[1000mp] mkv Finals burned out

[k5uj at mc.net]

The fan is supposed to come on after about a minute of tx in ssb class AB.  I avoid the class A thing completely.

Never had a problem in AB.  I also don't run it flat out at 200 w. pep.  I back the PA Ic pot down a bit.  Probably for 100% d.c. you need to run it at no more than 50 w. and for no more than 5 or 10 mins.  I'd check the heat sink the first time and watch it.  I know, this is all hindsight, sorry.

About 9 mos. ago I had the top cover off, the one with the speaker, and put it back on not realizing the speaker wires were down in the fan and jamming it.  I started fooling around with the rig adjusting this and that while txing SSB into a dummy load.  After around 15 mins. I put my hand on the heat sink and it was hot enough to fry an egg.  holy smokes I thought;  I stopped and put a fan on it real quick and cooled it down.  Saved the PA and found the fan wasn't coming on.  (I had been wearing cans and did not hear it not come on.)  Found the speaker wires down in the fan when I pulled the cover off to look.

Check your fan and make sure it is working.

rob/k5uj


-----Original Message-----
From: scottg at n3ok.com
To: k5uj at mc.net
Sent: Feb 19, 2005  7:35 AM 
Subject: Re: [1000mp] mkv Finals burned out

*This message was transferred with a trial version of CommuniGate(tm) Pro*



At 9:28 PM -0600 2/18/05, Skip Caswell wrote:
>I was wondering how the finals were burned out.  I have not seen very many
>posts for that problem.  I run my MK 5 at high power for long periods of
>time and thus far, knock on wood, have not had a problem.
>
>Skip KE9L
>


Well, the first time i was running an extended data broadcast (MT63) with
the rig
set for about 25 watts out.  Unfortunately, I failed to note that it was
still in Class A
mode (where I _used_ to use it consistently for SSB driving the VL1000.)
Finals
went belly up in smoke about 5 minutes into the transmission.

This last time I had taken the rig and amp in to work to use as high
powered signal
sources for testing some products.  Been using all week with no problems
because
have been mindful of duty cycles and have been using the MkV as low powered
driver
and the VL1000 for high power for long duty cycle tests. (The amp can take
it, the
MkV can't.)  However, as we were wrapping up tests yesterday afternoon so I
could
bring everything back home, was doing some short tests using just the MkV
at full
power CW (not in Class A mode - but using Packet FM mode to generate full power
signal) and we saw some problems in one of the devices under test - got
involved in
looking at the device and forgot about the rig needing duty cycle until I
smelled the
burn - too late. What a way to ruin a weekend!

So, both times was related to operator error/distraction. but I still think
that it is
ridiculous that a rig of this caliber has no thermal protection circuitry.
Mine does not
even seem to step up the fan as things grow hot and air flow from that could
definitely be better.


-- 
73 de Scott Galbraith
N3OK, Frederick County, MD
FM19ji
ARRL, QCWA 30013, GERATOL 2198, PVRC
NAVMARCORMARS - NNN0OPY, NNN0GAW
National Communications System SHARES
scottg (at) n3ok.com
nnn0opy (at) navymars.org
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