Well, It is kind of shift to the valves or tubes. It is really amazing how those glowing glassy things can amplify and turn receivers and transmitters on!
I know some people may say that transistor are or fascinating but I kind
of thinking the other way. How could you think that simple addition of
(grid and anode) to the bulb can make a triode out of it?!
Therefore, I will post some ingenious valve circuits involving regeneration, superhet and direct conversion methods. Specially the ones that have low number of valves for they look more interesting and brainy.
How much you can make out of one valve?!
Well, some valves are actually two valve in one spot like one triode and pentode packed in one glass.
Here, I selected for you a brainy project about direct conversion receiver made of one valve (tube).
Beam deflection tubes were designed to be used as balanced mixers. The
most interesting feature is that any signal applied to grid 1 will be
amplified and appear as an in-phase (common mode) signal at the two
plates. On the other hand, any signal applied between the deflector
plates will be amplified and appear as an out of phase (differential
mode) signal at the two plates. This allows the different signals to be
separated and redirected as necessary. This unique characteristic allows
reflexing the audio back through the tube without it breaking into
To work as a direct conversion receiver, the RF signal passes through a
tuned RF stage consisting of T1 and one section of the tuning capacitor,
and is applied to grid 1. A signal from the local oscillator (an
interesting differential oscillator design) running at the same RF
frequency is applied to the deflectors. The result of this mixing
operation is an out of phase audio signal at the plates. The out of
phase audio is detected in T3 and from the secondary is routed back to
grid 1. This audio signal is amplified and appears at the plates as an
in-phase signal which passes through the primary of T3, this time with
no effect, and then to T4 where it is impedance matched to the
headphones. Some cathode current is routed through a single turn winding
on T1 for regeneration which is adjusted by the parallel 50 ohm pot.
Because the regen is taken from the cathode, there is no local
oscillator component in this signal. After the usual amount of debugging
and tweaking, this thing ended up being an amazingly sensitive and
selective receiver. I was able to pick up stations up to 2200km away
quite clearly. Not bad for one tube.