26-05-2017, 05:20 AM
That would be the original version of the Jason/Jasonkit JTV, available both built and in kit form, and I think released later the second part of 1958, concurrently with the Jason/Jasonkit FMT3. I think that it lasted about a year before being replaced by the better-known Jason/Jasonkit JTV2, which then stayed available until the end of Jason. The JTV2 used a modified Fireball tuner, and had AFC but not a tuning indicator. The JTV2 circuit (less the AM noise limiter diode) was also used in the Jasonkit Mercury 2/Jason Monitor. In the Jasonkit case, it replaced the original FM-only Mercury. In the Jason built series, it arrived at a time when all of the previous Jason switched FM tuners had gone.
The original JTV and any detailed information on it appear to be very scarce, whereas that for the JTV2 and Mercury 2/Monitor is reasonably available. All I have is the valve line-up for the JTV, which as you have already stated, was ECC84, ECF80, EF89, EF80, EM81, EZ80. No doubt it had a pair of crystal diodes for FM demodulation, probably a ratio detector given that there were only two IF stages. (Jason used both this and the Foster-Seeley discriminator according to situation.) AM demodulation might have used another diode, although the JTV2 used the limiter grid as the source of demodulated AM. But then it had three IF stages of which the third was purely a limiter. In the case of the JTV, probably the EF80 was an amplifier/limiter.
Steve P.
The original JTV and any detailed information on it appear to be very scarce, whereas that for the JTV2 and Mercury 2/Monitor is reasonably available. All I have is the valve line-up for the JTV, which as you have already stated, was ECC84, ECF80, EF89, EF80, EM81, EZ80. No doubt it had a pair of crystal diodes for FM demodulation, probably a ratio detector given that there were only two IF stages. (Jason used both this and the Foster-Seeley discriminator according to situation.) AM demodulation might have used another diode, although the JTV2 used the limiter grid as the source of demodulated AM. But then it had three IF stages of which the third was purely a limiter. In the case of the JTV, probably the EF80 was an amplifier/limiter.
Steve P.
