[Yaesu] FT101 6146 modification

[Dennis]

Glen Zook wrote:

> A little while back, someone listed the article (or
> articles) about replacing the sweep tubes in the FT101
> series with 6146 type tubes.  Unfortunately, I did not
> save that particular information.
>
> Anyone out there remember just where the article(s)
> was?
>
> Glen, K9STH

Hi Glen...
    Before you go down this path I suggest you really look at the
benefits (there really aren't any) against the hassle of  converting the

101 to 6146 tubes.  First of all, I know someone who did it.  It was
disappointing.  Bear in mind that the circuit in the 101 is designed
around the 6JS6C which is different internally than the 6146.  The
original tubes have a lower plate impedence and are happiest at the
relatively low plate voltage and (600v) higher cathode current in the
101.  The 6146 is happiest at 800 or so volts on the plate with less
current .      There is far more to consider than simply plate
dissipation of the tubes.   You would be very lucky to get the same
power out of the 6146 that you got from the originals since you'd be
struggling to get enough plate current in to the tubes at the lower
voltage.... to say nothing of what might happen in the area of IMD,
neutralization, etc.  The 6146 needs neutralization and I have no idea
of the circuit in the 101 can accomodate the range needed to do that.
Different tubes need different values in the neutralization circuit to
get it done properly.. this is true EVEN among different versions of the

6146.
   I think this movement started some time ago when 6146s began
appearing in newer transcievers and "sweep tubes" were then seen as
inferior or of poorer quality.  They are not.  Consider my first radio..

an FT-101B that I purchased in 1971 from Wilson Electronics in Las
Vegas.  I used it hard for 10 years and sold it to a good friend of
mine.  He has it today still with the ORIGINAL 6JS6Cs that were in it
when it arrived on my doorstep in 1971... 31 years ago.   It still puts
out 120 watts.  I've known several others with the same longevity.  I
know that there are purported to be some differences in the newer
6JS6Cs.  This can be compensated for by far less extensive circuit mods
to the radio.  Also, the "original" tubes are available on the Ebay on a

regular basis.
   I admit that upon this writing I don't have commited to memory all of

the internal characteristics of both tubes.  I suggest you look them up
in a good tube reference and judge for yourself.  Look at the
interelectrode capacitances, typical operating voltage and currents,
grid dissipation, neutralization requirements, etc.. even filament
current may be different.  My only real experience was with a friend of
mine who did it.. I don't remember the details, but it was disappointing

and he changed it back to the original tubes.
   I'm curious what your goals are in wanting to do it?
73 and good luck!
Dennis,
N�SP