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Old 11th Dec 2017, 6:16 pm   #21
qualityten
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Default Re: Very odd fault with Dynatron Radiogram

Have you ruled out Biggles' suggestions about mains interference from a wifi router or mains extender in #16? I was puzzled about an elusive motorboating issue on a valve amp I restored, only to find that it went away when the internet mains extender was switched off! It was there even after extensive HT smoothing.
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Old 18th Dec 2017, 11:31 pm   #22
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Default Re: Very odd fault with Dynatron Radiogram

I've managed to sort it out, thanks to the good folk on here.

It was indeed the router system, not the wifi itself but the power line adapters supplied by Talk Talk.

The customer for the moment is happy switching the power line off when he wants to listen to his records.

The output amplifier was a pig to repair, but I got there in the end, the main cause being that the 1K preset for quiescent current had gone high.
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Old 19th Dec 2017, 9:45 am   #23
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Default Re: Very odd fault with Dynatron Radiogram

Thank you for the update.
So it is getting in via the mains supply, I presume, and not radiated, but why is it noticed only when disc is selected, I wonder?
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Old 19th Dec 2017, 10:50 am   #24
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Default Re: Very odd fault with Dynatron Radiogram

I hesitate to contribute to this thread as everyone is far more knowledgeable than I am, however I have found that putting a class X capacitor inside a mains plug helps greatly with modulation hum. Two or three of them dotted around the house has more or less removed it all.

If Talk Talk are unwilling to replace the adapters might this help here? A suitable resistor across the capacitor would avoid any surprises if the plugs were pulled and someone touched the terminals.
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Old 19th Dec 2017, 11:00 am   #25
AJSmith625
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Default Re: Very odd fault with Dynatron Radiogram

How about trying one or two of those clip on ferrite cylinders on the mains lead to the unit. Suggest fitting one close to where the lead enters the set. See 'clip on ferrite' at Maplins.

Best wishes Alan.
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Old 19th Dec 2017, 11:23 am   #26
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Default Re: Very odd fault with Dynatron Radiogram

Hi,
I wonder if another brand of power line adaptor ( same voltage and current specification, and correct dc plug ? ) would be a solution if Talk Talk are unwilling to help.
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Old 19th Dec 2017, 12:09 pm   #27
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Default Re: Very odd fault with Dynatron Radiogram

Powerline adaptors do seem to vary a lot. I have a pair of TP-link adaptors bought in a Sainsbury's sale last January and they don't cause detectable interference at all.
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Old 19th Dec 2017, 12:16 pm   #28
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Default Re: Very odd fault with Dynatron Radiogram

Quote:
Originally Posted by John10b View Post
So it is getting in via the mains supply, I presume, and not radiated, but why is it noticed only when disc is selected, I wonder?
I once had a pickup preamp that picked up the local taxi broadcasts so anything is possible. My modulation hum problem was definitely radiated from the mains as it happened on battery powered portable radios
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Old 19th Dec 2017, 5:35 pm   #29
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Default Re: Very odd fault with Dynatron Radiogram

Yes I have experienced that problem, but, if as in post 1, the “wiring was disconnected from the disc.....” how is it getting in?
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Old 19th Dec 2017, 10:25 pm   #30
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Default Re: Very odd fault with Dynatron Radiogram

I can't tell you how its getting in, but of course the phono preamp is very sensitive (though so is the tape head amplifier) however I also noticed it on MW.
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Old 19th Dec 2017, 11:44 pm   #31
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Default Re: Very odd fault with Dynatron Radiogram

Those datalink over the mains boxes are the spawn of the devil as far as anyone interested in shortwave (listeners and licensed amateurs) are concerned. They drive a coach and horses through the essential requirements of the EMC directive and the manufacturers just seem to be able to get away with it because of a loophole that enables them to class the mains connection as a "signal port" and thus not measure the conducted emissions from it! They then get radiated since the mains wiring is far from a balanced line at the frequencies involved.

It's probably getting in to the Dynatron directly via the mains so can be dealt with locally by filtering, but for anyone affected by the radiated racket it's a different story.
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Old 20th Dec 2017, 12:00 am   #32
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Default Re: Very odd fault with Dynatron Radiogram

Hi, glad you have found the reason for interference, well done for your persistence.
However I was puzzled by your first post, were you said it only occurred when disc was selected, i note you now say you notice it also on MW!
It did lead, however, to an interesting debate.
Cheers
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Old 20th Dec 2017, 12:39 am   #33
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Default Re: Very odd fault with Dynatron Radiogram

You could only hear it when disc was selected.

I did try a 470nF X class capacitor across the mains to no avail.

If it did get through the mains it also got through the toroidal transformer.
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