[AMPS] Distortion, amp design, and 813s (newbie alert!!)

[Geo Clute W7LFD]

I put a pair of 813's on 10 meters once and they worked nicely in AB1
config.  3350 volts on the plate and drove them with a Swan 500CX.
The plates turned red and then a little orange with more drive, but I
never could hurt them.  The plate coil was automotive 1/4 in tubing
with about 5 3.5inch turns.  Mechanical connections to stand
offs...solder melts with high standing waves.
No parasitic problem...I can't remember the plate current applied with
that supply...but the 813 has a 125 ma rating, and maybe double that
per tube in ssb mode.

I too would like to find out the recipe for building a single band 4 X
813's for a 160 meter amplifier.  It is my thinking that 4 tubes in
parallel would have output capacitance of about 65.2 pf.  I suppose
this could all be chassis mounted and connect them up to a sample coil
to check it with a grid dip meter....however someone out there
probably has built a pair and has the recipe for a pair.

George W7LFD


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