It'll trash an oxide cathode in a gridded tube, for sure. OTOH the 1B3 has no grid, so one gathers that it's meant to operate in the cathode-limited condition. The datasheet at
I have OCRed copies of Herrmann & Wagener's two volumes on "The Oxide-Coated Cathode" up on my website:
Cheers
Phil Hobbs
Page 109 of Volume 1 shows dead cathodes.
Cheers
Phil Hobbs
I used to use a 1B3 with variable filament voltage (pot and flashlight battery, long insulated shaft) to be a variable-conduction rectifier, to charge flashtube capacitors to ballpark 8KV, manually set. Seemed reliable, even starting with old 1B3's.
You can carry my current mirror linearization scheme...
all the way thru the output stage, thus making it far easier to stabilize....
...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at
There's no reason to both bias up MN2 with DZ1 (silly reference designators!) and use a depletion fet.
This still has a lot of quiescent power dissipation, in R3 and the fets.
Well, a rectifier that couldn't rectify very long wouldn't be much use, for sure. I don't know what they made 5U4 cathodes out of, either.
H & W talk about the damage mechanism being mostly internal arcing due to the voltage drop across the thickness of the oxide layer, which I hadn't thought about, but the pictures on P. 109 would seem to bear out. Seems like that would get worse at low filament temperature.
Tubes are fun. My last tube circuit was in about 1988--I used an 811A to drive some grids in an electrostatic drift experiment. (I was trying to use a laser-produced plasma to create air ions inside semiconductor process tools. An enthusiasm of my then manager's.)
The combination of high voltage drive and very low plate capacitance meant that I could easily pulse the grids and then disconnect in a microsecond or so. A relay would have worked except for being way too slow.
Cheers
Phil Hobbs
Relays aren't always slow. IIRR there was a time domain reflectometer that used a mercury-wetted reed relay to generate its sub-nanosecond rise-time pulse.
Getting them to turn on or off at a specific instant is trickier. They aren't so much slow as ill-coordinated.
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