Larry,
I took the spark gap out of the Henry 27 MHz plasma generator that I
converted for 14 MHz mono band operation. Mechanically it was
configured to support 'calibration' by means of winding the tread in
and out through the side of the case. I wonder if this was a factory
adjust on test?!
Originally, the amp. had a Pi-L output network, comprising no 'C1'
(valve output capacitance only); variable 'L1' (shorted tun affair);
variable 'C2' (flapper in parallel with some fixed caps.); and fixed
'L2'. I kept the Pi-L arrangement (different values) for 14 MHz use.
As there was no band switch, and no discrete C1 to flash over, I
recall debating (with the relative dimensions involved) whether the
spark gap would go first or the top of the valve anode to the
case! In the end, I decided that the spark gap was superfluous. C2
occasionally flashes as I think its got a deposit on the plate, but
if I remember to turn it through 180 degrees it gets by.
I shan't describe the "resistor in parallel with a bit of inductance"
that makes up the anode lead for obvious reasons (think there's a
picture on my website if you're a student of such things).
Arc, spark, bang!
Regards.
Mark.
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At 16:51 30/06/2006, Larry Carman wrote:
>Concerning the calibrated spark gap: Is this consistent to what I've seen in
>the Henry Plasma Gens? On the 3cx3000a7 RF gens they incorporated two
>aluminum half spheres with a small air gap between them. One of the half
>spheres was connected to ground and the other to the tube anode. What would
>be the formula to calculate the gap between the two? I'm sure it's based on
>operation frequency, so this brings up another question. Would a spark gap
>protect components on 160 as well as 10 meters??? Also, would this protect
>the tune cap and bandswitch both? Would the load cap be protected to any
>extent? I'm full of questions today.....
>
>Larry N5BIP
*******************************************
Mark Hill - G4FPH
E-mail: g4fph@mjha.co.uk
Current web pages at: www.g4fph.net
Old web pages at: www.qsl.net/g4fph
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Dipoles resonant on 1942 / 3720 / 7085 kHz
Three element wire beam coming soon on 14180 kHz!
----------------------------------------------------------------------
Remember - SIDE for HV safety:
S witch off
I solate
D ump
E arth
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