Sounds like the filament/cathode support.
Mark WB8JKR
On Sun, 7 Jul 2002 12:22:10 -0500 "Joe" <w5asp@earthlink.net> writes:
> Recently we had an SB-200 which suddenly refused to work. I'm not
> clear as
> to the exact symptoms as I wasn't there at the time. Previously the
> unit
> had performed flawlessly for some years after being upgraded with
> the entire
> suite of "Harbach mods ".
>
> While looking at it for signs of trouble I found one resistor (R7)
> on the
> PW-200 power supply board that was definitely "charred" ... however
> after
> removing it I found it still showed continuity with 900 Ohms
> resistance (R7
> is a 910 Ohm, 2 W). I think that this resistor provides the ALC
> bias
> voltage.
>
> When I removed the 572 B tubes (both GE) I noticed that one of the
> tubes
> had an "object" rattling around inside, completely unattached to any
> of the
> tube's internal structure. This "thingee" looks like a small spiral
> sprint,
> one end of which (i.e. a wire) is bent over and passes entirely thru
> the
> spring from one end to the other and protrudes quite beyond the
> other end.
> I'm guessing that the spring body is about 3/8" long and the wire
> protruding
> out the other end is maybe another 1/4 " in length. At the end of
> this
> "wire" is a "hook".
>
> Looking at the tube from the top, there is a ceramic piece roughly
> in the
> form of a cross. An identical "spring" is recessed in one arm with
> the
> "wire" passsing through the ceramic down into the interior of the
> tube and
> apparently hooked onto the wire mesh structure that I take to be the
> grid.
> On the other side of the ceramic cross is a empty recess with a tiny
> slot in
> the bottom that obviously once contained the "loose" spring/wire
> piece.
>
> I know very little about the physical structlure of such tubes.
> Obviously
> the fact the this item became unattached is a "failure" of some
> sort. (With
> a replacement tube the amp's OK.)
>
> But what is the function of this piece, what does it's loss do to
> the tube,
> how could it just fall out ?
>
> I'd appreciate any thoughts anyone might have. I'll probably never
> run into
> it again, but after all these years, it's got my curiosity up.
>
> Probably best to reply directly ..it's not a high profile issue.
>
> Thanks,
>
> Joe, W5ASP
>
>
>
>
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