[Techlunch] Winners and loosers

Dennis Gibson dennis.gibson@anu.edu.au
Thu, 06 Dec 2001 09:33:17 +1100

Was that OUR Gilbert Hughes that won box office tickets to the PM 11 cricket?

I take it that you all have heard that Wally & Meredith have tied the knot after a
few years of compatibility testing?  If knot, you have now!

Technical Problem Bit:

We at the ANU have a HyForce 30kW RF Heater.  Self oscillating magnetically
focused triode (STC 3RM-245G)  running about 350kHz determined by tank + load L.

The normal idling parameters are 7.5kV HT @ 2A, up to 7A @ full power.
Power is controlled by +ve DC on grid, shunted via transistors to reduce power.
At idle, it has 0V DC on the grid, at full O/P approx 650V,

Problem is that it can no longer reach full output (IP = 2.4A max) and at idle IP = ~0.5A.
Grid current is a little higher than usual (75mA), grid DC control volts appear ~ normal.


How con one PROVE without substitution, that the very expensive valve has actually
gone soft, which I suspect it has?

Failing that, any other explanation of the operational phenomena would be welcome!
(Not much experience at this end).

I take it tha


Dennis Gibson, Electronics Unit
Research School of Physical Sciences & Engineering
Australian National University, Canberra, ACT 0200

Ph: (02) 6125 2607  [Intl: +61 2 6125 2607]
Fx: (02) 6125 4433  [Intl: +61 2 6125 4433]

Email: dennis.gibson@anu.edu.au