01-07-2017, 10:47 PM
Re the JTV front end, my working assumption has been that it was a modified TV-FM 12-position turret. The modifications would have been the use of E-series rather than P-series valves (which was very likely an export option anyway) and the modification of the TV channel “biscuits” to provide a 10.7 MHz IF. But standard FM biscuits probably could have been used, given that some TV-FM front ends were designed to provide a 10.7 MHz IF on FM, but 38.15 MHz on TV.
But it might have been simpler than that. With the start of Band III TV transmissions in the UK, some front end makers produced units that could be used to modify existing Band I-only superhet receivers to receive cover Bands I and III. Cyldon and Brayhead appear to have been the main practitioners here, offering variations on their standard turret tuners, the TV12 in the Cyldon case. These conversion units were available with “E”, “P” or “U” series valves as required to match specific receivers, with a range of IFs, typically covering 10, 16 and 38 MHz groups, and with oscillator low or high as required. The IFs had a reasonable range of adjustment around their nominal values. I think that Cyldon offered a wider range than did Brayhead.
A couple of examples of such conversion front ends were the Cyldon E10L, with “E” series valves, 10 MHz IF and oscillator low, and the Brayhead 10P, 10.5 MHz sound IF and “E” series (Parallel heater) valves. With either of these, the IF would have been adjustable to 10.7 MHz, so for the JTV, the TV channels could have been covered with standard components. These conversion units would not normally have covered FM frequencies, but their respective makers’ standard FM biscuits (for 10.7 MHz) would have fitted.
So, the JTV front end might have been comprised of all standard components.
I do not know whether the JTV front end was oscillator-low or oscillator-high, but then it would not have mattered very much for this application. Band I-only superhet TV receivers with the sound IF around 10 MHz were mostly oscillator-low as far as I know, so 10 MHz conversions units may have been available only as oscillator-low.
I’d guess that the demand for conversion units would have waned by the end of the 1950s, so they were probably withdrawn from production about then. That would have been another reason for Jason to develop a bespoke solution for the JTV2, if in fact had gone the above suggested route.
In the HFN 1958 September article attached upthread, there is a picture of a turret biscuit, which is of the single-piece form. That might outrule a Cyldon TV12 derivative, as I think that had two biscuit pieces per channel.
Cheers,
Steve
But it might have been simpler than that. With the start of Band III TV transmissions in the UK, some front end makers produced units that could be used to modify existing Band I-only superhet receivers to receive cover Bands I and III. Cyldon and Brayhead appear to have been the main practitioners here, offering variations on their standard turret tuners, the TV12 in the Cyldon case. These conversion units were available with “E”, “P” or “U” series valves as required to match specific receivers, with a range of IFs, typically covering 10, 16 and 38 MHz groups, and with oscillator low or high as required. The IFs had a reasonable range of adjustment around their nominal values. I think that Cyldon offered a wider range than did Brayhead.
A couple of examples of such conversion front ends were the Cyldon E10L, with “E” series valves, 10 MHz IF and oscillator low, and the Brayhead 10P, 10.5 MHz sound IF and “E” series (Parallel heater) valves. With either of these, the IF would have been adjustable to 10.7 MHz, so for the JTV, the TV channels could have been covered with standard components. These conversion units would not normally have covered FM frequencies, but their respective makers’ standard FM biscuits (for 10.7 MHz) would have fitted.
So, the JTV front end might have been comprised of all standard components.
I do not know whether the JTV front end was oscillator-low or oscillator-high, but then it would not have mattered very much for this application. Band I-only superhet TV receivers with the sound IF around 10 MHz were mostly oscillator-low as far as I know, so 10 MHz conversions units may have been available only as oscillator-low.
I’d guess that the demand for conversion units would have waned by the end of the 1950s, so they were probably withdrawn from production about then. That would have been another reason for Jason to develop a bespoke solution for the JTV2, if in fact had gone the above suggested route.
In the HFN 1958 September article attached upthread, there is a picture of a turret biscuit, which is of the single-piece form. That might outrule a Cyldon TV12 derivative, as I think that had two biscuit pieces per channel.
Cheers,
Steve
