19-04-2018, 03:03 AM
(17-04-2018, 03:14 AM)Synchrodyne Wrote: Also used in FM front ends was the triode-pentode, with pentode as RF amplifier and triode as self-oscillating mixer. The 6JN8/12JN8 was used for this purpose, although whether it was designed just for that, or was purloined from the rather large American triode-pentode inventory as being the best-suited I do not know. But that there was a 12JN8 variant (150 mA heater) does suggest that it was conceived with radio applications in mind. And I am not aware that there were 450 mA or 600 mA variants, of which at least the latter was normal for American TV valves, in addition to the baseline 6.3-volt version.
I need to correct that paragraph:
The 150 mA series-string version of the 6JN8 (which was in fact 6.3-volt 450mA, not 300 mA) was the 19JN8, not the 12JN8. Rather the 12JN8 had a 12.6-volt heater for car radio applications. A separate series of 12.6-volt heater American valves was started in 1952 as American cars generally moved from 6-volt to 12-volt electrical systems. Most of these valves were drawn from separate series, particularly the 150 mA series, because they happened to have 12.6-volt heaters for other reasons. But there were a small number of new issues.
That suggests that the 6/12/19JN8 was issued as a radio valve rather than a TV valve. Another American radio triode-pentode was the 19HV8 (no apparent corresponding 6HV8 issue). Here the pentode was of the sharp cutoff type intended for use as an IF amplifier or limiter. The triode was a 70-mu AF amplifier. Its introduction recognized the increasing use of crystal diodes for demodulation, and the consequent move away from valves like the 6T8/19T8 triple diode-triode. The 19HV8 pentode would be used for example as the FM final IF amplifier or limiter, driving a pair of crystal discriminator diodes, and the triode as 1st AF amplifier, effectively replacing the triode that otherwise would have been provided by the now not-present 19T8. And of course, the 19HV8 pentode could also be used as an AM demodulator. This was done for example in the GE T-230A radio receiver of the early 1960s, which also used a 19JN8 for its FM front end.
Cheers,
Steve
