[Fox_Tango] Re: FT 101 low output

[W Sanders]

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.