Hello Folks Does anyone know of a power pentode or tetrode with a higher G2 voltage rating than a KT88 ? I'm running a KT88 as the shunt tube in a 300B power supply ( in triode mode ), but would like to extend this supply to approx. 700 to 750V for GM70 in the future. I've checked KT120, KT150 and F2a, but nothing higher than 600V there. Maybe there's an obscure one I've missed ? Would want to run about 50mA , so would have to be approx. 50W dissipation too.
I would have to see the schematic of your power supply to see if there are any reasonable alternatives. I even looked at some very high power, very high plate voltage RF power tubes. But even they had screen voltages of 600 Volts.
I once built a Triode-Wired 4-65 Tetrode SE amp (but the screen is limited to 600V, even though the plate is rated for 3000V). The next larger tubes in that family only have 400V screens, go figure. I love those Eimac tubes.
If you have some high voltage floating filament windings, then how about using Series Regulation, not Shunt Regulation?
Generally, series regulation is more efficient, you do not have to use as much voltage drop across the Triode Wired Pentode or Triode Wired Beam Power tube.
Help, anybody?
I once built a Triode-Wired 4-65 Tetrode SE amp (but the screen is limited to 600V, even though the plate is rated for 3000V). The next larger tubes in that family only have 400V screens, go figure. I love those Eimac tubes.
If you have some high voltage floating filament windings, then how about using Series Regulation, not Shunt Regulation?
Generally, series regulation is more efficient, you do not have to use as much voltage drop across the Triode Wired Pentode or Triode Wired Beam Power tube.
Help, anybody?
Good questions. Shunt regulation is the daddy in terms of sound quality. I ran series-reg for a few years before I built this ( 'T-Rex' - Broskie/Bench ) supply. Triodes - well... it would be nice to stay with indirect-heated valves - most high-voltage triodes are DHT's - which then requires another special filament supply to keep it quiet.
dhaen,
Great Call, Great Point!
With a Power RF triode, IslandPink can do high voltage shunt-ing.
Just be selective, or deal with most of those tubes that have Directly Heated Thoriated filaments. Work smart(er) to reduce their DH hum (balance pot, or DC filaments). Be prepared for Lots of Amps of filament current.
Great Call, Great Point!
With a Power RF triode, IslandPink can do high voltage shunt-ing.
Just be selective, or deal with most of those tubes that have Directly Heated Thoriated filaments. Work smart(er) to reduce their DH hum (balance pot, or DC filaments). Be prepared for Lots of Amps of filament current.
The other alternative is to:
Use an indirectly heated Pentode or Beam Power tube in shunt mode, but do not triode wire it. It only needs a regulated screen supply; but the advantage is with so much transconductance and voltage gain, it may not even need a control tube . . . just a small change in the sample of the voltage back to the control grid will cause a large change in the tube's shunt current to get the supply back to the correct shunted voltage.
Use an indirectly heated Pentode or Beam Power tube in shunt mode, but do not triode wire it. It only needs a regulated screen supply; but the advantage is with so much transconductance and voltage gain, it may not even need a control tube . . . just a small change in the sample of the voltage back to the control grid will cause a large change in the tube's shunt current to get the supply back to the correct shunted voltage.
Thanks for background info, as PM.
Hmmm... let me think about this. On one hand I was thinking it needs to be in triode mode for low plate resistance ( which is divided many times by the error amp part ) ; and pentodes are high Zout... but then the transconductance is high. Really it's the effective transconductance that sets the Zout on a shunt, isn't it ?
The current Vishay sheet doesn't show the 4.5V line on the Id vs Vds that the International sheet has. Does that mean anything?
You might want the tube for visuals, I don't know - nothing wrong with that - but if not, the sand parts can sound just as good . . . . if not better.
Instead of using a voltage divider to feed back the voltage sample to the shunt tube, use zener diodes to offset most of the voltage. Example, if the voltage is 500V, and you use 450V of series zener diodes, the 500V can change by 5V, and the sense resistor at the bottom of 450V diode string will change by 5V. No control tube is required, only the shunt tube.
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