[ARC5] Fall Project: Navy ATD, Part 1

[David Stinson]

(A lot of this is obvious to you "old hands," 
but I'm writing it for someone who may not have
as much experience as you.  Thanks for your
patience.)

WARNING:
There is 1000V B+ inside the ATD Dynamotor and
Transmitter.
If you get a finger on this, it will likely kill
you.  
Slow down. Look twice. Think twice. Stay alive.

The Bendix ATD is an interesting WWII Aircraft
transmitter.  
https://photos.app.goo.gl/I4Bc2YOB7D1TebC33
Reported to be a competitor to the ART-13, it
couldn't
match the capabilities of that fine transmitter, 
but neither does it compare in complexity,
estimate of 
price and ease of service.  Although- some
"features" 
of the ATD lead me to think it wasn't meant to 
be serviced, as we'll see.
Mike Hanz has kindly hosted the Maintenance manual
for 
the ATD, should you desire detailed information on

its specifications and accessories.
http://aafradio.org/docs/ATD.pdf

Most ATDs "in captivity" are in NOS condtion, with
accessories, dynamotor and connectors, having 
never been installed.  I was fortunate in
receiving mine
in this condition, with the exception that it had
been 
stored in some early form of foamed polyurethane
which had decayed, became powdery and spread
"frazz"
all over the place, including inside the Plate
Current
meter, which had its meter glass pushed-in.
Most of this was removed with "canned air," 
but the meter would need repair.

Restoration Goals and Principles:

1. Radios that play have the best chance of being 
preserved beyond my short time as their
care-giver.
Dead, cold "museum mummy" radios gather very
little
interest. These "mummies," if not thrown away at
once
by grand kids, end by being "donated" to museums 
and groups who do not really want them and who
will
either box them away, never to be seen until 
Judgment Day, or will leave them gathering dust 
until they are tossed into the recycle bin.  
Playing radios find homes.
"Mummy" radios find the dump.
 
2.  Preservation of the history and "story" of a 
radio with its original circuit design and mission
trumps performance.  Many circuits and stages will

continue to operate at an acceptable level with
parts 
as much as 20% out of spec or with greatly reduced

B+ Voltages.  Out-of-spec parts which still
function 
and do not damage circuits remain undisturbed. 
If that means a 50-watt radio outputs 40 watts, 
that is acceptable. 
I have plastic "Barbie Radios" for "performance."

3.  Preserving as many of the original components 
and circuits as possible, consistent with the
radio
playing is a priority.  Drilling holes, removing
whole
circuits and adding things like "S-meters" etc. 
is out-of-bounds.  Any change must be 100%
restorable 
to the original design- meaning disconnecting a
bad
WWII electrolytic and tacking in a modern
replacement, 
adding a plug-in removable IF filter, swapping a
wire from one terminal to another (easy FM for 
type-12 gear) is all ok as long as it can be
put-back to "stock" easily.
Preserving the operation and "story" of the set
is the primary goal.

General tips for work on the ATD:
Clearance is tight in this transmitter.  
Slow down, look close, think twice, be gentle.  
Your patience will be rewarded. Get a
compartmented
box for storing screws, nuts etc. as you remove
them.  
Screws on the bench will surely be stolen by the 
"Screw Gremlins" and make you unhappy.  
Use the correct-sized screwdrivers and ratchets;
many of these screws are seated in very soft
aluminum
which is easily scratched.  Some old carpet on
your 
bench will protect the finish and help catch
wayward
screws.  Be very careful when moving and
repositioning
the radio on your work bench.  You may break the 
antenna connectors, bend the tuning unit
hold-downs 
and do other things that will make you say mean 
things to yourself.

The ATD Dynamotor:
https://photos.app.goo.gl/CHgXyQd3gIviA8rB3
Refurbishing the ATD dynamotor and filter box is
fairly
unremarkable, with a couple of caveats. 
Remove the end bells.  Hand-rotate the armature to
check
for any problems. Clean and re-lube the bearings.

Go through the filter box.  Tighten grounds,
correct 
any corrosion.  First "caveat:"  Build HEAVY-gauge

primary power cables.  Wimpy 12 gauge won't cut
it. 
The ATD dynamotor takes about as much "umph" to
start
as does the dyno for the BC-375.  Batteries across

the supply for this one. For the
dyno-to-transmitter
cable, don't skimp on the Primary Voltage wire
size.
Use high-voltage-rated wire for the 1000V; 
I used inner conductor from RG-59 coax.

Second:  When run-testing the dynamotor without 
connection to the transmitter, pull the HV fuse.
While there are load resistors across the 1000V
buss,
they aren't fully effective.
If you run the dyno without the transmitter, the 
1000V buss will soar and cause arc-overs inside
C-203 
and possibly at the connector.  Pull the HV fuse 
to avoid this.  Once satisfied with your refurb of

the dyno, run it for at least 30 minutes to drive 
out moisture and listen for any "oddities" that 
need attention.

Restoring the ATD Transmitter:
*Do NOT attempt to remove the tubes for testing.*
*Do NOT attempt to remove the tuning units just
yet.*
More on this later. 
 
Examine the radio for anything unusual- loose or
broken
parts, meter glasses pushed-in, etc.  
How to remove the tuning units:
On one end of the transmitter is a silver, square
handle
you can lift up and turn clockwise to change the
active
channel.  Do not attempt to remove the active
channel 
unit; you will damage it if you try.
Remove the other three inactive channels and set
aside.
Lift the small, square silver handle on the side
of the 
transmitter and rotate it clockwise to disengage
the 
remaining tuning unit.  Note that when you lift
this
handle out for turning, it disengages the motor
drive
from the selecting shaft. 
Remove and set the last tuning unit aside.

Turn the radio bottom-side-up.  Remove the screws
that
hold the panels with the feet and shock mounts. 
Note there is one screw on each panel that is
under 
the shock assembly and a bit tricky to reach.
https://photos.app.goo.gl/JJLCAhyG16jlT9nB3
I'm tempted to leave this screw out when
reassembling-
don't tell on me.  Remove the left and right shock

assemblies and set aside.  Remove the bottom cover

with all the vent holes and set aside.  Say
"hello" 
to a whole bunch of resistors you'll soon be
testing.

Remove the cover from the side with the silver
handle.
You'll find the channel changing motor and gear
box 
under this cover.  See that chain driving the
front 
panel channel indicator?  If you have to repair
one 
of the meters, you're going to curse that vile 
contraption of the Devil.  More on that later.
https://photos.app.goo.gl/SLNEEU6YnQxQbemQ2

On the other side of the transmitter, remove the 
middle panel above the connectors.
https://photos.app.goo.gl/gWRg7Z9jcwwtjYJT2

Remove the back, and now you will see why you
should not try to pull the tubes for testing-
https://photos.app.goo.gl/THxwqa9utFqTZF923
the tube hold-downs appear to have been designed
by someone who either wanted to sell lots of tubes
or wanted any defective ATD sent to "Davey Jones"
and a new one set in its place.  The hold-downs 
have "spikes" which dig-into the tube's Bakelite 
base and make it nearly impossible to get the
tubes
out of the socket without breaking them.  The only

one without that infernal thing is the VR tube,
and
that's good because we need to remove it to get
to the gear box to oil it.
I needed to remove the 12SL7 Mic Amp to fix a 
problem.  I gently worked a screwdriver blade
under
the tube base and gently rocked the tube back-and-
forth, trying to walk it out of that Chinese 
Finger Trap.  This is the result:
https://photos.app.goo.gl/OXDVotw732B1hWgg2

I haven't tried to remove the other tubes- thank
Goodness they seem to work OK.  I'm going to try
cutting a thin piece of sheet brass shim stock
and see if I can push it down the base of the
tubes,
disengaging the spikes from the Bakelite so the
tubes will come out.  Any other ideas?

This transmitter has the weirdest T/R switch.
I thought its "little brother from a different
mother,"
the ATB switch was wild.  This thing also rotates
and- well, you'll see:  
https://photos.app.goo.gl/QKFZp8OT5WwOWlhg1
https://photos.app.goo.gl/GJlOJvBbPLQwRkNf1
Note: Do not use abrasives on these or any other
contacts in the transmitter.  Unless a contact is
eaten-up with corrosion, brown paper soaked in
De-Ox-It should be your first choice.
Be gentle- a bent contact from rough handling
will not be easy to mend.

Now put on some relaxing music, brew a pot or pour
a glass of your favorite beverage and get
comfortable.
Start at one corner of the rig and go over it 
inch-by-inch. Tedious, yes.  But it will pay
dividends.
Give every "ground" screw you find a small
"tweak;"
that's usually all that's needed.  There are lots
of
wiring screw terminals.  Check that they are
tight.
Look for any obvious problems.

More to follow in Part 2.

GL OM ES 73 DE Dave AB5S

P.S. Since it's "Halloween Time," here's a little
bit to scare some folks, heh heh...
https://photos.app.goo.gl/eiw10IaavfQ0u6pZ2