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 Volume control in Stromberg Carlson model 4A17
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 Return to top of page · Post #: 1 · Written at 11:26:10 AM on 26 June 2022.
Bowler's Gravatar
 Location: Bongaree, QLD
 Member since 26 October 2018
 Member #: 2308
 Postcount: 77

Good morning all, I have recently worked on this radio and whilst it is working well I can't get the volume control to completely silence the radio. Has anyone had a similar problem with this model. The valve lineup is 5y3 rect. 6a8 converter, ebf35 detector, and 6v6 output. Regards Bowler


 
 Return to top of page · Post #: 2 · Written at 12:07:29 PM on 26 June 2022.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 1245

Hi Bowler, my memory tells me the SC4A is a "reflex" IF/AF IF stage design that may suffer from "talk through".
The output valve derives audio drive from a tap between a AF resistive load and the IF coil primary load and the drive never goes to true zero on the volume control.
I need to brush up on the subject but roughly the "Talk through" effect is worst on high signal levels.
Some reflex sets had quite complex circuitry to reduce the effect, I did a fair bit of work on the effect with some of the sets I have worked on.
To be rid of the problem if it is not being worsened by some component problem, I did move the volume control direct to the output valve grid on one set. Its a complex problem and reading about the subject in the "Radio Designers Handbook" reveals what the compromises are in the design.

Fred.


 
 Return to top of page · Post #: 3 · Written at 12:25:17 PM on 26 June 2022.
DangerousDave's Gravatar
 Location: Toongabbie, VIC
 Member since 1 September 2020
 Member #: 2438
 Postcount: 129

Yes, this is just a tradeoff with most reflex receivers. I’ve just completed a 4A18 with a similar issue.


 
 Return to top of page · Post #: 4 · Written at 9:07:12 AM on 27 June 2022.
Bowler's Gravatar
 Location: Bongaree, QLD
 Member since 26 October 2018
 Member #: 2308
 Postcount: 77

Thank you Fred and Dave, Nice to see I'am not the only one with this problem. Bowler


 
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