[ARC5] 10 meter BC-454 - more

[Glen Zook]

	* When every thing is "said and done", the cause of the problem is almost certain to be something so obvious that one will "kick themselves" for weeks for overlooking it.

 
Glen, K9STH


Website:  http://k9sth.com


________________________________
 From: Kenneth G. Gordon <kgordon2006 at frontier.com>
To: Leslie Smith <vk2bcu at operamail.com> 
Cc: Arc5 mail list <arc5 at mailman.qth.net> 
Sent: Sunday, February 10, 2013 4:12 PM
Subject: Re: [ARC5] 10 meter BC-454 - more
 
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
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