[Boatanchors] Johnson Ranger R35

[Rob Atkinson]

You still have to figure out what's going on with the tap on the R35
going to the screen grid of the 6AQ5.  It's more than just a 20K
resistor to B- or ground (can't remember which now).

Solid stating the power supply:  this is one of those questions for
which very ham has an opinion.  mine is, "it depends."   I try to use
the vacuum rectifiers whenever possible.  One disadvantage is that you
can't bring up something with a variac if it has a vacuum rectifier
the way you can with solid state sticks.  So solid state rectifiers
are useful to have for that purpose.  They are also desirable if the
vacuum rectifier is placed close, as in almost up against, the
transformer.  I've seen that done.  The usual reason for solid stating
is to relieve the supply transformer from supplying the 5 v. filament
but I think there's more damage from heat due to the super hot vacuum
rectifier up against the transformer.  However, if none of that is a
problem, I tend to leave it alone.  The gear runs at its intended B+
and the gradual conduction of the vacuum rectifier on power up
provides a soft start.   If you want to run with solid state diodes,
put a sufficient power resistor in series to drop the voltage to its
vacuum rectifier level and consider adding a thermistor somewhere in
series with the h.v. primary transmit key line, or simply have it in
series with the on/off switch.  put it where its heat can dissipate.
Thermistors run pretty hot.

73

Rob
K5UJ




On Sat, Feb 22, 2014 at 9:35 PM,  <hwhall at compuserve.com> wrote:
>   Thanks for the comments, all!
>
> I re-read what the Handbooks (plural) had to say earlier this evening. Besides draining off the filter caps when power is turned off, there were two other reasons I saw for pulling all that power down a big bleeder.
>
> (1) To ensure that a necessary amount of current was drawn from the supply to make the filter choke inductance always met the critical inductance, a condition which keeps a choke-input filter section from acting more like a capacitor-input filter (which lets the output voltage with light loading to float closer to the peak rectifier output voltage than a well designed choke-input filter will do).
>
> (2) The above also contributed to reducing the peak current through the rectifier tube(s) so that more average current could be drawn for a given tube type without exceeding its max current ratings.
>
> Since the pubished modification solid-stated the rectifiers, the advantage of (2) isn't an issue anymore. As long as the other stages (VFO, etc.) & components don't mind the extra max supply output voltage or the (probably larger) swings between key-up and key-down supply voltage, then the supply regulation of (1) becomes no issue. If so, then the removal of hefty bleeder loading isn't obviously an example of a mod that fails to understand the original designer's wisdom.
>
> It's good to learn something new or relearn something every day. :-)
> ?
>
>  Wayne
> WB4OGM