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75A4 AGC Mod




 
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Author Topic: 75A4 AGC Mod  (Read 6535 times)
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W3NP
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« on: January 16, 2010, 10:38:34 PM »

The AGC action in my A4 has always been poor. When using AM and in fast speed it is not an issue but when on CW and in the slow position, it seems as though the attack is way to harsh (attack too slow causing distortion?) and the release is too fast. The beginning of a CW character is always a sharp crack or pop and the RF gain must be reduced to prevent it. Is this an issue with all A4's? I don't want to just start changing TC's without determining if this issue is a need for repair or a modification. I have recapped most of the receiver over the years.
I have heard of a common agc mod but can not find it anywhere on the net. I once asked K1MAN (back in the early 80's) while in QSO and he required money to tell me!! Is Collins info still not free among hams? Can anyone provide info and/or diagram for the mod?

Thanks...
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---Dave  W3NP
K4TLJ
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« Reply #1 on: January 16, 2010, 10:52:56 PM »

Maybe you should invest in the compendium...
http://www.ermag.com/index.cfm?v_link=product_detail&v_key=224
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Terry
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Pete, WA2CWA
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« Reply #2 on: January 17, 2010, 12:09:46 AM »

Improving 75A4 Slow-AVC
CQ Mag., Sept. 1966, page 37
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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
W3NP
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« Reply #3 on: January 19, 2010, 09:36:32 PM »

Many thanks to Joe KB9R for sending me the mod article. Hopefully it will improve the performance of the receiver. Thanks to the others that replied as well. I had thought about buying that ER book, but was really only interested in the the later (than 1966) AGC mod.
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---Dave  W3NP
KM1H
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« Reply #4 on: January 20, 2010, 08:52:23 AM »

How about sharing that article on here?  My ER's dont go back that far.  I installed a SS hang AGC in my A4 in 65-66 but dont recollect the CQ article which I'll have to chase down also. That A4 still does serious work on 80/160 CW DX and outperforms the SS rig.

Carl
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WBear2GCR
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« Reply #5 on: January 20, 2010, 08:05:02 PM »


I seem to recall reading one or more of those AGC mod articles and found some follow up letters or articles saying that at least in one case they didn't work right... I don't recall which mag or which article that was... sorry about that. Also I seem to recall a number of variations on the theme being published.

               _-_-bear
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_-_- bear WB2GCR                   http://www.bearlabs.com
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