This was found by accident.
While experimenting with the 1T4 electron tube as a microphone pre preamplifier it was wrongly connected.
Set up:
Mic - Step up input transformer - 1T4 - Step down output transformer - mic preamp
One side of the direct heater was connected to ground with battery (+) . The other side to the heater battery (-).
One side of the output transformer primary was connected to ground as usual.
The other side of the output transformer primary was connected to to grid 2, screen grid.
One side of the input transformer secondary was connected to grid 2, screen grid (ie one side of the transformers were connecte together too).
The other side of the input transformer secondary was connected to control grid.
So instead of connecting one side of the secondary of the input transformer to ground, it was connected to g2.
There was sound even without connecting any plate supply. The sound stopped when the heater was cold. How about experimenting also with directly heated diodes? The thermionic current provided a path for the transformers to communicate.
This circuit dire end by chance while trying to remake the Pleiades V1 which is just an electrometer tube with an input transformer. The positive of the 1.3V direct heater is also connected to anode through a load resistor. If memory is correct also through a high megohm resistor to control grid. The output of the input transformer is capacitively coupled to grid. The Pleiades V1 operates without any extra anode supply. It was connected to Tascam Porta mic input. It sounded very nice with a military proximity compensated input transformer but noise performance has to be improved.
While experimenting with the 1T4 electron tube as a microphone pre preamplifier it was wrongly connected.
Set up:
Mic - Step up input transformer - 1T4 - Step down output transformer - mic preamp
One side of the direct heater was connected to ground with battery (+) . The other side to the heater battery (-).
One side of the output transformer primary was connected to ground as usual.
The other side of the output transformer primary was connected to to grid 2, screen grid.
One side of the input transformer secondary was connected to grid 2, screen grid (ie one side of the transformers were connecte together too).
The other side of the input transformer secondary was connected to control grid.
So instead of connecting one side of the secondary of the input transformer to ground, it was connected to g2.
There was sound even without connecting any plate supply. The sound stopped when the heater was cold. How about experimenting also with directly heated diodes? The thermionic current provided a path for the transformers to communicate.
This circuit dire end by chance while trying to remake the Pleiades V1 which is just an electrometer tube with an input transformer. The positive of the 1.3V direct heater is also connected to anode through a load resistor. If memory is correct also through a high megohm resistor to control grid. The output of the input transformer is capacitively coupled to grid. The Pleiades V1 operates without any extra anode supply. It was connected to Tascam Porta mic input. It sounded very nice with a military proximity compensated input transformer but noise performance has to be improved.
No comments:
Post a Comment