Testing the 814 in triode mode
Worried about the G2 maximum voltage limit as per datasheet in class B, I decided to test the 814 carefully. So carefully that had a bit of smoke and fireworks (but not inside the valve)
Paul Leclercq suggested adding the grid resistors in G2 and G3 and do some baby steps whilst testing this lady.
Here is the test rig used:
The valve is astonishingly linear. At 600V anode voltage and 50mA quiescent current the valve only produced THD=0.01% at 15Vrms output!
Internal pannel meter wasn’t disconnected and apparently didn’t survive the 600V exposure so blew up and a domino effect provided some interesting fireworks inside my bench supply (series MOSFET regulator) 🙂
Evidently something went wrong with an unexpected short to ground, couldn’t be bothered with doing some proper root cause analysis so shut everything down and brewed myself a cup of tea….
Afternoon repairing the HT variable supply 🙁
Now fixed, need to look at the curve tracer. A new LCD panel and hopefully nothing else!
🙁 I hope it can be repaired?!
HT supply is done, need to look at the tracer, but fortunately is only a minor part of the circuit as tracer logic is not affected 🙂
My advice: use a MOSFET gate (CCS) and grid lamp (directly on the stem, as close as possible) “ferrite beads”. This will help denial hesitation. This may be one of the reasons – fireworks. Me this helped 🙂
I had an LCD panel meter that accidentally stayed connected in the HT line. This current meter wasn’t prepared for the 600Vdc supplied, so blew up. Have a look at the HT supply circuit I posted earlier…
PS: have gate stoppers on al mosfets in the supply 🙂
thanks
Ale
I recommend running tests at a larger level. For an output tube like this one, a 15Vrms THD isn’t very meaningful, folks will be using this with a minmum5k priary swinging more like 125Vrms, the morder of magnitude difference makes the THD measurement fairly meaningless. Still great discoveries, wish you a happy holiday
Agree 100%, but couldn’t drive the test signal beyond that point. Is not meaningless if you compare it with other tubes under the same test conditions.
I hope soon I can build out the driver and test this accordingly. Thanks and have a great Christmas!
Ale
Why you connect the G3 to plate and not the anode ?
Plate = anode , not sure what you meant?
Sorry for the error.
Why the G3 is connect to plate and no to cathode ?
I normally connect the G3 to cathode in a triode-strapped.
For triode-strapped both options are valid. I generally connect G3 to the anode…