[AMRadio] Re: I've decided (retry)

ne1s ne1s at neandertech.com
Wed Aug 8 12:31:26 EDT 2007

Geoff/W5OMR writes:
> I'm soliciting ideas on grid inputs on a 4-125. 
> Thoughts? 

Many ways to do this, Geoff, as I'm sure you know. 

What worked out well for me on the FR deck in the big PDM rig (pair of 
7527A's in parallel) was to load the grid with ~2500 ohms non-reactive (a 
bunch of non-X 7W resistors in series) and match it from a 50 ohm source 
with a T network - two series variable caps with a tapped/switched inductor 
from their junction to ground. This allows me to tune the grid circuit from 
160M - 10M, and the resistive loading is good for stability. Since to drive 
a class-C amplifier we LIKE harmonics there is no liability employing the T 
network. It takes about 25 - 30W on the low bands, more as the network 
becomes lossy at higher frequencies to get 30 mA grid current. (I use my 
TS-440S as the RF exciter, so no problem there). For a single 4-125 you will 
need less, of course. 


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