Rare! 1958 Sylvania

[jshorva65]

Since I'll be restoring the "sister set" to this 1958 Sylvania (Sylvania model 31C304M), it would be good to know whether anyone has data on feasibility of making an adaptor for interfacing this Sylvania color chassis to the GTE/Sylvania CK-3000 test rig (or a TeleMatic rig of similar vintage) for bench testing, since neither rig supports that chassis directly.

For both units, the earliest color chassis supported directly by its adaptor complement was the RCA CTC-7. If a correct set of Yoke Program, Convergence Ballast, and Yoke Cable characteristics could be determined, then the use of test rigs would help simplify these early sets' restorations greatly. It would seem that the correct yoke wiring harness could be as easy to create as making an adaptor to mate the leads of the existing "roundie" yoke harness to the correct plug for the older chassis. That would leave only the correct Yoke Program and Convergence Ballast values and pinouts to be determined, since the CRT cable should be directly compatible with all 21" color tube applications.

The most important consideration (aside from the obvious ones such as compatibility with 70-degree color chassis of any kind in the first place) in using a test rig with a particular model of 70-degree color chassis similar to one which it supports directly is matching the impedances of the respective yoke windings in the rig to those of the set's own yoke within a reasonable tolerance. For both windings, +/-10% is preferred, while +/-15% is about the maximum tolerable degree of mismatch. Most 70-degree color yokes will typically have similar impedances, within +/-20%, as an educated guess. Uncontrollable vertical "rolling" seems to be the most frequently occurring symptom when operating test rigs with 70-degree color chassis when there is a moderate mismatch of convergence ballasts. Of course, a severe mismatch of Yoke or Convergence impedance could easily damage the rig, the chassis, or both.

In the absence of a means to match my CK3000 to the chassis, I could fabricate extension leads and fit the set's own Yoke and Convergence components onto the good 21FBP22 in a "roundie" set I have here with a structurally sound cabinet and severely damaged faux finish. Cushioning the set top with a rug to avoid worsening the damage to its cabinet, I could then use the cabinet top as a workbench during phases of the Restoration where operation of the chassis with a CRT connected will be necessary (troubleshooting) or at least highly desirable (alignment, etc.) while the set's own cabinet is stored safely out of the way of the service bay area.