schaub: Weekend 57U 'Dual Conversion'

Technically yes, this radio has dual conversion. But Dual Conversion is usually on Short Wave (HF) to get IF good image rejection (High 1st IF) and narrow bandwidth (low 2nd IF).

In this case the 2nd conversion is so as to get some gain advantage from the DK96 Heptode Mixer/Osc usually disabled on AM/FM battery sets on FM, though technically it's possible to use it as an amplfier rather than Oscillator (on g2 as an "anode") and Mixer.

On LW, MW & SW the circuit is like any other AM set, but with 2 x IF Amps (which is the case on the Vidor Vanguard AM/FM valve (tube) Portable and some more deluxe AM models too), but the first DF96 stage is only single tuned. On VHF-FM the DF97 stage is also like any other Triodised Additive Mixer/Osc with 10.7MHz. The DK96 is then running with a fixed L.O. to convert the 10.7MHz to 6.7MHz. On VHF the first 460kHz tuned stage on the DK96 anode is "shorted out".

Design of true Dual Conversion Shortwave set though is possible with this valve line up. In this case one of the DF96 would be before the DK96 and on LW & MW only one IF amp, but the DF96 could be an RD preamp. The DF97 would be a LO only on SW and the DF96 a Mixer / 1st IF amp as on the Vidor Vanguard which uses only DF97 for ALL the AM & FM RF, Mixer and IF functions. On SW the DK96 would be 2nd conversion from 10.7MHz to 460KHz. In this hypothetical re-design the DK96 could be used as it is currently, but the 1st DF96 moved to before the DK96 might be better as a DF97, though the DF96 does work.

To thank the Author because you find the post helpful or well done.