[Fox_Tango] Re: FT 101 low output

Sun, 24 Mar 2002 16:39:13 -0500

I did a lot of work, and repair on FT-101 series. Biggest problem I seen was
guys running AM and toasting the final in less than 3 minutes due mainly to
the fact that if you follow the manual you should never run over 15 watts AM
and you will be fine. As for RTTY and other high duty cycle modes I would
not run more than 20 watts, and defiantly not more that 15 watts if your
passing a lot of traffic.

The best solution I have seen is changing the finals out for 6146's. then
you can run it all day long at 25 watts with no problem. For info on
modifying the final there is a article in QST and in hints and kinks, don't
remember the issue but if your interested let me know and I will look it up.
With the 6146's as finals you will only get 130 watts out max, but you don't
have to worry as much with these work horses. the 6JS6C's are TV sweep tubes
and will go south if you "crank then up too much" they are poor substitutes
for real RF amp tubes.

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of W Sanders
Sent: Sunday, March 24, 2002 4:08 PM
To: [email protected]
Subject: [Fox_Tango] Re: FT 101 low output

Hey the list is alive!

I don't think it's wise to drive the FT-101 continuously for more than a
minute or so regardless of the power level. I replaced me green band
(original) finals with NOS GE tubes and ran PSK 31 for a few weeks. I never
ran more than
35 W power output / 150ma plate (*) current and within weeks the output of
the
new tubes was down to 5 or 10 W. I even put a thermometer probe in the
output
fan duct to monitor temperature rise. (Like driving a Volkswagen by the EGT
gauge - you only go so fast as to keep the EGT below a certain level. But I
digress.) My problem is that the IC rose as power dropped. I am not sure I
actually fried the new tubes but I think their capacitances changed so that
the impednaces were all weird - seems like I had the Loading control at
either
0 or 10.

I put the original final tubes back in. I think the power amp is designed so
"close to the brink" in terms of operating the 6JS6Cs - which weren't really
designed to run at HF frequencies and power levels - that anything other
than
CW and SSB duty cycles gets things so hot inside the compartment that
component values drift. Remember what the manual admonishes: "continuous
operation for more than 10 seconds may result in destruction of final
tubes."

I wonder how many ops destroyed their brand-new rigs running RTTY back in
"the
old days?"

-Wiley KF6IIU

(*) From the schematic the metering is on the cathose side so you are really
monitoring all current through the tube - plate and grid current, right?
This
is actually a good thing.
_______________________________________________
Fox_Tango mailing list
[email protected]
http://mailman.qth.net/mailman/listinfo/fox_tango