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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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24th Jan 2020, 11:57 am | #1 |
Tetrode
Join Date: Dec 2006
Location: Evesham, Worcestershire, UK.
Posts: 83
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9 volt battery eliminator hum
Hello
I bought a 9v battery eliminator from eBay. The adaptor is 500ma and 9 volts. My R200 works great with it. My RT7 just hums both when switched on or off I don't understand why James |
24th Jan 2020, 12:12 pm | #2 |
Nonode
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 2,383
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Re: 9 volt battery eliminator hum
The power supply is likely emitting RF signals outside the range of the R200 domestic radio range but within the RF range of the RT7, which I think is UHF? This is quite likely if the 9v power supply is the switched-mode type. You will either need a different type of power pack or else insert some sort of RF filter in the 9v power lead. The other possibility is that whereas the R200 probably has an electrolytic smoothing capacitor on the 9v supply input the RT7 might not? Cheers, Jerry
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24th Jan 2020, 1:02 pm | #3 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,711
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Re: 9 volt battery eliminator hum
Are those Roberts model numbers?
Is the PSU you bought regulated? Could you post its make and model, or a link to it.
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-- Graham. G3ZVT |
24th Jan 2020, 1:13 pm | #4 |
Tetrode
Join Date: Dec 2006
Location: Evesham, Worcestershire, UK.
Posts: 83
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Re: 9 volt battery eliminator hum
Hello
I'm not affiliated with the seller but this is what I bought https://www.ebay.co.uk/itm/PP9-Batte...s/184133860353 James |
24th Jan 2020, 2:08 pm | #5 |
Nonode
Join Date: Jun 2016
Location: Bognor Regis, West Sussex, UK.
Posts: 2,296
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Re: 9 volt battery eliminator hum
Without getting into discussing e-bay items that looks like a switch mode supply so you are probably getting high frequency switching interference.
Try looping the output lead through a ferrite ring a few times or use a clip on ferrite suppressor. Peter |
24th Jan 2020, 2:37 pm | #6 |
Tetrode
Join Date: Dec 2006
Location: Evesham, Worcestershire, UK.
Posts: 83
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Re: 9 volt battery eliminator hum
What is wrong with eBay ?
I have one of those somewhere I will try it. James |
24th Jan 2020, 3:01 pm | #7 | |
Tetrode
Join Date: Dec 2006
Location: Evesham, Worcestershire, UK.
Posts: 83
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Re: 9 volt battery eliminator hum
Quote:
James |
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24th Jan 2020, 3:59 pm | #8 |
Dekatron
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,642
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Re: 9 volt battery eliminator hum
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24th Jan 2020, 4:02 pm | #9 |
Nonode
Join Date: Jun 2016
Location: Bognor Regis, West Sussex, UK.
Posts: 2,296
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Re: 9 volt battery eliminator hum
Check the Forum rules regarding e-bay, Rule 4
"No discussion is allowed about the eBay company (including subsidiaries), the eBay website, eBay auction items or eBay sellers." Peter Post Crossed with AC/HL Last edited by Electronpusher0; 24th Jan 2020 at 4:03 pm. Reason: Post crossed |
24th Jan 2020, 4:17 pm | #10 |
Hexode
Join Date: Nov 2003
Location: Ossett, West Yorkshire, UK.
Posts: 482
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Re: 9 volt battery eliminator hum
James is not promoting the product so I see no problem here?
OK. It is marked 50Hz so probably a transformer supply and not switch mode. The big clue is how much does it weigh? If it it quite light then it is switch mode and probably electrically noisy as most cheap power supplies are these days. On the other hand if it feels relatively heavy for it's size it is probably a transformer supply and the regulation might not be so good, I have one here that is DC output but does not have any smoothing capacitor inside so has a 100Hz hum on the output. You can confirm this by switching a voltmeter to AC and measuring the output. If it shows a voltage then the output is unsmoothed. Or you can simply add an electrolytic of anything between 220uf and 1000uF of 16 or 25 volts across the output. Be sure to connect it the correct polarity. |
24th Jan 2020, 4:53 pm | #11 |
Tetrode
Join Date: Dec 2006
Location: Evesham, Worcestershire, UK.
Posts: 83
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Re: 9 volt battery eliminator hum
Hii
see pics attached of inside the adaptor it has a 1000 uF capacitor inside is apparently 9 volts James Last edited by ssnjimb; 24th Jan 2020 at 4:56 pm. Reason: added another picture |
24th Jan 2020, 4:54 pm | #12 |
Dekatron
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,642
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Re: 9 volt battery eliminator hum
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24th Jan 2020, 5:13 pm | #13 |
Octode
Join Date: Jan 2003
Location: Ashby-de-la-Zouch (it's not by the sea)
Posts: 1,255
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Re: 9 volt battery eliminator hum
This doesn't look like a regulated PSU - just 4 diodes and one cap.
__________________
Now where on earth did I remove that from? |
24th Jan 2020, 5:20 pm | #14 |
Tetrode
Join Date: Dec 2006
Location: Evesham, Worcestershire, UK.
Posts: 83
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Re: 9 volt battery eliminator hum
Do you have a reccomended psu ?
Something that will work James |
24th Jan 2020, 5:51 pm | #15 |
Nonode
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 2,587
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Re: 9 volt battery eliminator hum
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24th Jan 2020, 6:14 pm | #16 |
Tetrode
Join Date: Dec 2006
Location: Evesham, Worcestershire, UK.
Posts: 83
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Re: 9 volt battery eliminator hum
Hi
Yes the RT7 does nothing but hum when switched off and on. It works fine when a 9v battery is connected James |
24th Jan 2020, 6:34 pm | #17 |
Nonode
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 2,587
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Re: 9 volt battery eliminator hum
The RT7 originally used a PP10 power pack with connecting pins, not PP9 clips, so what is the arrangement for connecting power (battery or eliminator) now? A photo might help.
Alan |
24th Jan 2020, 6:54 pm | #18 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,711
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Re: 9 volt battery eliminator hum
I have a very similar unregulated PSU powering my Bush TR82.
I expected the on-load voltage to be higher than 9V... ...but that's a little too high for comfort. Mind you it's been like that for 20 years James, I suggest you measure the voltage across the battery connectors with the set switched on. Does the set that just hums work OK if you revert back to batteries? Your supply looks as it has unpopulated holes in the PCB for a 78 series regulator.
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-- Graham. G3ZVT Last edited by Graham G3ZVT; 24th Jan 2020 at 7:08 pm. |
24th Jan 2020, 7:06 pm | #19 | |
Heptode
Join Date: Mar 2017
Location: Cedar Grove, Wisconsin, USA.
Posts: 823
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Re: 9 volt battery eliminator hum
Quote:
Try installing a extra 1000mfd, 16 cap inside the radio and see if there's an improvement. Battery only radios don't have a smoothing capacitor. Dave, USradcoll1, still trying. |
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24th Jan 2020, 7:07 pm | #20 |
Tetrode
Join Date: Dec 2006
Location: Evesham, Worcestershire, UK.
Posts: 83
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Re: 9 volt battery eliminator hum
Hello
Attached are pics of the original battery clips. and the power supply clips It hums on the power adaptor. It works fine on a 9v battery (pp9) Yes i know it ran from the pp10 which is no longer available. Thankyou for your help so far James |