Has anyone ever hooked up a transformer this way?

[KD6VXI]

In my experience, if you are using a pass regulator (like a typical Astron, etc) then you'll need to dump have the exoect d peak screen current in a resistor, depending on the tube.  Some tubes go negative on screen current actually dumping electrons and causing screen voltage to increase under some tuning conditions.

A shunt regulator eliminates that problem.

Keep this in mind.

I used a bipolar device for my shunt regulator out of a stereo.  Iirc they where good to 900 or 1200 volts.  I also had some mosfets I played with but wasn't happy with them and went back to bipolar.  For the life of me, I can't remember why though.


If your tube(s) won't go negative on the screen, a series regulator with a small amount of bleed R will be fine.  250B style tubes will need more bleed current.


--Shane
WP2ASS / ex KD6VXI

[K9MB]

In my experience, if you are using a pass regulator (like a typical Astron, etc) then you'll need to dump have the exoect d peak screen current in a resistor, depending on the tube.  Some tubes go negative on screen current actually dumping electrons and causing screen voltage to increase under some tuning conditions.

A shunt regulator eliminates that problem.

Keep this in mind.

I used a bipolar device for my shunt regulator out of a stereo.  Iirc they where good to 900 or 1200 volts.  I also had some mosfets I played with but wasn't happy with them and went back to bipolar.  For the life of me, I can't remember why though.


If your tube(s) won't go negative on the screen, a series regulator with a small amount of bleed R will be fine.  250B style tubes will need more bleed current.


--Shane
WP2ASS / ex KD6VXI

Thanks for the advice, Shane.
I actually have some high voltage NPN power transistors coming in.
They are ON FJP5027 high voltage devices in SO220 packs.
They are good for 1100v C-B and 800v C-E
Data sheet below:
The SOA graph is also there. I will be using about 300-350volts on my 4-1000A tubes. The DC graph shows about 40-50mA at 300 volts and maybe 30-40mA for 350 volts.
I figure that I can put 3-4 in parallel for my screen supply and ballast the emitters with (10ohm?) resistors to balance things and stabilize them. Three of them would give at least 100mA at close to 400 volts, I think, which is more than the 80-90mA I will see in Grounded Grid operation at about 4500 volts and about 350 screen volts.
Comments on this device?

Yes, I am very familiar with the 4CX250B, 4CX300A and 4CX350A tubes.
Screen currents would almost always go several mA negative in AB1 for SSB. I used 0xx cold cathode tubes as shunt regulators and they would brighten with modulation on a pair in AB1. I still have a box full of 0B3, OA2, etc…
Nice blue glow like 866 rectifiers. I do not use them- opting for the souless but compact silicon stacks….😉
Have you parallel bipolar pass transistors- like this with emitter ballast for higher currents?
A pair of 4-1000A tubes will not go negative, I think, but if I decided to push them, the screens could pull 0ver 200mA, though that is not my intent, beimg focused exclusively on low IMD, not high output.
73, Mike