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Author Topic: The TCS-12 Transmitter is alive  (Read 3371 times)
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KF9CM
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« on: December 21, 2006, 12:47:08 PM »

After rewiring P101 socket on the TCS-12 Transmitter, that someone cleverly rewired,    the Transmitter is working. I used a 40 watt light bulb as a dummy load and I got almost full brilliance on CW and half that on AM. I plugged in the T-17 Carbon mike and seemed like I was getting a lot less then 90% Modulation. Humm? Huh any thoughts on that?



Gary KF9CM
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AJ1G
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« Reply #1 on: December 21, 2006, 01:31:40 PM »

There are a couple of reasons the T17 is not providing full modulation.

First, many, if not most of them have a very low output, and or the carbon grains are packed up in the element.  They are sone of the worst sounding mics around.

Secondly, you are driving the grids of the 1625 modulators diretly with the mic and its DC excitation through a small input transformer.  No additional premaplification at all!

I have had better results with all of my mil radios desoigned for a carbon mic using a regular telephone company T-1 element.  I have it intallled in an old navy radio telephone type handset with PTT switching, otherwise wired as the T-17 is with a PL-68.

You also could drive the mic input line wilth external audio, putting an approximate 0.5 mf cap in series with the signal lead to decouple the carbon mic DC excitation from what you are feeding into the TCS.

I believe there was an ER article a while back on making a small preamp specifically for use with mics like the T-17.

The TCS was designed to be used with the Navy RS-38 "hockey puck" mic  They are also relatively low output and you really have to talk loudly with them for full modulation.
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Carl WA1KPD
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« Reply #2 on: December 21, 2006, 02:11:52 PM »

seemed like I was getting a lot less then 90% Modulation. Humm? Huh any thoughts on that?
Gary KF9CM

I ran a TCS back in the late 60s. At the time I built a 12AX7 speech amp in the space where the internal xmt crystals went. Fit very nicely and drove the input of the mod transformer with it. Did not have no stinkin scope in those days so can't tell you the % mod I ended up with but I can tell you that it got good reports
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« Reply #3 on: December 21, 2006, 02:23:49 PM »

I used that same spot (the crystal "bay") to mount a small pc board with a one-transistor class A speech amp wired to the original mic jack, and powered from the filament supply. It probably only makes 50-100 milliwatts but it's certainly more than lung power into a carbon mic element! Looks decent on the scope with my D104 driving it.

The only receiver I have at home for 75m (other than an ARC-5 that just doesn't have adequate selectivity) is an HW-12 single bander... when I get home this weekend I'll try zero-beating the carriers and maybe I'll be able to work some of you above 3800. If you can hear a PW 20 watts into a 113' trap dipole thirty feet up, that is  Wink

I did make one AM contact on 40 last year (an ARC-5 transmitter with homemade screen modulator) also running about 20W carrier, but it was only 200 miles  Tongue

-Charles
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WU2D
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« Reply #4 on: December 22, 2006, 08:54:25 PM »

Gary,

A long time ago I did a little circuit which went inside the T-17 (a defunct one) replacing the carbon element. I think I sent it in to ER in the early 1990's. Anyway it used an electret element and a darlington transistor and stole the bias voltage right from the radio. I still use it on the TCS and my GRC-9. It also worked FB on the ARC-2. I can not upload the schematic because the server is apparently full.

Ahh upload Working Today MM

Mike WU2D


* CARBONMIC.jpg (21.66 KB, 361x221 - viewed 300 times.)
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KF9CM
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« Reply #5 on: December 26, 2006, 08:29:33 AM »

Mike,

On your schematic, is the emitter resistor 6.8 ohms, or 68 ohms?
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m0ghq
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« Reply #6 on: December 26, 2006, 08:49:23 AM »

Hi, A lot folk have a great deal of success by using the microphone hand number 3, the lolipop type used by number 19 sets, big carbon element and gives good modulation without modifying the radio, use the one with the blue element.  I have not found a good t-17 yet and I have many of them, good for display but no good on air. 73 Max M0GHQ
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WU2D
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« Reply #7 on: December 26, 2006, 01:05:10 PM »

Mike,

On your schematic, is the emitter resistor 6.8 ohms, or 68 ohms?

Actually, I had a 100 Ohm trimpot in series with a 4.7 Ohm so I could fool with it, but when I actually took the mic apart and measured - the composite value was closer to 6.8 Ohms. The idea is to measure the circuit parameters with the original carbon element in line (voltage drop and current) and then try to duplicate this condition with the biasing of the darlington. 

I also remember that the circuit was a bit bassy so I put some pre-emphasis in by using a smaller than normal coupling capacitor (.05 uF).

Mike WU2D
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Tim WA1HnyLR
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« Reply #8 on: December 27, 2006, 11:08:55 AM »

Ahh yes!TheTCS!. I have a TCS set that I fixed up and works quite well Get rid of the carbonium microphonim supply voltage. Hardwire the primary of the inpoot transformer directly to the inpoot jack. I used the output of a typical broadcast audio processor to feed the inpoot. I have the whole TCS station including ,the AC power suckply.I graetly increased the filter capacity of the PTT relay suckply. The voltage went up to 24V. I reversed the polarity of the rectifier to make the suckply -24V I serised up the coils of the two relays in the transmitter to deal with the 24V . I used the -24V for the mod biass . I directly connected this voltage to the centertap of the  secondary of the inpoot transformer. I eliminated the 300 Ohm cathode biass resistor from the mod tubes. I also eliminated the 20K modulator screen dropping resistor and took the modulator screen voltage from the keyd side of the set of relay contacts that apply tthe LV B+ to the lower level stages. This allows the modulator to work in hard regulated AB2 operation.The modulator is capable of significantly more audio power than the stock configuration. As you know only one 1625 is used in AM fone position. Both tubes are used in CW mode. I enabled both tubes Rather. than trying to load to 2X plate current I figured on about 125Ma plate current. The 1625 tubes have separate. screen and grid bias resistors.I eliminated the use of the screen resistor of one tube. I just parallelled up the screen feeds using one resistor.How well does in work? It is my finding that the stock mod transformer begins to saturate above the requsite 80Ma. At 125 MA the positive peaks did not quite make 100% but close. At 80Ma the transmitter easily did 125% positive and sounded better. So this is where I leave it. About 25-30 watts outpoot. The VFO is very stable. The RX is a little broad but works well too. I changed the 5R4s in the stock suckply th a pair of 816 mercury vapor tubes. Yep a trippy blue glow eminates from the power suckply as well as an increase of outpoot voltage to near 500V. Use of xenon or mercury vapor tube is as good as solidstating the suckply .Just fillament power is added in to the total electric bill. Good luck with the TCS .De Tim WA1HnyLR
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Opcom
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« Reply #9 on: June 07, 2010, 09:46:08 AM »

Hello Gary,

Do you happen to have an electronic copy of the TCS-12 TX and RX manuals? A friend of mine might sell me a couple of the complete sets and if so, I would like to get them working. He says they are parts sets but there is enough there to make a good one.

thanks,
Patrick
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w3jn
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« Reply #10 on: June 07, 2010, 10:30:28 AM »

TCS-13 manual right here, Patrick

 http://bama.edebris.com/manuals/military/tcs13/
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« Reply #11 on: June 07, 2010, 08:46:33 PM »

Is that the same as the TCS-12?
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w3jn
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« Reply #12 on: June 07, 2010, 10:40:57 PM »

Beats me, can't be too many differences.
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