[ARC5] 10 meter BC-454 - more

[Kenneth G. Gordon]

On 16 Feb 2013 at 10:38, Bill Fuqua wrote:

>     Now that is really strange.
> Is it dependant on speaker volume?

Yes, somewhat. I have gotten it pretty well fixed by what I did to the tuning capacitor.

What would happen was that if I had the BFO on, tuned to a signal from one of my signal 
generators, and then tapped on the case anywhere, it would ring. Then, if I put the speaker 
close to the receiver, and turned the volume up, THEN tapped on the case, the ringing would 
start and get louder to a poiint and keep ringing until I either turned the volume down or 
moved the speaker. It was highly annoying.

With the BFO off, and still tuned to a strong signal from one of my sig gens, it would still ring, 
and could be made to "sustain", but not quite as easily.

Since I removed the tuning capacitor and removed the unused plates then reinstalled it. the 
receiver will no longer ring with the BFO off, and the receiver is far more stable than before. I 
can still get it to ring with the BFO on, but cannot get it to sustain any more.

Furthermore, whereas before if I touched the receiver practically anywhere around or near 
the front panel, the frequency would change, now it does not.

All those extra, un-necessary stator plates were causing big problems.

Obviously (now), both the BFO AND the tuning capacitor were contribuiting to the previous 
weirdness. At the time, the problem was very confusing, and I was not sure that the BFO was 
contributing to the problem. Now I know it was.

I have not yet fixed that problem, but will.

Furthermore, all this had nothing to do with the tubes at all. I swapped all the tubes, three 
times, with NOS and it would do the same thing.

There was an additional problem uncovered in that it would very easily "jump" in frequency at 
times. This was eventually tracked down to loose slugs inside the coil forms. ALL were loose, 
but that one in the HFO coil was the worst. It literally rattled. I fixed those by the application of 
some beeswax inside the coil forms.

Now, with the BFO off, even vigorous tapping on the case or chassis results in only a little bit 
of instant noise, and no ringing or feedback at all. This last bit of noise is caused by the way I 
had to mount the can-cap replacement capacitors. I'll fix that by the proper application of coil 
dope in strategic places around the mixer/HFO socket. 

Ken W7EKB