[Milsurplus] 2019: A TCS Oddity

[David Stinson]

Been working on a long article about reviving TCS
receivers.  Found a nice-looking, unmolested TCS-6
at the HamComm 'fest in Plano last June, so put it
on the bench to resuscitate.  Doing the job and
taking notes will prevent my either forgetting
steps or trusting in memory, which can lead to
some dumb writing I'd have to correct.

So did the Clean-Lube-DeOxIt ritual and replaced
the bad caps in the main chassis, then measured
the B+ busses, which looked OK.  Haven't pulled
the modules for their "transplant surgery" yet.
Decided to see if the thing could breath.  Brought
the B+ busses (pins 2 and 3) up slowly to 200V
sans filaments and watched the current for a half
hour- all seemed well, so powered the filaments.
The audio and other stages seemed to be working,
but the set was deaf.  Could barely hear a strong
broadcast station at 1500 KC.   Touched the
antenna, through a capacitor, to the C206 at the
RF Amp's grid.  The radio took a deep breath and
started bellowing accordion Mexican music.  The
alignment had received "The Golden Diddle-Stick,"
but that's "no hill for a stepper," as my father
the DI would say.  

First thought was that the Antenna section of the
band switch had a broken contact wiper- a
too-common and almost-always fatal condition.  You
ain't seen nasty until you've tried to change a
TCS band switch.  But very careful examination
with a strong light showed it intact.  A lot of
head-scratching and poking around, then I put the
Ohmmeter on the Antenna coil primary switch.  It
should read near-short to ground, but it showed
open.  All three of them.  Grabbed a strong
flashlight and looked down the inside of the
Antenna coil forms.  On all three coils, the tiny
pigtail of wire that goes through the ceramic form
to the Primary input side was melted open.
Someone, for some crazy reason, put voltage on the
Antenna connector and than racked the band-switch,
burning-open all the Antenna coil primaries.  This
is going to be bear to fix.

In the mean time, I connected a 30 pFd capacitor
from the Antenna lead to the Antenna coil
Secondary switching contact on the end of C206 and
this has got the radio playing until I can fix
these coils.  We'll probably never know how it
happened, but it would be an interesting story.

GL OM ES 73 DE Dave AB5S