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Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
I'm not a 100% confident advising about the tube oscillator (still learning myself), but I can see some issues with the filament.
In the first schematic the filament power is shorted out by the ground line, no current is actually reaching the tube.
The second schematic also has some filament issues. I not sure if it's better to ground the cathode centre-tap, or if it's better to ground one of the filament inputs and leave the centre-tap alone (a quick Google search reveals circuits using both configurations - perhaps it's not critical). Either way, it's a good idea to place a bypass capacitor across the filament leads to ensure no RF feeds back into the transformer.
Aaand that's pretty much the extent of my knowledge, hopefully someone else with more hand-on experience can be more helpful.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
the center tap is used as a cathode, the ends are supplied with the filament power, for high power/frequency applications it is best to bypass the filaments with caps.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
These circuits are kind of "black magic", even if you try to replicate someone's work, your layout may work very differently.
Probably the most reliable circuit is the base feed method, for which you would need to wind an additional DC choke (called the radio-frequency choke) in series with the plate and connect the base of the resonator to the plate. Then you would also need to make a screen supply with around 600 V output.
A substantial problem of these circuits is that the plate voltage is present on the output, so it can easily kill you if you accidentally touch the arc. Concerning this, a better circuit uses a primary coil around the resonator (its bottom is then grounded), the feedback can be taken from a tap near the bottom of the resonator.
Note that none of these circuits use an additional tank capacitor - the capacitance of the plate itself is sufficient.
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HF VTTC schematics
