[AMPS] FAILURE OF PARASITIC RESISTORS IN AL-811X AMPLIFIER

[Peter Chadwick]

Phil says:

>I suggest that 90% of the modern-day suppressors are under-engineered by at
least 50%.

I feel you're right there, Phil. My 2 times 4-250A amp is the chassis from a
Naval tx. The parasitic suppressors are 33 ohm glo-bar style resistors rated
at 20 watts, and the coils are 14SWG (about 12 AWG) tinned copper. Those
resistors are man enough.

As designed, the amp was blown from the top, so the parasitic suppressors
were in the (comparatively) cool air stream. The original tubes are 6155 or
some number like that (actually QY4-250A) : they don't have the metal base
shell of the 4-250, so the cooling requirements are theoretically less on
the filament pins. I blow from the top, with a muffin fan blowing on each
socket from underneath as well to cool the filament pins. Lower temperature
in the parasitic suppressor resistor has got to be desirable for
reliability.

73 

Peter G3RZP



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