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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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24th Jan 2020, 9:46 pm | #41 | |
Nonode
Join Date: May 2004
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Re: 9 volt battery eliminator hum
Quote:
Alan |
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24th Jan 2020, 10:18 pm | #42 |
Nonode
Join Date: Oct 2017
Location: Bristol, UK.
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Re: 9 volt battery eliminator hum
I suspect Alan is right. It's too late now, if the PSU has been returned, but the next steps I would have recommended are on-load voltage tests at the PSU terminals to see if there was an over-voltage or under-voltage issue. It would also have been informative to measure current drain particularly with the RT7 which seems to be making sounds when switched off. Cheers, Jerry
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24th Jan 2020, 10:20 pm | #43 |
Tetrode
Join Date: Dec 2006
Location: Evesham, Worcestershire, UK.
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Re: 9 volt battery eliminator hum
I measured the voltage and it was 19 no load. I will check the loaded voltage in the morning. I have yet to send it back fortunately
James |
24th Jan 2020, 10:51 pm | #44 |
Nonode
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Re: 9 volt battery eliminator hum
19V seems high for the no load voltage. 12-13V as indicated in Graham's post #18 would be more of the order I'd expect. Interesting that the R500 doesn't seem to mind. Looking forward to finding out what happens under load.
Alan |
25th Jan 2020, 12:21 am | #45 |
Dekatron
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Re: 9 volt battery eliminator hum
Notwithstanding everything else that's been said, it's my experience that most (older?) transistor radios don't work at all well on basic unregulated dc power supplies. Adding extra C may help but the only really effective solution is to add a regulator circuit. There's usually enough headroom on a lightly loaded unregulated supply for the regulator's I/O differential voltage requirements especially if you have a 9V nominal psu and use an 8V output regulator. (8V is well above the end of life voltage of a 9V battery). The jelly bean variable LM317 type with a couple of resistors and capacitors is just fine. You can add the regulator as a "bulge in the wire" between the PSU and the set!
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25th Jan 2020, 1:09 am | #46 |
Dekatron
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Re: 9 volt battery eliminator hum
That O/C voltage isn't surprising on a supply like that with a bridge rectifier and a great big single smoothing capacitor. The rated 9 volts could well be when it's delivering close to its 500mA (originally intended) load.
As said, the pre-made battery snap connectors are always colour coded like that, as they're intended for replacements for the actual radio, so nothing to worry about, although opposite coded sleeving should ideally have been fitted. There's lots of unanswered questions: Voltage on load measured with a DVM on each radio? And compare. Measure current in mA drawn by both radios? And compare. We still don't seem to know (unless I've missed it) whether the hum is coming from just the power supply itself as a 'physical' vibration, or is actually emanating from the radio as a 'physical vibration, or is actually coming from the radio speaker? These questions need answering before returning the power supply, otherwise the same problem may well be experienced with another one that replaces it. |
25th Jan 2020, 1:15 am | #47 |
Nonode
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Re: 9 volt battery eliminator hum
If Chris is right about using a regulator it looks like the PCB of the eliminator could accommodate the components - see first photo attached to post #11. Probably even simpler to use a fixed LM7xxx 9V regulator. There's certainly likely to be enough headroom for a regulator chip as the no load voltage is 19V.
All this led me to compare the schematics for the R200 and RT7 to see if there might be a reason why one works with the unregulated eliminator and not the other. Nothing shouts at me but the audio circuits are really quite different. A more expert eye might be able to spot something. Alan |
25th Jan 2020, 1:24 am | #48 | |
Nonode
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Location: Halifax, West Yorkshire, UK.
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Re: 9 volt battery eliminator hum
Quote:
Alan |
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25th Jan 2020, 10:30 am | #49 |
Dekatron
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Re: 9 volt battery eliminator hum
I always buy regulated switch-mode plug-top power supplies from CPC and have found them excellent. I've used 9V 1.6A ones and 12V 1A ones. Regulation is to within 5% regardless of AC input Voltage, which incidentally can range from as low as 90V to as high as 264V. They have over-voltage and over-current protection and short-circuit protection.
I use two to power my homebrew amplified loop antennas - not a hint of hum, and likewise to power transistor radios. I also use one to power a homebrew tachometer for my woodturning lathe, and a homebrew PCB circular saw. Here are the links: 9V 1.6A https://cpc.farnell.com/powerpax/sw3...ted/dp/PW02349 12V 1A: https://cpc.farnell.com/ideal-power/...power%20supply They're made in China - where else, but if CPC sell them, that's good enough for me. (The specs are available at the links. Note: 50,000 hours MTB - mean time before failure!). Of course, you may need to cut the 2.1mm connector off and fit new connectors if you need PP3 or PP9 battery snaps, but that's no hardship. Hope that helps.
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25th Jan 2020, 10:51 am | #50 |
Heptode
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Re: 9 volt battery eliminator hum
Two possibilities, the most likely is that the radio is pulling more current than the nasty PSU can supply and the other possibility is that there is a faulty diode in the pack.
The radio needs to be fed from a decent, regulated power supply for testing. Bear in mind that you don't need a specific "battery eliminator". You can run the radio off any PSU of the correct rating that you like. You just need to add a pair of PP9 snaps, or go straight in to the wiring via a 2.1mm power connector. I am in Gloucester and if you want to drop it in sometime, I will test it and provide you with a suitable PSU if required. AJL Electronics 01452 311031 |
25th Jan 2020, 11:03 am | #51 | |
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Re: 9 volt battery eliminator hum
Quote:
Forum rules prevent me for saying what I really think about the item... Lawrence. Last edited by ms660; 25th Jan 2020 at 11:09 am. |
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25th Jan 2020, 12:39 pm | #52 |
Rest in Peace
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Re: 9 volt battery eliminator hum
I have a Lowe HF225 which runs off the manufacturere's supplied transformer type wall-wart.
This served very well for years, until I physically rearranged the set-up. Afer that, I had quite some hum coming from the speaker of the '225. The cause turned out to be magnetic field-induced AC in random parts of the receiver from the transformer in the wall-wart. Repositioning of the wall-wart cured the problem. I wonder if the O.P.'s problem could be something similar? Tony. |
25th Jan 2020, 1:01 pm | #53 | |
Nonode
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Re: 9 volt battery eliminator hum
Quote:
Alan |
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25th Jan 2020, 1:05 pm | #54 |
Tetrode
Join Date: Dec 2006
Location: Evesham, Worcestershire, UK.
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Re: 9 volt battery eliminator hum
I have tested the R200 and rt7 with the power adaptor.
The pics are both off and then on. 111454 R200 off 111457 R200 on 111626 RT7 off 111704 RT7 on James |
25th Jan 2020, 1:22 pm | #55 |
Dekatron
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Re: 9 volt battery eliminator hum
Ditch that PSU and use something more suitable....Also check the output components and B-ve decoupler, the output stages in the RT7 and R200 are different.
The resistance in series with the emitter in the RT7 is less than half of that in the R200 according to the schematics. Lawrence. Last edited by ms660; 25th Jan 2020 at 1:35 pm. Reason: addition |
25th Jan 2020, 1:35 pm | #56 |
Nonode
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Re: 9 volt battery eliminator hum
It looks like the RT7 is drawing far too much current. Can you measure the current James?
Alan |
25th Jan 2020, 1:41 pm | #57 |
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Re: 9 volt battery eliminator hum
That Alan is what I said earlier re the difference in current drawn by the 2 sets.Though no way would I risk an unregulated power supply,which looking at those voltages it is.
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25th Jan 2020, 2:09 pm | #58 |
Nonode
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Re: 9 volt battery eliminator hum
So do you think the RT7 should be drawing over half an Amp? The PP9 won't last long if does. It looks like the RT7 has a fault which might take us back to a suggestion made earlier by Mike T regarding the possibility of failing electrolytics. By the way, the fact that the PSU is unregulated was established early on in the thread.
Alan |
25th Jan 2020, 2:15 pm | #59 |
Dekatron
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Re: 9 volt battery eliminator hum
My fault Alan,the RT7 certainly should not be drawing that.Not read the whole thread!
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25th Jan 2020, 2:15 pm | #60 |
Dekatron
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Re: 9 volt battery eliminator hum
17.3 volts for a 9 volt transistor radio is potential suicide....I would call it a radio eliminator rather than a battery eliminator.
Lawrence. |