[MRCA] ARC-2 Audio final report (I hope)

[DSP3]

OK, looks like the ARC-2 audio odyssey is about over.  Recall that I 
found I had only about 50% modulation from the get go. I did the 12H6 
limiter mod and that helped about 10%.. maybe?  The amplified D-104 mic 
trick yielded zip-point-nothing in this circuit.  I tested the modulator 
tubes and the 12A6 driver, all acceptable.  I tried a total of 8 various 
known good carbon and FAA carbon-compatible aircraft mics.  None made a 
marked difference except maybe an old TS-??, the Y-cord handset.  That 
did a bit better job of maybe up to 60%-65%, at times.  I was ready to 
go inside again and drive the 12A6 grid with the amplified D-104 when I 
happened upon a defective Telex carbon-compatible aircraft mic, just 
gleaned from boxes of electronic detritus dropped on me by a friend on 
Friday (a retired USAF E-9 FAC).  The mic problem was a broken wire in 
the molded PL-68 plug.  I clipped it off and installed a new one.  
Trying it with the ARC-2...presto... Excelsior!  Huzzah! 100% 
modulation. Never would have thought, but there you are!  Sometimes a 
pearl is found in the strangest places.

The broadband IF issue was solved, as previously mentioned, via tapping 
in to the 4th IF and using either the R-390A or the HQ-160 as a tunable 
Q5-er.  Works like a champ. The conversion formula for 80 meters is the 
incremental kHz divided by 3 + 1000 kHz.  For example, for 3885 kHz, 
take the incremental frequency 885 and divide by 3.  Answer is 295 added 
to 1000 = 1295 kHz on Q5-er dial.  Recall that the tunable IF goes from 
1000 to 1500 kHz.

Jeep - K3HVG

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