>
>> At 06:53 AM 8/1/99 -0400, you wrote:
>> >
>> >> If the tank is resonated with too-light loading, the 'loaded' Q of the
>> >> circuit will be much higher and so will the voltage. This can happen
>> >> due to an inexperienced operator or antenna switching mistake, etc. I
>> >> think the bandswitch doesn't have a great enough margin of safety.
>> >
>> >You are correct Vic.
>> >
>> >The voltage will soar to whatever value necessary to until
>> >something absorbs the power.
>> >
>> >It is virtually impossible to build a tank that will withstand voltages
>> >with no load at full drive.
>> >
>> >One of the demonstrations I used to do was with a MRF-150 FET
>> >running at 12 volts, driving a tank with a loaded Q of ten. When the the
>> >load is removed the tank voltage goes to over 100 volts on peaks.
>>
>> I'm inclined to agree with this, based on my own experience, but how does
>> this square with S56A's empirical data from an SB-220? Mario's no dummy,
>> technically, so I have to wonder why he wasn't seeing even 2 x the anode
>> voltage.
? Because Mario was measuring the potential on the Tune-C, not the
potential at the anode.
>
>Mario did not try all phase angles or even measure at full drive, he
>did not want to ruin his PA.
>
? Quoting Mario:
">>I have facilities to measure PA stages, and an actual SB-220.
>>With the amplifier in the SSB position on 7 MHz at 1100 watts output I
>>measured 2.4 kV peak on the tuning cap. When I mistuned the amp by fully
>>meshing the loading cap and adjusting the tuning cap for maximum voltage
>>I measured 3.7 kV peak. The supply voltage was ~ 3kV when mistuned.
-- When you make stuff up to support your case, Tom, you only undermine
it. .
>No one on this reflector is dumb enough to think the switch in the
>SB-220 will handle 5 kV or more,
? Anyone with a breakdown tester can find out. 5 min/. ago I checked a
SB-220 bandswitch, and it starts to show some leakage at 5kV.
> when the tuning cap breaks down
>at ~3.5 kV.
? The Tune-C in my SB-220 breaks down at a bit under 4kV. .
> If the switch did break down at 5 kV plus, it could NEVER arc.
? provided that there was no dust in the air and the air wasn't extra
humid, like it is today. .
> The tuning cap would always arc first, or the tubes or
>some other component would arc first.
? My Tune-C has always arced first in my SB-220.
>
>What Measures was claiming, and what Mario initially thought,
>was that peak voltage could never exceed supply voltage.
? I did not claim such a thing. My postition was that your claim of
tank voltage soaring up, up and away to more than 9000v was imaginative.
> Mario's initial comments to me was that exceeding the supply voltage with
>peak tank voltage would amount to "perpetual motion". Once Mario
>went well beyond proving his own initial view wrong, he quit. It was
>obvious Rich's claims and Mario's initial thought that dc anode
>voltage limits peak tank voltage is wrong.
? You made the claim and put my name to it, Mr. Rauch.
>
>Let me add one more common sense thought.
>
>Rich claims parasitics can arc the band switches and tuning caps,
? sometimes.
>yet he claims or would have his "customers" think desired RF can not.
? I previously discussed how ordinary HF can produce tank arcs. For
instance, I know that when the antenna tuning capacitor arcs in my remote
160m tuner, it sends a glitch back to the amplifier that produces a tank
arc -- and it's time to clean out insect feculence again. . . Spilt
coffee can also produce tank arcs.
> If the peak anode voltage can not exceed the supply voltage as
>Rich claims, then how does it do that with his parasitics?
>
? Because VHF energy uniquely can not pass through a conventional HF
tank, it has no place to safely dissipate, and therefore runs amok. .
>Rich has to have it his way, because it helps sell parts and kits.
>Just like the "high quality expensive diodes" that he pays extra for
>but won't name the manufacturer.
? To find out, I would have to walk out to the breezeway. . How about
naming some good manufacturers and some not so good manufacturers, in
your opinion, before I take the walk, Tom.
>If he doesn't have the only cure
>for every problem, his stuff has no special value.
>
? My VHF suppressors exhibited 40% less VHF Q than conventional VHF
suppressors at 100MHz in Wes' suppressor tests. . Granted, 40% isn't
much. However, is higher Q more desirable in a dampening device, Mr.
Rauch?
>
- Cheers, Tom
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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