On Mon, 14 Jul 1997 00:16:57 -0500 philk5pc@connect.net (Phil Clements)
writes:
>At 09:26 PM 7/13/97 +0000, you wrote:
>
>snip.......
>>Where does the dc current you think bends the filaments come from, if
>
>>the specific peak emission is 8 amperes and the absolute peak
>>emission capability is 10 or twelve amperes?
>>
>>Once we find the source, we can calculate the force.
>>
>snip......
>
>Hi Tom et al.....
>
>IMO the source of the current that bends the filaments is the same
>source
>that has sent Ip meters sailing out of their holes and across the
>room.
>It is the filter capacitor in the PS. When we all threw away the
>filter
>chokes and 4 mfd filter caps in the early days of linear amplifier
>proliferation, replacing the above with 30-80mfd capacitor input
>filters,
>and plugging it all into 240 volt mains, we created a monster just
>waiting
>to strike. Many posts have covered the fact that the old ways of
>protecting
>circuits from "big bang" events are far too slow for use in modern
>amplifiers.
>
>As amp manufacturers and home brewers began to push the envelope (no
>pun
>intended) with tubes running at maximum Ep and Ip there became less
>and less
>room (and time) for error. There now exists very cheap technology for
>removing
>the source of 99% of the "big bang" events by simply removing the PS
>filter
>cap. from the circuit in less than 3-5ms after a fault or arc occurs.
>
>No sources = no forces.
That is where the 10-15 Ohm wirewound in series with the HV line comes
into play. In the SB-220, simply remove that silly little VHF choke and
put in the resistor. The same holds true with the TL-922.
I am also suprised that the plate RFC in the 220 does not melt down
during a short; the #28 wire is mighty thin. Altho I suppose the #30 wire
in the grid RFC is the weakest link.
It all makes me really wonder exactly what is the true path and source of
the "big bang".
At least the grid choke school of thought and possibly Rich's "network"
act as fuses and can often save the tube. The directly grounded grid
offers no such protection which IMO is why the AL-82 (and similar
designs) often causes considerable damage when whatever it is does its
mischief.
I do know as fact, that any 220 that I have reworked with my own
parasitic suppressors, series B+ resistor and original grid circuit has
not lost a tube. Over the years that is a considerable number of amps.
73...Carl KM1H
>(((73)))
>Phil, K5PC
>
>
>
>
>
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