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In Reply to: RE: Why Build a Regulated Tube Power Supply? posted by megasat16 on July 10, 2016 at 16:29:37
There does seem to be some sentiment here lately to the effect that regulation itself is to be avoided when possible and practical. For example, in the output tube power supply. However, lately I have also seen posts to the effect that VR tubes are not a "nice" way to regulate, when regulation is beneficial. There are some very good solid state based regulation schemes, if it comes to that.
Follow Ups:
Hi Lew and everyone,
This is not a question of tubes. It's a question about why a designer would want to add a regulation circuit for Tube Preamp when it's not necessary in my opinion.
Kind Regards,
James
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
"I have also seen posts to the effect that VR tubes are not a 'nice' way to regulate"
I would be very interested to see articles or posts describing measured degradation resulting from the use of VR tubes. These tubes were used for years as regulators in receivers, transmitters and transmitter modulators, often in situations that demanded excellent signal-to-noise ratios. It has always been my belief that their absence from pentode-design consumer audio amplifiers is solely the result of cost cutting.
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Buy Chinese. Bury freedom.
"It has always been my belief that their absence from pentode-design consumer audio amplifiers is solely the result of cost cutting."
I'm inclined to agree. A stack of 2X 0A2s/pair of 7189s, for g2 B+, and a fairly tall anode B+ rail would make for a heck of a nice PP amp. VR tube noise is easily suppressed by bypassing the stack with 0.068 muF. of capacitance. Maybe a single regulator stack would be sufficient in a stereoblock.
Eli D.
I'm updating a number of HK pentode-mode amps in the near future. I'm thinking along the same lines, Eli. Will probably add VR tube screen regulation in all of them.
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Buy Chinese. Bury freedom.
Hi Triode Kingdom,
The VR tube like a zener diode is a shunt regulator with limited current capability. By itself and a current limiting resistor it can provide voltage regulation for small loads but for something like the output stage in a power amp additional amplification will be required. The VR tube would be the reference and there would be be a loop amplifier such as a small pentode or high mu triode and a big pass tube such as a 6080. All that adds considerable cost, size, and heat.
Compared to zeners they are not very good. Sometimes folks got cheap (Even HP. Look at the vertical amp in their model 150 oscilloscope.) and used little neon bulbs as VR tubes. Now those were real crap.
Phil
When they were used, VR tubes were the ONLY way to achieve regulation (in the absolute sense). Compared to zeners, they absolutely suck. The lowest noise way to achieve a high-voltage reference is to put together a string of 5.6 volt zeners to whatever total voltage you need.Except for the nice color, I can see no reason to use VR tubes in a new design.
Edits: 07/11/16
Zeners are avalanche devices, and thus quite noisy.
Not a problem if you use current-source plate loads.
Hi Lee of Omaha,Better than that, use a TL 430 which is a programmable shunt regulator. They have a rating of about 30 Volts, but you can put them in the cathode circuit of a medium mu triode with the grid grounded and get whatever voltage you need. Chose a mu low enough to get the cathode voltage high enough to operate the TL 430 (~ 3 or 4 Volts should be OK).
By the way I used a TL 430 to regulate the B+ in my Citation 4. I used a photo isolator powered from DC heater supply to couple to the power MOSFET pass device.
Phil
Edits: 07/11/16
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