On 6th October, Jordan wrote...
"...After 1 minute output dropped by about 50 watts. At higher wattages the
loss is more pronounced, at 600 watts it may drop to 400 over a minute
time..."
****************************
Hi Jordan,
This may be offbase to your problem there, but I experienced a similar
situation here last year with my homebrewed 2x813 kilowatt...
My issue was the direct result of heating inside the padder capacitors that
were installed in parallel with both my plate tuning and plate loading air
variable capacitors in the rig's final output pi-tank circuit...
The internal heating whilst under load like that would cause the values of
these fixed capacitors to change, thus throwing the tuning parameters of the
amplifier way off base...
Tell me this: omce your RF output has dropped like that, can you "re-peak"
it to its original level (or can you re-peak it to any degree at all) by
tweaking either the plate tuning, or the plate loading, capacitors...? (I'm
assuming, of course, that your design employs padders --- my issue occurred
only on 160-meters, where "door knob" padders were used extensively on both
sides of the final pi tank coil).
My final permanent "fix" in this regard was to replace ALL of the doorknob
padders with a combination of fixed vaccuum capacitors / pre-set air
variables...
~73!~ Eddy VE3CUI - VE3XZ
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