[ARC5] 10 meter BC-454 - more

[Kenneth G. Gordon]

On 11 Feb 2013 at 8:35, Leslie Smith wrote:

> Ken,
> When I was in my teens I watched my neighbour (Geoff, VK7ZAS) "tap"
> around a circuit using the plastic head of a 3 inch (Stanley)
> screwdriver. He was looking for a dry joint. He observed the relative
> noise as he tapped each component.  Very useful to watch him do that.
> I learned a lot.

Hello, Les. Well, in this case, I know there is a "dry joint" somewhere: maybe 
more than one. The thing is so sensitive, that even if I used a toothpick and 
held my breath it would be very difficult to track it down. Even touching the 
outer case as lightly as possible results in what I call "wobble" or even 
"jumping".

In fact, I sneezed very loudly on the other side of the shack once, and even 
THAT produced a noticeable effect in the receiver.

> Further to the point about "NIB" valves/toobs.  I built a radio, and
> (as usual) it didn't work.  Geoff debugged it. He  measured voltages
> around a 12AT7 "tube".  He replaced the 12AT7 with a NIB "toob".    No
> change. More measurements.  Geoff reached up for a SECOND 12AT7. I
> protested.  "But you just replaced that!"
> 
> He said:  "Don't think, just because you get a valve out of a
> nice-looking cardboard box, it's good.
> Never forgot that lesson.  I know it's unlikely, but don't be afraid
> to try a third 12K8.  (A lovely black metal one).

So far, I have tried three: one original, and two NIB, all lovely black-metal 
ones. At this point, it ain't the toob.

Thanks, Les.

Ken W7EKB