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Pass Tubes Candidates
Since triodes are the most common pass tubes, a list of possible triodes candidates, along with key specifications will be given here. Triode-connected beam tetrodes or pentodes work well as pass tubes since they have decent plate dissipation and often have low mu. They are also plentiful, since millions were made as vertical and horizontal deflection amplifiers for TVs. A few representative TV types are shown here, but there are many more. Refer to a good tube manual for more data. Note that several different tube types have identical pass characteristics although may have different bases or heater voltages. These identical types are grouped together. Many types have variations with different heater voltages - refer to a tube manual for these variations (i.e. 5V6GT, 6V6GT, 12V6GT).
The following table lists key parameters obtained from tube manuals. It is useful when comparing types, especially when looking for good attributes for a series pass tube: low plate resistance (rp) and high amplification factor (mu). As noted below, many good candidates are missing from the table because triode-connected behavior of beam tetrodes was seldom published. Note that the rp is for the current given, and will change with different currents.
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