The November 2002 Freezeframe question, “Name the early TBCs from RCA and Ampex, define the acronym and tell the key difference between the two,” resulted in some great answers.
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Exacting and correct answers were received from David Fibush, Don Eckis, Jim Borgioli, John Turner and Tim Stoffel. Shown below are answers from Turner and Stoffel. For you newbies out there, this represents real history!
Editor's note: This question generated a number of excellent responses. Shown below are two of the most complete answers to the question.
From John Turner:
First of all, you cannot equate AMTEC and CAVEC to each other as they perform very different signal corrections.
AMTEC:
This is an electronically variable delay line based on varicap diodes invented by Charles Colson of WBBM-TV and originally called ColTEC. When Ampex hired Colson away from WBBM, the name was changed to the “Ampex Time Element Compensator”, i.e., AMTEC. When used with the Ampex “Intersync” servo, the machine would output FCC stable monochrome video.
The RCA equivalent to AMTEC was called MATC for “Monochrome Automatic Timing Corrector,” which worked with the RCA “Pixlock” servo.
For color stability, the manufacturers used COLORTEC and CATC circuitry, respectively.
CAVEC:
This was a module (at least pre TR-600) that performed two very different functions. The acronym stands for “Chroma Amplitude and Velocity Error Corrector.” The Ampex equivalent to the RCA “CA___” was the “AutoChroma” circuitry. This portion of the CAVEC acted to equalize on a line-by-line basis the amplitude variations of chroma using the fixed amplitude of demod burst as a reference. The correction was applied to the demod and had nothing to do with the downstream TBC systems.
The RCA “__VEC” section is analogous to the Ampex “Velcomp” accessory. Both of these devices measured the burst phase at the beginning and end of a single line. This data was used to create a line time linear ramp error signal, which was added back in to the TBC error signal to reduce the appearance of color hues that shift horizontally across a picture. This correction was needed due to the “step” nature of the MATC/CATC/AMTEC/COLORTEC error signal derivation.
Just my two cents.
John Turner
Proud owner of Camden and Redwood City Big Iron
From Tim Stoffel:
AMTEC-AMPEX Ampex Time Element Compensator
CAVEC-RCA Chroma Amplitude and Velocity Error Corrector
The timing corrector used in earlier quad VTRs consisted of three blocks. These timing correctors used electronically variable delay lines to effect their correction. The first of these three was a coarse timing error corrector. This corrector would eliminate all but say, 30 nanoseconds, of timing jitter. (The input jitter had to be low to begin with. This is why video heads had air bearings and the female guide position was servo'ed.) This was good enough for black and white.
The Ampex device for this was the AMTEC (invented by Charlie Coleman, who lives out here somewhere in the deserts of Nevada), and the RCA device was the ATC (Automatic Timing Corrector). (RCA loved acronyms! A good future question would be to define some of them, like BALPS, BALLS and PLACH.)
The second of the three correction steps was a fine corrector. This corrector worked to get the residual jitter down to a point where color was possible. It used a shorter but faster variable delay line. The Ampex device for this was the COLORTEC. The RCA device was the CATC.
The third stage of timing correction, which was optional, removed residual errors caused by changes in video head velocity as the head scanned through each band of the picture. These errors were of a nature that required an analog memory circuit to keep track of the error from beginning to end of a video line, as well as the average error for each line in a band, for each of the four heads. These devices, which were bleeding-edge technology for their time, were generically referred to as velocity compensators. Their error correction signal was summed into the CATC or COLORTEC's error signal. The RCA velocity compensator was called the CAVEC, and the Ampex velocity compensator was simply called an “Automatic Velocity Compensator.”
So, the answer to your third question might be: The AMTEC was a first stage or monochrome timing corrector, and the CAVEC was a velocity compensator.
BTW, great issue of the magazine!
Tim Stoffel, KNPB-TV
Reno, NV
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