The AM Forum

The guys on the Old Military Radio Net (CW Edition) which meets on 3570 kHz at 9:00 PM EDT on Sunday Evenings, laid a challenge to see how many TCS stations that we could get on the air. I usually check in with an ARC-5 or my ART-13, both of which are somewhat tamed. If you have ever heard a TCS on CW, it is a scary thing with all of the relays banging. Actually the ART-13 was worse before I put grid block keying and a changeover timer in.

Well anyway I have a TCS station which has not seen much action on AM and has never been fired up on CW. Last time I had it on it had a snapping crunching sound coming out of the speaker even with the volume control all the way down, and this discouraged me from using the darn thing. Anyway, today I decided to see if I could get the station operational on CW.

The TCS Receiver that I have is broad as a barn. But everybody knows that. The ARC-2 XCVR's RX section is pretty much in the same league, as is the R-105/ARR-15. All of these rigs are wide, probably for good reason in wartime, when somebody calls you and he is a bit off frequency, you still hear him. I have used the R11 or ARC-5 Q-5er on these in the past to good effect.

First I had to clean and lube both the TCS TX and the RX. This did not take too long.

I pulled tubes in the Rx until the snap crackle pop stopped. I had to go all the way to the last tube, the output tube, the 12A6. I should have realized this since the volume pot did not effect the noise. This actually was a good thing. It meant that the problem was down to just three caps, the cap across B+ feed to the PA, the grid coupling cap or the 12SQ7 first audio/BFO plate bypass cap. It didn't think it could be the cap across the output transformer because the noise went away when I pulled the tube. 

Anyway, it turned out to be the Bypass cap. The 12SQ7 is in a reflex circuit. the tube functions as a BFO, AGC, Detector and first Audio Stage, all at the same time. How clever of those Collins engineers. Anyway, the bypass cap was for the BFO only so it was a 50 pf cap, a postage stamp type. It failed nicely. Breaking down; this cap was sending noise right into the grid of the 12A6 PA.

Now for selectivity..
I decided to try the modification published in Feb 2005 or ER, which adds a ceramic filter between the First IF Can (Z202 tap)  and the First IF grid (V205). The author K3HVG, warned that the gain would go down some. Anyway, I had a nice Murata CFS-455 in my junkbox which is a pretty large metal can filter and a bit wider than I thought would do much, but I put it in anyway. All I can say is wow! Not only was there not any perceptable derease in gain, but 75M AM is now listenable on a Saturday afternoon. The IF cans were re-peaked, but honestly, there was not much of a change. I can not believe how much of a difference this made. According to my measurements, I went from 16 kHz wide to around 7 kHz and sharp... No matching, no caps no transformers, no nuthin- just the filter.

Tonight I made several CW contacts on the setup and it worked great with only a slight hint of chirp and full break-in that really works.

Next I have to try a Q-Multiplier. See my TCS setup in the station photos section.

Mike WU2D

A good source for filters is castoff CB radios. There were some decent ones used years ago.

Mike you could be breaking the law changing the design of that radio.

It is, after all, a Collins.  Are you calling Art Collins an incompetent engineer!?!

 ;D

A "TCS" is what it is,like a BC-348, BC-312, etc. Yes, they are a bit on the broad side to say the least. I use one on occasion with it's companion transmitter and pray the band doesn't get too congested!
Regards,
           Joe Cro N3IBX

Didn't he decide you could talk in 2.4Khz ?

Citizens,
             Try a TOKO ahCFM2  ceramik filt, 12kc wide@6db down........  these things are kinda cheep   ....  twernt there a mod in ER r/e dis??

OMG you're right - Art Collins could be turning over - I put a 100 Yen Japanese filter in a Collins... I do not want that on my resume. Maybe I should yank the filter  back out!  ;)

Mike WU2D

As an RM in the USN, we had a TCS "clacking" combo for a backup, back in 1963.  I frequently put it on 75m AM on Sunday mid-watches (in SDIEGO) for "proof of performance" tests - hi hi.  Yes, one needed well padded headphones to use it on CW (to keep the relay clacking out of your ears), but it worked quite well with the Navy "standard" 35' whip.  My 1943 vintage TCS-9 receiver was donated to the USS STUART memorial in Galveston, TX.  Tom - W0EAJ

I have been on the OMRN (with Mike, recently (I am Don #3) on my TCS station.
The TCS transmitter is not by the way the only radio in the world using a clacking relay on CW.
My biggest complaint with the receivers is the BFO. So I rigged up what I call a pseudo BFO using a gimmick cap across the grid and plate of the first If and switch the grid wire so hooked up from a push button switch on the front panel. Really smartens up the radio. I can now copy Cw AND SSB with ease.  I use my TCS station regularly.

donVE3LYX

I wanted to use my TCS12 receiver in the recent Classic Exchange, so I brought out a signal from the last IF and sent it to my BC348R.  The crystal filter gives very effective single signal reception, and it worked well with the TCS.  The signal on the other side of zero beat is almost inaudible.  If I had a heathkit q-multiplier I would try it, so I'm looking for one.  Try it, you'll like it.

Best regards,
Fox