[AMRadio] Safe Metering for Blind Operators

Mike Duke, K5XU k5xu at jam.rr.com
Mon Jan 3 13:43:25 EST 2005

K4KYV wrote:

"In my homebrew rigs with triode finals, I place the plate meters between 
common point for grid leak/bias supply and PA filament, and ground.  The
Gates BC1-T does it the same way, with no HV on the meter."

I've been reading the discussion of safe metering with great interest, as 
perhaps explained by my subject line and signature.

I would love to find a good plate modulated transmitter in the power class 
of a DX100 or Valiant, in which the plate meter would not have the full 
plate voltage across its terminals. Is anyone aware of a commercial or 
surplus transmitter with this design feature?

I could easily and safely tune such a transmitter by connecting an audible 
meter-reading device across the meter terminals. I still have the circuit 
which I used successfully with a DX60, and very cautiously with a Viking 
Ranger from 1969 - 1974. I learned quickly that the ranger meter is at full 
plate potential. The good news is that I lived to tell about the experience.

I also recall reading somewhere of using a voltage divider in order to 
obtain a safe potential level in the external audible reader. If anyone on 
this list has ever encountered a transmitter which was modified in this way, 
I'd like to know more about how it was done, since I'd love to put a Ranger 
on the air in order to re-create my first station.

The point can be made that the easiest route is to put a rice box and linear 
combination on the air. Yes, that would be the easiest thing for anyone, 
but, not nearly as much fun!

Mike Duke, K5XU
American Council of Blind Radio Amateurs

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