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Overhauling high voltage vacuum tube (valve) power supply
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calexanian:
In a pass tube configuration where we are not amplifying, only bringing the cathode up to as close as we can to grid potential where is no real benefit to having a regulated screen supply as both plate and screen voltages will remain relatively constant. In cathode coupled load circuits plate resistance is so effectively low it does not really do you any good being able to move the screen supply around. As a matter of fact, many supplies used 6AS7's as the pass tube. Both sections in parallel. That tube can really conduct. Lots of cathode and its shot very fluffy for high emission density. Somewhere around here i have a photocopy of the original Tung Sol prints on that tube. Cool stuff..
proschuno:
Yeah would totally love for you to upload those, that would be a treat! But yeah, i've been wanting to build a power supply using these bad boys, but I can't seem to identify what they are, and they puzzle many other tube enthusiasts like myself. They're clearly in the 276a/804/242 family, but now true way of testing :(
T3sl4co1l:
Beefy!  Probably not well suited for a power supply though... they typically need high plate voltages.  Lots of dissipation means lots of raw output capacity, but only if you put in a thousand volts or so to start with..

If nothing else, you can hook up the filament and get yourself an industrial grade night light. :D

Tim
calexanian:
Just use a variac and a step down transformer and increase voltage until near incandescence. the common filament voltages would be 5, 6.3, 7.5 or 10. There are some higher but for triodes it gets tricky. Thats usually reserved for big rectifiers and RF tubes. It looks like a sand blasted Moly anode. It may be zirconium coated but it looks a bit light in color for that. Moly anodes have a max dissipation of about 5 watts per square CM in the electron beam area and will usually glow a dull red at that. Get some meters and a few supples together and start making some curves and figure out what you can use them for. First run an Eb/Ib test. That is base voltage over base current. That is tube testing terminology for how much does the thing conduct in plate current. Tie the grid to the plate via a 1K resistor or so. Slowly begin increasing plate voltage and plot plate voltage vs current. Use a plate balast resistor so to not tear up your power supply but take the voltage measurement right from the plate. Start at a lower filament voltage and work your way up.  If the tungsten filament has a white coating then it may be thoria bonded in which case the emission will be much higher than just thoriated tungsten, but it is most likely just thoriated tungsten. Bright yellow is about the optimal temp for thoriated filaments. Not quite white. Think light bulb with the dimmer switch turned down just a bit for mood lighting. Then apply say 250 to 300 volts on the anode and lower the grid voltage to cutoff. Don,t be surprised if at 0 grid volts its already near cutoff. Many specialty RF and oscillator tubes actually  were used in grounded grid service and need a positive grid voltage to conduct at low anode voltages.

Are there any marks on them? A manufacturer perhaps?
calexanian:
I ran down a quick list of types those may be based on no plate cap and short pin medium metal ceramic shell base triodes.


203A, 838, or some kind of variant of the 845 or 211. There were many firms out there such as United Electronics, ETI, Cetron, etc etc who made many special variants of standard tubes for various customers needs. All of those tubes mentioned have a 10 volt filament. 
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