Mezijora At W output the valves would also dissipate nearly W intermittently. Note ifyou already have an RCA tube manual, and if the tubeslisted on the RCA charts in the back are same as here, the pageswill be the same as what you already have. The wirewound resistor 10—50? Because of the dissipation and closeness of the power valves, a heat-resistant coil former is a must: In constructing the cabinets, I have learned to first make the holes for the valve sockets in a sheet of single-sided print-board and wire it completely, with sockets on the bare side and the resistors, decoupling caps, grounding strips and the 4: The cooling clip keeps the temperature of the top within reasonable limits at high dissipation. Because the control grid is loaded with a resistor, the amplifier is in principle stable. Another method of insulation is to cement two flat isolating washers e.

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This method can be used up to frequencies of several MHz without noticeably reducing fundamental power. The main function is to provide a high impedance path in series with other tank circuit elements. However such method can be used only where the fundamental and parasitic frequencies are sufficiently far apart, so that excessive resistive losses of the fundamental frequencies are avoided.

Can be precautionary mounted. A value of 22 to Ohms is fine. The traditional suppressor. Damping can be achieved by paralleling the hairpin circuit inductor with a non-inductive resistor and by making the inductor from resistive material. A mat surface rather than a polished surface may provide sufficient surface resistance.

This amplifier was stable and build without a parasitic suppressor in the plate lead. If any instability occurs fit a suppressor. My experience with hairpin parasitic suppressors is that they work better than inductors with parallel resistors. It is not necessary that they have to be made of nichrome wire. If you use 1 - 2 mm diameter tinned copper wire, it will have sufficient skin resistance for VHF. Cut off a 12 cm long piece of wire and bend it around a piece of pipe 25 mm od.

However, least problems arise with one-layer chokes. Because of the dissipation and closeness of the power valves, a heat-resistant coil former is a must: the heat and intense IR-radiation of a power valve at maximum dissipation can make phenol board at 2 cm distance burst out in flames! A sturdy ceramic wire-wound resistor, with its resistance wire removed, will make a good former. A diameter of about 2 cm and a length of 10 cm is satisfactory.

Closely wind the former with one layer of 25 — 28 swg-enamelled wires over a length of 5 — 10 cm. In most cases its inductance is sufficient, even at a lowest frequency of 3. If there are none, you are lucky. If there are, try to shift them by removing or adding some turns. Another solution is to remove 1 cm of the windings and start again, leaving a gap of 5mm between windings; then check again.

My favourite choke has a diameter of 2 — 2. The wire may seem too thin for some currents, but in all my experiments it never burnt through. The wirewound resistor 10—50? Replacing them is much cheaper than replacing the valve. The inductance for 3. That is much smaller than the usual air-core coil. This was not often seen but I am using the toroids more than 25 years in my home made amplifiers. It has 6 turns with an inner diameter of 25 mm and a length of about 40 mm. This wire being tinned, I believe the high skin-resistance helps in preventing parasites.

Adjust for maximal power at The 20—80 m coil is wound on an Amidon T toroid core. This was done in order to limit the overall dimensions of the amplifier. A toroid, self-shielding because of its low external field, facilitates compact construction. Before winding, several layers of Teflon plumbing tape must be applied to the core, to insulate it from the coil-windings. Another method of insulation is to cement two flat isolating washers e.

Apply a small quantity of super glue, possibly only a few drops, around the sides of the core. Work swiftly; the glue hardens quickly.

The glue prevents the washers from moving out of alignment while the core is being prepared for winding. For a T core, the inner diameter should be 28 mm diameter and the outer diameter 55 mm. With this last construction it might be even possible to use bare copper wire for the 25 turns with of respectively taps on 4 and 11 turns of 14—19 SWG enamelled wire.

At the output end of the pi-circuit, a RF-choke between antenna-terminal and earth ensures a low-resistance DC-path, as a safety measure in the event of a short between the anode and the output-circuit. The Telecom authorities also require it. When the anode voltage is shorted to the output, without a DC-path to earth for blowing the HT fuse the wire-wound resistor in the anode-circuit will curtail the flaming arc across the blown fuse , the antenna cable and antenna will become death traps.

An adequate choke is a short ferrite rod with 30—50 turns of 25 SWG enamelled wire. Check it with a GDO for absence of series-resonance in any amateur band. During non-transmit periods the second contact set on the changeover relay Rel1 opens and the 10 k? Eventually L2 can be wound with close trifilar turns on a ferrite rod from an old MF radio or on a ferrite toroid.







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