In message Wed, 26 Mar 97 11:08:09 CDT,
"David Kreinberg" <kreinbd@ccgate.dl.nec.com> writes:
> Here's the rub - using the FT-840 on every band except
> 30m, (running 5 watts) the rig stays nice and cool. Only
> after keying for about 15-20 minutes at 20+ wpm does the
> rig's cooling fan kick on for a few seconds.
>
> On 30m, however, after about 3 minutes of keying, the rig's
> heatsink gets warm (not burning hot, but warm) and the fan
> needs to run. I'm super worried about damaging my finals
> before I get to enjoy this rig. How hot is too hot?
>
> Is this a sign that my set-up is inefficient on 30? Even
> though the tuner provides a good match to the rig, does
> the rig have to "work harder".
>
TOO HOT--that is hot enough to damage the finals, the heat sink will be so
hot that it will be impossible to keep hour hand on it for more than a
second or so. Therefore I wouldn't be concerned about the amount of heat
you're talking about. However, that difference on 30M is strange. The
antenna shouldn't have any effect on it if the SWR measured between the rig
and tuner is 1:1, then it looks like a 50 ohm load. I think that on 30m that
you MAY have a parasitic oscillation. A good test is on key down at about 5
watts output look at the collector current on several bands. The current
should be about the same on all bands. I would think that it would be about
2-3 amps max. If you find it high on 30m, say 8-10 amps then this is why the
heat sink is getting warm. Try the same test with a 50 ohm dummy load
connected in place of the tuner/antenna.
[
QRP-L Archive |
]
[
1993 |
1994 |
1995 |
1996 |
1997 |
1998 |
1999 |
2000
]