P&H Linear w/ 837 Tubes

William Gode wiley at INTERACCESS.COM
Mon Sep 29 12:51:27 EDT 1997


I bought a nice P&H LA-400C "800 Watt PEP" Linear Amplifier at a
hamfest this past weekend.  Anyone remember these from the early '60s?

The amplifier came with four parallel 837 final amplifier tubes, plus
a spare set of NIB 837s.  (The 837 was offered as an option to "modified
1625s" which required that the internal suppressor to control grid
connection be broken by drilling a hole in the tube bases.)

When driven by my Heath Marauder, the LA-400C actually makes 500 watts
PEP output on 75 meters, with a beautiful, sharp scope pattern.

I had always thought the LA-400C was "pushing the envelope" with (4)
1625s (each with 30 watts of plate dissipation) for 800 watts PEP input.
BUT...my Handbook shows the 837 with only 12 WATTS of plate dissipation!
Is this correct?  I operated the amplifier continuously for 15 minutes
in SSB mode (until I became hoarse) and the darned 837s were still
cranking out 500 watts PEP, venting plenty of heat from the cabinet
and showing absolutely no plate color.  In a normal QSO, the thing runs
cooler than the transmitter...with no fan!

Can anyone offer an opinion/explanation as to how these 837s can operate
this way and for how long?  Is this the most under-rated tube in history?

Thanks and 73,

Bill, W9NHQ

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