An 8877 Linear Amplifier

"The Octatron"

The 8th amplifier project at this QTH currently under design.

These schematics were adapted from my 4CX600JA project .
mostly by deleting those portions relevant to the grid and screen circuits.
Some of this circuitry has been built and tested, some has not.
Some of the parts values may be subject to ... revision...

8877 cathode

This detail of the heater cathode circuitry was extracted from several of the schematic pages.

Note that the bias generator placed in the "grid return" line, rather than in the typical cathode (grid + cathode current) location.   The grid remains chassis grounded as usual.   This implies that the HV return must be allowed to float at least as positive as the bias value.   The advantage of this arrangement is that the bias generator need only support the grid current which is typically 1/10 of the cathode current.

Standby bias is developed across the 10K resistor in parallel with the power FET which switches the cathode circuit from standby to transmit.

IC instrumentation amps (3 op amp topology) unintrusively sense and amplify the plate and grid currents, from the voltages across the small value R's, to read 1.5 amps and 150 mA full scale respectively, on 5V meter movements returned to ground.

8877 interconnect

The drawing above details the pin assignments for the 'D' connectors that are used almost exclusively for interconnections in this design.

RF Deck Control Power Supply Remote Control