>
>Rich,
>
>If the tank is resonated with too-light loading, the 'loaded' Q of the
>circuit
>will be much higher and so will the voltage.
During the grate parasitics debate, Tom Rauch claimed the following"
---------
From: W8JITom@aol.com
Newsgroups: rec.radio.amateur.homebrew
Subject: Re: Good source for amplifier tips
To: <amps@contesting.com>
Date: 8 Nov 1996 05:45:01 GMT
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Hi Rich,
........
>> The RF voltage in a tank can soar to
>> several times the HV supply when the tank is underloaded. Surely you know
>> that. ...snip...
-------------------
Mr. Rauch's statement presumably means tank voltage would or could soar
to more than three times the HV supply. In a SB-220, the anode supply is
c. 3kV. Thus, the tank potential should reach more than 9000v during
mistuning, according to Rauch.
// Marijan Miletic, S56A measured worst-case tank potential in a SB-220
--------------------
>In a message dated 96-04-14 12:54:03 EDT, Mario wrote:
>Subj: Perpetual motion
To: <amps@contesting.com>
>Date: 96-04-14 12:54:03 EDT
>From: s56a@s55tcp.ampr.org (Marijan Miletic)
>To: cq-contest@tgv.com
>CC: W8JITom@aol.com
>
>> Tom, W8JI refrained from further discussion of exotic QRO topics but in
>> a private email convinced me to repeat his tests on my good, old SB-220.
>
>> I made simple 10/1000pF = 1:100 divider from tune cap, used 1N4148 diode
>> for a peak rectifier and achieved almost the same results as he did!
>>I was initially suspecting that some measurement error was involved...
>
>>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.
----------------------
> 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.
>
? The bandswitch in a SB-220 appears to have a margin of safety of c.
2000v. No amount of mistuning in my SB-220 will make the Tune-C or
bandswitch arc.
- cheers, Vic
..................................................
>Rich Measures wrote:
>
>> ? The bandswitches used in the AL-80, SB-220 and SB-1000 are similar and
>> have a measured breakdown potential of over 5500v. The actual tank piv
>> in these amplifiers is around 3000v when the tank is tuned to resonance
>> and loaded for max. P out. When the tank is tuned out of resonance, less
>> peak V appears across the bandswitch and Tune C. // Photographs of
>> arced AL-80 and AL-82 bandswitches may be seen on my Web site.
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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