amperage through the VR stack, I say "don't". Too much circuit fiddling. The proxiy value of 35 mA is “good enough”. The preamp circuits or sections will take a few mA each, Call it about 10 mA for both. Well, that's still 25 or so mA thru the VR tubes.
All in all I wouldn't change a thing. Just live with the fact that some VR tubes are flickery. From my half-century back experience, I can attest to that. VRs, especially the bluish variety, can flicker quite a bit. Argon. Likes to flicker.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
I thought I checked and the specs called for no more than 0.1uf - otherwise it may oscillate.
Did I interpret that incorrectly?
Did I interpret that incorrectly?
Not sure about the math. He says his tubes consume 27mA. You calculated 35mA total. That leaves only 8mA at best for the VR tubes. I can see flicker.
If all of that is correct, the design is marginal at best.
Does that also hold for a series connection? You get twice the negative impedance, so you can only allow half the capacitance.