I purchased an AC line powered fan that has a clamp mount.
It can be moved around to pass air over any QRO rig on the
bench...and there's a few, hi hi, mostly boat anchors. The
reason for getting the fan is detailed below:
When the finals (one of two actually) in my 1978 Icom IC-701
let go, I should have seen it coming but was too engrossed in
the QSO I was having at the time. It has an internal fan but
when the XMIT/VOX switch is on VOX that fan only comes on for
the duration of the VOX. When operating CW, my primary mode,
that fan only came on for the duration of a dit or dah. This
wasn't long enough to cool the finals. Also, when the final's
temperature got too high the frequency display was supposed
to flash. I never noticed it but after the finals blew I did
confirm the display would flash by heating the thermistor with
a heat gun. To answer your question, the heatsink on the IC-701
was only warm to the touch, never so hot that I couldn't lay a
hand back there and hold the heat sink area.
I could have switched the rig to XMIT and the internal fan would
have come on as long as necessary to cool the rig. That is, until
I wanted to receive then I would have to have switched the rig
back to VOX (which would have shut off the fan). Manually switching
the rig from XMIT to VOX would no doubt have added a few more years
to the life of the original finals.
I acquired a new matched set of final transistors from RF Parts.
Fortunately I had the tools and experience to do the job myself so
the repair cost was very reasonable. And now I have this small and
reasonably quiet external fan that I picked up at Home Depot. I can
direct the flow of air to any of my rigs where needed and it works.
The fan on the Icom seldom if ever comes on now that I am using the
external fan. Of course my code speed has increased and I believe
the shorter dits and dahs contribute to reduced heating in the finals.
So, in summary, the internal fan on my Icom IC-701 was designed to
shut off anytime the rig was in receive. Combined with the VOX this
was detrimental to the finals during long and slow CW sessions. The
heatsink never felt hot to the touch. With new finals and an external
fan I've had no repeat problems of overheated final transistors. The
rig was gone over by Icom this year and pronounced aligned & healthy.
And the Icom technician complemented me on my rework :)
Enjoy!
Stephen Lee, AB7HI, Tacoma, WA
slee@u.washington.edu
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