My ancient Heathkit SB220 built from a kit by myself in 1972 works at full
power that is on the SSB setting without any problem. But I have replaced
the original EHT transformer with a toroidal one that is out board and fan
cooled.
It still has the original pair of Eimac 3-500z from 1972. I have run it in
so many RTTY contests that it really is proven to be rock solid. I use it in
single band entries in preference to my Alpha 99. I find that the 4CX800s
are OK but I have got through a couple of pairs since I acquired the
amplifier in 1999.
My thinking is that as long as the PA does not over heat after a few minutes
of continuous RTTY transmission then the cooling of the active devices is
good. Then it is down to the PSU as the limiting factor. In a valve PA case
that is the transformer. Given thermal inertia of the block of steel
laminations then it may take an hour or two before it overheats if it is not
big enough. Fan cooling a transformer makes a huge difference to how much
power can be taken from it without overheating. Which is why the Alpha 99
sucks in the air passing around the transformer before going into the PA
compartment to cool the 4CX800s.
73 David G3YYD
-----Original Message-----
From: RTTY [mailto:rtty-bounces@contesting.com] On Behalf Of Bill Turner
Sent: 22 October 2016 19:52
To: Stanley Zawrotny
Cc: RTTY Reflector; Jerry Flanders
Subject: Re: [RTTY] New amplifier announced
------------ ORIGINAL MESSAGE ------------(may be snipped)
On Fri, 21 Oct 2016 18:23:06 -0400, you wrote:
>
>Doesn't RTTY at full legal limit overheat most amplifiers? Can they stand
full duty cycle during contesting? My kilowatt starts running warm, but not
overheating, at 600 watts.
>
>Stan, K4SBZ
REPLY:
Yes, most amps, even those rated as "legal limit" will only do that on CW or
SSB. Only a few will do legal limit on RTTY for any extended period of time.
73, Bill W6WRT
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