A spark gap is much like a bi-directional transient-suppressor.
There is no reason to use spherical conductors. I make the gap screw-
adjustable so that it can be calibrated with a high-potential
tester. Also, a sturdy 50 -500 ohm globar type resistor seems to
help snub things during a glitch. Setting the gap for about 2.2 x
the anode supply voltage seems about right. In most cases, this
procedure will protect the Tune-C.
On Jun 30, 2006, at 8:51 AM, 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
> 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
> the tune cap and bandswitch both? Would the load cap be protected
> to any
> extent? I'm full of questions today.....
> Larry N5BIP
> -----Original Message-----
> From: firstname.lastname@example.org [mailto:amps-
> email@example.com] On
> Behalf Of R L Measures
> Sent: Friday, June 30, 2006 6:16 AM
> To: Tom W8JI
> Cc: firstname.lastname@example.org
> Subject: Re: [Amps] Ideal bandswitch brand for 3 kW out am?
> On Jun 30, 2006, at 2:20 AM, Tom W8JI wrote:
>> We couldn't possibly know the ideal bandswitch anyway based
>> only on mode, frequency, and power.
>> There isn't enough information.
> Good point. As a rule of thumb, the bandswitch needs to have a
> comfortably higher BDV than that of the Tune-C, and the Tune-C needs
> to have a BDV slightly higher than the anode's DC supply. The idea
> here being that an arc at an air variable cap is no big deal, but an
> arc at a bandswitch is. Also, vacuum-variable caps do not tolerate
> arcs well, so they need to be protected by an external, calibrated
> spark gap.
> .. end
>> 73 Tom
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> R L MEASURES, AG6K. 805-386-3734
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