> I have done a little thinking about this realized that a cathode
> driven 4CX250 may be more linear than a Hi Mu triode.
Cathode driven tubes are for the most part extremely linear,
especially when driving impedance is high and grid currents low.
The inherent negative feedback and loading of the exciter reduces
or eliminates most concerns about grid current, just as you can do
in a grid driven PA with proper feedback and with grid resistance
swamping.
Cathode driven tubes with screen and grid bias have been around
for a long long time. They are nothing new, and are still not a cure
for overdriving problems although the negative feedback certainly
helps make them more like the better SSB triodes.
Low distortion has been a claim most tetrode amps fail to meet.
Arm waving aside, the real test is to measure one and give a
measured number.
Is the PLA-800 type-accepted as required by law? I can't seem to
find it on the FCC's data base but maybe I'm searching wrong.
Has it been tested for IMD, or is all the talk about low distortion
tetrodes just a guess?
> I think the circuit that is used in the PLA-800 deserves some
> study. We may learn something from it. Should not be hard for some of you
> amp wizards to duplicate and do some test. I'd sure like to have a
> schematic. I have a TMC amp that was partly scavenged that would be a
> great candidate for conversion to cathode driven. I just need spare time.
> I do recall that Riley Hollingsworth showed quite an interest in
> the little amp at Dayton a year ago or so. I don't recall any
reports of
The people doing the inspections were from the Detroit office. As
far as I know no one was actually cited, but several people were
told they could not display non-type accepted gear and if caught
again they would be cited.
73, Tom W8JI
W8JI@contesting.com
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|