There's generally a good reason to not use a regulated bias supply at all - unless in the case of pentodes your screen is regulated or in the case of triodes or ultra-linear the B+.
If you regulate just the one then mains voltage variations will pull the actual quiescent current around, whereas if neither are regulated then the HT/screen supply will change in step with the bias supply, which tends to mostly cancel out leading to a relatively stable bias current. The effect isn't perfect but generally good enough to keep things within a sensible window.
If you regulate just the one then mains voltage variations will pull the actual quiescent current around, whereas if neither are regulated then the HT/screen supply will change in step with the bias supply, which tends to mostly cancel out leading to a relatively stable bias current. The effect isn't perfect but generally good enough to keep things within a sensible window.
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That would need to be fixed before I'd design a regulator. Do your neighbors report the same brown voltage?
A certain amount of variation is expected and allowed. Often excessive variation is due to your own local
step down transformer. They would put a monitor on your power line for a week to check before replacing it.
In summer deliberate brown-outs are common to reduce utility demands.
Perhaps me telling you the fastest Internet I can get is 1.344 meg DSL will tell you where I live! I am 75 miles North of Boise Idaho in a tiny town. Power outages are common during heavy snows. All of my PCs and my server have battery backups. Speaking of battery backups, how well will a tube amplifier work plugged into a battery backup? Wanted to add, when we lose power, we have no water and no heat. We are on well water and we have electric heat!
Recent, pure/true sine wave DC/DC power converters are much better, and voltage stable.
That's real important for tubes. Pure Sine Inverter | The Inverter Store
Dude, that is some sweet DSL. I'm 3 miles from a 250K city and the best ATT can give me 768K. You must be near a phone trunk line.
To backtrack for a moment, and answer one of OPs questions..
Yes, zener diodes are noisy. They generate a weighted broadband noise - it sounds like a 'hiss' to most people. Bypassing the diode(s) with 220n - 1u is a very good idea, but it may not entirely squelch the noise. You can try increasing the value of C but it might create an instability - effectively converting the zener / cap circuit into a relaxation oscillator.
In my exp. this can be controlled by reducing the value of the bias resistor and as such increasing current through the diode(s). Pi-filtration is also an option, but naturally it will raise the Zout of the regulator.
Incidentally, all of this applies to gas-discharge tubes as well, like the 0A2, VR150 and so on. Though with the tubes, they seem even more sensitive to the value of any bypass capacitor.
Yes, zener diodes are noisy. They generate a weighted broadband noise - it sounds like a 'hiss' to most people. Bypassing the diode(s) with 220n - 1u is a very good idea, but it may not entirely squelch the noise. You can try increasing the value of C but it might create an instability - effectively converting the zener / cap circuit into a relaxation oscillator.
In my exp. this can be controlled by reducing the value of the bias resistor and as such increasing current through the diode(s). Pi-filtration is also an option, but naturally it will raise the Zout of the regulator.
Incidentally, all of this applies to gas-discharge tubes as well, like the 0A2, VR150 and so on. Though with the tubes, they seem even more sensitive to the value of any bypass capacitor.
I have used zener regulation with many of my constructions and never found noise problems that are mentioned above.
Also the temperature drift is not a problem.
Many tube amplifier power suplies are not regulated and the performance is still acceptable. How could it be worse if regulated with zeners?
Below one example that I have used with GU50 PP-amplier. Adjustable bias- and screen voltages are regulated with zeners.
Also the temperature drift is not a problem.
Many tube amplifier power suplies are not regulated and the performance is still acceptable. How could it be worse if regulated with zeners?
Below one example that I have used with GU50 PP-amplier. Adjustable bias- and screen voltages are regulated with zeners.
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Not "as well", but to VR tubes only. Zeners don't ignite, so don't oscillate. They can be shunted by any capacitance.
I use similar regulators, except Zener string and 2 MOSFET outputs, +400 for preamp tubes, and +270 for screen grids. Also I regulate filament DC for preamp tubes.
Ray,
without water and electric power an UPS for a tube amp appears a rather minor problem to me...
To your 1st posting: Keep in mind that the 783 is a positive regulator. So the whole circuitry needs to float, with only it's positive output tied to ground. And what's that DC Input for?
Best regards!
As was said before, it is true for triodes. For pentodes it is enough to stabilize G2.
Same thoughts here.
Given the real power needs, I´d *forget* any battery backup, besides keeping stuff working for a few minutes until emergency power generator starts and catches up speed.
I wouldn´t worry about losing Music playing ability for a few minutes, specially since my attention would be concentrated on cursing the d*mn "no Power" Company, not the best mood to enjoy fine Music
By your description, and if it happens often enough, I´d invest in a simple gasoline generator if power out is infrequent and lasts little or a good Diesel powered one if longer.
Uh-oh.. Either I didn't make myself clear, or you misread me.
I never said zener noise was necessarily a "problem" or some kind of deal-breaker - I simply stated the fact that yes, zener devices +do+ generate a broad-band noise, which manifests like a hiss. Like yourself, I've built a lot of tube equipment that used zener regulation in various ways, and it was always** acceptably quiet.
(** Or more accurately - if it did have noise issues, they weren't due to the zener elements..)
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