10-07-2020, 12:16 PM
(This post was last modified: 10-07-2020, 12:24 PM by Mike Watterson.)
Great.
I've been doing a belated "spring clean" of my workshop. I've a few projects to finish and then I'll take a look again at the 1j24b, 1j29b, 1j42a and compare the DM70 with the Russian battery Magic Eye and maybe the DM160 with the Russian VFD indicator which only uses a 0.6V filament. I did try two of the 0.6V Vf Russian indicators in series with one as a phase splitter and one as an AGC amp. The idea also was to mount them on a perspex the tuning cursor to illuminate it. The set uses 2 x 1j24b as push pull using a very miniature mains transformer; the push pull means no risk of Saturation and it's more audio power than DL94 with 1/4 of the filament current.
I've not done the AM and VHF RF and mixer stages yet. For first iteration I'm using the rectangular small Philips AM/FM IFTs as used in the 1950s Philips mains and battery AM/FM sets. Later I'll try home brew air core IFTs using capacitor tuning to see if the Q is better.
AM detector is 1N60 and the FM diodes are 1N4148. AGC via g2, hence the diode detector for AM is Positive and the indicator amplifies a little, inverts and level shifts to the +20 to +55 AGC range needed for the 1j24b g2. The +55V being the indicator off. The negative bias for that and the 1J24b are from a battery for testing, but will be from a low pass filter connected to the 1j24a g1 local oscillator. Valve oscillators generate a more negative voltage on the grid than on the cathode/filament. The Philips Colette uses this (even on Gram and VHF) from the DK96 g1 as output valve bias as it's push pull.
I've been doing a belated "spring clean" of my workshop. I've a few projects to finish and then I'll take a look again at the 1j24b, 1j29b, 1j42a and compare the DM70 with the Russian battery Magic Eye and maybe the DM160 with the Russian VFD indicator which only uses a 0.6V filament. I did try two of the 0.6V Vf Russian indicators in series with one as a phase splitter and one as an AGC amp. The idea also was to mount them on a perspex the tuning cursor to illuminate it. The set uses 2 x 1j24b as push pull using a very miniature mains transformer; the push pull means no risk of Saturation and it's more audio power than DL94 with 1/4 of the filament current.
I've not done the AM and VHF RF and mixer stages yet. For first iteration I'm using the rectangular small Philips AM/FM IFTs as used in the 1950s Philips mains and battery AM/FM sets. Later I'll try home brew air core IFTs using capacitor tuning to see if the Q is better.
AM detector is 1N60 and the FM diodes are 1N4148. AGC via g2, hence the diode detector for AM is Positive and the indicator amplifies a little, inverts and level shifts to the +20 to +55 AGC range needed for the 1j24b g2. The +55V being the indicator off. The negative bias for that and the 1J24b are from a battery for testing, but will be from a low pass filter connected to the 1j24a g1 local oscillator. Valve oscillators generate a more negative voltage on the grid than on the cathode/filament. The Philips Colette uses this (even on Gram and VHF) from the DK96 g1 as output valve bias as it's push pull.
