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 Post subject: Heathkit W4-AM
PostPosted: Aug Tue 03, 2021 7:00 pm 
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Joined: Jan Tue 29, 2019 7:01 pm
Posts: 484
Location: 20653
I picked this amp and was looking it over and I found 1 item that confuses me when i compare the amp schematic to wiring I see in pictures on line. On my amp I noticed that a wire coming form the power transformer was just wrapped around a few others and not connected to anything. I looked at the schematic and it shows that the 6.3v filament winding has a center tap that is not used. But, I also saw a few pictures online that showed that center tap connected to ground. Is there an advantage to grounding it that others are taking advantage of? Was there a production change (I can only find 1 version of schematic)? Should I just leave it as found?

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w4 am power supply.png
w4 am power supply.png [ 612.78 KiB | Viewed 600 times ]


Andy


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 Post subject: Re: Heathkit W4-AM
PostPosted: Aug Tue 03, 2021 9:55 pm 
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Joined: Jan Tue 31, 2012 1:55 am
Posts: 18287
Location: Mountains of Mourne. Ireland.
RT✵M... :)

Final schematic attached below, from this discussion...
https://audiokarma.org/forums/index.php ... ns.459630/

+ 19-page assembly manual.

click image to enlarge.


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page 13.png
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W4-AM_Manual.pdf [3.24 MiB]
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Final schematic EDITED heathkitw4m.pdf [91.92 KiB]
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 Post subject: Re: Heathkit W4-AM
PostPosted: Aug Tue 03, 2021 10:19 pm 
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Joined: Jan Tue 29, 2019 7:01 pm
Posts: 484
Location: 20653
Well now, that says it all! Thank you so much for the info and links. That last schematic and the audiokarma discussion is very interesting.

Andy


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 Post subject: Re: Heathkit W4-AM
PostPosted: Aug Tue 03, 2021 10:44 pm 
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Joined: Jan Tue 31, 2012 1:55 am
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Location: Mountains of Mourne. Ireland.
Very good Andy.
I didn't digest the thread at Audiokarma or study the edited schematic... so be careful.

Most of my test-gear is Heathkit... 8)
Regards, Greg.


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 Post subject: Re: Heathkit W4-AM
PostPosted: Sep Wed 01, 2021 4:42 am 
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Joined: Nov Fri 10, 2006 12:24 am
Posts: 3025
Location: Thornhill, Ontario, Canada
egg wrote:
click image to enlarge [about the hum-pot].
Kind of obvious, but if you are mixing any pre-amp and power amp that has a hum-bucking pot anywhere, don't ground the 6.3 VAC center tap on the PT so as not to short out half the heater winding when the hum pot is turned to one end or the other... easier to see than explain!
I always use the hum pot slider ground, typically in the preamp, and never ground the PT 6.3 volt CT.
Cheers,
Roger

_________________
Roger Jones,
Thornhill, Ontario
Ontario Vintage Radio Assoc. http://www.ovra.ca


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