[Boatanchors] P&H LA-400 linear

[Rodger Singley]

Ron,



P&H made a series of these amplifiers, using some parts from Command Set transmitters, with ever more optimistic  power ratings.  I have one of the early ones along with a homebrew copy I picked up at a hamfest years ago.



Some were shipped from P&H with 837 tubes which are sort of a variant of the 1625 except unlike the 1625 the suppressor grid comes out to its own pin.  The 1625 tubes used in the 400 series amps were modified by sawing an access hole in the base and disconnecting the suppressor grid at the base so that they could run in full GG operation; NOTE some 1625 tubes have the shorting connection to the cathode inside the envelope and cannot be modified so be careful if you buy one of these amps that the spare tubes that you acquire can be modified for use in GG service.



The 1625 (and 837) tubes were run at well over their ratings which they would somewhat withstand in SSB service and it made sense when they were almost free but there are much better vintage amps out there that provide plenty of power without abusing the tubes.  In many of the models, they used a surplus filter that was also run a bit over its voltage rating but those oil filled caps were very conservatively rated and they seem to hold up OK to a little abuse.



Rodger WQ9E



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________________________________
From: boatanchors-bounces at mailman.qth.net <boatanchors-bounces at mailman.qth.net> on behalf of Ron VE8RT <ve8rt at yknwt.ca>
Sent: Wednesday, August 14, 2019 7:49:51 PM
To: boatanchors at mailman.qth.net <boatanchors at mailman.qth.net>
Subject: [Boatanchors] P&H LA-400 linear

  I'm giving some thought to having a linear amp available (I'm
comfortable with low power most of the time).  In my collection of old
tubes are a single 811, a pair of 813s, a 4CX250, some 6146s and
variants, and a few 1625s.  It may not be the only amplifier, but I found
that the P&H LA-400 (early models) used the 1625s.  How difficult would
it be to find a 1625 based amplifier?

      Ron VE8RT
--
Ron VE8RT <ve8rt at yknwt.ca>
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