25-06-2022, 09:49 PM
Continuing to play with the two valve receiver.
As I am limited at present with a 150 Volt psu, I am just trying a few serial resistors in line with the HT.
With a 47 K Ohm in series from the psu the main HT is at 89 volts, then I have another 68 k Ohm to drop the HT down to 50 - 51 Volts for the first reaction and detector valve. What is surprising is that audio level is still listenable in the speaker. OK I need a better speaker, it is a 4 Watt speaker it's driving, so base is low, but not bad.
Overall the radio is drawing 1.3 mA. Approx 0.75 mA in the audio amp and 0.55 mA in the first stage.
What gets me is what low output one can still listen on a speaker? I have over 2 volts peak to peak of audio from the detector valve and approx 18 volts pk - pk on the LF valve, probably driving the speaker at around 5 milliwatts of audio.
Adrian
As I am limited at present with a 150 Volt psu, I am just trying a few serial resistors in line with the HT.
With a 47 K Ohm in series from the psu the main HT is at 89 volts, then I have another 68 k Ohm to drop the HT down to 50 - 51 Volts for the first reaction and detector valve. What is surprising is that audio level is still listenable in the speaker. OK I need a better speaker, it is a 4 Watt speaker it's driving, so base is low, but not bad.
Overall the radio is drawing 1.3 mA. Approx 0.75 mA in the audio amp and 0.55 mA in the first stage.
What gets me is what low output one can still listen on a speaker? I have over 2 volts peak to peak of audio from the detector valve and approx 18 volts pk - pk on the LF valve, probably driving the speaker at around 5 milliwatts of audio.
Adrian
Learning as I go!
Youtube EF91 Valve
Youtube EF91 Valve
