It is now confirmed that the valves under test were indeed rebranded 6Д20П/6D20P.
https://frank.pocnet.net/sheets/112/6/6D20P.pdf
6D20P anode on pins 2, 7 and 9 vs. EY88 anode only on pin 9.
Update on booster diode stress testing:
Even More Voltage !
Finally - Success ... ! ... Two blown tubes.
Again voltage doubler but now 4 of my 230/230V safety isolation transformer secondaries in series.
Total unloaded AC in 1060V RMS (thats 1500V peak amplitude.
Capacitor chain has now 8 x 470uF / 450V in series with bleeders and 1N5408 protection diodes.
The diodes are reverse and in parallel to protect the caps in case of a tube flashover.
Each damper working directly into 117uF with just the transformer secondary DCR of 168 ohm.
Load is 10 lamps 230V / 25 / 40 in series.
Rectified DC w/o load is 2670V (less than the expected 3kV because of the bleeder's 14mA draw).
10x25W lamps: DC current 115mA at 2200V, rectifier peak current 720mA, plate dissipation 4 W.
This was the last successful run.
10x40W lamps:
during warm up at around 800V DC a not very spectacular flash happened right underneath the cathode cap.
Load current dropped to zero.
Optical inspection revealed that the connecting strap from the top electrode to the cathode sleeve was gone.
May have been a bad weld ...
The defective tube was replaced with a new one, and power on.
This time a veritable flash over in the lower third of the new valve occurred.
The protection diodes did their job and blew the transformer primary fuse.
One could argue that the surviving tube had had some good preconditioning by the previous test runs,
while the new tube's getter should have been given more time to remove residual gas.
https://frank.pocnet.net/sheets/112/6/6D20P.pdf
6D20P anode on pins 2, 7 and 9 vs. EY88 anode only on pin 9.
Update on booster diode stress testing:
Even More Voltage !
Finally - Success ... ! ... Two blown tubes.
Again voltage doubler but now 4 of my 230/230V safety isolation transformer secondaries in series.
Total unloaded AC in 1060V RMS (thats 1500V peak amplitude.
Capacitor chain has now 8 x 470uF / 450V in series with bleeders and 1N5408 protection diodes.
The diodes are reverse and in parallel to protect the caps in case of a tube flashover.
Each damper working directly into 117uF with just the transformer secondary DCR of 168 ohm.
Load is 10 lamps 230V / 25 / 40 in series.
Rectified DC w/o load is 2670V (less than the expected 3kV because of the bleeder's 14mA draw).
10x25W lamps: DC current 115mA at 2200V, rectifier peak current 720mA, plate dissipation 4 W.
This was the last successful run.
10x40W lamps:
during warm up at around 800V DC a not very spectacular flash happened right underneath the cathode cap.
Load current dropped to zero.
Optical inspection revealed that the connecting strap from the top electrode to the cathode sleeve was gone.
May have been a bad weld ...
The defective tube was replaced with a new one, and power on.
This time a veritable flash over in the lower third of the new valve occurred.
The protection diodes did their job and blew the transformer primary fuse.
One could argue that the surviving tube had had some good preconditioning by the previous test runs,
while the new tube's getter should have been given more time to remove residual gas.
Attachments
Rumination on the previous experiment.
The good news is, that the booster diode which suffered the flash over is still alive.
After an hour of burn in with filaments on it now works flawlessly.
The bad news is that the valve which I first thought had survived, actually did not.
Guess what, the same strap to the cathode failed open ... once again.
This little wire to the cathode seems to act as a fuse, accidentally or intended.
I now have 2 dead valves with open cathode, and one reanimated.
The good news is, that the booster diode which suffered the flash over is still alive.
After an hour of burn in with filaments on it now works flawlessly.
The bad news is that the valve which I first thought had survived, actually did not.
Guess what, the same strap to the cathode failed open ... once again.
This little wire to the cathode seems to act as a fuse, accidentally or intended.
I now have 2 dead valves with open cathode, and one reanimated.
