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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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25th Apr 2017, 1:50 pm | #1 |
Heptode
Join Date: Aug 2004
Location: Woodbridge, Suffolk, UK.
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Hacker Sovereign II RP25 Oscillation Power Supply
I need some advice please. There is a high pitch noise on this radio, Regardless of volume setting. I have powered the amp section on it own, thats fine.
What may induce such a noise on the supply rails. Scope set to 20mV AC, 2mS / div. Thankyou |
25th Apr 2017, 2:28 pm | #2 |
Dekatron
Join Date: Nov 2006
Location: London, UK.
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
Hello,
So you're showing a modified square wave with a period of around 1millisecond. That's approx 1 Mhz. The other day, I posted an inquiry into sources of mains-borne interference and together we pinned it down to some of the newer bulbs producing a vicious square wave with a fundamental (in just one case) of 46Khz and a peak to peak voltage of 40V! 1Mhz is the 21st harmonic of 46Khz. Not saying it is that specifically - we have no idea yet, in your case - ...but just to illustrate the problem, let's pretend it's the 21st harmonic of a 46Khz square wave. You show it's around 8 millivolts on your Y axis, so that means it would be 21 times higher voltage even if the signal source was right inside your radio (which I'm assuming it isn't). That is a lot of electromagnetic energy to content with, and radios are built to receive microvolt (comms receivers) to submillivolt /millivolt strength signals. The Fourier series that describes a square wave shows how it is the sum of a series of odd harmonics of sine waves. (See diagram) These may or may not occur at tighter intervals than the radio's 10Khz (typical) for a domestic receiver, but in any case, we have giant pulses of electromagnetic energy being induced into our sets, whether via the mains lead or via the aerial. Try switching off energy saving bulbs and halogen spotlights or strip lights. This enables me to get some quiet spots on MW that is otherwise unlistenable to. And please report back! Be interesting to see what you find. I doubt it's a fault with your radio in the least. Obviously, there is an alternative explanation, but only remotely unlikely, that your radio is suddenly producing deformed square waves at around 1MHz!
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Al Last edited by Al (astral highway); 25th Apr 2017 at 2:50 pm. |
25th Apr 2017, 2:33 pm | #3 |
Dekatron
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
Err..
Lawrence. |
25th Apr 2017, 3:41 pm | #4 |
Heptode
Join Date: Aug 2004
Location: Woodbridge, Suffolk, UK.
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
Thanks for the comments, I have a couple of jobs to finish, then I will sort out batteries and turn the main switch off. Will let you know.
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25th Apr 2017, 4:11 pm | #5 |
Dekatron
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
Great!! I' excited to find out what happens. Typo: the line with 10KHz should say selectivity of (historically speaking, maybe !) 10KHz between broadcast channels on Medium wave
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Al |
25th Apr 2017, 4:24 pm | #6 |
Dekatron
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
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25th Apr 2017, 5:22 pm | #7 |
Heptode
Join Date: Aug 2004
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
The noise is from my bench PSU.
Re pictures ect I am struggling shrinking them for this site, using Linux now, not so idiot friendly. I may have stated the scope settings incorrectly. Radio now on batteries and is fine. This is what I am getting from the PSU. Settings 20mv, 1ms. AC. PSU set at 6v. PSU is a Thurlby PL154 Let me know if this attachment works. |
25th Apr 2017, 5:31 pm | #8 |
Heptode
Join Date: Aug 2004
Location: Woodbridge, Suffolk, UK.
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
Don't think it has worked. When I get home I will see if the kids can help me with upload to you tube. At the moment I am getting a error message.
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25th Apr 2017, 5:38 pm | #9 |
Dekatron
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Location: Heckmondwike, West Yorkshire, UK.
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
Windows certainly can't open it.
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25th Apr 2017, 5:45 pm | #10 |
Heptode
Join Date: Aug 2004
Location: Woodbridge, Suffolk, UK.
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
Took some pictures, no need for video.
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25th Apr 2017, 8:25 pm | #11 |
Nonode
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,562
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
Hi.
I wonder if it could still be mains borne interference passing through the Thurlby PSU rather than a problem with the PSU itself. I had a similar situation a few months ago with my Farnell PSU powering an old Perdio transistor radio. I didn't trace the source of the interference but it could have been associated with my neighbour's solar panel control unit putting hash on the mains. Regards Symon. |
25th Apr 2017, 8:47 pm | #12 |
Dekatron
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
The PL154 is a linear lab power supply, so when working correctly, the output should be clean and free from ripple, even at 5mV/div and below...
The noise at ~1kHz (not 1MHz, as Lawrence was rather cryptically trying to say earlier) is most unusual. It's too low in frequency to be a switched-mode power supply, and I'm not sure it'll be conducted in via the mains lead, but I suppose anything is possible. Can you safely observe your local mains on the 'scope? There might be a fault on the control PCB - there could well be frequencies of that sort floating around to drive the digital readouts, and an unhappy capacitor could be responsible (as well as the usual failure modes, they have a habit of leaking electrolyte which turn causes electrical leakage on the PCB). Electrically, there are 2 versions of that power supply around - the earlier one uses the ADD3701 IC to drive each meter; the later ones use a separate ADC and a PIC to drive the displays. I put some details of the later model in this thread: https://www.vintage-radio.net/forum/...ad.php?t=50989 Cosmetically, there are 2 main styles - brown case and grey case. The electrical changes happened before the change of case, so if you have a brown one, it could be either. The easiest way to tell them apart at a glance is the "Damping" switch. On the later models, it's a small push-button. The earlier ones use a rocker switch. As you've found, the Hacker sets of this vintage are generally very sensitive to noise on their supply rails - and they definitely don't like those switched-mode power supplies that are so common today, and based on those pictures it's no wonder it's unhappy with the unwell PL154. At least we know the set itself is probably fine |
25th Apr 2017, 9:22 pm | #13 |
Dekatron
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
Ah, so you would be! Brain scramble... If you overlook the detail of a thousand-fold error, ( there's a mitigating reason, but I don't want to overshare) I was still onto something relevant, it turns out! Thanks for your diplomatic way of dealing with it
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Al Last edited by Al (astral highway); 25th Apr 2017 at 9:43 pm. |
25th Apr 2017, 9:37 pm | #14 |
Dekatron
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
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25th Apr 2017, 10:04 pm | #15 |
Nonode
Join Date: May 2007
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
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25th Apr 2017, 10:48 pm | #16 |
Dekatron
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Location: Evesham, Worcestershire, UK.
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
The simplest way would be to use a small mains transformer. The frequency response will fall away at HF, but you can check that first with a signal generator and take it into account for your observations. Small 3VA frame transformers are quite reasonable - I used one in this project: http://www.markhennessy.co.uk/mdu/ - I haven't got around to fully characterising it yet, and I wouldn't expect it to work past audio frequencies, but for most observations, that's not a problem.
The transformer gives the required galvanic isolation, provided care is taken in the construction. For anyone who has successfully built something that is mains powered, it should be straightforward. Another approach is to use a differential scope probe that carries the necessary safety approvals. Here is an example: https://www.eevblog.com/product/hvp70/ These things are not cheap, but it's CAT III 1000V rated... If you need the high frequencies, this is the price of entry, sadly. Resist the temptation to use a 'scope probe directly on the mains - most of them are not designed with that in mind. If you have probes with a CAT rating, then maybe - I think the best I've seen is CAT II 300V, so that might be OK, but still I'd be very cautious. Of course, to observe 230V AC (650V pk-pk), you need a scope that does 10V/DIV - some stop at 5V/DIV. Hope this helps, Mark |
25th Apr 2017, 10:49 pm | #17 |
Dekatron
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
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26th Apr 2017, 12:45 pm | #18 |
Heptode
Join Date: Aug 2004
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
Sorry this has drifted away from domestic radio. Checked the mains on the scope via isolation transformer and variac. Normal sine wave as would be expected.
Tried the power supply on the variac supply and noise is still present. So must be within the power supply. mhennessy the damping switch is a rocker, the case is brown. |
26th Apr 2017, 12:54 pm | #19 | |
Nonode
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
Quote:
Thanks for your reply and your usual very thorough explanation. The link to your website project is very interesting and I shall be building this set up. The point about HF attenuation due to the mains isolation transformer is worth bearing in mind but it's also a good suggestion to test the set up with a signal generator. Regards Symon. |
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26th Apr 2017, 1:14 pm | #20 |
Dekatron
Join Date: Jul 2007
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Re: Hacker Sovereign II RP25 Oscillation Power Supply
No problem, Symon
I'll try to make time to measure the frequency response of my unit - perhaps over the B/H weekend... |