Is the chassis to screen check, the same as the chassis to grid check that should be 90-100 vdc. one book said AC the other book said DC and if I have a tube with 3 grids are all 3 need to have the 90-100.

Thanks, KY

Regarding the chassis, you should consult the schematic for the radio model in question. Not all radios have their voltages referenced to the chassis as shown in the schematic. For some radios the chassis isn't even part of the DC circuit.

Generally, for B voltage and bias analysis, a DC voltage measurement is made from the grid in question to B-, which is often the chassis.

For 3 grid pentodes, the supressor is often at or below the cathode's voltage, which is rarely more than 40 volts above B-, so the supressor should measure from 0 to 40 volts, depending on the tube and circuit in question, and in rare cases the supressor might measure negative with respect to the chassis or B-.

The screen grid of a 3 grid pentode and a 2 grid tetrode is often held rather positive with respect to B-. This all depends on the radio's design. In some early radios, the screen grid voltage can even be variable. In all radios this voltage can range from about 60 to 300 volts.

The control grid of a 3 grid pentode, a 2 grid tetrode, and a single grid triode is usually held at or below B- or chassis voltage. The grid leak method of negative bias is often used for 1st audio tubes, and this negative voltage is often not measurable by ordinary DC meters, and, in any case, is only present when a signal is present, and varies with the signal. The grid of the output tube(s) is often negative with respect to the cathode by a measurable amount, and may or may not be negative with respect to B- and/or the chassis, depending on the wiring scheme. The control grid of most RF tubes is negative with respect to the RF tubes' cathodes, and possibly B-, depending on the wiring scheme, by a variable amount. In radios with AVC, this amount depends on the strength of the incoming signal, and subsequent AVC voltage. In radios with manual RF gain control, this voltage varies with the operation of that control, if the gain control in fact controls grid-cathode bias.

Most oscillator control grids will measure negative by a few volts with respect to the oscillator cathode, and possibly the B- bus or chassis, and this amount varies with oscillator frequency.

T.