15-04-2017, 02:07 AM
Thanks, Trevor.
I suspect that Dynatron must have made a “running change” to the EF86 during the T99 production run, having previously used a different valve in that position.
Both the EF86 and its Osram counterpart, the Z729 were released in mid-1953, whereas the T99 I can trace back to 1951 October, and the T99A to 1952 September.
Dynatron was unusual in offering four-position variable selectivity, a feature that was found, as far as I know, on the T69, T99, T57, T139, T10 and T11 series models. This allowed it to include a very narrow position of just 5 kHz bandwidth, really more in the communications than in the entertainment class. This, combined with two IF stages, would account for the very good selectivity of the T99.
For comparison purposes, here is a partial list of what other makers of variable selectivity AM tuners did along this vector, quoting nominal IF bandwidths:
Dynatron various models: 5, 10, 15 and 20 kHz.
Chapman S4 & S5: 14 and 20 kHz.
Chapman S6BS and S6: 10, 14 and 20 kHz.
Leak VS: 6 to 24 kHz continuously variable, “stops” at 6, 12 and 24 kHz.
Rogers RD Junior: 7, 15 and 23 kHz.
Armstrong various models: Unknown, but some evidence that narrowest (of 3 positions) was 7 kHz.
Lowther DT4 & DT5: Unknown.
Quad AM & AMII: 10 and 24 kHz.
Jason AM/FM2: 8 and 16 kHz.
Heathkit AFM-1: 8 and 16 kHz
Quad AM3: 7 and 24 kHz.
Cheers,
Steve
I suspect that Dynatron must have made a “running change” to the EF86 during the T99 production run, having previously used a different valve in that position.
Both the EF86 and its Osram counterpart, the Z729 were released in mid-1953, whereas the T99 I can trace back to 1951 October, and the T99A to 1952 September.
Dynatron was unusual in offering four-position variable selectivity, a feature that was found, as far as I know, on the T69, T99, T57, T139, T10 and T11 series models. This allowed it to include a very narrow position of just 5 kHz bandwidth, really more in the communications than in the entertainment class. This, combined with two IF stages, would account for the very good selectivity of the T99.
For comparison purposes, here is a partial list of what other makers of variable selectivity AM tuners did along this vector, quoting nominal IF bandwidths:
Dynatron various models: 5, 10, 15 and 20 kHz.
Chapman S4 & S5: 14 and 20 kHz.
Chapman S6BS and S6: 10, 14 and 20 kHz.
Leak VS: 6 to 24 kHz continuously variable, “stops” at 6, 12 and 24 kHz.
Rogers RD Junior: 7, 15 and 23 kHz.
Armstrong various models: Unknown, but some evidence that narrowest (of 3 positions) was 7 kHz.
Lowther DT4 & DT5: Unknown.
Quad AM & AMII: 10 and 24 kHz.
Jason AM/FM2: 8 and 16 kHz.
Heathkit AFM-1: 8 and 16 kHz
Quad AM3: 7 and 24 kHz.
Cheers,
Steve
