Replacing cables, etc.

[K7LXC at aol.com]

In a message dated 96-04-14 00:59:55 EDT, you write:

>This is the third crank up I have owned and it doesn't take a rocket
>scientist to maintain them.

Hiya, George --

    Thanks for your comments.  Yes, you are correct about rocket science.
 Yes, a two or three section, non-motorized crankup is pretty straightforward
to re-cable.  My comments had more to do with motorized versions since they
are much more complicated mechanically.  Were any of the crankups that you
re-cabled motorized?

>Send a crank up back to the factory?  YOU have got to be kidding. 

     George, that was my point.  The statement made by the tower manufacturer
is pretty impractical if you have to either have a professional/factory tech
do it or send it back to the factory.

     I would say that you are probably a little more clever and mechanically
inclined than the average amateurs I described in my post.  I still wouldn't
trust most of them to do it correctly.

73,  Steve   K7LXC


>From Marijan Miletic <s56a at s55tcp.ampr.org>  Sun Apr 14 21:51:38 1996
From: Marijan Miletic <s56a at s55tcp.ampr.org> (Marijan Miletic)
Date: Sun, 14 Apr 96 16:51:38 EDT
Subject: Perpetual motion
Message-ID: <16322 at s55tcp.ampr.org>

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.

>1.) You say the peak tank voltage can NEVER exceed the supply voltage,
>and so arcs can not come from underloading the tank.

Unloaded tank easily reaches 3kV from DC HV plus 100V peak from a driver
giving 100W to 50 Ohms in-phase cathodes in grounded grid configuration.

Part of the over-drive power can ONLY be consumed in the high impedanse
very selective output tank and so the voltage overshoots for another 20%!

Under above conditions, SB-220 tuning capacitor tested for 3.5kV may arc!

I am still curious about the tetrode circuit details where 8 x HV occured!?

>2.) You now seem to support the "weird science" that an intermittent
>parasitic can cause peak voltage that greatly exceeds the supply voltage
>and thus create an arc.

I only said that VHF oscilations should be given "due" consideration
meaning protection of the clean RF environment from unwanted emissions!

73 de Mario, S56A, N1YU.

P.S.  I only melted OUT coax connector during an ANT short test!