[AMRadio] Re: Need list of good AM radios to start lookingfor.

peter markavage manualman at juno.com
Wed Nov 16 17:30:29 EST 2005

Although I haven't followed all the threads on this topic, if you want to
reduce the power output of the Ranger, why don't you just reduce the
screen voltage of the final. A simple circuit, using a few components,
with a small pot mounted directly behind the crystal opening and
accessible from the front, appeared in a past issue of ER. Allows
variable output control over a wide range. Why screw with dropping HV,
large resistors, jumpers, plugs, etc.
If this is not dropping the power" of the Ranger issue, just ignore it,
and I'll go back to sleep.

Pete, wa2cwa

On Wed, 16 Nov 2005 15:32:24 -0600 "John E. Coleman (ARS WA5BXO)"
<wa5bxo2005 at pctechref.com> writes:
>         You are correct of course Jim.  I would mount the resistor in 
> its
> own case and construct a cable so as to plug the modulator into the 
> new
> chassis with the resistor and bypass cap, and then the new chassis 
> would
> plug into the Ranger.
>         To conserve power and heat, another power supply with lower 
> voltage
> output or variable output would be better.  But some time you do 
> with what
> you have and if the 2000 ohm 50 watt resistor is handy and you have 
> an old
> scrap chassis well there you go.  I once needed a stiff bias supply 
> so I
> used a single diode and 400 uf filter right off the AC line.  Then I 
> placed
> a 100 watt lamp in series with a large variable 100 ohm 100 watt 
> resistor to
> ground.  Not a very efficient thing to do but it did hold the bias 
> steady on
> the 805s modulator.  This was long before I had access to the HV
> transistors, ETC.
> John, WA5BXO   
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Jim candela
> Sent: Wednesday, November 16, 2005 3:37 PM
> To: Discussion of AM Radio
> Subject: RE: RE: [AMRadio] Re: Need list of good AM radios to start
> lookingfor.
> John,
>     If you go this route with a series dropping resistor, think 
> about the
> heat and safety of the modification. On the Central Electronics 20a 
> (modified BC-458, arc-5), there is a similar resistor on the back of 
> the
> chassis that drops the B+ from about 300 to 105 volts (OC3?). The
> connections are bare, and the resistor gets so hot it will burn you 
> in a
> split second, and if the heat don't get you the B+ will! I been 
> burned and
> shocked several times. I keep saying that I'm going to make that 
> more safe,
> but I never do.
>  I cannot recall if the ranger has keyed HV B+ like a Viking II. If 
> it does,
> maybe you can use a relay to switch the LV B+ to the final and 
> modulator,
> and key the relay with the transmit switch. This way you won't have 
> to use a
> dropping resistor from the HV B+. Those folks that know Rangers out 
> there
> can jump in to clarify a yah or nah on this idea.
> Regards,
> Jim
> -----Original Message-----
> 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
> lookingfor.
> 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...

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