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


Geoff/W5OMR ars.w5omr at gmail.com
Wed Aug 8 14:09:48 EDT 2007


ne1s wrote:
> Geoff/W5OMR writes:
>> I'm soliciting ideas on grid inputs on a 4-125.
>> Thoughts?
>
> 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.
> GL,

Thanks, Larry...

This has been added to my folder of notes on construction.

--
73



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