Hi all,
I have some VR tubes and I need to drop voltage from the B+ (550V) to about 350- 450V. I was thinking shunting would be the quietest...plus offer regulation.
However I was looking for othes' opinion/ knowledge on which option would result in the least noise? Or should I stick to resistors?
I'm not game for solid state components...
Thanks
I have some VR tubes and I need to drop voltage from the B+ (550V) to about 350- 450V. I was thinking shunting would be the quietest...plus offer regulation.
However I was looking for othes' opinion/ knowledge on which option would result in the least noise? Or should I stick to resistors?
I'm not game for solid state components...
Thanks
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Option one would be best, and would be better with a CCS instead of a series resistor. The easiest option would be a DN2540 cascode, but you could go without solid state by using a high inductance choke in series with that resistor or maybe a Pentode if you want better PSRR.
Option one is still good even with a basic resistor though.
Option one is still good even with a basic resistor though.
Do you just want to use up some VR tubes for the fun of it (a worthy aim!), or do you have something special in mind wrt noise that simple RC droppers can't provide (given that very low noise amps are made using just RC supply distribution).
KISS a resistor - then measure your noise level (hurdle one), and try and work out where the noise is coming from (hurdle two).
KISS a resistor - then measure your noise level (hurdle one), and try and work out where the noise is coming from (hurdle two).
As voltage regulator valves are unlikely ever to be made again, it might be best if they are used where they are useful rather than merely cosmetic.
For the early stages of a phono preamp you may need to stop mains voltage variations getting through so Option 1 is the only one of the three options in post 1 which will do this. Option 2 will make things worse. Option 3 achieves nothing - but at least it won't make things worse.
For the early stages of a phono preamp you may need to stop mains voltage variations getting through so Option 1 is the only one of the three options in post 1 which will do this. Option 2 will make things worse. Option 3 achieves nothing - but at least it won't make things worse.
It is for more than cosmetic... They seem to be a very simple way to regulate voltage. I even thought of using 2050 Thyratrons that I have as rectifiers or other gas rectifiers. I read that these regulate voltage... but reading can be different from reality.
They are common as peas on this side of the pond, and IMO very unlikely to run out in our lifetimes. Tube sellers here can't give them away, and I know this because more than one has dumped piles of them on me at one time or another.
They're not just performing a cosmetic function in this design, they're injecting lots of noise into the supply voltage they are regulating, and that admittedly snarky comment aside they do have some benefits in assuring a relatively consistent operating point (dependent only on the individual tube characteristic) in driver circuits that must swing large output voltages in the course of normal operation - definitely the case here.. The relatively low source impedance at audio frequencies may be of benefit as well.
It's certainly worth trying IMHO, other approaches can be tried later if desired.
They can't operate with substantial shunt capacitance, so must be buffered from any stage B+ supply decoupling. Although some minor (eg. 47nF) shunt capacitance is supposedly of benefit, which I added across 2x VR150 for a 300V vintage regulated screen supply for a PP output stage. I also added a small current sense resistor in the cathode, so I new where the regulator was biased.
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rcollege, the regulated supply has a low impedance when operating within its current range. So as such there is no need to install a bypass capacitor per se (as the capacitor does the same function of proving a low impedance when used as an RC dropper supply).
The outcome is to use one type of supply, RC or R-reg, as you can't mix them without consequences
The outcome is to use one type of supply, RC or R-reg, as you can't mix them without consequences
I use a 100nF Russian K40 PIO cap across a 0A3 0D3 pair with no oscillation detectable. It's fed with a cascoded CCS in my 26 preamp. Works great and looks great. I think the sensitivity to capacitance is a bit overstated, IMO.
Put enough capacitance across a regulator valve and it will oscillate. This is because it has negative resistance. The reason smaller cap values don't cause oscillation is that the discharge is too slow to react to voltage changes. To a first approximation, if the cap is too small to cause oscillation then it is probably too small to do any useful smoothing or noise reduction too.
That's what a cap across the VR tube does, but only for the noise generated by the VR tube itself. You need much larger decoupling for the power supply noise filtration before the VR tube, but the VR tube must be isolated from the PS decoupling capacitance with either a resistor or (preferably) a CCS.
This doesn't seem like much noise....unless the noise is being amplified by the circuit...
I guess the real question is... Is there any possibility of improvement that makes the extra sockets and tubes worth the effort?
It's a tropical hardwood chassis...3 more holes that cannot be easily filled if it doesn't improve the sound....
Decisions, decisions....
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