VTTC – The Main Circuit

Following some further research, I have decided to try this circuit first as the one shown at the end of the page seems to be a bit radical in it’s design and probably not for suitable raw beginners. This one might not have the same output but it should be easier to get running and safer for the tube.

main-circuit 2

Circuit 1

C2 – Filter cap, 1360pF 10kV ceramic.
C3 – Tank cap, 1880pF 20kV ceramic.
C4 – Grid cap, 1360pF 10kV ceramic.
C5 / C6 – Filament filters, 0.1uF 1000v polypropylene.
L1 – Primary coil, 25 turns insulated wire on a 150mm former.
L2 – Feedback coil, 20 turns insulated wire on a 150mm former, mounted 1cm below the primary coil, moveable for tuning.
L3 – Secondary coil, 1000 turns 0.315mm wire on a 68mm former.
L4 – Anode choke inductor, 10 turns close wound on R1.
R1 – Anode choke resistor, 100R 10W wirewound.
R2 – Grid leakage resistor, 5-10k 10W wirewound.
R3 – Screen bias resistor, 21k 40W wirewound.
V1 – GU-81M Tube.

In the circuit 1 above, the tube is wired as a pentode. The center tap of the filament is grounded to the RF ground system along with the base of the secondary and the zero volt supply rail.

main-circuit

Circuit 2

C2 – Filter cap, 470pF 8kV ceramic.
C3 – Tank cap, 2040pF 20kV ceramic.
C4 – Grid cap, 1410pF 20kV ceramic.
C5 / C6 – Filament filters, 0.1uF 1000v polypropylene.
L1 – Primary coil, 48 turns insulated wire.
L2 – Feedback coil, 21 turns insulated wire.
L3 – Secondary coil, 1000 turns 0.25mm wire on a 68mm former.
L4 – Anode choke inductor, 10 turns close wound on R1.
R1 – Anode choke resistor, 100R 10W wirewound.
R2 – Grid leakage resistor, 500R 85W wirewound.
V1 – GU-81M Tube.

In circuit 2, the tube is wired as a triode and not a pentode, this makes it a bit easier to set up. The center tap of the filament is grounded to the RF ground system along with the base of the secondary and the zero volt supply rail. The anode choke prevents VHF parasitic oscillations. C2 protects the power supply from spurious RF pulses on the supply rails

 

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