12-06-2022, 10:30 AM
You can even run the dual filament 1.2V x2 = 2.4V off 2 volts and use the 1j29p as a replacement for any 2V triode, screen grid type and pentode. HT of 45V to 90V
Simply increase a filament series resistor if the gain is too high for the original circuit. Strap g2 and anode but g3 to f- or f+ for a triode. Just use it with g3 to f- or f+ in any tetrode/screen grid circuit. The rod tubes are only pentode like, they are not actually Pentodes. The 1j24b works well as a Pentode mixer if the anode of a rod tube wired as a triode oscillator drives and biases g2 directly. The g3 is always to f- or f+, but can give limited gain or mixing action. Because the g2 varies from nearly zero to (Ia at max)to nearly Ia they can be unstable with just a resistor to set g2 volts, but all the old SG circuits used an HT tap to set g2 volts which really suits rod tubes. I've had to add a potential divider (second resistor to 0V on g2) to replace DF91/1T4, DF92, DF96, DF97 in IF or DAF9x preamp (1N60 as diode, which predate DAF96 anyway!)
Note that the ECH83 = ECH81 exactly and many 6.3V valves will work series/parallel off 12 to 14V heater and 12V to 14V HT, though 24V HT is better. ECH81, EF89, ECC81 etc. At 12V HT the grid bias can be +1v.
At regular HT (or even 90v) the ECH81 can drive a speaker as as well as a DL92 could.
You can use a mains transformer at low bias currents single ended for audio, or any bias on a 110-0 -110 transformer with push pull.
A shaver transfomer can work as 1:2 stepup or phase splitter to
Simply increase a filament series resistor if the gain is too high for the original circuit. Strap g2 and anode but g3 to f- or f+ for a triode. Just use it with g3 to f- or f+ in any tetrode/screen grid circuit. The rod tubes are only pentode like, they are not actually Pentodes. The 1j24b works well as a Pentode mixer if the anode of a rod tube wired as a triode oscillator drives and biases g2 directly. The g3 is always to f- or f+, but can give limited gain or mixing action. Because the g2 varies from nearly zero to (Ia at max)to nearly Ia they can be unstable with just a resistor to set g2 volts, but all the old SG circuits used an HT tap to set g2 volts which really suits rod tubes. I've had to add a potential divider (second resistor to 0V on g2) to replace DF91/1T4, DF92, DF96, DF97 in IF or DAF9x preamp (1N60 as diode, which predate DAF96 anyway!)
Note that the ECH83 = ECH81 exactly and many 6.3V valves will work series/parallel off 12 to 14V heater and 12V to 14V HT, though 24V HT is better. ECH81, EF89, ECC81 etc. At 12V HT the grid bias can be +1v.
At regular HT (or even 90v) the ECH81 can drive a speaker as as well as a DL92 could.
You can use a mains transformer at low bias currents single ended for audio, or any bias on a 110-0 -110 transformer with push pull.
A shaver transfomer can work as 1:2 stepup or phase splitter to
