Hi all,
Quick ?,
I am rebuilding my RH84 (EL84 Pentode SE) and am considering regulating G2.
I have never used Gas tubes before, only zeners but have a VR150. So, I am thinking about the VR150 and was wondering if there would be a problem using it with SS rectification for the B+.
I have been doing some reading on them but never saw mention of this.
IOW, is there an issue with the gas tubes being "hit" suddenly with voltage?
I considered this since the gas tubes are from an era before SS. I did read somewhere that they do not like being turned on and off and on again quickly.
Thanks.
Quick ?,
I am rebuilding my RH84 (EL84 Pentode SE) and am considering regulating G2.
I have never used Gas tubes before, only zeners but have a VR150. So, I am thinking about the VR150 and was wondering if there would be a problem using it with SS rectification for the B+.
I have been doing some reading on them but never saw mention of this.
IOW, is there an issue with the gas tubes being "hit" suddenly with voltage?
I considered this since the gas tubes are from an era before SS. I did read somewhere that they do not like being turned on and off and on again quickly.
Thanks.
I use VR150 to regulate the solid state rectified bias supply in my 300B SE amplifier. (I want the supply bias to come up almost instantly. No problems in 4 yrs.)
You need to make sure that there is sufficient voltage for the tube to strike properly and in this case something like 220V should be sufficient. Minimum current through the VR tube should not be less than 5mA, and no more than 40mA before your screens start to draw current. You want to make sure that at amplifier clip there is still enough current (5mA or greater) available to keep the VR tube from extinguishing. Some tweaking will be required.
One very important thing to mention is that the screen voltage should not be there before the plate voltage as this can have catastrophic consequences for the screens in your output tubes. The reverse is not an issue.
I have seen VR tubes break into relaxation oscillations with as little as 0.047uF - 0.1uF across the tube, and generally use no more than 0.022uF in parallel with the VR tube.
You need to make sure that there is sufficient voltage for the tube to strike properly and in this case something like 220V should be sufficient. Minimum current through the VR tube should not be less than 5mA, and no more than 40mA before your screens start to draw current. You want to make sure that at amplifier clip there is still enough current (5mA or greater) available to keep the VR tube from extinguishing. Some tweaking will be required.
One very important thing to mention is that the screen voltage should not be there before the plate voltage as this can have catastrophic consequences for the screens in your output tubes. The reverse is not an issue.
I have seen VR tubes break into relaxation oscillations with as little as 0.047uF - 0.1uF across the tube, and generally use no more than 0.022uF in parallel with the VR tube.
With no bypassing cap it is no surge current. Opposite, to ignite it you need a bit more of a voltage that is needed to keep it glowing.
It depends on the current: if it is too low the toob discharges the cap then stops conducting until a voltage on it is back enough to ignite it.
kevinkr said:
It depends on the current: if it is too low the toob discharges the cap then stops conducting until a voltage on it is back enough to ignite it.
Wavebourn said:
May be your output stage helped it to oscillate causing a B+ sag?
Nope, totally independently powered, and as I only build SE amplifiers these days I use them solely for bias supplies. Above some threshold capacitance level it no longer matters what the current is - all that happens is the relaxation frequency shifts around.. (more current = faster repetition rate.) Too much current and the tube enters the region where the behavior is more analogous to an arc than a glow discharge and the tube fails quickly at that point.
Have done this experiment on the bench with tightly regulated power supply as the source, just cap, resistor, and VR tube. Outcome is the same - there is always a point where regardless of the current through the tube above a specific capacitance the regulator becomes a relaxation oscillator. (Generally with values of 0.1uF and above.)
Some useful information on VR tubes in general is here:
http://en.wikipedia.org/wiki/Voltage_regulator_tube
http://en.wikipedia.org/wiki/Voltage_regulator_tube
I think you'll probably be ok with a single VR tube or series string to get the voltage you need. The EL84 generally does not require more than 10mA of screen current per tube, and if you use a tube rectifier to delay the B+ there will be a window within which the VR tube can live. The issue is just to make sure that you are ready to draw screen current when the VR tube starts to conduct.
You can also just use a B+ delay relay with a simple timer circuit.
Alternately you can use 0A2/0B2 pairs for each channel.. More glow = more fun..
You can also just use a B+ delay relay with a simple timer circuit.
Alternately you can use 0A2/0B2 pairs for each channel.. More glow = more fun..
All of the datasheets I've seen, as well as my own experience, suggests that 0.1u is fine. Why all the sudden concern?
dsavitsk said:
Hi Doug,
I think that was only one of the concerns, and I have had problems at 0.1uF (probably cap tolerance issues) and generally use less..
The other concerns related to not roaching the VR tube(s) during warm up..
I use them all the time too, and have not had any problems recently.. I have seen others put them in arc mode under certain unanticipated operating conditions though which can be rather exciting.. (Like driving the outputs into cut off with already excessive current present in the screen regulator VR tube.)
Them pyrotechnics were somethin' to see..
kevinkr said:
That's why I like the CCS option: VR Safety for Dummies. The extremely high impedance ratio also drive noise well into the dirt.
On the topic, how does everyone handle series VR tubes? Currently I'm running a single 0.1uF cap across a series pair. It seems to me possible that ~0.05uF across each VR and one across the series string would also work. Individual VRs would see the 0.05uF across it in parallel with the other two 0.05uF caps in series, effectively 0.075uF across each VR but .15uF in the supply. Make sense? Worth it?
Guys,
How do you calculate the voltages when using a CCS to feed a VR150 tube?
Let us say that the VR150 needs 200V to work correctly and ignite, and that the CCS needs a voltage drop of minimum 30V to work.
Can I just make sure that my power supply delivers minimum 230V (220V + 30V) to the CCS?
How do you calculate the voltages when using a CCS to feed a VR150 tube?
Let us say that the VR150 needs 200V to work correctly and ignite, and that the CCS needs a voltage drop of minimum 30V to work.
Can I just make sure that my power supply delivers minimum 230V (220V + 30V) to the CCS?
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