[ARC5] Collins xfmr ratings

[Dennis Monticelli]

Dennis,

I respectively disagree that the same amount of power will be wasted.  That
is only true if no current is tapped off the string.  As the bleed current
flows down the resistor toward the VR tubes it takes useful shunt paths.
 For example the current for the osc is fed from current that would
otherwise be "wasted" in the VR tubes.  The current for the osc would
otherwise have had to come from yet another current path off the HV rail.

Dennis AE6C


On Fri, Aug 15, 2014 at 11:42 PM, Dennis DuValll <w7qho at aol.com> wrote:

> For the same total current and voltage values the same amount of power
> will be dissipated (wasted) in either a bleeder resistor or a string of VR
> tubes. Elementary power supply parameters and calculations are covered in
> the ARRL (and other) handbooks all the way back into the 1930s and probably
> earlier.
>
> I (crit) = DC voltage/L (choke inductance in henrys)
>
> Dennis D.  W7QHO
> Glendale, CA
>
> ************
>
> On Aug 15, 2014, at 10:22 AM, Dennis Monticelli <
> dennis.monticelli at gmail.com> wrote:
>
> I like choke input power supplies, but the critical inductance issue is a
> serious one for CW usage as Ken noted.  You either have to find a high
> value "swinging" choke or put up with wasting a lot of power in the form of
> bleeder heat.  I would like to share a workaround.
>
> In lieu of a high wattage bleeder, use a VR tube stack to maintain the
> requisite minimum load current.  Then pick off the appropriate voltage
> points for feeding the Osc and PA screens for the ARC-5.  This is what I do
> in my setup so my bleeders are not power hungry and less power gets wasted.
> You only need 150mA total (not 200mA) at 500V for this scheme to power an
> ARC-5.  Your keying note will improve as well.  A fringe benefit is the
> attractive glow of the VR tubes.
>
>
>