[Boatanchors] Johnson Ranger R35

[Bill Cromwell]

Hi Rob,

My Ranger also has the resistor inside the VFO shield replaced with a 
higher power resistor and still inside the shield. When I first saw the 
recommendation to move it outside I wondered about it's value as an 
"oven" and then later I read that was the case. I'm very reluctant to 
make changes. Sometimes those engineers didn't have the materials and 
techniques available to us and a modification might actually make an 
improvement. Another way that a modification could be beneficial is when 
parts are not available (or too expensive if they are available).

73,

Bill  KU8H


On 02/23/2014 12:03 PM, WQ9E at btsnetworks.net wrote:
> I tend to agree with Rob on power supply modification-well actually modifications in general.  It seems every popular piece of gear has multiple modifications published and unless:
>
> 1. You know that the person developing it really understood and has foreseen all of the direct and indirect effects of the mod AND
> 2. The developer understood  and applied good engineering and design practices AND
> 3. Has exactly the same wants and needs as you do from the modification change
>
> then you are making a change that may not have a good outcome.
>
> I will leave it to someone else who is more interested in looking at the specifics of this particular modification but two things jump out just from a superficial read:
>
> 1. replacing the rectifiers with SS and then reducing the load current without being sure that the filter is still acting as a choke rather than capacitor input runs the risk of having much higher peak charging current which DOES make the already hot transformer hotter.  You will find that many transformers do have published specs as to allowable current draw with choke and capacitor input supplies, the allowable current draw is lower for the capacitor input configuration.  By itself the SS rectifier allows somewhat higher peak repetitive current because of its lower forward resistance.  The two factors combined are a bad idea unless the transformer has the necessary thermal reserve and even then resistance should be used to control for higher voltage.
>
> 2. I have not run tests on either my Ranger or Ranger 2 but I was curious about the Valiant VFO when I restored my second one around 10 years ago and I ran some simple tests with the VR current limiting resistor both inside and outside the VFO case.  The Valiant was more stable with the resistor inside than out and approached stability much more quickly.  With that constant source of heat inside, the VFO is heating up fairly quickly and more importantly it becomes less influenced by the heat cycling that occurs between transmit and standby conditions.  This may vary between different models, ambient environments, and specific component behavior within your VFO so as they say your mileage may vary.
>
> One can argue that the original design engineers weren't perfect and everyone makes mistakes but without strong evidence to the contrary I am going to go with the professional engineer.  I have at least one of pretty much every one of these built-in VFO Johnson rigs (Navigator, Ranger 1 and 2, Valiant 1 and 2, Pacemaker, and 500) and all are running happily with a higher wattage same value resistor inside the VFO enclosure.  They are never going to approach the stability of a DDS rig with a TCXO standard but the Ranger I use to drive my Desk KW is pretty typical and after 10 minutes warm-up I will correct the VFO slightly twice while I am operating as net control of an AM net that runs about 60 to 90 minutes.  Those are very slight corrections within a few hundred hertz and really don't matter for AM but it does provide a zero beat standard for other net members.  Corrections are made based upon a stable receiver (typically either a Telefunken E-1501 or SRT CR-91 which are bo
>   th highly stable, the CR-91 tunes in 1 hertz increments).
>
> Rodger WQ9E
>
>