23-10-2023, 11:46 AM
(This post was last modified: 23-10-2023, 11:56 AM by Mike Watterson.
Edit Reason: 1j37b
)
Small choke in series with grid and small cap on anode to 0V. The electrode capacitances are extremely low compared to D9x valves.
Years ago I used quad high profile DIL transformers for isolated CPU I/O cards on an industrial controller. One connection was 1MHz which was used as both PSU (multiple + and - voltages using 1N4148s and regulators for cpu and op-amps, ADC or DAC.) and CPU 1MHz clock. The other three used as shift clock,serial data in and serial data out. The CPU hadn't a true UART, just a parallel read/write shift register.
I'm sure the 11mA is possible for a 1j24b. Not sure if they could do the 1j29b. Possibly an idea with them is to suitably feed the filaments in antiphase as the top end is common. Then HF ripple on the two parallel beams reaching anodes would cancel. One plate of g1 is shared and other two g1 plates are in parallel. Similarly for the g2 rods. But the g3 rods and anodes treat it as a single beam.
There are four sheet beams from the filaments. A pair in each horizontal direction from the red dots. There is some attempt at shielding using 3 shield rods at either side of beams symmetrical with the two rods used for the separate ends of filaments which are spring loaded. So the common f+ ends of the two filaments are at the base. All the rod pentodes have spring loaded filaments and you can see the filament end of the spring move with filament power on /off
The top common connection of the two filamentary cathodes is regarded as LT+ and the separate bottoms are LT-, so series operation is slightly nonsymmetrical and not as good. They always recommend decoupling the centre tap on series operation.
Note 1j29b-r and 1j29b-v have different bases.
Note the labels are wrong on the photo for the 1j29b I examined. That's Joe Sousa's photo.
Note in Pentode OR Triode mode the g3 must go to a low voltage, either f-, f+ or within + or - a few volts. So with isolated filaments the g3 ought to go to common of filaments. F3->f1, F1->f2 and F2 and F2 in the photo are shield rods.
It's possible the shield rods on most are for additional support. The 1j37b has only one dedicated shield rod. The diagonally opposite rod is feeding top end of filament via the usual spring.
Triode mode allows a bit more power or much lower HT.
Here is a failed attempt at Push Pull at 45V HT. Small/Miniature mains transformers work far better. None of the available sub-miniature transformers are suitable. Most are for old Germanium transistor designs.
A 600 Ohm to 10K step-up transformer for microphones might work for a very low power o/p on a 1j24b to drive a 64 ohm speaker or 2 x 32 Ohms earphones in series, but it might easily saturate and pretty poor.
A ceramic "beeper" disc fed from a 10K Ohm anode load works at 18V to 22V on a 1j24b, and can be rigged as an earpiece. Having it in a short 6mm to 8mm long tube closed at one end and mounted a few mm from a 6mm to 8mm hole in the other end works well.
Years ago I used quad high profile DIL transformers for isolated CPU I/O cards on an industrial controller. One connection was 1MHz which was used as both PSU (multiple + and - voltages using 1N4148s and regulators for cpu and op-amps, ADC or DAC.) and CPU 1MHz clock. The other three used as shift clock,serial data in and serial data out. The CPU hadn't a true UART, just a parallel read/write shift register.
I'm sure the 11mA is possible for a 1j24b. Not sure if they could do the 1j29b. Possibly an idea with them is to suitably feed the filaments in antiphase as the top end is common. Then HF ripple on the two parallel beams reaching anodes would cancel. One plate of g1 is shared and other two g1 plates are in parallel. Similarly for the g2 rods. But the g3 rods and anodes treat it as a single beam.
There are four sheet beams from the filaments. A pair in each horizontal direction from the red dots. There is some attempt at shielding using 3 shield rods at either side of beams symmetrical with the two rods used for the separate ends of filaments which are spring loaded. So the common f+ ends of the two filaments are at the base. All the rod pentodes have spring loaded filaments and you can see the filament end of the spring move with filament power on /off
The top common connection of the two filamentary cathodes is regarded as LT+ and the separate bottoms are LT-, so series operation is slightly nonsymmetrical and not as good. They always recommend decoupling the centre tap on series operation.
Note 1j29b-r and 1j29b-v have different bases.
Note the labels are wrong on the photo for the 1j29b I examined. That's Joe Sousa's photo.
Note in Pentode OR Triode mode the g3 must go to a low voltage, either f-, f+ or within + or - a few volts. So with isolated filaments the g3 ought to go to common of filaments. F3->f1, F1->f2 and F2 and F2 in the photo are shield rods.
It's possible the shield rods on most are for additional support. The 1j37b has only one dedicated shield rod. The diagonally opposite rod is feeding top end of filament via the usual spring.
Triode mode allows a bit more power or much lower HT.
Here is a failed attempt at Push Pull at 45V HT. Small/Miniature mains transformers work far better. None of the available sub-miniature transformers are suitable. Most are for old Germanium transistor designs.
A 600 Ohm to 10K step-up transformer for microphones might work for a very low power o/p on a 1j24b to drive a 64 ohm speaker or 2 x 32 Ohms earphones in series, but it might easily saturate and pretty poor.
A ceramic "beeper" disc fed from a 10K Ohm anode load works at 18V to 22V on a 1j24b, and can be rigged as an earpiece. Having it in a short 6mm to 8mm long tube closed at one end and mounted a few mm from a 6mm to 8mm hole in the other end works well.
