[AMRadio] Home brew AM Cathode modualtion


Clay Curtiss W7CE w7ce at curtiss.net
Mon Oct 4 00:35:25 EDT 2004


I appreciate all of the suggestions.  I'm not locked into a particular tube
configuration yet, but I have to admit there is something appealing about
running the 450TH.  It's probably my mental image of two of them lit up
behind a glass window in the front panel :)

Clay  W7CE

----- Original Message ----- 
From: "John Coleman, ARS WA5BXO" <wa5bxo at pctechref.com>
To: "'Discussion of AM Radio'" <amradio at mailman.qth.net>
Sent: Sunday, October 03, 2004 12:37 PM
Subject: RE: [AMRadio] Home brew AM Cathode modualtion


> The "Rice" neutralization circuit works better with a higher Q
> grid tank and, if possible, some input swamping or grid load resistor.
> The biggest trouble with the circuit is that the loading of the grid
> tank is not constant over the full RF cycle as a result the "Q" and
> balance is shifted somewhat over the period of the RF cycle.  Starting
> with a higher "Q" or C value is one way of minimizing this effect.
>
> The circuit does work because I used it as well and also with a 304TLs,
> back in the days of experimenting with the ultra modulation or balanced
> high level modulation circuits.  I eventually went to standard "Push
> Pull".
>
> John, WA5BXO
>
>
>
>
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Donald Chester
> Sent: Sunday, October 03, 2004 12:45 PM
> To: amradio at mailman.qth.net
> Subject: RE: [AMRadio] Home brew AM Cathode modualtion
>
>
> >The 450th is a big triode, so I don't think you can run it single ended
> pie
> >net output, you would need to do 2 250th tubes in push pull or
> something,
> >but the 450th would do the cathode modulator quite well.
>
>
> You could use a single-ended pi-network type output circuit, with a
> balanced
> grid tank coil.  That is knows as "Rice" neutralisation.  You don't get
> as
> perfect null as you can with a balanced plate tank cincuit or a pushpull
>
> arrangement, but it works well enough that it became the standard design
> of
> tube type broadcast transmitters starting in the late 50's.
>
> I used that circuit with the first high power rf final I ever built,
> using a
> 304-TL in the final, because I didn't have a large split stator tuning
> capacitor on hand.
>
> Don K4KYV
>
>
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