Good evening,
I can't seem to find the answer to this question on the internet.
If I have a number of VR tubes (around 8-10), like the OA2 near eachother, will there be any issue with EMI or RF or do they all play nice together? I could buy the shielded 7-pin sockets, but only if necessary.
I can't seem to find the answer to this question on the internet.
If I have a number of VR tubes (around 8-10), like the OA2 near eachother, will there be any issue with EMI or RF or do they all play nice together? I could buy the shielded 7-pin sockets, but only if necessary.
Data sheet (that I found) recommends a 0.1uF cap in parallel to prevent parasitic oscillation.
If there is no oscillation then there is only DC...no change in voltage.
AC has a change in voltage or current. (dv/dt, di/dt, change in voltage or current with respect to time)
If there is no di/dt or dv/dt then there can be no EMI.
Hope that helps.
If there is no oscillation then there is only DC...no change in voltage.
AC has a change in voltage or current. (dv/dt, di/dt, change in voltage or current with respect to time)
If there is no di/dt or dv/dt then there can be no EMI.
Hope that helps.
Gas discharge tubes make a lot of racket over a very wide bandwidth, but aren't particularly susceptible to it themselves, they just infect everything else. They also have negative resistance regions and require a significant starting voltage. I like glowing glass bottles as much as the next guy, but Zener diodes were heaven-sent.
Like mercury vapor rectifiers, I can't quite get there. But that's my problem.
All good fortune,
Chris
Like mercury vapor rectifiers, I can't quite get there. But that's my problem.
All good fortune,
Chris
Thanks for the responses, most helpful! I have a few of these onhand and the PS design is fairly classic, so I think I'll give them a whirl.
If you read the datasheet more carefully you may find that it says that any parallel capacitor must not exceed 0.1uF (in order to avoid relaxation oscillation). This is because a voltage regulator valve exhibits negative resistance.DUG said:
Or a bit more practical: install a bypass cap if you have HF noise from the regulator. When it turns into an oscillator reduce capacitance until stable. When things go well the HF noise is still dealt with.
I find they work very well when a CCS is used to set the total current. I use them in my 26 preamp/DAC to set the voltage at 225V (0A3+0D3 in series) and it is very, very quiet, and sounds excellent. Total current = 29mA, current through 26 = 7mA.
I bypass the pairs on each side with a 0.1uF K40Y-9 Russian PIO, BTW.
And yes, they look very cool in operation but if they sounded like crap they'd be outta there! Not the case.
I bypass the pairs on each side with a 0.1uF K40Y-9 Russian PIO, BTW.
And yes, they look very cool in operation but if they sounded like crap they'd be outta there! Not the case.
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In the world of RF design we use a device called a noise figure meter to evaluate the noise performance of low noise RF electronics, especially receiver front ends. The noise figure meter uses a calibrated noise source in its operation. Todays meters have a specialized solid state device for the noise source. The meters made before the 1960's used a gas discharge tube that is a close relative of the VR tube as the noise source.
The popular 0x2 and 0x3 type VR tubes do indeed generate a wideband noise spectrum from DC well into the MHz region, as does ANY device that operates via gas ionization. Neon and fluorescent lights are also noise sources.
The noise RADIATED by these devices is rather weak. It will not interfere with AM radio more than a foot away, and shouldn't interfere with electronics in the near proximity, although I wouldn't put my phono stage right next to one.
VR tubes so close to each other that they touch is not a problem electrically, although they do have a light sensitivity. If light sensitivity is a problem, then you do not have enough striking voltage.
The RF noise that is CONDUCTED out of the tube can be in the millivolt range, and it can usually be killed with a bypass cap. As stated, do not put more than 0.1 uF directly across a VR tube. I would use less if possible.
If you are feeding an active error amp from a VR tube, especially a mosfet gate, include a low pass RC filter between the tube and the gate. Mosfets have high Gm and gain well into the MHz range.
The popular 0x2 and 0x3 type VR tubes do indeed generate a wideband noise spectrum from DC well into the MHz region, as does ANY device that operates via gas ionization. Neon and fluorescent lights are also noise sources.
The noise RADIATED by these devices is rather weak. It will not interfere with AM radio more than a foot away, and shouldn't interfere with electronics in the near proximity, although I wouldn't put my phono stage right next to one.
VR tubes so close to each other that they touch is not a problem electrically, although they do have a light sensitivity. If light sensitivity is a problem, then you do not have enough striking voltage.
The RF noise that is CONDUCTED out of the tube can be in the millivolt range, and it can usually be killed with a bypass cap. As stated, do not put more than 0.1 uF directly across a VR tube. I would use less if possible.
If you are feeding an active error amp from a VR tube, especially a mosfet gate, include a low pass RC filter between the tube and the gate. Mosfets have high Gm and gain well into the MHz range.
In relation to Zeners VR tubes have a few advantages:
In higher t° environment they are much stable and drift less than zeners, especially the voltage reference tubes. (5651,etc...) They have a better tempco which can be a big plus in tube circuits generating much heat.
High voltage (over 100V) zeners are notoriously unreliable and multiple (strings) of diodes connected in series are usually needed to achieve higher voltages and spread dissipation issues. Even then they're failure prone but I still have to see a failed VR tube used within its ratings. I've replaced numerous shorted zeners in tube power supplies but never had to replace a VR tube in the same applications. Looks that VR tubes are much "tube-circuits friendly" than zeners. Like any tube they will ultimately worn out but (unlike zeners) don't produce catastrophic (destructive) failures to adjacent circuits or components and are easy to replace.
VR tubes looks great and displays a nice (purple or orange) glow which tells you about the good working of the circuit in which they're used.
Zeners are actually specialized diodes used in their reverse breakdown (avalanche) region and are also inherently noise generating but have a different noise spectrum than VR (discharge tubes). Both can (and need to) be filtered out with a little bypass cap.
In higher t° environment they are much stable and drift less than zeners, especially the voltage reference tubes. (5651,etc...) They have a better tempco which can be a big plus in tube circuits generating much heat.
High voltage (over 100V) zeners are notoriously unreliable and multiple (strings) of diodes connected in series are usually needed to achieve higher voltages and spread dissipation issues. Even then they're failure prone but I still have to see a failed VR tube used within its ratings. I've replaced numerous shorted zeners in tube power supplies but never had to replace a VR tube in the same applications. Looks that VR tubes are much "tube-circuits friendly" than zeners. Like any tube they will ultimately worn out but (unlike zeners) don't produce catastrophic (destructive) failures to adjacent circuits or components and are easy to replace.
VR tubes looks great and displays a nice (purple or orange) glow which tells you about the good working of the circuit in which they're used.
Zeners are actually specialized diodes used in their reverse breakdown (avalanche) region and are also inherently noise generating but have a different noise spectrum than VR (discharge tubes). Both can (and need to) be filtered out with a little bypass cap.
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Hi,
+1
I've used thousands of small VR tubes (7 pin a la 0A2 etc. ) in almost all audio stuff I designed and never had any problem with any of them.
Sure some can be noisy some times but if that's important then just select them.
Most of the time I don't bypass the vr tube when used in a series reg.
I also find that whatever noise spectrum they have is less intrusive then the one generated by zener diodes.
In general it's best practice to use tubes in tube circuits. Be that for rectification, regulation or amplification. That is if you want it to sound good and last like forever and a day. 😉
Not that I haven't sinned in the past....😀
Cheers, 😉
+1
I've used thousands of small VR tubes (7 pin a la 0A2 etc. ) in almost all audio stuff I designed and never had any problem with any of them.
Sure some can be noisy some times but if that's important then just select them.
Most of the time I don't bypass the vr tube when used in a series reg.
I also find that whatever noise spectrum they have is less intrusive then the one generated by zener diodes.
In general it's best practice to use tubes in tube circuits. Be that for rectification, regulation or amplification. That is if you want it to sound good and last like forever and a day. 😉
Not that I haven't sinned in the past....😀
Cheers, 😉
Have had exceptional and reliable results using a DN2540 or 10M45S constant current source feeding any combination of VR tubes. Repeatable strike, zero 60/120Hz hum, and no audible or measurable noise with a soundcard and Audiotester software. Extremely quiet.
No, I do not have access to an RF spectrum analyzer, but with 100 MHz analog scopes everything seems very quiet to me.
There is just something in the engineer in me that is satisfied knowing when I see the beautiful orange or purple glow that my circuit is operating in the exact designed spot I want it to, and it can take a pretty significant beating and still survive.
No, I do not have access to an RF spectrum analyzer, but with 100 MHz analog scopes everything seems very quiet to me.
There is just something in the engineer in me that is satisfied knowing when I see the beautiful orange or purple glow that my circuit is operating in the exact designed spot I want it to, and it can take a pretty significant beating and still survive.
Shielded sockets aren't necessary with VR tubes. Never had any problems with noise when using these as voltage references for active screen voltage regulators. Your OA2s should all play together nicely. The only thing is when using these in series strings. It's helpful to connect each plate to the main DC source with 1.0M resistors to ensure all the tubes strike on power up.
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