[ARC5] Fall Project: Navy ATD Transmitter, Part 2

[David Stinson]

Re:  Fall Project: Navy ATD Transmitter Part 2

Finally got back to the keyboard- let's see how
long before work drags me off by the hair again.
;-)

Once you have reworked all the grounds you can
find, it's time for switch cleaning, relay
burnishing and general lubrication.  For this, you
will need De-Ox-It and a "pen oiler" loaded with
good "Electric Motor" oil to reach into the tight
quarters of this transmitter and spot a few drops.
You can turn the front of the transmitter up and
leach a few drops of De-Ox-It into the front of
the toggle switches, working them a few times.
This will usually revive their contacts.  Gently
burnish all the relay contacts.  The large
contacts on the backs of the tuning units and
their mating contacts in the tuning unit sockets
are, I think, Silver plated, so abrasive should be
avoided.
https://photos.app.goo.gl/YT1rWOytwl7XBlKM2
These can be cleaned with brown kraft paper soaked
in De-Ox-It.  If a contact is particularly
stubborn you can use a soft-bristle tooth brush
with De-Ox-it to *gently* scrub the contact,
followed by the brown paper treatment.  The
contacts in the tuning units will need burnishing
as well and their mechanicals will need lube.

Most of the mechanicals needing lubrication are
fairly obvious.  There are a couple of unusual
places that need a few drops.  You'll need one of
those little LED flashlights to see well into
them.  One is the channel-changer gear box.  Open
the tube cover.  Assuming the rear cover is still
off the set, remove the voltage regulator tube.
This should give you several angles of access,
though cramped, to the gears in the box which you
can reach with the pin-oiler.

The next item I admit to "fudging" a bit.  The
channel-changer motor is held in some kind of
clamp:
https://photos.app.goo.gl/2RlsVZ28uzaP9Ynq1
Three wires - Forward, Reverse and 28V, connect
it.  The motor armature engages the gear box using
some kind of odd-looking contraption.  I am not a
"mechanical" person and I've found no documents on
exactly how this thing is put together.  I could
put a small paint drop, marking the clamp and the
motor so it would be re-positoned exactly as it
was, but I have no idea what will happen if I take
it apart "in the blind."  I tilted the
transmitter, used the oiler to leach oil down the
motor armature into the front bearing and left it
at that for now.  The only "saving grace" is the
very low duty cycle to which the motor will be
subjected.  So far, it turns without incident and
seems OK.
https://photos.app.goo.gl/EIAIJDEOWY5Y3Hrr1
But I intend- until I get some documentation on
how to remove it for service- to minimize the
cycles of the channel changer and save wear.

There is also this odd-ball rotating TR relay,
K103.
https://photos.app.goo.gl/ALzqMbGNVOxjdkom2
There is a terminal board mounted on the side of
this relay.  If you remove the three long screws
that mount the terminal board and the screw in the
REC terminal, then gently pry the panel up
slightly, you can use your flashlight and oiler to
get some lubrication to this rotating armature.

Time to start looking for parts that have "gone
off the reservation."   As I wrote in Part 1, it's
a priority to get the radio to play with the least
amount of parts changes necessary. Many of these
old warriors will play just fine with resistors
10% or even 15% out of tolerance.  If the part is
in a circuit where precise values count, the
circuit's functionality will tell us that.  

I start at one end of the rig and go to the other,
using an ohmeter to test each resistor in-circuit.
If an in-circuit resistor reads 10%+ higher than
its value, one end gets cut to mark it for
replacement.  Of course, the resistor might read
much lower because it's in parallel with other
things, but if it reads higher than our "bad"
line, it goes.  If one seems "odd," we can check
the schematic.
https://photos.app.goo.gl/FYPtazHWR453pOu72
One funny thing about the resistors in this rig:
In the other rigs I've done recently, especially
the TCS and BC-669, resistors with Orange (10K) or
Yellow (100K) multipliers were usually bad; black,
brown and red multipliers were usually OK (green
was 50-50).  In this rig, brown (100) and red
(1000) were the bulk of the "baddies" and the
orange-yellow multipliers were tolerable.  Go
figure that one...

Capacitor tests were also surprising.  I clipped
one wire on ten of the "postage stamp" caps and
tested them.  All of them tested good.  Tacked
them back in and decided if one was bad, circuit
operation would tell me.  I suppose this is due to
this transmitters NOS, never issued condition.
Under the tube deck in the rear, there are three
large oil-filled double caps.  The two dual .5 uFd
tested good.  The dual .1 uFd, C-107, leaked
badly.  This cap is rated at 600V, but it's across
the filament of the MO, V101 and the common of the
two caps goes to the tap on the MO tank, not
ground, so a smaller DC voltage rating will work.
I disconnected C107, leaving the "common" terminal
as a tie-point and mounted the replacement caps
there at the tube base.

There are two 25 mFd 50VDC electrolytics, C-102
(mic filter) and C-126 (audio driver cathode), one
mounted on each side of the transmitter.  They
were, of course, shot.  This is a good example of
"doing the least harm."  One could pull these out
and re-stuff them, but doing so would require
moving and possibly breaking several things.  It's
just not necessary.  A modern replacement for
these cans is about half the size of a pencil
eraser.  I removed the wire from the Positive
terminal and tacked the new cap to that wire and
the other end to the grounded Negative connection.
Here it is before adding some shrink-tubing to the
Positive connection:
https://photos.app.goo.gl/Bb6fYUhmZNEae37q2

Another "oddity:"  The hook-up wire used in this
rig is stubborn about taking solder.  You need to
either abrade a spot on this wire or "scrub" with
the iron while tinning this stuff.  A good hot
iron and quality solder helps.  No idea why this
stuff is so hard to tin.

Once we've replaced our baddies, it's time for
some testing.  
We'll cover that in Part 3, along with a simple,
non-destructive way to put the BCB tuning unit on
630 meters and simple ways to feed a 50-ohm,
non-reactive load on 160-80-40.

GL ES 73 OM DE Dave AB5S