19-06-2017, 08:48 AM
Here is the original article on the Jasonkit JTV, from Hi-Fi News (HFN) for 1958 September:
This shows the schematic for the IF strip, but not for the turret. The make and model of the turret is not identified. At the end of the article it was noted: “A reprint of this tuner unit will be available shortly in booklet form, and will contain additional drawings, photos and circuitry of the turret tuner for those who are interested in a more detailed description of this design.” So one would have to find the HFN Reprint for a full schematic. And preferably the supplement that was mentioned in HFN 1959 June as being scheduled to appear in the 1959 July issue.
As far as I can see, the schematic does not show provision for the feedback of AGC bias from the limiter grid to the RF stage. As this was mentioned in HFN 1959 June, possibly it was an early amendment.
The article includes an interesting comment about the choice of a ratio detector, thus: “There still exist a legend that the Foster Seeley discriminator has the best performance. In fact it is often used because it gives the cheapest form of detection. In practice the performance of the Ratio Detector is better, provided that it is designed for minimum distortion and is preceded by a limiter stage. (In cheaper radios the Ratio Detector is designed for optimum noise rejection and nor preceded by a limiter and only under those conditions is the distortion greater than that from the Foster Seeley discriminator.)”
That may have been a slight simplification of the actual situation. Johnstone, in Wireless World 1957 May, page 238ff, stated that distortion-wise, a Foster-Seeley discriminator was better than a ratio detector of comparable bandwidth, but not necessarily better than a wide-band ratio detector. It was difficult to design the Foster-Seeley discriminator for wide bandwidth, whereas it could be done with the ratio detector. But then the latter lost its AM rejection capability, and had to be preceded by a limiter stage (or stages). The JTV was said to have a wide-band ratio detector.
HFN 1958 June also included an advertisement for the “built” Jason JTV, with the note that a Jasonkit version would shortly be available.
Cheers,
Steve
This shows the schematic for the IF strip, but not for the turret. The make and model of the turret is not identified. At the end of the article it was noted: “A reprint of this tuner unit will be available shortly in booklet form, and will contain additional drawings, photos and circuitry of the turret tuner for those who are interested in a more detailed description of this design.” So one would have to find the HFN Reprint for a full schematic. And preferably the supplement that was mentioned in HFN 1959 June as being scheduled to appear in the 1959 July issue.
As far as I can see, the schematic does not show provision for the feedback of AGC bias from the limiter grid to the RF stage. As this was mentioned in HFN 1959 June, possibly it was an early amendment.
The article includes an interesting comment about the choice of a ratio detector, thus: “There still exist a legend that the Foster Seeley discriminator has the best performance. In fact it is often used because it gives the cheapest form of detection. In practice the performance of the Ratio Detector is better, provided that it is designed for minimum distortion and is preceded by a limiter stage. (In cheaper radios the Ratio Detector is designed for optimum noise rejection and nor preceded by a limiter and only under those conditions is the distortion greater than that from the Foster Seeley discriminator.)”
That may have been a slight simplification of the actual situation. Johnstone, in Wireless World 1957 May, page 238ff, stated that distortion-wise, a Foster-Seeley discriminator was better than a ratio detector of comparable bandwidth, but not necessarily better than a wide-band ratio detector. It was difficult to design the Foster-Seeley discriminator for wide bandwidth, whereas it could be done with the ratio detector. But then the latter lost its AM rejection capability, and had to be preceded by a limiter stage (or stages). The JTV was said to have a wide-band ratio detector.
HFN 1958 June also included an advertisement for the “built” Jason JTV, with the note that a Jasonkit version would shortly be available.
Cheers,
Steve
