[R-390] Fw: R-390A L-601 swing choke question

[Jim Whartenby]

Larry, thanks for the reply.
Two of the three chokes in the R-390A have a DC resistance of 137 ohms maximum (L601 & L602),  the third has a DC resistance of 113 ohms maximum (L603).  The DC resistance of the windings are specified in the drawings found in Nick England's site.  At 200 mA L601 will drop about 25 volts. I don't know the current split through the other two inductors but I would guess 50 mA for the Audio and 150 mA for the RF & IF modules so another 20 volts for the RF & IF modules and 5 volts for the AF module.
It seems that the 26Z5 rectifiers are operated above their spec limit.  The voltage drop across the rectifier is some 30 volts at 100mA per the graph for the choke filter.  The graph has a 120 mA current limit so I guess the rectifiers don't last all that long.  So all of this raises questions that are not addressed in any of the R-390A documents that I have seen on the web including the Pearls of Wisdom.
Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy 

    On Sunday, June 29, 2025 at 02:47:59 PM CDT, Larry Haney <larry41gm2 at gmail.com> wrote:   

 Hi Jim, I forgot to  include that I haven't seen any criteria anywhere
about the ESR of the swing choke.  I'm not sure that at 60 cycles, it
is that important.  It may be,  but I haven't seen it.

Regards, Larry

On Sun, Jun 29, 2025 at 12:03 PM Larry Haney <larry41gm2 at gmail.com> wrote:
>
> Hi Jim,  Sorry for the delay on this post.  You are right about the
> different methods to satisfy the spec, the 390/urr does it by
> regulating the B+ and thereby the screen voltages on sensitive tubes.
> The 390A/URR does it by only regulating the screen voltages (the +150
> supply).  The plate voltage in most of the circuits is not critical
> for frequency stability.  I used my variac to change the input volts
> from 105 to 125 vac with no frequency drift.
>
> Regards. Larry
>
>
> On Fri, Jun 20, 2025 at 11:54 AM Jim Whartenby via R-390
> <r-390 at mailman.qth.net> wrote:
> >
> > Has anyone measured B+ current and voltage in the R-390A/URR as the function switch is set to various positions?  I'm curious as to what trade offs were made in the power supply during the cost reduction program.  The differences between the two power supplies are substantial but the specifications with respect to line voltage specifications are quite similar, if not exactly the same.
> > The R-390/URR regulated power supply holds B+ variation to less then one volt for a line voltage variation of some 15%.  The R-390A/URR seems to have a much greater variation in B+ for the same line voltage variation but it still meets the same spec.  The papers on the reflector that look into the power supply seem to ignore the ESR in the inductors used in the R-390A/URR.
> > Does anyone have any data to share?Regards,Jim
> > Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy
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