[AMPS] explain this one

[Tom Rauch]

> 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.

Mario did not try all phase angles or even measure at full drive, he 
did not want to ruin his PA.

No one on this reflector is dumb enough to think the switch in the 
SB-220 will handle 5 kV or more, when the tuning cap breaks down 
at ~3.5 kV. If the switch did break down at 5 kV plus, it could 
NEVER arc. The tuning cap would always arc first, or the tubes or 
some other component would arc first. 

What Measures was claiming, and what Mario initially thought, 
was that peak voltage could never exceed supply voltage. 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.

Let me add one more common sense thought.

Rich claims parasitics can arc the band switches and tuning caps, 
yet he claims or would have his "customers" think desired RF can 
not. If the peak anode voltage can not exceed the supply voltage as 
Rich claims, then how does it do that with his parasitics?

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. If he doesn't have the only cure 
for every problem, his stuff has no special value.


73, Tom W8JI
w8ji@contesting.com

--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm