[Techlunch] Winners and loosers

Mike Dower mjdower@asiaonline.net.au
Thu, 6 Dec 2001 12:51:33 +1100

I turned down a free offer of a ticket to the cricket ...

Congratulations and best wishes to Wally & Meridith.  Speaking of Wally:
early last Saturday morning I received a call on my not-very-well-known
landline number at home.  The male caller sounded like they were on the
other end of a satellite telephone link or something equally distant, and
was asking for someone called Wally.  Being very early in the morning after
a hard week, I wasn't at my best - all I could answer was "No", at which the
caller paused and then said "Sorry, I must have the wrong number" and hung
up.  It's only afterwards that it dawned on me who the caller may have been
... I shall asked him next time I see him.  :-)

Anyway, to the triode problem:

Another issue I can think of is the HT: is this holding up to the normal
loaded output voltage under the "full load" conditions imposed by the tube
in its current state of health?  Testing such a supply with a load (other
than the suspect tube) to check that it can deliver the correct current and
voltage under full load may be somewhat difficult (52.5kW if 7.5kV is
maintained at 7A).

Or, has some form of negative feedback path arisen between the load tank and
the grid which may be tending to kill the oscillation?


Mike Dower                       "Quoth the Raven, 'Nevermore'."   Poe
VK1ENG (& VK2ENG)                           Mobile: +61 (0)419 280 944
mjdower@asiaonline.net.au (via OzEmail)

> -----Original Message-----
> From: techlunch-admin@happy.emu.id.au
> [mailto:techlunch-admin@happy.emu.id.au]On Behalf Of Dennis Gibson
> Sent: 06 December 2001 08:33
> To: Techo Lunch
> Subject: [Techlunch] Winners and loosers
> 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.
> Question:
> 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
> Cheers,
> DG
> --
> ____________________________________________________
> Dennis Gibson, Electronics Unit
> Research School of Physical Sciences & Engineering
> Australian National University, Canberra, ACT 0200
> Australia
> Ph: (02) 6125 2607  [Intl: +61 2 6125 2607]
> Fx: (02) 6125 4433  [Intl: +61 2 6125 4433]
> Email: dennis.gibson@anu.edu.au
> (VK1DG)
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