[AMPS] blocking cap current

[Peter Chadwick]

Rich says:

	>>you might want something a bit bigger on 160.

	>?  It apparently doesn't seem to make a discernable difference if
the 
	>tank caps are adjustable. .  

I only said 'might'...............I agree it doesn't make appear to make any
discernable difference. It used to, of course, in days of plate and screen
modulation on AM, when you wanted a small value to avoid shunting the higher
audio frequencies too much. Showing my age now....

	>?  Agreed.  Anyone who doubts this should take a look at the anode 
	>waveform with a 1000 to 1 HV multiplier probe and an oscilloscope. 

Unfortunately, HV probes are very expensive new, and I've never seen one in
a flea market. I'd like one, though.

	>During the grate parasitics debate, when we were discussing
gold->evaporation from an 8877's grid, I showed that RF grid-current in an
8877 >(operating at its max. ratings of 4kV and 250MHz) exceeds 43RMS
>amperes.   

This does suggest why you can get troubles with poor grid grounding
techniques. Does the 8877 have a grid ring for a collet, or does it rely on
grounding through the pins in the base? 

Even a 3-500Z would appear to have 1.8 amps of RF in its grid connection at
28MHz. This suggests to my mind that something better than disc ceramic
capacitors ought to be used to bypass the grid.

I suppose that you can get away with a lot on SSB, but SSTV or RTTY really
separates the men from the boys when it comes to reliability.

73

Peter G3RZP



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