Bill said:
>Recently someone posted to the effect that in a tuned plate tuned grid
oscillator, if the anode resonant frequency was lower than the grid
resonant frequency, the tube would not oscillate. Did I catch that
right? And does this apply in a grounded grid oscillator as well as a
grounded cathode one?
So, in the context of the dreaded grounded grid VHF
para-you-know-what, is it really that simple? Keep the cathode-grid
resonance higher in frequency than the anode-grid resonance and it
won't oscillate? <
This is from Terman, Langford-Smith et al. I would argue that it does apply to
GG oscillator, too, since where the 'ground' is is somewhat arbitrary for an
oscillator. Back in my far off youth (sounds of violins playing off stage!)
there were some IFF units for British navy use - Transmitter type 7AD. They
interrogated at around 140 to 180MHz: the tx used a pair of 7193s in a pulsed
oscillator, push pull, with nice silver plated lines tuned by disc capacitors.
The grids were grounded through a forled structure that would have been a about
a quarter wavelength at about 3 times the oscillator frequency. Incidentally,
the 7193 is basically a 6J5 with anode and grid brought out through top caps.
Anyway, these things had a tuned cathode line, a tuned anode line, and a tuned
line coupling to the antenna. The cathode line had to be tuned right for the
whole thing to oscillate; from memory, it had to be lower i.e. the discs much
closer together.
With crystal control on 2, rather than self excited oscillators, they weren't
much use for amateur work. They would jam the high band VHF TV, but they were
best used for parts for 2m PA stages with 829 or 5894 tubes.
73
Peter G3RZP
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