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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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11th Mar 2019, 10:33 am | #1 |
Triode
Join Date: Nov 2018
Location: Diss, Norfolk, UK.
Posts: 15
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ITT-KB Weekend Automatic - distortion?
I just got this neat little radio (destined for the Kitchen shelf).
It's essentially clean, and works well. But at anything other than quite low volume there's a lot of distortion. Is this simply a limitation of the product/design or "other? My personal suspicion, based on limited knowledge, is that the smoothing capacitors in the main PSU aren't supplying a solid voltage. Diagnoses, or pointers to diagnostic techniques, welcomed. BugBear |
11th Mar 2019, 12:52 pm | #2 |
Heptode
Join Date: Nov 2009
Location: London, Ontario, Canada
Posts: 675
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Re: ITT-KB Weekend Automatic - distortion?
Hi BugBear,
Chances are the final audio amp in the radio is off. RM has the schematics: https://www.radiomuseum.org/r/itt_we...automatic.html Do check if the common emitter point of the final transistors (CS1909, CS1910) are indeed at half the supply voltage (DC), and continue from there. Regards, Peter |
11th Mar 2019, 1:43 pm | #3 |
Rest in Peace
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
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Re: ITT-KB Weekend Automatic - distortion?
Like all ITT-KB radios, distortion is not normally a feature. Don't rule out checking the speaker for rubbing or loose diaphragm inner support.
The ITT Service information is also on the KB Museum website, it includes a printed circuit layout to help you locate the components. http://www.kbmuseum.org.uk/itt_servi...omatic_ITT.pdf Good luck, they sound good when working correctly. Mike |
11th Mar 2019, 7:23 pm | #4 |
Heptode
Join Date: Jan 2009
Location: West Lothian, UK.
Posts: 762
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Re: ITT-KB Weekend Automatic - distortion?
The circuit shows a battery/mains switch - so that should quickly eliminate the power supply.
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George |
11th Mar 2019, 8:29 pm | #5 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,724
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Re: ITT-KB Weekend Automatic - distortion?
First think I'd suspect with distortion at low volume, is an out-of-centre speaker cone
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-- Graham. G3ZVT |
15th Mar 2019, 3:07 pm | #6 |
Triode
Join Date: Nov 2018
Location: Diss, Norfolk, UK.
Posts: 15
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Re: ITT-KB Weekend Automatic - distortion?
Thanks for the practical suggestions; a quick go with a set of batteries, and wiring external speakers via the headphone socket should answer some questions, at least for starters.
BugBear Last edited by bugbear; 15th Mar 2019 at 3:13 pm. |
19th Mar 2019, 10:53 am | #7 |
Triode
Join Date: Nov 2018
Location: Diss, Norfolk, UK.
Posts: 15
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Re: ITT-KB Weekend Automatic - distortion?
Oddly, the radio has simply "settled in" and is now behaving much better.
I note that the RM website doesn't have a "covers off" photo of the innards. Would they like one (I took one for my own purposes) ? [img]https://farm8.*****************/7808/46695600424_d231ec5037_b.jpg[/img]le_weekend by plybench, on Flickr BugBear |
19th Mar 2019, 7:28 pm | #8 |
Rest in Peace
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
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Re: ITT-KB Weekend Automatic - distortion?
I think possibly an electrolytic capacitor has reformed, this can happen sometimes. I have had radios which dont work at all then after a little while they slowly start to work, and often they continue to improve over the next 30 minutes or so.
Thanks for the photo of the insides. https://www.radiomuseum.org/r/itt_we...automatic.html Mike |