Tuesday, October 30, 2012

MW_Direct Conversion_1V_Pentode tube 6ME8_Beam deflection tube

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 oscillation.

 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.


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