The Henry 8K Ultra uses solenoid contactors to select fixed caps in lieu of
a bandswitch. The inductor is a rotary and a small vacuum cap is used for
fine tuning, both motor driven with 10 turn pots or presets.
Carl
KM1H
----- Original Message -----
From: "Fuqua, Bill L" <wlfuqu00@uky.edu>
To: "Al Kozakiewicz" <akozak@hourglass.com>; "MU 4CX250B"
<4cx250b@miamioh.edu>
Cc: <amps@contesting.com>
Sent: Sunday, January 19, 2014 12:05 PM
Subject: Re: [Amps] Building an Amp 101
Most relays are not constructed of materials suitable for RF. Plastic
rather than ceramic is an example. They use a leaf spring material that
can handle current just fine at 60HZ or DC but it has a higher resistance
than copper. And since the current doesn't flow thru the entire cross
section, only on the few microns of skin depth the RF resistance is much
higher. To get the gap needed you would need open frame relays, which take
up a lot of space. I have had one surplus relay bandswitched amplifier
which used the open frame relays that used to be used as ladder line
antennas switching relays. But it was a very large box with a pair of 813s
in it.
73
Bill wa4lav
________________________________________
From: Amps [amps-bounces@contesting.com] on behalf of Al Kozakiewicz
[akozak@hourglass.com]
Sent: Sunday, January 19, 2014 10:43 AM
To: MU 4CX250B
Cc: amps@contesting.com
Subject: Re: [Amps] Building an Amp 101
To make it clear, I've never tried this so I'm not speaking from personal
experience.
But it seems logical to me that if a vacuum relay is required for the
voltages and duty involved, then a bandswitch is out of the question as
well, isn't it? My thought is that, putting aside questions around
stray-L that might arise from the insertion of a relay, it's easier to
find a relay with sufficient contact spacing than it is to find a
bandswitch with a large enough diameter to maintain the same spacing
between contact elements.
I guess these sorts of problems is why it's called engineering and not
science!
Al
AB2ZY
-----Original Message-----
From: MU 4CX250B [mailto:4cx250b@miamioh.edu]
Sent: Sunday, January 19, 2014 9:32 AM
To: Al Kozakiewicz
Cc: amps@contesting.com
Subject: Re: [Amps] Building an Amp 101
Relays are certainly a possibility, Al, but for a nine band amplifier
things get a bit complicated. My latest project ( 90% completed) is a
duo - band 80m/160m amplifier with a pi- L tank circuit, and for that I am
using two DPDT vacuum relays, each of which cost over $100.
Scaling that up to a nine band amplifier doesn't seem very practical or
cost-effective.
73,
Jim w8zr
Sent from my iPhone
On Jan 18, 2014, at 8:52 AM, Al Kozakiewicz <akozak@hourglass.com> wrote:
Why not use relays appropriate for the switching duty? Then the
bandswitch can be just about anything or even remotely controlled. Plus
you can locate the switch where it's convenient to operate instead of
being constrained by the necessity to place it close to the RF
components.
Al
AB2ZY
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