If you are going to put in a roller, my suggestion is to lay out the tank so
that should you later want to change from the roller and implement a
switched tank, then you physically can if needed.
The real mistake I made was not in using the roller, rather it was to tuck
the roller down in the corner so it's got a wall and floor on two sides, and
the other two caps on the other two sides. I literally boxed that thing in.
Fast forward to the present, where I want to move to a switched tank, but
doing so would involve moving one of the caps at a minimum. And in my case,
the move of the cap also involves relocating the associated stepper motor
and position sensor. I wish I had considered the outside chance that maybe
someday I would need to go to a switched tank...
One way to do this is to stack the caps vertically near the wall of the amp.
With the roller next to them and only free space above and on the other side
of the roller, you have options. In the event the roller works great, then
great! You are done. But if you run into some roller strangeness that you
just can't resolve as I did, then you would have the physical room to swap
out the roller for the switch and associated coil structures, without having
to rework the front panel as well.
Good luck!
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
-----Original Message-----
From: nemo zilch
Sent: Thursday, September 29, 2016 5:00 PM
To: amps@contesting.com
Subject: [Amps] Ameritron/MFJ ROLLER INDUCTOR for GS35b amp
Well, the replies are pretty close to 50/50 yea and nay. I plan to build a
sort of breadboard of the basic amp to test cooling, rf choke, fil choke
and tank, etc. So I think I'll chance it and invest in the roller inductor
and give it a try. If anything weird happens, then I'll go to a switch and
tapped inductor.
As for roller inductors in general not shorting out the unused turns, that
is not necessarily the case. I have a couple of large ones I bought at
Hamfests and both of them do short out the unused turns. All that is
necessary is to connect the end of the shaft which the rolling contact
slides on to one end of the coil via a rotary contact. Then connect
the the opposite end of the rotating coil via another rotary contact to the
plate circuit. Use the end of the coil which connects to the rolling
contact shaft to connect to the loading capacitor side. Pretty much
analogous to the tapped inductor/switch setup, perhaps more stray
inductance though.
My present HB amp uses a pair of 4-400's and I am using the roller
inductor/tuning capacitor from an old Johnson Thunderbolt amp and it works
fine all bands through 10M.
Thanks everyone for your replies, I value and appreciate them all.
Bob W4AOS
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