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Author Topic: Collins KWM2A very weak audio on LSB and USB but OK on CW  (Read 499 times)
AD4U
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Posts: 2521




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« on: February 01, 2019, 04:25:53 PM »

I recently bought an "almost mint" Collins KWM2A. This is the late round emblem model. In the 1960's I drooled over Collins. I finally got one some 50 years later.

Problem: On receive I get almost no audio on LSB and USB on any signal and on any band even with the AF and RF gains full open. While listening to the same signal, when I change the mode switch to CW, the audio blows me out of the room.

On any signal and on any mode the S meter reads the same signal strength on LSB and USB and CW, just no audio in LSB and USB but LOUD audio in the CW mode.

IMO this indicates that the "front end" of the receiver is working OK on all modes and on all bands up to the S meter circuit, which I think is in the IF. Again IMO the problem must be after the S meter circuit.

I have tried two Collins PS and two Collins speakers with the same results.

I cleaned the mode switch and I changed the product detector tube 6BN8. This did not help.

I do not have a manual but one is on the way but it may take a week to arrive. Until the manual arrives, does any Collins guru's have any ideas?

Thanks - Dick AD4U

 
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WA4JQS
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Posts: 246




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« Reply #1 on: February 01, 2019, 07:25:07 PM »

Dick:
go here  http://collinsradio.org/archives/manuals/KWM-2%20Collins%20Manual%203rd%20edit.%20Mar_'62_Gaylord%20Hart.pdf

I would check V 13 and V 17 also the switch contacts on i think it is S 9. I find you are getting any copy at all in lsb and usb. i would think a dirty contact. or one of the resistors in the lsb usb ckt has changed value . good luck 73 Tony WA4JQS
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WD8AJY
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« Reply #2 on: February 02, 2019, 09:19:55 AM »

Does it work in transmit.

Bob WD8AJY
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AD4U
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Posts: 2521




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« Reply #3 on: February 02, 2019, 09:54:42 AM »

Thanks for the posts. I found the problem. The wire spring clips that hold the two relays into the relay sockets were loose. One of each wire spring clips were attached where they hook into the relay socket base. The two relays got loose in shipping - I guess. As soon as I re-set the relays and re-hooked the two wire spring clips, the rig worked as it should.

While in there I re-cleaned the switch contacts on the mode switch.

I think the rig works OK but I will do a full alignment as soon as the manual arrives.

Thanks Again:

Dick AD4U
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