[Boatanchors] Diode replacements for 866 tubes, ratings needed ?
Rick Poole WA1RKT
wa1rkt at comcast.net
Thu Nov 13 08:31:58 EST 2014
Rob;
A 4x811A amp (any 4x811A amp) can THEORETICALLY run at about 270 watts carrier output on a continuous-duty mode like RTTY, figuring 45 watts plate dissipation per tube in continuous commercial service (CCS) and 60 percent efficiency in class AB2. Class B push-pull might give you a little more, but not much. That's assuming everything is perfect... the tubes are in tip-top condition and perfectly matched, the circuit guarantees equal power handling in each tube, the amp is correctly neutralized, the amp is perfectly tuned and driven, the amp design provides ample cooling for the tubes, and the power supply is perfectly matched to the tubes. Few if any of those conditions ever happen in the real world, so trying to run a 4x811A amp at much more than about 200 watts out in RTTY service is a crap shoot at best.
The Warrior is little different from modern day 4x811A amps like the Ameritron AL-811H except for the power supply... the swinging-choke-input filter does theoretically give a bit better regulation on power peaks.
I have no interest in RTTY and little interest in other 100%-duty-cycle digital modes so the limitations of the 4x811A class of amp in those modes are somewhat less relevant.
As for selling the Warrior and getting something else... see my page on QRZ. Down the page a bit, you'll see a rack with a 51J-4, a Heath Marauder transmitter, and a rack-mount 30L-1 amp. The Warrior is going where the 30L-1 is now, and is intended to match the Marauder in styling. That's really the only reason I went for it, otherwise I'd just leave the 30L-1 there since it works pretty well in that setup. I do have an SB-221 and was considering converting that to rack mount, but these days the thoughts are to repaint that in Collins colors and put it beside my KWM-2A. Meanwhile it sits on the other operating table next to my TS-950SDX.
Rick WA1RKT
----- Original Message -----
From: "Rob Atkinson" <ranchorobbo at gmail.com>
To: "Rick Poole WA1RKT" <wa1rkt at comcast.net>
Cc: "Boat Anchors List" <boatanchors at mailman.qth.net>
Sent: Thursday, November 13, 2014 6:33:50 AM
Subject: Re: [Boatanchors] Diode replacements for 866 tubes, ratings needed ?
I've never owned a Warrior but I have heard about them and a friend has one
and I have had a chance to look it over (although I don't recall much about
the specific circuit details). My observation: The Warrior was designed
and built at the tail end of the AM days when gear was designed and built
more for continuous duty. It's a relatively big heavy brick compared to
modern ham RF amplifier products today. Much is conservative with that amp
including the plate voltage. This means you won't get 1.5 kw or even 1000
watts; maybe more like 500 or 600 watts out, but, it will sit there putting
out that power at 100% duty cycle with no time limit especially if you put
a small fan over the RF cage. I'm told that for this reason, the amp is
sought after by vintage RTTY ops--the green key crowd. There may be some
on this list. I expect at the time it was marketed it was indeed a "legal
limit" amp--1 KW input in the U.S. (which should still be the legal limit
in my opinion).
I see you have wisely decided to avoid any big revisions to the plate v. so
this comment is for general consumption. I don't wish to seem pedantic
but if it were me and I wanted to run more power but at 50% or less duty,
I'd pretty much leave the Warrior alone and sell it and look for a SB200 or
SB220.
73
Rob
K5UJ
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