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[Amps] FW: Ideal bandswitch brand for 3 kW out am?

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Subject: [Amps] FW: Ideal bandswitch brand for 3 kW out am?
From: "Larry Carman" <>
Date: Fri, 30 Jun 2006 13:00:37 -0500
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   The plasma gens I've dealt with were 13.56 MHz. They had a C1 and it was
made as you described for c2 for the  27MHz gen. A few years ago I had build
a 3cx3000a7 amp but didn't use the spark gap safety. It did arc once blowing
the ceramic fastener into a million pieces which held the HV choke in place.
Seems that the screws holding the ceramic HV insulator and HV choke were at
the right separation to serve as a spark gap to save my 3cx3000 tube from
total annihilation.

Larry N5BIP

-----Original Message-----
From: [] On
Behalf Of Mark Hill
Sent: Friday, June 30, 2006 12:27 PM
To: Amps Reflector
Subject: Re: [Amps] Ideal bandswitch brand for 3 kW out am?


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!



At 16:51 30/06/2006, Larry Carman wrote:
>Concerning the calibrated spark gap: Is this consistent to what I've seen
>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
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Dipoles resonant on 1942 / 3720 / 7085 kHz
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E arth

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