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


John E. Coleman (ARS WA5BXO) wa5bxo2005 at pctechref.com
Wed Nov 16 17:14:55 EST 2005


Now that I think more about this a small box with a small power XFMR of
20-30 watts would do the job.  Of course you would need to re4ctifiy and
filter but you could choose full wave center tap, full wave bridge, voltage
doublers or quadrupler.  I found that adding a input capacitor to a choke
input supply raises the voltage output just about enough to double the power
or vise versa. Then you could just forget the HV in the Ranger, as for as
plate/screen supply is concerned.  Or if a guy was home brewing a modulator
of 20 watts or so, he might just use the PS from it.

John,
WA5BXO

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of John E. Coleman (ARS
WA5BXO)
Sent: Wednesday, November 16, 2005 3:32 PM
To: 'Discussion of AM Radio'
Subject: RE: RE: [AMRadio] Re: Need list of good AM radios to start
lookingfor.

	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 VFO
(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
WD5JKO

-----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...


    Cheers

John  KB6SCO

   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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