10-10-2021, 06:25 PM
The 1j29b would have a bigger dynamic range for RF input than the otherwise brilliant 1j24b.
The 1j24b can do maybe 250mW audio and a pair in push pull with and ordinary miniature 110-0, 110-0 dual i/p mains transformer works fine as the bias currents cancel, roughly like 1/2 a DL96 (i.e. economy mode). That will give more audio than one 1j29b.
I think the main limitation on Rod Pentodes and possibly all battery / direct filament valves is the cathode current. Parallel operation allows a little more power than series and in any case a "centre tap" (dual filament) on a direct type needs a decoupling capacitor when in series mode.
Series battery sets also have ballast resistors due to the varying cathode currents and a simulator for B7G series needs suitable resistors from g2 & anode to f- and f+
The 1j24b can do maybe 250mW audio and a pair in push pull with and ordinary miniature 110-0, 110-0 dual i/p mains transformer works fine as the bias currents cancel, roughly like 1/2 a DL96 (i.e. economy mode). That will give more audio than one 1j29b.
I think the main limitation on Rod Pentodes and possibly all battery / direct filament valves is the cathode current. Parallel operation allows a little more power than series and in any case a "centre tap" (dual filament) on a direct type needs a decoupling capacitor when in series mode.
Series battery sets also have ballast resistors due to the varying cathode currents and a simulator for B7G series needs suitable resistors from g2 & anode to f- and f+
