Hi again all...thank you for the replies and possible areas to check for
the GS-35B linear problem...Three areas to look at it seems...
One is the placement of the electronic bias board in the cathode
compartment possibly getting Rf on to the board even though it is
bypassed with .01 ceramics on both input and output.I am going to move
that circuit and locate it on the front panel sub chassis..
Two..Parasitic oscillation...A real possibility...I have a parasitic
suppressor on the anode consisting of 3 turns of 3/8 inch copper strap
and a 3 watt 68ohm 3 watt resistor....When the amplifier faults I have
an off the scale reading on the wavemeter above 250mhz....I will look at
the placement of the pi input network which is located close to the
cathode..
Three Try another tube...I currently have two new tubes in transit from
Ukraine....I have tried a New GS-31B tube in place of the 35B with the
same fault occurring...I think I can discount the 35B tube faulty...
I have another 160 meter single band GS-35B which I have been using
constantly on 160 meters for two years, quite often running CW for 2 to
3 hours...It is a pussycat and has never faulted or shown any signs of
instability...I only run the tubes to 1kw output and expect them to last
for years...
Once I solve this problem I will let you all know what stupid mistake I
have made with this linear....I have built more than 40 amplifiers over
30 years and this is the first one to give me problems...I guess I may
be getting old and maybe missing something in my dotage..(Grin)..
73.....Bob VK3ZL...
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