[Boatanchors] P&H LA-400 linear

[Robert Downs]

One subject that I don't recall being mentioned in this thread but that has
been in almost every similar thread in the past is that some if not most of
these 200 watt nominal linears using four 807's or four 1625's are wired as
grounded grid amps.  And that the beam forming plates inside the tubes that
must be grounded are electrically connected to the cathode, not brought out
to a separate pin.  So stock tubes apparently won't work but must be
modified.  I never paid that much attention to the threads but seems like at
this point most threads split off into which brands of tubes could be
modified and which couldn't.  Some 1625's apparently had the cathode and
beam forming plates electrically connected inside of the tube envelope and
cannot be modified.  Some had the connection made inside of the tube bases
and can be.  I've long ago forgotten which brands could and which couldn't.
And why the grounded grid configuration was preferred over the conventional
grounded cathode.

Robert Downs