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

[Larry Haney]

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
> > ______________________________________________________________
> > R-390 mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/r-390
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:R-390 at mailman.qth.net
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html