[Boatanchors] TCS Receiver Resurrection Tips. (LONG)

[David Stinson]

The TCS receiver gets a bad rap. Granted; it's best 
used for that which it was intended: Modest range AM.
It was designed to use a short whip antenna. 
A full-size dipole gathers a lot more signal so overload
can be a problem. BFO "injection" is too low for
very strong signals. And of course, it's very broad.

It also sounds wonderful on AM, is very stable, 
Has good dial calibration once aligned, is almost
too sensitive, is easy to fix (if you know some tricks) 
and is built like the proverbial battle ship.
I like the receiver for casual SWLing and jawing
with the local AM guys. And, when paired with
the TCS transmitter, it looks "pre-historic," which
is always a plus for me.

Here are some refurb tips learned "the hard way."
It's a big job and it takes some time, 
but "your patience will be rewarded."
And if it was easy, everyone would do it and 
it wouldn't be nearly so cool.

If you don't have a manual copy, you need 
to get one.  It's invaluable, especially for the alignment
procedure.  While the receiver I'm working on is
a TCS-13 and my manual is TCS-12, and there are
minor differences in where some wires go
and in the types of IF cans used, these are 
minor annoyances.

Important:
When you first get your TCS receiver (or transmitter),
do not start twisting the band switch and MO switches.
The band switch, while built "heavy duty," is 75 years
old now. The leaf-spring contacts can get "gunky"
and stick. If you go twisting, they may be bent 
or even broken. Yes; learned the hard way. 
This is a common problem with these sets.

Place the rig on its back, face up.
Leach De-Ox-It into the toggle switches around
the bat handle and give them a good working.
Do this a couple of times each.  
Use De-Ox-It and a toothbrush to gently scrub 
the pins in the power connector. 

Open the rig. Remove the screws holding
the cover plate over the RF/Converter/MO section
and remove the plate.
The entire back panel is removeable and that will
make for easier access to many parts.

Go inch-by-inch over the set and panels.
Find every ground point and ground screw you 
can reach and give them a little "tweak."  
If they look cruddy, give them a drop of De-Ox-it.
High-Z grounds is becoming the second most common
problem I see in old rigs, first being leaky caps.
Yes, it's tedious.  But it will pay dividends.

Lubricate the mechanical parts of the switches
and controls, including the bearings through 
the front panel.
Carefully inspect each band switch 
and MO switch wiper. 
Here's what they look like (red arrow)
https://goo.gl/photos/ztxA1z6RHboPn4TS7
Use a thin probe or jeweler's screwdriver to 
gently lift the contact wipers to make sure 
they're not stuck.
If none of them stick now, they can still drag,
stick and bend on cruddy adjacent contacts.
Watch for that.  
If you already have a bent one, do not despair.
I managed to straighten my bent one with a
small hemostat and patience.
You can fix it with a few moments observation
and thought. Look closely, think twice, move slowly.

Clean and lube all the wipers and switch contacts 
with your "De-Ox-It of choice."
Now gently rock the switch back and forth, 
inspect the motion of each wiper, watching
for any "stickiness." Switch slowly and carefully
as you inspect. Do this for all three bands
and five MO postions. Use brown kraft paper 
soaked in contact cleaner followed by dry paper
to burnish away any crud causing a problem. 
Do not use abrasives on these contacts.
Once you take the time to clean, lube and
adjust these switches, they will outlive both of us.

The phenolic in the IF transformers and 
Detector/BFO cans is hygroscopic- it sucks-up 
moisture and will leak high voltage to the chassis. 
If you hear what sounds like "thunder storm static" 
with no antenna, it's likely to be this problem 
and you need to fix it right away because it can
 blow-open IF transformer windings.
You will need some corona dope, like this:
http://www.circuitspecialists.com/content/101117/4226-55ml-0.jpg
I got a bottle at the local Fry's outlet.
And there are "postage stamp" paper caps 
and decayed-high resistors in the IF/DET/AUDIO
stages that need changing.  Even if the paper caps 
in these four stages test "good," change them.  
Unless you want to take this thing apart again.

To do this repair, you need to remove the four 
IF/Det/Audio modules from the receiver. 
Now that sounds daunting, but it's really not that 
bad if you're patient. You have to remove them
in a specific way because of their interconnection; 
you can't get a soldering iron everywhere you need 
to do them one at a time.

https://goo.gl/photos/FZNeGbJrP1qjt1N18

>From the front panel to the back are four modules:
Audio (with the BFO coil), Detector/BFO, 
2nd IF and 1st IF.   The BFO tuning shaft
goes through the panel from the audio module 
and there are wires between the Audio and Detector
modules which cannot be easily disconnected.
Module #3, 2nd IF, must come out first.
Once it is removed, the Audio and Detector
modules can be shifted toward the rear to clear 
the BFO tuning shaft and lift those stages out as
a single assembly.

There are two bare-wire busses running between
the four modules.  The outside buss, which supplies
filament voltage, can be unsoldered and removed.
The inner buss, carrying ground, will have to be
cut and bent out of the way.  
https://goo.gl/photos/bR2zjJ2Y9sNrM3Qk7

A wiring harness connects to terminals on 
each of the phenolic boards used in the 
individual stage modules.  Lacing cord 
secures the wires from the harness to each
board.  Cut the laces.  Mark each wire and
each terminal so you can get them back correctly.
Unsolder the wiring harness connections.
There is one wire from the harness into 
the Audio module that is down on the side,
connected to the inside end of C-235.
https://goo.gl/photos/YUscrcHo7yNAwDAR7
You will need thin needle nose and a small iron
to remove and replace this wire.  It's a tight fit,
but can be done with a little care.
You can also see in the photo how I marked
the wires and boards.

There is a single wire that feeds through the 
shield between the 1st and 2nd IF and two
wires that feed through the shield between
the 2nd IF and the Detector.  
View from detector side of shield
https://goo.gl/photos/XuApGRj2S63yixiC8
View from 2nd IF side of shield
https://goo.gl/photos/5VSyY93vpqoTAesU7
These can be reached with an iron and needle nose 
from the open side.  Carefully remove them and 
pull them through the rubber grommets.
Important note:
The insulation on these wires has become fragile.
As you can see, I was too rough with it and
it began to fray.  Be gentle pulling these back
through the grommets.  You might give them 
a coat of that Corona Dope to stiffen them.

Remove the four screws holding the 2nd IF
stage in place and carefully pull the stage out.
On the back panel of the receiver should be a 
holder with two spline wrenches.  Use the larger
wrench to remove the BFO tuning knob.  
There is an index mark on the shaft but you'll
need to add another to tell which way is "up."
Losen the two screws on either side of the 
panel where the BFO shaft comes trough.
Do not remove them- just losen them.
Remove the eight screws holding the Detector
and Audio stages.  Pull the two modules 
straight back to disengage the BFO shaft
from the front panel and lift the modules out
as one unit.  

The remaining stage, the 1st IF, has a shielded
lead going to the Converter stage.  This is a little 
tricky to remove and replace.  I cut the ground 
wire and tagged a short piece of wire to the cable
shield so I could ground it in an easier spot when
reassembling.

Replace all the "postage stamp" caps.  
In most cases the oil-filled caps are good, but 
test them and replace any baddies.  Replace any
that leak oil regardless of test results.
Lossen and re-tighten all hardware and grounding 
points, except the bolts holding the tube sockets.
Unless they're falling off, leave those alone.  
More on that later.
Reflow any suspect solder joints.

I used De-Ox-It on all the tube pin recepticals and
had no issues doing so.  These old ceramic tube
socket pin connectors are made with two parts
that are rivited together.  They get oxidized 
between the two parts.  I had trouble with the 
Converter socket and tried to gently, carefully
tap the rivits to tighten them.  Big mistake.
The ceramic shattered like an egg shell.
Talk about a pain to fix.  That's why I say don't 
mess with the mounting screws.  I put De-Ox-It 
on each pin receptical, inserted the tube and 
flexed it in a circular motion to work the 
connections.  That's done the job so far.

On the big resistors- I nip one end in the middle 
of the lead and test them.  If out of spec, replaced
them with 1 or 2 Watt metalized resistors from the
local surplus house for about 15 cents each.
If good, I clean the ends and tack them back together.
All of the 47K resistors were off.  None of the
100K or any below 10K were bad. A couple of
the 10Ks went.  Surprising- the 1 Megs were fine,
but I replaced them anyway because I just don't 
trust them.  

Now comes good news for some and terrible
news for others- the IF and BFO cans.
There are two types of IF cans used in the TCS.
The ones in the manual pictures above with two
holes, tuned by trimmer caps and those like mine,
with one hole in the top tuned by iron core slugs
and with fixed caps inside them.  If you have the
single hole type, give thanks to The Almighty for 
you have been blessed.  If you have the "two holer"
with the trimmer caps, mix yourself one of your 
favorite adult beverages and make it a double.
You're gonna need it.

The IF trimmer caps are the type recently discussed 
in the thread about restoring the RBM receiver-
the type with a press-fit nut holding the rotor
shaft at the proper spacing and tension.  Many of 
these nuts have split, the rotor shaft falls down upon
the stator plates shorting the cap, thus detuning the 
IF and resulting in poor sensitivity.  If you have these
caps, I promise at least one of them has this problem.
That kind of trimmer is in all the BFO cans and 
it was split in the one I just finished.  
Careful application of JB Weld and spacers fixed it.  
But I haven't had any of the "trimmer" type IF cans.
I don't know how they are done.  You'll need 
to put on your thinking cap.  I'll bet someone 
reading this has seen and solved this problem.
 
Carefully remove the cover from the IF and BFO cans.
Remove the screws or bolts that hold the phenolic 
base of the IF transformer to the module and lift 
it above the module chassis enough to work
under the transformer base without having to
disconnect the wires.
Coat the phenolic with the Corona Dope, being 
careful not to get it into any adjustment screws.
Also coat any phenolic waffers in the top of 
the transformer.  Coat around and in the module 
chassis holes where the connections pass through
the module chassis and the top and bottom 
of the screw holes.  
The point is to keep high voltage from leaking from 
the connection points to either the chassis or the 
screw holders through the phenolic.  
Let it all dry and reassemble.

Audio amp stage:
There is no electrolytic filter across the 330 Ohm
cathode resistor of the 12A6.  I don't know why 
Collins decided to live with the degeneration.
Someone speculated that they didn't want 
electrolytics in the set due to reliablitly problems.
I don't know.  I did add 10 mFd across the 
cathode resistor.  It boosted the audio gain
and I think the audio quality- good to start with-
is even better with the cap installed.
15 mFd would probably have been better.

Reassemble the IF/Det/Audio stages.  
Put the 1st IF in first so you have plenty
of room to reconnect that shielded lead.
Then the Audio/Det as one unit, 2nd IF last.
Don't forget to reconnect that single wire to 
the side of C-235.  If you think it's just 
too tight to get that wire back as it was, there's 
no harm in using two "pig-tails" of wire to bring
the connecton up in range of your soldering iron
before you reinstall the stages.  Just solder them 
together, cover with heat-shrink and tuck the 
connection out of the way.

Double-check every connection as you go.
As my Daddy told me: "A little time looking 
will save a lot of time cussing."

RF, Converter and LO stages.
The phenolic board behind these stages mounts
most of their suspect parts.  Remove the screws
and lift the board to get to an oil-filled cap.  
If this cap is bad, you can nip the wires to 
it and mount replacements above.  One will 
go at the tube base of the LO and another will
mount on the top of the board.  Just follow 
the wires.   Replace any bad resistors.

On the "postage stamp" caps in the tuned
circuits:  These are all in low-voltage grid circuits
and I've never had trouble with them.  They are
mounted in places that would require removing 
coils to reach them and I worry about that old
ceramic cracking.  Unless you have reason to 
believe one of them bad- like a stage that won't 
align- I recommend leaving them alone.
Clean and De-Ox-It the three sets of tube socket 
pins.  

Reassemble the panels.  Be sure to put all the 
screws back in the plate over the tuned circuits.
I recommend bringing the B+ up slow without 
filament voltage to check for any shorts.  
Then cross your fingers, say a prayer and 
power up.

Align the radio per the manual.
Note:  If you plug a speaker into the headphone 
jack, your audio is being fed through an 1800
Ohm resistor.  Check the diagram.  For best
audio, use the audio feed from the power plug
and a properly matched speaker.  
You'll get all the audio you can stand.
The rig should be quite sensitive.
If you use a full-size resonant antenna, it
will overload on strong signals.  The BFO
injection is too low for really strong SSB 
signals unless you turn down the RF gain
and turn the Audio up to compensate.

I used a service monitor to feed 455 KC at
0 dBm into the antenna jack.  This made reception
of strong SSB and CW signals much nicer.
I may build a little external oscillator just 
for those times I want that.
The radio sounds excellent on AM and is 
very stable after warmup ( I use the original
TCS-13 dual dynamotor supply).

I hope this is helpful and I will be glad to answer
any questions I can.  I don't know everything 
and there are lots of people her smarter than me.
Between us, we can find a way to get you going.

GL OM ES 73 DE Dave AB5S.

P.S.  After some sleep, I'd like to discuss a 
non-destructive way to install a crystal filter 
in the set to "sharpen" it a bit.