back in the day....
some TV shops in the US had picture tube rebuilding equipment. i think the gun assemblies came pre-assembled, and the assembly jig (a large plexiglas cabinet with a steel frame) would be where you cut off the old gun assembly, fitted the new one and (using a ring shaped burner) sealed the new gun assembly to the tube. then a vacuum pump would evacuate the tube, and the evacuation stem would be sealed, and an RF coil would be used to fire the getter. i don't know how much these rigs cost, but only very large shops had them. i worked at a shop that had one, but never saw it in use. i'm sure that with the demise of CRT TVs and monitors, you could pick up one of these from a shop that has one taking up space. i don't know how difficult it would be to make tube assemblies, but on many well established tube types (like 6L6, etc...) the tolerances are rather tight. one tube that would be interesting to make would be a "field effect" triode. they were made and used for a short time in the 1920's. basically it was a diode with the cathode at one end of a small tube about the size of a 50EH5 (tall 7 pin power amp tube) and the anode at the other end. the grid was a metal band around the OUTSIDE of the tube. one of the advantages of the tube was that grid current with a positive biased grid was impossible, since the grid wasn't in the electron path, cutoff voltages for the grid were very high (-70 ot -80V). the grid charge pinched the electron "beam" rather than blocking it directly. i suppose a very small diameter triode made this way might have a lot of gain compared to the ones made in the 1920's, but probably still very short of a 12AX7. getter materials will be very difficult to get and difficult to handle, since they oxidize rapidly (maybe use a glove box filled with helium??)
some TV shops in the US had picture tube rebuilding equipment. i think the gun assemblies came pre-assembled, and the assembly jig (a large plexiglas cabinet with a steel frame) would be where you cut off the old gun assembly, fitted the new one and (using a ring shaped burner) sealed the new gun assembly to the tube. then a vacuum pump would evacuate the tube, and the evacuation stem would be sealed, and an RF coil would be used to fire the getter. i don't know how much these rigs cost, but only very large shops had them. i worked at a shop that had one, but never saw it in use. i'm sure that with the demise of CRT TVs and monitors, you could pick up one of these from a shop that has one taking up space. i don't know how difficult it would be to make tube assemblies, but on many well established tube types (like 6L6, etc...) the tolerances are rather tight. one tube that would be interesting to make would be a "field effect" triode. they were made and used for a short time in the 1920's. basically it was a diode with the cathode at one end of a small tube about the size of a 50EH5 (tall 7 pin power amp tube) and the anode at the other end. the grid was a metal band around the OUTSIDE of the tube. one of the advantages of the tube was that grid current with a positive biased grid was impossible, since the grid wasn't in the electron path, cutoff voltages for the grid were very high (-70 ot -80V). the grid charge pinched the electron "beam" rather than blocking it directly. i suppose a very small diameter triode made this way might have a lot of gain compared to the ones made in the 1920's, but probably still very short of a 12AX7. getter materials will be very difficult to get and difficult to handle, since they oxidize rapidly (maybe use a glove box filled with helium??)
i once made a fuse out of a gum wrapper (not the way it's usually done where somebody wraps the gum wrapper around the outside of a blown fuse).
i cut a piece of gum wrapper in an hourglass shape, with the center about 1mm wide. when i connected a battery across the "fuse", the center part blew. i have no clue how much current it was, but it worked. the only problem is that the foil on gum wrapperi is too fragile to make a real workable fuse from. i've made a lot of RF coils and chokes with wire and a pencil. i've made plate glass capacitors and tesla coils. if you have black plastic from antistatic bags, you can cut it into strips to make resistors.
i suppose if you have an old catwhisker detector, you could make a rudimentary transistor with a second catwhisker placed close to the first on a germanium or silicon crystal.
i cut a piece of gum wrapper in an hourglass shape, with the center about 1mm wide. when i connected a battery across the "fuse", the center part blew. i have no clue how much current it was, but it worked. the only problem is that the foil on gum wrapperi is too fragile to make a real workable fuse from. i've made a lot of RF coils and chokes with wire and a pencil. i've made plate glass capacitors and tesla coils. if you have black plastic from antistatic bags, you can cut it into strips to make resistors.
i suppose if you have an old catwhisker detector, you could make a rudimentary transistor with a second catwhisker placed close to the first on a germanium or silicon crystal.
Not really, but it brings back memories... you know, as "young en" starting out, taking nothing on trust.
Remember trying to "make" transistors out of two diodes, despite careful metering I could never get any current gain... but they read the same (nearly 🙂) as a real one.
I always wanted a voltmeter (or any meter) and came up with the idea of a motor and pulleys and a slipping belt etc. The faster the motor ran the "more" the second pulley might move round... ohms per volt... ohhh about 0.1 😉
I'm afraid it's a definite non starter...
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