[ARC5] 10 meter BC-454 - more

[Kenneth G. Gordon]

Over the past few days, I have "solidified" the coils and their included slugs.

I also did some careful adjustment (using my Millen GDO), and rewinding of 
the RF amp plate/mixer grid coils (L2/L3) by 1) eliminating the 9 turn 
interwound RF plate coil (L2), and winding a 14 turn (from the original ARC 
documentation) separate coil above the mixer grid coil (L3), positioning it 
identically to the original coil, and 2) adjusting the spacing of L3 to tune it 
with the C4D and C4F "centered" (1/2 open) to 28 MHz.

Result of solidifying the coils was to reduce, but not eliminate, the ringing, 
but it did eliminate the "jumping" of frequency. The jumping was obviously 
caused by the loose slugs.

Result of reworking L2/L3 was a vast increase in the gain through the 
system. Obviously, the original ARC method of coupling L2/L3 is far more 
effective than the CQ-magazine-suggested method.

Interwinding L2 with L3 was suggested by the original article which stated 
that doing so would increase RF gain. Instead, this seemed to cause L3 to 
tune VERY low, and instead vastly REDUCED the gain. I suspect that the 
very close mutual coupling had something to do with this, and that the 
reduced gain was caused by inability to tune the mixer grid coil to the proper 
frequency.

I have about exhausted every normal reason for the ringing, except two: 1) 
the tuning capacitor (which I am almost convinced there is nothing further I 
can do about), and 2) the bypass capacitors I used to replace the can-caps 
around the mixer stage.

I used some small high-quality rectangular-shaped dark-orange-colored .047 
MFD 400 VDC caps to replace all the shot can-caps, and mounted them 
right at the tube sockets as stiffly as I could. However, the mixer stage, which 
also contains the HFO, appears to be very sensitive to movement of any 
component associated with it.

Therefore, I plan to "solidify" every possible bit in that area with some of 
Mike's coil dope.

At this point, I am almost convinced that the ringing problem is centered in 
the tuning capacitor. One clue is that even very slight movement or touching 
of the front-panel, or the box that covers the tuning cap, or the tuning knob, 
or the coax that connects to the antenna connector results in significant 
frequency shift.

Some of this, of course, can be put down to the 10X increase in the HFO 
frequency, but not all either. Techniques that work well at 3 MHz, don't 
always work as well at 30 MHz.

BTW, the original ARC documentation concerning circuit values (capacitance 
and inductance, and turns on the coils) provided by one or two of our 
members here, are almost exactly what I am now using. I will re-post those 
details when I have finally run out of patience with this....thing....

Kenneth G. Gordon W7EKB

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