[R-390] R-390 Question

[David C. Hallam]

I have uncovered some circuit resistance measurements that don't correspond
to those given in manual and don't understand what might be the cause.  They
are in the filament circuit of the R-390 (non A)IF module.

The background is that there are 4 series filament strings for the tubes in
the IF module. They are as follows (a) V501 through V504 (each 6.3V) with
V501 at the ground end and V504 at the hot end; (b) V507 and V510 (each
12.6) with V510 at the ground end and V507 at the hot end through a 22 ohm
resistor; (c) V505 (6.3V), V506 (6.3V) and V511 (12.6V) with V511 at the
ground end and V505 at the hot end; V506 (6.3V), V701 (6.3), and the ballast
tube.  Those of you who have a R-390 schematic can refer to it to see what I
mean.

Voltage measurements taken at the tube sockets give values consistent with
the values given in the manual.

Resistance measurements taken at the same points give values sufficiently
close to manual values to be considered within component tolerance and
ability to read values less than 10 ohms EXCEPT for reading taken at the pin
of V504 and V505 (pin 4) that connect to the hot side of the filament
transformer.  Here the manual calls out 7 ohm and I am reading 0.2 ohm on my
DVM indicating an almost direct short.  To me this indicates a shorted
bypass capacitor.  Checking with my capacitance meter I don't find any
shorted bypass capacitors.  If the resistance is really 0.2 ohm, why aren't
I blowing fuses?

Any ideas or suggestions?

David
KC2JD