[ARC5] ATD Transmitter Longwave Tuning Unit Repair

Mon Jan 4 11:22:23 EST 2021

I am of the opinion that mice have no reason to exist on this planet. 
They serve no useful purpose for anything!   I have had so much ham gear 
ruined by them that I cannot see straight when I hear the name "mouse" 
mentioned.  I spent most of last summer mouse proofing my remote ham 
shack. I am not sure how I did it, but I eliminated all access into the 
building so that it is now mouse free for the first time ever!

My favorite (or worst) mouse story involved a 2.3 GHz contact in the 
June VHF contest.  The gear had sat idle for most of the winter and now 
we were turning stuff on for the first time in the June contest. I had a 
rack mounted 25 watt TWT amplifier and turned it on when the possibility 
of our first 2.3 GHz contact arose. Lo ad behold, the TWT never went out 
of the "STANDBY" phase. It would not automatically go into the "OPERATE" 
phase. The big light never came on, and then we smelled burning phenolic 
smell.  It seems that mice had entered the TWT amplifier through the 
carrying handle openings on one side of the case and decided to make a 
nest inside the TWT amid a couple of circuit cards that handled the 
protection circuits.  They hauled in paper, insulation, etc.  and made a 
nest, then had a bunch of baby mice that died, so they ate them all and 
then crapped all over the place. As a final bit of showmanship, they 
decided to eat the vinyl plastic covering on many of the exposed wiring 
inside. When I turned it all on there were shorted wires everywhere. It 
took me almost a year to get that thing running again!  We renamed the 
amplifier "America's Only Microwave Rodent Hotel" in honor of those 
despicable creatures.  Did I mention that they don't even have the right 
to exist on this planet?

Thanks for the informative and entertaining story!  I have a Bendix 
TA-12 that is on my list to get running. It needs a lot of work.

Dave K1WHS

On 1/4/2021 9:56 AM, David Stinson wrote:
>
> For those with an interest in the Bendix ATD
> transmitter- Repair of a scarce, possibly rare
> 200-500 KC Tuning Unit.
> https://s3.amazonaws.com/files.qrz.com/s/ab5s/ATD_RAX.jpg
>
> The Longwave tuning unit for the ATD transmitter
> is not often seen.   This one is Serial #8:
> https://photos.app.goo.gl/4ohMv7rxtwLeDm3o6
> https://photos.app.goo.gl/GHHkoJznE9S5zEEV8
>
> The largest coil on the left of this view is
> the PA Tank Coil.  It is variometer-tuned.
> https://photos.app.goo.gl/waZmDUVhXihq2fNq6
>
> When I received the tuning unit, one of the
> phenolic members which mounts part of
> the channel-switching mechanism was broken
> in two.  I used glue and some scrap perf board
> to repair and strengthen it.  NOTE:  The little
> piece of perf-board on the outside interfered
> with the channel-changer, so I had to remove
> that piece.  Still appears strong enough without it.
> https://photos.app.goo.gl/1W19hj4112ejBQnu9
>
> While cleaning the unit and inspecting it, I saw
> that the litz wire at the bottom of the PA coil
> was no longer connected to its terminal.
> A mouse had chewed it.  Had to peel-back
> part of the last turn and extend it
> to the proper contact.
>
> Inserted the tuning unit and tested.  Got
> Plate current, but no dip or power out.
> Pulled the unit and looked closer at the PA
> circuit.   Mr. Mouse wasn't done it seems.
> Here's the internals of the PA variometer
> from the 500-1500 KC tuning unit:
> https://photos.app.goo.gl/tak7FqJSMgHAjZK57
>
> The variometer coil's axel is hollow.  Flexible,
> cloth-covered wires go through it and provides
> a solder-point for the coil's litz wire turns.
> The cloth-covered wire then exits the axel,
> is wound a couple of turns- one side
> clock-wise, the other counter-clockwise,
> so it "loosens" when you tune the thing
> from 0 up to 100.
>
> This was the inside of the 200-500 KC
> PA variometer:
> https://photos.app.goo.gl/6sshHDfWRFW1fWmc7
> The little mousy creep had eaten the variometer
> connection wires like candy-canes, and even ate-
> off the cloth-covered wire solder connections right
> down to the axel.   Between the copper fibers and
> the lead solder he ate, I hope he shortly found
> himself in Mouse Hades, to be forever
> batted-about by Tom-cats demons.
>
> Removing the coil is fairly straight-forward,
> with one "oddity."
> https://photos.app.goo.gl/kkRqNQ39T1saHL7t7
>
> Set the control to "0" and carefully note the
> mechanism that projects the tuning shaft
> through the cover.  It has to go back in the
> same configuration for the "stops" to be in
> the correct places.  There is a friction plate
> on the inside that is used to friction the
> tuning knob and to lock the control
> in place.  If you remove just one of the
> cylindrical nuts, the plate will flip left out
> of the way and you can pull the coil out.
>
> The PA coil has selectable taps. Marked which
> side was "up" when the variometer coil is "0",
> then set to work disconnecting the taps from
> the PA range switch.
>
> The oddity:
> If you number the coil taps from the top
> to the bottom, it's 1-2-3-4-5.
> If you label where the taps connect to
> the switch from the bottom up to
> the top, than taps are connected
> 1-2-4-3-5.
> https://photos.app.goo.gl/RxDA6hBHS9Mg7sQL8
> Wonder if that was intentional
> or some sort of error.  Be sure to note
> closely how everything goes back together.
> There's a little sheet of insulating material
> under the coil which is easy to forget.
> "Voice of experience."
>
> With the coil out, I removed  the cloth-covered
> wires in the axel, noting which end was wound
> clock-wise and which counter-clockwise
> so that, when the coil is rotated to "100,"
> it loosens the turns and when rotated to "0"
> it tightens them again.
>
> Striped about 2mm back from the chewed ends
> and tinned them.  Straightened and "rounded"
> the end of the wire that makes contact on
> the outside of the coil, gave that end a slight
> bend and fed the wire back through the axel
> from the inside to the outside.   A little tricky,
> but "your patience will be rewarded."
> There is just enough wire to work- not a bit more.
>
> One side of the coil litz winding had enough of
> a pigtail to clean and solder, so a jumper there
> was easy.  The other side- the little vermin
> ate right down to the wire hole, so I had to
> peel back the end of the winding, scrape
> and curse and clean that litz wire and feed
> a jumper through the cleaned-out hole.
> The hole wasn't large enough for the
> green jumper wire and I wasn't going
> to enlarge it, so stripped the green jacket
> from the jumper and that fit just right.
> https://photos.app.goo.gl/Jvp5jZxA56KdWWFL9
>
> Put everything back together, and the
> tuning unit now works as it should on 473 KC.
>
> Hope this is helpful to someone.
> GL OM ES 73 DE Dave AB5S
>
>
>
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