06-07-2020, 06:26 PM
In 1949 an EB91 dual diode ( EB91 = 6AL5 = EAA91 = 6B32 = 6D2 = CV140 = CV283 = DD6) was cheaper than 1 x 1N34 or 1 x 1N60.
If you had a AF preamp, you could get one with a diode built in virtually the same price as a triode or pentode on its own. So when superhets with AGC were the norm from 1935, there were also triodes with diodes (free) in the same envelope.
Occasionally there were RF/IF pentodes used with a detector diode, for superhets with no preamp, only one audio valve. Or the EBL1, EBL31, EBL21 and EBL71 output Pentodes with dual diodes.
There is no real need for a second diode for AGC, but it was "free" and usually driven with a capacitor and was across the AGC line to 0V, so it or the main diode ( xAC series triodes and xAF series Pentodes, in 2V, 1.4V, 4V, 5V, 150 mA, 200mA, 300 mA series and 6.3V etc) gives a more negative voltage the stronger the signal. AGC isn't so common on TRFs, except late ones like the Philips Superinducance series.
Early TRFs adjusted the filament current on the RF Triode or SG (RF Tetrode) for a volume control, if it wasn't purely by Reactance feedback.
The Infinite Impedance detector is rare, because before combined triode-diodes and pentode-diodes in superhets the gain was an issue, so reaction, leaky grid, etc was used. Very occasionally in early 1930s to save a valve they used a semiconductor rectifier, I think usually copper oxide. Germanium diodes started to be used in professional equipment in 1938 or 1939. The 1N34 and 1N60 easily available by 1947.
The first common use of semiconductor diodes was in battery radios with FM. Germany started FM in 1949 because of the Allies taking MW & LW allocations. Thus unlike UK 1955 to 1971 (approx) the FM actually had extra stations. The first models used DC90 as FM mixer/osc. One early model might have used the EC90 (150mA 6.3V). They almost all used DK96 as AM mixer/osc with DAF96 as the AM detector and AF preamp. All used two semiconductor diodes for the FM detector. A valve solution was too much filament current. Later the DF96 was replaced by DF97 on some for IF and on all a triodised DF97 instead of the DC90. They are interchangeable with little shift in tuning, though the DC90 is 50mA and DF97 is 25mA. On some DF97 sets you need to cut an extra earth wire to use a DC90, which doesn't seem to affect operation. AFAIK all AM/FM battery valve sets are parallel and the US never made any, because FM was regarded as HiFi only. There was one USA "novelty" battery valve model, an FM super regenerative single valve type.
It would be interesting to see what is the maximum frequency the 1j42a does. The other Rod Tubes certainly are roughly as good as an EF80 for VHF oscillators.
If you had a AF preamp, you could get one with a diode built in virtually the same price as a triode or pentode on its own. So when superhets with AGC were the norm from 1935, there were also triodes with diodes (free) in the same envelope.
Occasionally there were RF/IF pentodes used with a detector diode, for superhets with no preamp, only one audio valve. Or the EBL1, EBL31, EBL21 and EBL71 output Pentodes with dual diodes.
There is no real need for a second diode for AGC, but it was "free" and usually driven with a capacitor and was across the AGC line to 0V, so it or the main diode ( xAC series triodes and xAF series Pentodes, in 2V, 1.4V, 4V, 5V, 150 mA, 200mA, 300 mA series and 6.3V etc) gives a more negative voltage the stronger the signal. AGC isn't so common on TRFs, except late ones like the Philips Superinducance series.
Early TRFs adjusted the filament current on the RF Triode or SG (RF Tetrode) for a volume control, if it wasn't purely by Reactance feedback.
The Infinite Impedance detector is rare, because before combined triode-diodes and pentode-diodes in superhets the gain was an issue, so reaction, leaky grid, etc was used. Very occasionally in early 1930s to save a valve they used a semiconductor rectifier, I think usually copper oxide. Germanium diodes started to be used in professional equipment in 1938 or 1939. The 1N34 and 1N60 easily available by 1947.
The first common use of semiconductor diodes was in battery radios with FM. Germany started FM in 1949 because of the Allies taking MW & LW allocations. Thus unlike UK 1955 to 1971 (approx) the FM actually had extra stations. The first models used DC90 as FM mixer/osc. One early model might have used the EC90 (150mA 6.3V). They almost all used DK96 as AM mixer/osc with DAF96 as the AM detector and AF preamp. All used two semiconductor diodes for the FM detector. A valve solution was too much filament current. Later the DF96 was replaced by DF97 on some for IF and on all a triodised DF97 instead of the DC90. They are interchangeable with little shift in tuning, though the DC90 is 50mA and DF97 is 25mA. On some DF97 sets you need to cut an extra earth wire to use a DC90, which doesn't seem to affect operation. AFAIK all AM/FM battery valve sets are parallel and the US never made any, because FM was regarded as HiFi only. There was one USA "novelty" battery valve model, an FM super regenerative single valve type.
It would be interesting to see what is the maximum frequency the 1j42a does. The other Rod Tubes certainly are roughly as good as an EF80 for VHF oscillators.
