"ken scharf" wrote in message
...

Cathode bias resistors on rf power amps were a safety measure.
If the tube lost drive with no bias it could draw enough plate current to
MELT the plate, especially if run with a high voltage near (or OVER!) the
maximum ratings. Of course, using a C- supply would serve the
same purpose. Many rigs actually used batteries. Since the grid current
flowed in the reverse direction from the battery, a C battery would
actually be RECHARGED in normal use, so they tended to last a long time.

Parasitic suppressors were not used in the early days since no one was on
the vhf frequencies there wasn't anybody to interfere with!

Actually, parasitic oscillation might show up in other ways making the
amplifier hard to load, and if detected this way the builder would take
steps to stabilize the circuit.


The reason I asked this that Bill (Exray) ran
into some problems with his early TX project.
The old neon lamp trick showed
the presence of VHF parasitics, and adding suppressors
improved a few of the problems he was having.

We were discussing the use of cathode bias resistors, and
I couldn't quite grasp the reason for using them, but
tube protection makes sense.

Pete