Notes on 1LA6 Conversion from Bill Harris

A Replacement for the 1L6 in Zenith TransOceanics
In the T/O's that use the miniature all-glass tubes, the 1L6 pentagrid converter can be hard to find and expensive. One trick is to replace it with a 1R5. The electrical characteristics of the 1L6 and 1R5 are different and this can lead to problems of low sensitivity on some of the higher frequency bands and alignment problems.

Fred Gordon of Fred's Old Radio Emporium in Corsicana, Texas offers another solution.

Upon checking his RCA tube manual, Fred discovered that the 1LA6, which is used in the earlier T/O models, is an electrical equivalent of the 1L6. The 1L6 is a 7-pin miniature, while the 1LA6 is an 8-pin loktal.

As an expirement, Fred wired the 1LA6 loktal tube base to a 7-pin male plug that will insert into the orginal 1L6 socket on the T/O chassis. The wiring between the 8-pin loktal socket and the 7-pin male plug is pin-for-pin except for one wiring change. The interconections between the male plug and the loktal socket are shown below.


1L6  Socket Pin #  1  2  3  4  5  6  7  
                   |  |  |  |  |  |  |
1LA6 Socket Pin #  1  2  3  4  5  6  8

Fred says that after completing the modification the set worked on all bands from broadcast to 18 MHz with normal sensitivity. The dial calibration on this particular set was a bit off, maybe due to the extra wire length used in the modification, which upsets the original local oscillator portion of this circuit. This was corrected by a touch-up of the oscillator coils for each band.