01-08-2022, 11:05 AM
Certainly the 1j37b ought to work as osc, mixer or mixer-osc up to 60 or 70 MHz, but the 1j24b and 1j29b are probably superior. Unlike a Wunderlich
https://www.radiomuseum.org/tubes/tube_wunderlich.html
or a dual gate fet it's actually just a rod tube with the grid plates that are either side of the filament brought out to separate connections.
Top view of all single filament rod tubes. The dual filament types have a 3rd g1 plate between the two filaments as well as an extra pair of g2 rods. All the tubes have two wedge like electron beams electrostatically focused by g2 and g3. The pair of g1 plates "pinch" the beam and eventually cut it off. If AC is applied ONLY to g1, biased at zero volts then the two g1 plates act as anodes of a rectifier.
The 1j37b and 1j42a can thus be two rectifiers to 0V. The output at g1 is negative.
The rod tubes with g1a and g1b, i.e. the two plates are not internally shorted will thus steer the two beams with any differential voltage, so to enhance the drop in anode current the anodes are wedges instead of plates.
No doubt prototypes where made with the two pairs of g2 rods or anodes brought out separately, but it's obvious that a differential voltage on the two g1 plates will have the greatest effect as they are very close to either side of the filament.
Here is sketch of one half of the tube, one beam:
The dotted rods would be screen rods, connected to f-, f+, s or g3 wires depending on model.
Here is 1j42a, the 1j37b is similar
and to compare, any single filament tube with the g1a and g1b plates internally connected:
Advantages of the 1j37b over the 1j24b
Disadvantages of the 1j37b over the 1j24b
Filament currents vs voltage is interesting.
I'm not sure on the differences on electrode capacitance or maximum frequency.
Note the 1j24b used to replace an existing valve in an aligned radio needs padding cap on at least anode as it is lower capacitance than DK91, DK92, DK96, 1L6, DK40, 1T4/DF91, DF96 on g2, g3 and anode. I'm not sure about DF97 and DC90. I'm not sure if grid needs padding in any circuit. I do plan to replace a 1L6 in USA Worldband sets (I have maybe 4 models). I have to add series and parallel resistors in filament circuit to match the 50mA nominal at 1.35V approx series operation as even two 1j24b as triodised osc and pentode mixer is less than 25mA! I've done one pair with additional capacitors to replace a DK96 without retuning LO or IFT.
The DK92 (without adaptor or DK40 with adaptor) will directly replace the 1L6, but mucks up alignment at shorter wave bands. Some UK/Europe sets used DK40 with Dx9 series valves till the DK92 was available. The DK91 and DK96 are inferior, hence even some 1957 model with SW used the DK92.
The electrode capacitances of all rod types is very low compared to regular B7G types.
Also remote cutoff/variable mu while allowing greater AGC range causes intermodulation if there is an unwanted strong signal. It's achieved by a varied spacing of the helical grid wire. All rod tubes are more linear with a sharp cut off. Some Western commercial or military sets didn't use variable mu valves except at IF to give better IM performance. Also tended to not to use heptodes or octodes (as was common even on USA mains sets) but a separate LO and mixer for better IM performance, no FM modulation of LO and less LO leakage to the aerial.
https://www.radiomuseum.org/tubes/tube_wunderlich.html
or a dual gate fet it's actually just a rod tube with the grid plates that are either side of the filament brought out to separate connections.
Top view of all single filament rod tubes. The dual filament types have a 3rd g1 plate between the two filaments as well as an extra pair of g2 rods. All the tubes have two wedge like electron beams electrostatically focused by g2 and g3. The pair of g1 plates "pinch" the beam and eventually cut it off. If AC is applied ONLY to g1, biased at zero volts then the two g1 plates act as anodes of a rectifier.
The 1j37b and 1j42a can thus be two rectifiers to 0V. The output at g1 is negative.
The rod tubes with g1a and g1b, i.e. the two plates are not internally shorted will thus steer the two beams with any differential voltage, so to enhance the drop in anode current the anodes are wedges instead of plates.
No doubt prototypes where made with the two pairs of g2 rods or anodes brought out separately, but it's obvious that a differential voltage on the two g1 plates will have the greatest effect as they are very close to either side of the filament.
Here is sketch of one half of the tube, one beam:
The dotted rods would be screen rods, connected to f-, f+, s or g3 wires depending on model.
Here is 1j42a, the 1j37b is similar
and to compare, any single filament tube with the g1a and g1b plates internally connected:
Advantages of the 1j37b over the 1j24b
- The grid capacitance is lower in some circuits because there isn't the internal short and the g1 pair are separately connected.
- Frequency doubling is simple. Feed AC differentially to g1a and g1b.
- Detector has more gain. Feed AC differentially to g1a and g1b.
- DC gain control can use a low positive OR negative voltage on g1a or g1b, or differential. The 1j24b needs 15V (near cut-off) to 55V (max gain) on g2 assuming 80V HT. Varies with Anode volts/HT. The control range of the 1j37b is largely unaffected by HT/Anode/g2 volts.
- Mixer operation uses a low level LO. But any LO is likely x20 level needed.
- A full level LO can ALSO be fed to g2 as well as differential signal on g1a and g1b.
Disadvantages of the 1j37b over the 1j24b
- The common mode g1a and g1b capacitance may be higher due components needed.
- The filament current is 58ma to 60mA vs 11mA to 12mA at ideal 1.25V, FIVE times!
- The LO needs attenuated. The 1j24b g2 can be driven direct and biased at DC by the anode of the LO valve.
- The transformer balance to g1 and g2 is critical and centre tap common mode gain must match. Tricky as frequency increased.
- DC control of (differential or one of g1 and g2) must not affect RF match at g1 or g2 or max gain is reduced and there can be partial frequency doubling/rectifying (though you might want this).
- Less screen rods.
- It's a larger tube.
Filament currents vs voltage is interesting.
I'm not sure on the differences on electrode capacitance or maximum frequency.
Note the 1j24b used to replace an existing valve in an aligned radio needs padding cap on at least anode as it is lower capacitance than DK91, DK92, DK96, 1L6, DK40, 1T4/DF91, DF96 on g2, g3 and anode. I'm not sure about DF97 and DC90. I'm not sure if grid needs padding in any circuit. I do plan to replace a 1L6 in USA Worldband sets (I have maybe 4 models). I have to add series and parallel resistors in filament circuit to match the 50mA nominal at 1.35V approx series operation as even two 1j24b as triodised osc and pentode mixer is less than 25mA! I've done one pair with additional capacitors to replace a DK96 without retuning LO or IFT.
The DK92 (without adaptor or DK40 with adaptor) will directly replace the 1L6, but mucks up alignment at shorter wave bands. Some UK/Europe sets used DK40 with Dx9 series valves till the DK92 was available. The DK91 and DK96 are inferior, hence even some 1957 model with SW used the DK92.
The electrode capacitances of all rod types is very low compared to regular B7G types.
Also remote cutoff/variable mu while allowing greater AGC range causes intermodulation if there is an unwanted strong signal. It's achieved by a varied spacing of the helical grid wire. All rod tubes are more linear with a sharp cut off. Some Western commercial or military sets didn't use variable mu valves except at IF to give better IM performance. Also tended to not to use heptodes or octodes (as was common even on USA mains sets) but a separate LO and mixer for better IM performance, no FM modulation of LO and less LO leakage to the aerial.
