|[AMRadio] Re: Need list of good AM radios to start lookingfor.|
John E. Coleman (ARS WA5BXO)
wa5bxo2005 at pctechref.com
Wed Nov 16 16:22:26 EST 2005
If the supply voltage is 600 V and you normally run 120 ma at about 72 watts
input a 2500 OHM 50 watt resistor with a 20 uf bypass capacitor across it
should reduce the voltage to 300 V and current to 60 Ma input power to about
18 watts. Output should be about 10 watts. The bypass capacitor will
conserve your modulation power will allowing the modulator to look into the
same load as it did before.
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of John Lawson
Sent: Wednesday, November 16, 2005 3:22 PM
To: Discussion of AM Radio
Subject: RE: RE: [AMRadio] Re: Need list of good AM radios to start
On Wed, 16 Nov 2005, John E. Coleman (ARS WA5BXO) wrote:
> The best way is still to reduce the supply voltage at the
> plate/screen modulation point. A large resistor that has a bypass cap
> across it works well.
As has been wisely pointed out to me - in the case of the Ranger,
placing a suitable variable resistance in the plate line will accomplish
this handily, it seems - unless I'm missing something very obvious.
These wires are conveniently brought out to pins 2 and 6 on the rear
octal plug, with 6 being the line from the supply to the mod trans
secondary, and 2 being the 'start' of the secondary. The 'finish' goes to
pin 3, and the line to the final plate goes to pin 5. These are jumpered
in the mating plug.
I'd be inclined to reduce the voltage before the mod trans - thus
reducing the DC saturation a bit. But that's probably Nit #68 in the
grand scheme of things...
PS: I'm going to try this, perhaps this weekend if I can get a spare
hour of bench-time on it.
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