[1000mp] mkv Finals burned out

[Hans Remeeus]

Hello Scott,

I did have exactly the same with my Mk-V 200W. During a Class-A transmission 
of 25 Watt instead of 75 Watt the finals blew out.

Here what KC3VO wrote about it some time ago:

Remember that when running in class "A", power output is 75 watts, and if
you REDUCE the power output, the finals will get HOTTER at the LOWER output,
because the D.C. input power DOES NOT decrease with lower output power when
operating class "A", unloke operation in class "AB".  If LESS than 50 watts
output is desired, it is best NOT to operate class "A" to avoid overheating.
Operating in class "A" at LOWER power levels results in MORE D.C. power 
being
converted to HEAT instead of R.F.-73, KC3VO, Bob.

This fact, and the overheat when using 200 Watt output which I noticed all 
the time, I switched from the Mark-V 200 to the Mark-V Field. In combination 
with my Acom2000A linear IMHO this is a better choice. The Field never gets 
noticable overheated. And driving Class-A 25 Watts (which is a very good 
drive for the linear) never is a problem. The Field is noticable quieter 
too; not those ventilator noise as the Mk-V 200W has.

I had the Mk-V 200W for about three years and the Field for more than half a 
year now.

Very pity about your weekend. I can understand that you are disappointed.

Good luck and all the best!


73,
Hans Remeeus (PA1HR)
http://www.remeeus.nl
Communication is about people, the rest is technology.


---- Original Message ----
From: "Scott Galbraith" <scottg at n3ok.com>
To: "All about Yaesu 1000mp" <1000mp at mailman.qth.net>
Sent: Saturday, February 19, 2005 2:35 PM
Subject: Re: [1000mp] mkv Finals burned out

>
> 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.