RadioBanter - View Single Post

April 29th 05, 02:43 AM

On 28 Apr 2005 10:08:05 -0700, wrote:

While I have been active in electroincs since 1962 I
managed to miss Nuvistors. Started wtih regular tubes
(valves) and went on the bipolar and FETs. Is it reasonable
to find a plate voltage of about +30V?
My recollection is 30V is probably on the high side, I remember
running one at 22V. It is planar UHF triode with very small
dimensions. It didn't take much.

I was recently given a RCA multiset coupler that uses Nuvistors.
The primary in the power is open. I disasembled the transformer,
but the open is not in the first few layers. A friend is going
to rewind it, he rebuilds vintage tube guitar and HiFi amps.

Whne I inspected the rest of the circuitry I found the power
supply caps rated at 50V. the faded and amost unreadiable schematic
on the inside cover give the plate voltage as 30V +/-5. I owned a
R392 which used special tubes with plate volatage of 26.5V, but
I have never seen "normal" tubes operated at this low a voltage.
Normal tubes have MUCH MUCH larger inter-electrode dimensions. What
counts in a tube is the e-field, and the if the distance between the
cathode and the plate is 1 cm, and you have 400v, that is 4000v/mm.
On a nuvistor, the cathode to plate distance is measured in mm, and it
isn't many mm either, so you can hefyt e-fields without much voltage.

Nuvistors were typically operated a microwatt/milliwatt output levels.