Ran a Mark V in Class A driving a homebrew pair of 3-500Z tubes. Ran it for
more than six years with no trouble.
W0ZD/3
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Jim Thomson
Sent: Saturday, August 18, 2012 9:03 AM
To: Charles Harpole; amps@contesting.com
Subject: Re: [Amps] Available Class A in Yaesu
From: Charles Harpole
Sent: Saturday, August 18, 2012 4:22 AM
To: jim.thom@telus.net ; amps@contesting.com
Subject: Available Class A in Yaesu
Correction: xcvrs with choice to xmit Class A are, at least, the following:
FT-1000MP Mark V, FT-9000Contest, FT-9000d, and FT-9000MP. The latter three
also have a bias adjustment on the front panel to slide Class A downward away
from pure Class A in SSB or CW modes. I burned up a Mark V by running it full
Class A (only choice on that rig) and at about 40 watts... great techs tried to
fix it and it blew two more sets of finals before I lost track of it. Morale,
do not run a Mark V in Class A.
Today, I own K3f, FT-9000d, and IC-7800, as well as KWM-2A, and several other
rigs. Very fun to compare them.
GL 73
Charles Harpole k4vud@hotmail.com
### And none of em (except the 400w version of the 9000) is capable of 100 w
pep put in class A ! I own TWO MK-V’s... and alek is correct, in class
A, you gotta run it full bore at 75 w pep out.
Here’s why. In Class A, the MK-V sucks a constant 10 A of current @ 30 vdc
= 300 w dc input. 300-75= 225 watts of CCS diss !!! Which is a blast
furnace. If you decide to run the mk v in Class A,
but say at only 40 w pep output, now it’s 300-40= 260 watts diss. The
heatsink design + toilet roll tube blower is a fubar design in the MK-V.
There is NO air going down between heat sinks 1 +2 at all,
due to the fact the motor on the end of the squirell cage blower is blocking
off the airflow. My fix was to use some thin teflon sheeting, and tuck it in
behind the blower, front panel side of blower.
Then tape off the 3 x huge gaps between each of the 4 x top mounted heatsinks,
sorta like tunnel rams. Ok, now you get a whole bunch more air down all 4 x
heatsinks. The teflon sheeting is curved towards the rear
and is secured to the top lid. The stock, upwards firing loudspeaker is
removed, and tossed. The teflon sheeting stops a ton of air being misdirected
towards the front panel. The blower has No housing around it,
like a normal squirel cage blower, rendering it semi useless at best.
## there is no point at all in using Class A on CW. It buys you nothing.
There is NO imd problem on CW-FM-RTTY, etc. What can be done to improve iMD,
yet not cook the xcvr is to reduce the idle current
on the pair of final PA transistors, and also the pair in the driver stage.. in
class A. If you read the service manual, you will see there is FOUR
individual bias adjustments for those 4 x transistor’s , 4 in total for Class
A, then
4 more adjustments for class AB. Eight in total. You have 2 x choices.
Either DECREASE the idle current of all 4 of em a bit, when in Class A mode....
or B, INCREASE the idle current of all 4 of em, when in class AB.
## Then you can obtain excellent IMD.... that is midway between the oem Class
A and class AB modes. Class A on the MK-V is overkill for imd. Class AB
isn’t good enough. Class A idling current is a whopping 10A.
Class AB idling current is 2A. Some where between 2-10 A of idling
current you will find a good compromise between max power output, IMD, and
heat..and eff. On the newer yaesu xcvr’s, the idle current can be tweaked
via the front panel. No point in having –60 IMD3..... when your table top kw
amp is only capable of -40 IMD3. I’d tweak the idle current on the mk-v,
such that the IMD is SLIGHTLY better than the amp you are driving,
and no more. Then you end up with the best imd that you can possibly obtain
from the COMBO xcvr-amp. Total system imd will always be the lesser of the
xcvr or amp.
Later....... Jim VE7RF
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