This 21" 'Super Set' (as it is called in a 1951 magazine ad) was my second antique TV to buy. I purchased it on E-bay in October of 2000. It was a mere dollar to bid, and I was the only bidder. So, a friend and I drove up to Kansas City to pick it up. Now this thing is a real beast, and moving it around can be difficult, especially since the cabinet back is missing care has to be taken not to bump the back of the CRT on door frames. It weighs 143 pounds and was priced at $450 when new.
The KCS68 series chassis was apparently RCA's top of the line chassis when it was produced. It was apparently manufactured from 1951 to 1954. Several variations of the KCS68 chassis were made, being given A, C, CB, E, F, and H designations (my model 21T177 uses a KCS68CB chassis) The KCS68 chassis series was used in RCA models 21T156, 21T159, 21T174, 21T176, 21T177, 21T178, 21T179, and 21T179. The KCS68 series chassis used 25 tubes (including the kinescope [chassis KCS68A &KCS68H were 24 tube]) and employed direct-drive type horizontal outputs and high voltage circuits. The synchroguide circuit was also used in the horizontal oscillator employing a 6SN7-GT dual triode. Period literature also touts improved picture brilliance and reduced hazard high voltage. My chassis, the KCS68CB, is really a slightly modified KCS68C
|6X8||R-F Oscillator and Mixer|
|6AU6||1st Picture IF Amplifier|
|6CB6||2nd Picture IF Amplifier|
|6CB6||3rd Picture IF Amplifier|
|6CB6||4th Picture IF Amplifier|
|6AU6||1st Sound IF Amplifier|
|6AU6||2nd Sound IF Amplifier|
|6AV6||1st Audio Amplifier|
|6SN7-GT||Vertical Sweep Amplifier and Vertical Sweep Oscillator|
|6AQ5||Vertical Sweep Output|
|6SN7-GT||Horizontal Sync Amplifier|
|6SN7-GT||Horizontal Sweep Oscillator and Control|
|6CD6-G||Horizontal Sweep Output|
|1B3-GT||High Voltage Rectifier|
|1N34||Crystal Diode Video Detector|
|Electrical and Mechanical Specifications|
|Picture Size||227 Square Inches|
|12 channels VHF||54mc. to 88mc., 174mc. to 216mc.|
|Picture IF Carrier Frequency||45.75mc.|
|Sound IF Carrier Frequency||41.25mc. and 4.5mc.|
|Video Response||To 4mc.|
|Power Supply Rating||115volts, 60 cycles, 300 watts|
|Audio Power Output Rating||5.0 watts Maximum|
|Loudspeakers||12" PM dynamic, 3.2 ohms|
|Model Weight||Chassis With Tubes in Cabinet||Shipping Weight|
|21T177||143 Pounds||174 Pounds|
|Receiver antenna Input Inpedance||Choice: 300 ohms balanced or 72 ohms unbalanced.|
|Cabinet Finish||Limed Oak|
Upon getting it situated in its new home in my room, I began to probe around inside its cavernous cabinet. The cabinet back was missing and the guy I purchased it from had lost the power cord in storing it. So the first thing I had to do was find a power cord that would fit the safety interlock. No sweat, I had one somewhere, and when I found it I plugged it in and turned it on. All of you may know that this is the absolutely worst thing you can do when testing out an old piece of electronics equipment for the first time. The best thing to do would have been to plug it into a variac, but I don't have a variac, so I just turn it on and watch everything inside waiting to jerk the plug if I have too.
When the set came on the picture tube was still dark, but I did have sound. More investigation revealed that the high voltage lead was not connected to the right place at either end. No problem. Firing it up again I had a raster, and depending on the fine tuning control, snow. The sound, much to my surprise worked from the beginning, and having the set attached to cable, picked up sound on channels 2-13 perfectly. After letting the set play for about 1/2 hour while I played with the front controls, the sound faded to silence, and I could no longer get snow. Some capacitor voodoo must have been at work.
Taking the chassis out from the cabinet revealed the rats nest of wiring inside. It also revealed a whopping 60 wax and paper capacitors. Oh no!!! So I took the time to record all of different values down and how many of each there were and contacted AES for some parts. By this time I had taken the time to go to the library and look up the schematic for that set. But much to my horror, someone had already removed the pages I needed from both of the Rider's manuals where my set was listed, as well as the Photofact folder!!! Luckily a couple of weeks later I was able to buy a complete Rider's TV manual Vol. 11 off of E-bay for only $4.00. What a steal!
It was not long after getting all those caps replaced that the next major problem surfaced, an overheating horizontal output tube!! After posting many questions on Nostalgia Air's tech forum and replacing many resistors that were suspect, the problem was isolated to the flyback, which apparently had died. So, the restoration work has stopped there. I don't know why the flyback stopped, perhaps it was the original fault that put the set out of service, and by the time I acquired it the leaky caps had reduced the voltages going to it. At any rate, I am now hunting for a replacement flyback transformer. Once the electronic phase of the work is completed, the cabinet will be given attention. The cabinet is really in very good condition, and work on it will probably not involve very much at all.
After much searching, a horizontal output transformer has been found. It will be installed as soon as I can obtain a 33 pf 10,000 volt ceramic capacitor. This capacitor goes across one of the VOT's windings and acts as a fixed trimmer. Although its possible the set could be used and adjusted without it, I'm not wanting to take that risk, as finding the flyback took long enough.
Yes, that's right. A picture. If you read about my big mistake on the TV trouble page, you will now know why the Horizontal output tube was overheating. The cap in question was a .0015mfd capacitor that I had inadvertently installed a .015mfd cap in its place. Thanks to an electrical engineering friend, Ken Parker, who pointed out the troubles that would happen with a capacitor difference of that much.
After replacing a gassy horizontal output tube, I had a raster, and a very bright one too. Still, after a little more work twiddling controls and replacing a couple filter caps (eventually, the whole power supply will be rebuilt) I had sound with the raster, and with the brightness turned down a bit, a picture from my test pattern generator.
Sync is almost non-existent, particularly vertical sync. This is most likely because the voltages on the plates and screens of the video IF sections and video output are low. The audio is plenty strong, however, the optimum tuning point for audio and picture is not the same point, so it might alignment, but I am not going to check that until I can look at a number or resistors and other components in the mentioned circuits.
I have received several emails from readers who have other sets like this one that use the same chassis. These sets are essentially the same, but with cabinets that have different styles.
John and Regina Arroyo wrote to say that they have a 21T178. Here's a picture:
Bob Gary wrote to say he has a 21T176, which he is restoring. He also has an RCA 9T126.
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