| OSCILLATOR SCHEMA |
| C3: filter cap made with 4 caps (polipropilene 2.2 nF @ 2 kV each) in serie for a total of 550 pF @ 8 kV. C4: primary cap made with 5 ceramic caps (10 nF @ 4 kV each) in serie for a total of 2 nF @ 20 kV. After some tunning and tapping the caps don't heat at all, even after long runs. C5: grid capacitor made with 5 polipropilene caps (6.8 nF @ 1600 V each) in serie for a total of 1.3 nF @ 8 kV C6: bypass fillament cap = 200 nF @ 1600 V polipropilene R1: grid leakage resistor has a very low value. Initialy it was used a 550 ohms @ 20 watts resistor. Now I am using a light bulb 220 V @ 100 watts for a resistence of at least 484 ohms. The grids are not redding even after long runs. R2: 96 ohms @ 10 watts ceramic T: GU81M pentode used as triode. The grid 3 is connected with the middle of the fillament and to the ground. The grids 1 and 2 are connected together (paralleled). Fillament voltage is 12.6 V under load. L1: primary coil, wound on a white PVC pipe, 14 cm (5.51 inches) diameter, total lenght = 20 cm (7.87 inches), wound lenght = 18 cm (7.08 inches), 48 turns of plastic insulated multistrand wire with tapping points at each turn, after the 10-th turn. Tapping point for the cap is at 34-th turn, tapping point for the plate of the tube is at 48-th turn. L2: feedback coil is wound on a white PVC pipe, 14 cm (5.51 inches) diameter, lenght = 5 cm (1.96 inches). It has 21 turns of plastic insulated wire (1 mm diameter) and is located at 1 cm under the primary coil (the two coils are separated by a plastic plate (the base for the pri and sec). L3: the secondary coil is wound on a white PVC pipe, 3 inches diameter, wound lenght = 9.6 inches. It has 960 turns of 0.25 mm magnet wire L4: 10 turns of plastic insulated copper wire (1.5 mm diameter) clouse wound on R2 the fillament transformer is a toroidal one 220 V / 12 V @ 150 VA. With the initial secondary the fillament voltage under load was only 10.6 V, that was too low for the tube (the average voltage of the rated fillament voltage under load is 12.6 V). So I added 11 more turns to get this value under load (14.3 V without load). |
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