[AMRadio] 51J3 or 75A3?

John E. Coleman (ARS WA5BXO) wa5bxo2005 at pctechref.com
Sat Mar 4 16:23:20 EST 2006

	I agree with you Brett.  The Collins rigs were strictly
communication rigs, not HIFI.  I had a 75A4 for a long time and compared it
to other 75A4 RCVRs at the time and all of them had poor audio reproduction.
A good bit of the distortion was with the detection and audio output stages.
I built a MOSFET source follower where I picked up the 455KC IF and fed it
to another AM/FM stereo HIFI radio with its on 10-15 watt audio output
stage.  I disable the mixer and OSC in the outboard HF and fed the 455KC
from the 75A4 into the IFs of the outboard HF radio.  This helped a lot but
found some of the distortion was from the mixer of the 75A4.  I understand
there is a modification for that now, requiring a tube swap to a dual triode
and rewiring.  The 75A4 and its type are famous for accuracy and stability.
As for as stock receivers go on fidelity, the HQ129, HQ145, S-85, NC303 (not
NC300) has outperformed all for me.    

John, WA5BXO

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