[Boatanchors] TCS Receiver: "More than one way to skin..."

[David Stinson]

Tinkered around some more and found a way to "down-size" and 
simplify the Collins 353-series Mechanical Filter adaptor to fit 
inside the TCS receiver.  Yes; I could make some solid-state 
fancy thing.  But if I did that, I'd feel soiled.  No way.  So 
it's tubes or nothing.

First- there's so much gain "head room" here that triodes do the 
job just fine.  I used two 6026 sub-mini triodes.  Why, when a 
single 12AU7 or similar would do the job?  Just because I enjoy 
tinkering with these tiny tubes, they don't need sockets and I 
have them laying around.  Nothing more complex than that.
But then, a 12AU7 might not provide enough isolation between 
input and output.  I dunno; try it and see.

There was a "hitch" (isn't there always): The TCS B+ is 220 
Volts, and sub-minis want max 150.  Boogering under the chassis 
was again forbidden; the adaptor must plug in place of the tube 
with no other changes.  A 1N5378, 100 Volt Zener with a .047 
across it to bypass it for RF connected as shown in the diagram 
fixed the issue.  220 Volts on one side, 115 on the other.  Mr. 
Mini Tube is happy.

The input tube runs with very low plate voltage- about 19 Volts. 
This is because it is powered from the Screen buss and must do so 
to isolated it from the Plate buss, which powers the other tube. 
V1 draws 4 mils and the TCS screen dropping resistor is 47K, so 
that only leaves about 19 Volts.  Fortunately, the stage works 
fine at that level.  One could adjust the screen resistor, but I 
opted not to start diddling under the chassis when it clearly 
wasn't needed.  If you adapt this to other rigs, you many need to 
adjust screen resistor values at the tube socket.

I'm going to build this up with two, switchable filters- one for 
.8 KC CW, one for 6 KC Phone.
Note:  For this adaptor to work, one must align the radio 
properly.  The old "ham" trick of turning-on the BFO and 
diddling/twiddling everything to maximum noise will not work. 
The BFO needs to be 455.0 KC when the knob is pointing to "0" and 
the IFs need to be aligned to 455 KC per the manual.  If you go 
to the trouble to build this and do not have a properly-aligned 
set, you shall be unhappy.

Here is the circuit.  Simple and it works.  Many improvements 
possible.
http://home.netcom.com/~arc5/TCS/TCSFilterAdaptor1.jpg

This, plus the "ear saver" clipper, makes the radio excellent on 
CW.
Still tunes fast, but, as my Daddy would say: "Well for Heaven's
sake, son! What do you want? Egg in your beer?" (I don't know
why egg in a beer would be a good thing, but I loved my Daddy's
smile when he said it).  So tune slow.  It ain't hard.

Looking forward to adapting this for an ARC-5 receiver.

73 DE Dave AB5S