26-05-2017, 11:32 PM
Of course, the use of 6.3-volt heater valves was the norm for hi-fi equipment including tuners, and the Jason JTV followed this norm. The JTV and JTV2 were both self-powered, but some Jason equipment, such as the Mercury 2/Monitor was externally powered, requiring both HT and LT supplies. Where a suitable power supply from an associated amplifier was not available, Jason offered a power supply unit, both in built and kitset form.
As far as I know, proprietary TV front ends were usually available with both conventional 6.3-volt heater valves and series-string 300 mA heater valves. In fact, in the USA, the makers catered for both 600 mA and 450 mA series strings. In this part of the world, most valved TV receivers had “proper” power supplies, with double-wound power transformers, and used 6.3-volt valves. Thus, the ECC84 and ECF80 were commonly found in front ends. So, there was really nothing strange about Jason’s use of the ECC84 and ECF80 in the JTV. Both were also found in UK FM tuner and receiver practice.
Re information about the JTV, apparently Hi-Fi News (HFN) ran an article about it when it was released. HFN claimed to have been instrumental in persuading Jason to develop the JTV and then offer it in both built and kitset forms. I don’t know which HFN issue it was in, but I would guess somewhere in the second half of 1958. How much detail is also unknown, but I should expect at least a circuit description if not a schematic. Unfortunately, back issues of HFN are not readily available. The front end circuit might be available separately if the make and model of the unit are known; Cyldon, Plessey, AB Metal Box would be candidates amongst others. As mentioned, for the JTV2, Jason used the American-origin Fireball front end, which I think was made in the UK by AB Metal Box. So maybe the latter had also been the supplier of the regular turret used in the JTV. It would have been modified to provide a 10.7 MHz IF output on TV sound as well as FM, but probably was otherwise standard, unlike the JTV2 case, where the front end was significantly modified.
Given that the JTV had a fairly short production life, I suspect that it was not entirely satisfactory, and may have been wanting in the gain and stability departments. Hence the JTV2, with greater IF gain (although probably with less front end gain) and AFC.
Re Pro-Electron valve designations, three-digit suffixes appear to have arrived in the late 1950s, presumably because there were not enough in the allocated two-digit ranges. Early examples include the EF183, EF184 and ECC189. And three-digit suffixes in the 500 series appear to have been used for magnoval-based valves from the beginning of that type, starting with the EL500, which was a very common TV valve here.
Steve
As far as I know, proprietary TV front ends were usually available with both conventional 6.3-volt heater valves and series-string 300 mA heater valves. In fact, in the USA, the makers catered for both 600 mA and 450 mA series strings. In this part of the world, most valved TV receivers had “proper” power supplies, with double-wound power transformers, and used 6.3-volt valves. Thus, the ECC84 and ECF80 were commonly found in front ends. So, there was really nothing strange about Jason’s use of the ECC84 and ECF80 in the JTV. Both were also found in UK FM tuner and receiver practice.
Re information about the JTV, apparently Hi-Fi News (HFN) ran an article about it when it was released. HFN claimed to have been instrumental in persuading Jason to develop the JTV and then offer it in both built and kitset forms. I don’t know which HFN issue it was in, but I would guess somewhere in the second half of 1958. How much detail is also unknown, but I should expect at least a circuit description if not a schematic. Unfortunately, back issues of HFN are not readily available. The front end circuit might be available separately if the make and model of the unit are known; Cyldon, Plessey, AB Metal Box would be candidates amongst others. As mentioned, for the JTV2, Jason used the American-origin Fireball front end, which I think was made in the UK by AB Metal Box. So maybe the latter had also been the supplier of the regular turret used in the JTV. It would have been modified to provide a 10.7 MHz IF output on TV sound as well as FM, but probably was otherwise standard, unlike the JTV2 case, where the front end was significantly modified.
Given that the JTV had a fairly short production life, I suspect that it was not entirely satisfactory, and may have been wanting in the gain and stability departments. Hence the JTV2, with greater IF gain (although probably with less front end gain) and AFC.
Re Pro-Electron valve designations, three-digit suffixes appear to have arrived in the late 1950s, presumably because there were not enough in the allocated two-digit ranges. Early examples include the EF183, EF184 and ECC189. And three-digit suffixes in the 500 series appear to have been used for magnoval-based valves from the beginning of that type, starting with the EL500, which was a very common TV valve here.
Steve
