|[AMRadio] K4KYV monitor scope|
k4kyv at hotmail.com
Thu Mar 31 20:19:23 EST 2005
>If you are around, some time ago there was a discussion where you described
>what you did to your heath kit monitor scope to reduce the hum on the
I would have to dig up the documentation, but relying on my memory, I recall
beefing up the HV filtering, rerouting the filament circuitry and replacing
the magnetic shield on the scope tube.
As I recall, I substituted a separate filament line for the original design
that depended on the chassis for one side of the circuit.
The piece of tin wrapped around the neck of the tube is worthless is a
magnetic shield. I had an old military RTTY monitor that used a similar
shaped scope tube, and cannibalised the special black anodised magnetic
shield and managed to shoehorn it in place by relocating some of the
original scope components.
I got rid of most of the hum that shows up on the vertical trace, and the
additional filtering got rid of the hum that modulated the brightness of the
I also modified it to add some astigmatism control, which results in a
sharper, better focused and better defined image.
The original designers could have done a much better job. The manual even
mentions the problem; they pass it off as "insignificent" in a scope that is
"only" designed to monitor modulation.
Since I use mine only on AM, I pulled out the tube from the two-tone
generator and vertical amplifier. That lightens the load on the
failure-prone power transformer. I excite the vertical deflection plates
directly with rf.
Instead of running the rf feedline through the scope, I use a remote
toroidal pickup link to feed the scope some distance away from the rf
feedline. I had to locate it on the transmitter side of the antenna relay;
otherwise the pickup link was inducing an intolerable level of noise from
the scope into the receiver.
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