Одноламповый приемник с питанием 1.5V
On the top of this page, I must say you that this page is not practical. I made some experimental projects about useing the valves with low voltage. And I had a theme that "Challenge the lowest voltage of use of valve!". This project is one of my result of this theme.
I have about 100 types of valves. 99% of them are picked up from the thrown away TV set about 25 years ago by my younger brother. I examined a lowest voltage of his plate able to make plate current with many types of valves. The result was that 2HA5 was the champion. (2HA5 will be Japanese original tube.) The grid of this triode can control the plate current with 1.5V voltage of plate. Heater of this valve was made originally 2.4V-0.6A. This valve was made to use the tuner of color TV set. I think this tube may be Japanese original. And I discovered that this valve can act with 1.5V of his heater voltage. See the right side of the figure! This is low voltage character of 2HA5. Plate current is changed from 2.5uA to 32uA when the grid voltage changed from -0.3V to 0V. Yes it is controlled. But on the same tome, the current of grid changes from 14.5uA to 145uA. Yes the current gain (same dimension from hfe of transistor) is 32/145=0.22. It is very low , is'nt it? And, because the grid requires the current to act, the input impedance of this valve is also very low. It is 0.3V/145uA= 2 kohm.
Therefore I made the radio shown on the left side of the figure. In this radio , the grid is tapped down on the tune coil, in order to adapt the low impedance of grid. The total voltage gain of this radio (from ANT to Phone) was 18dB. It is bigger gain than the "gerumanium radio". My gerumanium radio has 6dB voltage gain (not power gain!). I compared to hear this radio with the gerumanium radio. I felt that this radio has slightly bigger sound than the gerumanium radio.
This radio uses the plate detector. The voltage gain of this radio is culculated as follows. Gain A = (5 /1) [turn of coil] * (32-2.5) mycro ampere [plate current] / 0.3V [grid voltage] * 20k [load impedance] = 10 times (20dB). 20dB (culculated gain) is near from 18dB (measured gain).
Kazuhiro Sunamura, (JF1OZL)