Restoration Idea 20
Putting Back to Service A Post War Odd Ball
SICO TV Cross-Bar Generator
Superior Instruments Company (SICO), New York, New York
Purpose: Early analog TV test pattern generator to set horizontal and vertical linearity and insert horizontal and vertical sweep signal to the TV sweep circuits for troubleshooting. Sold between 1949-50 (no channel 1 on panel).
Well known for making low cost multiple function test equipment, SICO rapidly jumped into the TV repair equipment business in the late 1940s. The flood of World War Two surplus electronic components and hardware made SICO's promise of affordable test equipment possible. It would not be surprising to find the same model number of SICO equipment having components with vastly different descriptions. Also, it was a common to find parts used in SICO equipment that were over rated to what was actually needed. If you got a hold of a piece of SICO equipment, opening one up will definitely make one do a lot of "scratching your head" curiosity. The use of oddball parts also makes restoring these a challenge at times.
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Putting It Back into Service.
This was done on and off over a span of years and was completed Dec 7, 2017.I picked up this TV Cross-Bar Generator on Ebay at least 5 years ago. You see these every so often and of course there is no manual with them or accessories. I have been looking for a schematic off and on since that time and found none except at the "Radio Museum" site but you need to be a member, which I declined because I generally find what I am looking for without having another ID and password to save. When I first opened it up to look inside here what I found that made me start "scratching" my head.There are 3 vacuum tubes, 2 954 Acorn VHF tubes ( Ch 2-6 VHF oscillator and Modulator) and a 7193 (2C22) HF Triode with plate and grid connected together to form a rectifier. The rotary function 10 position switch was modified to work 4 functions, but the operating deck had no stop position. The remaining deck had the contact points removed as is non-operating. SICO used it as a terminal connections. The resistors and capacitors were a mixed bag, the twist lock electrolytic filter cap had an unused section, some caps were connected in parallel to get the right value, resistors were a mixed of of 1930 to 1950 designs and resistors were hooked up in series to get the right value. I looked in the internet to see other versions of this, and one can see the variations of part and part combinations used to assemble this. The power transformer of mine only used the center tap and one end on the high voltage secondary. The other end was not connected. Other versions used all 3 wires on the high voltage secondary. Here goes the restoration of this odd ball.
Photo from mbear2K LINK: http://www.videokarma.org/showthread.php?t=247769
Photo from bandersentv LINK: https://www.youtube.com/user/bandersentv/about
My version, some components looked like those shown here but there were others that were really different.
LEFT PHOTOS:
Shown is an example of the components used in the TV Cross-Bar Generator. Notice the mixed technology.
Lower Left PHOTO:is the chassis side up. The vacuum tubes at the top end are the 954 acorn tubes. NOTICE ON RIGHT PHOTO that the left tube is connected in the opposite direction of the right acorn tube. This was a major factor why my unit never worked and a couple of the resistors were overheating. My unit was worked on and the left tube was in the same direction as the right tube. Notice the tube at the bottom, this is a 7193 or 2C22. The tube caps are the plate and grid, they are connected together so it is a rectifier instead of a high frequency triode.
As can be seen, for the most part I removed all the paper capacitors and put modern ones in. I only restuffed the parts on the chassis top side.
Notice on the left picture two 2 watt resistors were used. A 5600 ohm and a 18000 ohm. They should be 0.5 watt resistors. My version was modified in the past. So I tried to match other versions on the internet to mine. Mine had a 18000 ohm instead of 5600 ohm and a 3300 ohm instead of the 18000 ohm. After I made the changes, turned it on and I got smoke from the 5600 ohm. Decided to reverse engineer it and drew a schematic. Found that the 5600 is connnected to the 954 tube's control grid and the 18000 ohm connected to the screen and supressor grid. Voltage checks indicated the tube to be conducting backwards. control grid voltage at +10 and Screen grid at +6 while the plate was essentially grounded. No wonder the resistor smoked so I put the big watt ones until I can figure what's wrong.
I was pretty sure that the 5600 ohm should go to the plate and the cathode should be close to ground potential. The photos from other collectors were hard to know this. I tried the "Radio Museum" site again and you can see a low resolution schematic and I was right, the plate needs the high voltage connection and control grid should be near ground. That can only be done if the 954 acorn tube was flipped the other way. When that was done no more smoke and signals coming out. The voltages look good and I left the 2 watt resistors there, somehow they look cool and old looking.
Changing Position of the Modulator Acorn Tube
Upside down or right side up?
LEFT PHOTO: Foreground: 954 Acorn Tube used as Channel 2-6 OscillatorCarefully notice the position. The wire connecting to the tube is the PLATE side.
RIGHT PHOTO: Chassis turned around, in the foreground: The other 954 Acorn Tube used as a modulator for Horizontal and Vertical signal source. The wire connected to the control grid side.
The acorn tube has a HEAD (tall side) and TAIL (short side) The HEAD is always the Plate and the TAIL is always the Control Grid. >>>>>>>>>
954 Acorn Pentode Tube: The longer top is the HEAD and has the PLATE connection, while the lower shorter part or TAIL has the CONTROL GRID connection.
Checking the Channel 2-6 RF with Tektronix TDS-1002 DSO configured as a Spectrum Analyzer:
The SICO Channel Selector is continuously variable so I needed to try to set the pointer knob to center of Channel 2, the other channels followed in.
Checking the Modulator (Horizontal and Verftical Sweep) with Tektronix TDS-1002 DSO configured as an oscilloscope:
LEFT TO RIGHT:1. Sweep Frequency near "0" (Horizontal)2. Sweep Frequency near "10" (max H bars)3. Sweep Frequency near "0" (Vertical)4. Sweep Frequency near "10" (max V bars)
Notice on photos 1 and 2 the envelope on the tail end of the wave. That is the RF carrier from the 954 oscillator set for channel 2.
Using the generator on the RCA 630TS Similar Vintage Set: Unlike newer pattern generators, the SICO is very touchy and I had to slowly adjust the sweep frequency control slowly to get the RCA TV to synchronize. Also the V LIN / SWP and H LIN/ SWP selector don't always do what it says so there are often times I will use the wrong setting to get what I need. The Vertical is the worse, and I had to use the V SWP selection to get the vertical bars to function on RF input (shouldn't operate like that).
LEFT TO RIGHT:
1. H LIN set for fewer bars2. H LIN set for many bars3. V LIN set for fewer bars4. V LIN set for many bars
1. H LIN set for fewer bars2. H LIN set for many bars3. V LIN set for fewer bars4. V LIN set for many bars
Conclusion:
Rather inconvenient for servicing but better than nothing to check severity of horizontal and vertical linearity settings on the TV. Still worth keeping in my collection because of how odd ball the components are and the influence of World War 2 on the post war growth of electronics. It is an example of the challenges of restoration of vintage equipment.------------------------------------------------------------------
Need a Schematic of the SICO TV Cross-Bar Generator? Try Mine:
25 Years: TV Pattern Generator Digital (IC's) vs Analog (Tube) mid 1970's CONAR 682 and 1949-50 SICO
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