[RTTY] Amp/Temp

[David G3YYD]

RTTY contesting when running with not many takers is when the highest long
term duty cycle happens. It can get as high as 70 to 80% TX time. Otherwise
it is normally around 50%. If worried about this make short CQ calls with
longer gaps in between. For comparison CW is about half that and SSB lower
still.

There are two areas of concern, the active device temperature and the other
is the power supply. In the case of most Tube amplifiers then if the
amplifier has not failed then the tube cooling is OK. The transformer
temperature is another matter being lots of steel and copper it has a
thermal mass much higher than the tube coolers on the typical 4CX type
devices. The transformer may take several hours of high duty cycle before
its maximum temperature internal is reached.

If the transformer is a concern then turning down input power will help and
fan cool it.

One thing that needs to be done once contesting has finished is let the
amplifier cool down for about 10 or more minutes. Do not switch off too
quickly as there is stored heat energy in the anode cooler of the 4CX type
tube. This needs to be dissipated before switch off otherwise the
temperature will rise and the anode to ceramic seal maximum of 250c will be
exceeded. I normally go and make a hot drink (being a Brit that is tea) and
once I have drunk that return to the rig and shut it down.

73 David G3YYD

-----Original Message-----
From: RTTY [mailto:rtty-bounces at contesting.com] On Behalf Of Courtney Judd
Sent: 07 October 2017 14:58
To: RTTY Reflector
Cc: ACG; SECC
Subject: [RTTY] Amp/Temp

I am looking for any ideas or your thoughts on what would be the safe or
maximum operating temperature of a HF amplifier in rtty operation. My setup
here is a FT5000 driving an Alpha 86 to about 1200 watts on rtty.... it will
do considerably more on cw/ssb and rtty but I felt that I should limit it on
rtty. What started all this is that after about 20 years of just sitting up
on the shelf doing it's thing, I decided to take the 86 apart and give it's
internals a good cleaning. Sure enough, the dust bunnies had been doing
their thing. Gave it a good cleaning but when i went to put it back together
i noticed that on the back panel where the air enters the amp there was a
pre-made place to install a fan. I put a 115 v fan to push air into the amp
which goes past the transformer then into the fan below the tubes and then
out the top thru the tube shields. On top over the vent holes I built a
Styrofoam box with two fans to help pull the air out. Sorta a push-me-pull
setup. I bought a couple of digital thermometers with sensors. I placed the
probe in the airstream coming out of the amp over the fans in the Styrofoam
box and the other the air coming out of the 5000. This is where it got
interesting. On rtty when running the 5000 would get up to about 103 deg F.
from a resting temp of 79 deg. The amp would go from 90 deg up to a high of
155 deg which sorta made me nervous. I asked my wife if eggs would fry at
155 and she said probably! SO, do you guys monitor your amp's temperature
and what do you all think is save? Sorry to be so long winded but I am
curious! thanks and 73's Cort K4WI
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