Amplifier Schematic


Posted on Feb 7, 2014

In a grid driven amplifier it is necessary to match the low impedance of the driving transmitter (typically 50 ohms) to the high impedance input of the tube (typically several thousand to several million ohms). The signal from the input jack travels via RG-58 coaxial cable through relay K1 to the input link L1, which consists of three turns of insulated hookup wire on coil L2. L2 is


Amplifier Schematic
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tuned to resonance by the grid tuning capacitor C1. The transformer action of L1 and L2 steps up the voltage, matching the low impedance of the driving transmitter to the high impedance input of the tube. If extra driving power is available, as is the case with the 6CL6 transmitter, the grid tuning control is used as a drive level control, and is tuned off resonance to reduce the drive to an acceptable level. Grid bias is fed into the bottom of L2 and travels through the 15 ohm resistor to the grid of the tube. When operated as a linear amplifier (SSB), the tube does not draw grid current and the 15 ohm resistor has no effect. However, if the tube is driven hard enough for grid current to flow (CW operation), the 15 ohm resistor introduces additional grid bias and the tube operates as a non-linear class C amplifier. In an RF amplifier it is necessary to supply DC plate voltage to the tube (about 600 volts in this case) and at the same time extract the amplified RF that appears at the plate of the tube. In the circuit at right, the 1 mH plate RF choke allows the direct current from the plate supply (B+) to pass through it, while preventing the RF on the plate of the tube from flowing back through the plate supply. At the same time, the 1000 uuf plate coupling capacitor (at the top in the schematic) permits the RF on the plate to flow though to the output tank circuit while blocking the plate voltage. The 0. 01 uf capacitor...




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