30-06-2020, 01:51 PM
They are electrostatic lenses. A curved rod won't work apart from the huge assembly difficulties.
A insulated indirectly cathode is HUGE compared to a filament. About 500 um.
Joe Sousa writes: "For example, in the case of the 1Zh37B the distance from the 0.07mm (70micron!) thick coated filament to the two grid rods on either side, is only 0.12mm (120micron!)."
Re-read these two links and look at images:
https://www.radiomuseum.org/forum/russia..._id=200277
https://www.radiomuseum.org/forum/summar...todes.html
Download the translated Russian article http://www.radiomuseum.org/forumdata/upl...1_2011.pdf
A conventional variable mu or indirect version isn't possible. The USA tried making indirectly heated "rod tubes" in late 1930s due to the g2 working well as a pair of rods instead of a wound wire grid in some heptodes / pentagrid converters, the g2 being effectively the "anode" for the oscillator part and the electron source for the rest of the valve. Also RCA producing the "Kinkless Tetrode" AKA Beam Tetrode, the alternate to the Philips Pentode by replacing the wound wire g3 with a pair of beam forming plates (the same electrostatic lens function as the two pairs of rods labelled g3 in an Rod Tube). It didn't work, though many Noval Pentodes and Beam Tetrodes did develop into oval shaped grids with all the rods in a line and two anodes at either side under the outer shield.
See especially the "tear down" of a real indirectly heated Pentode, the EF89
The cathode tube is HUGE!
https://www.radiomuseum.org/forum/ef89_anatomy.html#1
![[Image: ef89_12_electrode_labels.jpg]](https://www.radiomuseum.org/forumdata/users/14211/EF89/ef89_12_electrode_labels.jpg)
![[Image: ef89_16_electrodes.jpg]](https://www.radiomuseum.org/forumdata/users/14211/EF89/ef89_16_electrodes.jpg)
![[Image: ef89_19_grids.jpg]](https://www.radiomuseum.org/forumdata/users/14211/EF89/ef89_19_grids.jpg)
The Russians were developing these over a 20 year period and made them up till 1990. The 1j42a and 1j24b were the most advanced devices. The 1j18b and 1j37a are earlier but not the first. The 1p24b, 1j29b are incremental improvements on earlier doubled types (two filaments and three grid plates). There are essentially three generations of these. The Russians either used g2 voltage and/or a 1j37b for agc. The gain varies so much with g2 it has to be from either a LO, a fixed supply or a pair of resistors as a potential divider.
Anyone though is welcome to set up a lab and try. However both variable mu and indirect cathodes have been discussed by valve experts and they conclude both are impossible.
The DM70 / DM71 DOES have a slanted element like you suggest so that it varies the length of the bar.
However it's a very simple device with poor gain. It's also totally brilliant!
https://www.radiomuseum.org/forum/dm70_operation.html#1
A insulated indirectly cathode is HUGE compared to a filament. About 500 um.
Joe Sousa writes: "For example, in the case of the 1Zh37B the distance from the 0.07mm (70micron!) thick coated filament to the two grid rods on either side, is only 0.12mm (120micron!)."
Re-read these two links and look at images:
https://www.radiomuseum.org/forum/russia..._id=200277
https://www.radiomuseum.org/forum/summar...todes.html
Download the translated Russian article http://www.radiomuseum.org/forumdata/upl...1_2011.pdf
A conventional variable mu or indirect version isn't possible. The USA tried making indirectly heated "rod tubes" in late 1930s due to the g2 working well as a pair of rods instead of a wound wire grid in some heptodes / pentagrid converters, the g2 being effectively the "anode" for the oscillator part and the electron source for the rest of the valve. Also RCA producing the "Kinkless Tetrode" AKA Beam Tetrode, the alternate to the Philips Pentode by replacing the wound wire g3 with a pair of beam forming plates (the same electrostatic lens function as the two pairs of rods labelled g3 in an Rod Tube). It didn't work, though many Noval Pentodes and Beam Tetrodes did develop into oval shaped grids with all the rods in a line and two anodes at either side under the outer shield.
See especially the "tear down" of a real indirectly heated Pentode, the EF89
The cathode tube is HUGE!
https://www.radiomuseum.org/forum/ef89_anatomy.html#1
The Russians were developing these over a 20 year period and made them up till 1990. The 1j42a and 1j24b were the most advanced devices. The 1j18b and 1j37a are earlier but not the first. The 1p24b, 1j29b are incremental improvements on earlier doubled types (two filaments and three grid plates). There are essentially three generations of these. The Russians either used g2 voltage and/or a 1j37b for agc. The gain varies so much with g2 it has to be from either a LO, a fixed supply or a pair of resistors as a potential divider.
Anyone though is welcome to set up a lab and try. However both variable mu and indirect cathodes have been discussed by valve experts and they conclude both are impossible.
The DM70 / DM71 DOES have a slanted element like you suggest so that it varies the length of the bar.
However it's a very simple device with poor gain. It's also totally brilliant!
https://www.radiomuseum.org/forum/dm70_operation.html#1
