[AMRadio] Broadcast transmitter rescue


Dudley kdud1 at hughes.net
Sat Feb 14 17:13:29 EST 2009


Hello Al, alot of info on the 20V's @ Collins 20v group @ yahoo.com, if you 
need more 20v info contact me @ kdud1 at hughes.net, Dudley Parkin/W5DUD
----- Original Message ----- 
From: "D. Chester" <k4kyv at charter.net>
To: <amradio at mailman.qth.net>
Sent: Saturday, February 14, 2009 2:09 PM
Subject: Re: [AMRadio] Broadcast transmitter rescue


>>> So my question to the group. Who is the Collins 20v-2 guru and how much
>>> will
>>> be involved to move it from 610khz to 1885khz.
>>>
>>> 73, Al  K3TKJ
>
> Why be content to operate on just ONE frequency?
>
> It is very easy to convert those xtal oscillator stages to function as
> buffer stages for an external VFO, and to make rf stages the rig tuneable
> across the band so that the rig will function with VFO or multiple xtals.
>
> If you have a VFO with low impedance output, and capable of at least 0.25
> watts, the best solution is to ground the grid of the xtal oscillator 
> stage,
> disconnect any feedback circuitry going to the cathode, add an rf choke 
> from
> cathode to ground if necessary, and inject the rf signal from the VFO
> directly to the cathode through a coupling capacitor.  That is what I do
> with my Gates BC1-T and homebrew HF-300 transmitter.  With the other
> homebrew rig presently tuned to 40m, I inject the VFO signal directly to 
> the
> control grid of the 6AG7 1st buffer/amplifier stage.
>
> I converted my BC1-T to external VFO, which is a modified T-368 m.o. unit,
> and it will tune from 1800 to 2000 with all the transmitter tuned circuits
> accessible from the front panel, and the neutralisation holds perfectly 
> from
> one end of the band to the other without readjustment.
>
> One of the faults I find with much of the present-day AM operation on 160
> and 75 is the same as with the SSB dead-air groups: insisting on operating
> on one and only one frequency, with daily 8 to 10 member roundtables 
> amidst
> QRM from adjacent QSO's less than 5 kHz away in both directions, while 
> there
> may be tens of kHz of vacant space in other parts of the band.  We need to
> spread out a little and maintain more widespread AM presence throughout 
> the
> bands, with reasonable sized QSO's and roundtable groups.
>
> Don k4kyv
>
>
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