[ARC5] 10 meter BC-454 - more yet.

[Kenneth G. Gordon]

I may be slowly zeroing in on the problem with this receiver.

To recap, there is something in it which is horrendously microphonic. 
Tapping, even very lightly, anywhere on the receiver results in it literally 
ringing like a bell. It is so microphonic that when I sneezed violently clear 
across the room on the other side of the shack, you could hear it in the 
receiver. I have never in my entire 56 years in electronics ever run across 
anything as microphonic as this thing is.

Touching the receiver anywhere at all, even as lightly as possible, results in 
the frequency to which it is tuned to vary. Whacking the chassis with a 
hammer makes the tuning jump to another frequency. Whacking it again, 
makes it jump to another frequency, but sometimes back where it started.

So, today, I did the following, having received some more suggestions from 
the crew here.

1) Using my big 250 watt Weller AND my smaller 150 watt Weller, one in 
each hand, I flowed solder into every joint I could reach on the 
pressed-together parts of the  main tuning capacitor.

2) I carefully checked out C-10 and removed its bracket, cleaned under it, 
wiped the areas between the bits with DeOxit 5, then screwed them back 
together tightly.

3) I removed all the screws from the 4 resistor blocks, cleaned under them, 
wiped the mounting posts and the chassis with DeOxit 5, then re-mounted 
them and carefully tightened the screws.

4) I removed the BFO "box", carefully cleaned under it, wiped it with a bit of 
DeOxit, then remounted it, making sure the screws were tight. There was 
some corrosion between the BFO box and the chassis, but the screws were 
tight.

5) Checking for microphonics, I removed each tube, and replaced each one 
with an NOS tube. I did this twice. So, so far there have been three complete 
sets of tubes in this thing.

Results for all of the above: no change.

As far as I can see, there are only two other things I can check out and deal 
with: 1) remove and carefully inspect each IF can, and 2) resolder all 
connections. I have already resoldered several of the connections on and 
around the 12K8, but will do all the rest.

So far, there has been absolutely no change in the microphonics following 
everything I have done.

Although I am pretty stubborn (ask my sweet wife), I am beginning to lose 
patience...

Kenneth G. Gordon W7EKB

"Courage is being scared to death but saddling up anyway."--- John   Wayne