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Author Topic: Suggestions for Collins 75A-4 Headphones?  (Read 1027 times)
KM1H
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Posts: 4772




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« Reply #15 on: October 17, 2018, 02:38:32 PM »

The output transformer is a POS for much over low headphone audio. That receiver was full of various problems as designed particularly in the audio section plus AGC and rather deaf front end. Collins didnt have a decent AGC in anything until the 75S3 and that was superb to the point I modified a pair of Drake R4C's to use it. Earlier 75A models were horrible on AM yet tell that to the rabid CCA members Grin Roll Eyes I also own an A2 and A3.

I dont understand the Mills mystique, there are several others that turn the A4 into an OPERATORS radio, and not a pricey showpiece.

Mine was highly modified between 65-66 with dual 7360 mixers, 6GM6 RF amp, Cascaded filters with a zero gain IF amp between them, hang AGC plus timing component changes, audio change, and probably others I dont remember at the moment. All paper caps were replaced.

In more recent years several leaky silver mica caps were replaced, several out of tolerance carbon resistors, all electrolytics, many weak or gassy tubes. However Ive swapped in NOS 7360's and they made no difference, maybe the lower B+ compared to other apps preserved them.

The NF on 10M is now 6.5 dB which opens up several more layers of signals;I had to add a 1dB NF preamp to my Kenwoods to equal it.

I have also found this low noise beneficial on 160 and 80 CW using very low noise RX antennas with negative gain and not needing overload and stability prone 40+ dB gain external preamps. The A4 outperforms my TS-940 and 950SD for weak signal CW DXing and there are no artifacts, distortion, or phase noise to deal with.

Dont get me going on those PP 6V6 audio Nationals, I own and use several along with several Johnsons and a 32V2 TX on AM.

Carl
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