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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Hello Patric, the basic VTTC circuit is this: (by Steve Ward from ) The basic components are the primary coil which forms a tuned circuit with primary (tank) capacitor, and a feedback (grid) coil with somewhat less turns of thinner wire than the primary, with the grid leak RC circuit. The RL rf blocking element on the plate is usually not needed for a single tube.
Registered Member #2899
Joined: Wed Jun 02 2010, 06:31PM
Location: Deinze, Belgium
Posts: 255
Thanks for the replay, I know the original scheme, but this one I got from: I simply did redraw it to better understand it... I do not want my 811A load too heavy, the circuit must work for several hours.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
The basic VTTC circuit I posted is a class-C oscillator, it is the most efficient self-excited oscillator you can make with a tube (around 75% efficient) and when properly tuned, will do what you want; there is no reason to use a more complicated circuit. The schematic you posted in your original post, will not work.
PS. If you don't want to use two separate windings, it is possible to reconfigure the oscillator with a tapped primary. Plate goes to one end of the winding, grid is connected to the other winding end through a grid leak capacitor (which must be properly rated voltage-wise). The grid leak resistor goes from grid to cathode. The plate supply goes to the tap.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
The schematic is badly drawn; he has the cathode connected to the negative point of the plate supply (which you do not have in your circuit). The coil from the link might work, however the circuit is badly designed and will probably operate inefficiently.
Registered Member #2899
Joined: Wed Jun 02 2010, 06:31PM
Location: Deinze, Belgium
Posts: 255
I really do not see it, but nevertheless, I will follow your good advice, and use the circuit from Steve Ward. But can I use the 811A directly on the transformer, without diode (D1) or capacitors (c3 and c4), to become a lower tension and save my precious tube?
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Is this correct?
