[Yaesu] 6LB6 in FT-101E / Low power output results

[certified-electronics at juno.com]

Frank,
It could be due to either one of the following and weak tubes would
definitely show
up as low power first on the higher bands.  This has been my experience
using known
good / new 6JS6C finals.  An FT-101 with good tubes will usually do right
at or near
110 / 120 watts (keyed down briefly) on 10 meters and the power will go
up as you
go down in frequency.  Typically 15 and 20 meters will show 120 or
better, and by the
time you reach 40 and 75 meters you typically see 140 watts maybe even
more
150 or 160 watts.  Now this may all be up for debate by other 101 users. 
But I'm only going by my rule of thumb and the rigs I have serviced over
the years.
Keep in mind this is maximum key down and you would not do that but for a
few seconds.
I'm using a bird watt meter on my work bench and I belive it's accurate,
but again you
could get 10 different readings from 10 different meters / give or take a
little but all 
should be close. Due to the cost of finals and their availability these
days, if I see 100 w
on 10 meters I would more then likely be happy and leave the tubes in
there.

On the other side of the coin, weak tubes will show up first on 10 meters
and the power
starts dropping below the 100 watt level.   Typically a working pair (But
weak) set of finals
will show something like 90 watts or less on 10 meters and only upwards
to 100 watts
key down on 75 meters.  Given a lot of leeway for the term WEAK TUBES,
they could be so bad that they won't do anything either.
But just weak per say will usually still do something out.  Since finals
are getting harder
to come by in the 21st century then one could even live with a pair of
weak tubes by
merely using an external amplifier. But if your a perfectionist then you
would be like me
and you want it to work properly then you will  want to replace them.

So I'm not sure what it is exactly you are battling here Frank. Keep in
mind again too
with neutralization.   A typical transmitter when properly neutralized
you will see
maximum power at minimum current.  Now if I'm not wrong here the 101 is
reading
I.C. in the cathode of the two final amplifier tubes and they often show
maximum power
just outside of the dip because you also have screen currents and things
like this that need
to be taken into consideration.  (If I'm wrong here, someone please
correct me).  
So the neutralization procedure in the Yaesu manual in my experience is a
bit
of a tricky thing to pull off and do it right as they explain it in the
service manual
and get it right.

Now the reason I bring up the neutralization thing again,  is that the
rig will 
often put out a whole lot more power when neutralized properly and it
shows
up on 10 meters the most.  If it's not neutralized it will not always
make the
full power as I explained at first. So it's just something to keep in
mind.
As it's been explained on the forum before the 100 Pf  capacitor in
series with
the neutralizing capacitor should be changed to 10 Pf / 1 Kv
when using anything other then Toshiba / NEC finals.   This was found to
be the
case a long time ago when using American made tubes. So just keep that in
mind.
I'm not saying that's your problem, but it should be changed if you have
not already
changed it.  10 Pf Mica caps are available from RF parts for a about a
$1.90 a piece.
And finally in the case where you have changed the tubes, a slight
alignment may
also be necessary of the 12BY7 driver. Check your trimmer input and
output
alignment.  In a perfect world, we should be able to pull out two tubes
and pop
in two new ones and expect it all to work properly.  But Toshiba / NEC
finals
are NOT readily available on the shelf today, so any time your conditions
change using
American made finals, or even little things like changing from a 6JS6C to
a 6JS6A or
6JS6B you can expect the take circuit to act different and now with  your
having changed
over to the 6LB6.....who knows.  At least it's working to some extent and
it provides
an alternative to making major surgery by one going over to something
like  6146 finals.
I've seen 6146 modifications before and I REALLY DON'T RECOMMEND
DONG THAT ONE.  The engineers at Yaesu who designed the original
101 series of transceiver designed the rig around the interelectrode
capacitance 
of the Toshiba 6JS6C finals.  It was a smart move at the time as the
tubes
were not more the $3 bucks a piece. The very early FT-101 came out around
1970 and I belive they hit the U.S. market around 1971 / 1972  maybe even
earlier.  They were being sold by Spectronics East and Spectronics West.
Sweep tubes were used in just about every television set and they were
cheap
and readily available at the time and did the job well.  So in todays
world anytime you change
something in that tank circuit you can expect to get oscillations and
even get birdies
showing up on the receiver as an unexpected result, as was the case in
ALL the
6146 modifications I've seen done to FT-101 transceivers.

Keep up the good work and let me know what kind of success you are having

with those 6LB6 finals. I have a set here that I have been holding back
on just in
case I were to attempt the same thing.   If you really like your rig and
you can't get those
tubes to perform, I recommend just getting a set of 6JS6C finals and a
driver
set off  ~ EBAY.  (GE type work fine)  I see them there all the time, 
they are a bit expensive but worth the investment.  A working set of new
/ old
stock tubes can give you MANY years of good service if you
only watch your key down time and monitor you I.C. during tune up from
here
on out as long as you own that rig.  I always recommend using an external
watt meter
on these rigs and from here on out and for EVER MORE monitor your I.C.
on the front panel.  It will tell you when things are going south, long
before
the tubes start glowing or the rig burns up and you smell something !

Wow, I've got to get a move on here.  I hope this is of some help to you.
Good Luck with those tubes.
Best 73's
Carol Maher
W4CLM


.

On Wed, 3 Mar 2004 05:32:55 -0500 "Frank Mayer" <domino at worldlynx.net>
writes:
Carol,
I tried the 6LB6 tubes yesterday.  I neutralized them as per the manual
on 10 meters.  The tubes are a used set I bought some time ago.  They are
supposed to be good.  Anyway the output was low, less then 50 watts on
the upper bands and just fine on 160, 80, and 40.  They did not oscillate
and seemed to neutralize fine.  I'm just wondering if the low output was
due to weak tubes or due to incompatability.
Frank


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