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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 12th Oct 2018, 5:02 pm   #21
roffe
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Default Re: Reviving Radio in old German Radiogram

Agree with ms660. It has to be a Stern radio Weimar 4680 in a radiogram cabinet.

I even googled the number on the loudspeaker and it turned out to be a Stern loudspeaker. Furthermore-look at the fasteners that hold the loudspeaker and compare these and also the radio chassis as a whole with this link:-

https://sprzedajemy.pl/stare-radio-w...299-nr41957412

That 'knob' on the sliding door is also a typical Stern.

The original is a Blaupunkt Arkansas.
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Old 3rd Nov 2018, 7:57 pm   #22
beachboybuff
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Default Re: Reviving Radio in old German Radiogram

Hello All,

Thank you for all of your help and advice. I have been busy recently so not had too much spare time to look at Radiogram, but I am still keen to get it working properly. I have removed the cartridge from the radiogram, and this has had no effect on the feedback. I tried touching the wires that the cartridge attaches to when the radiogram was on, and there was no buzzing or static noise at all, which I expected there to be, which suggests to me that it is a problem of some description with the record playing part of the circuitry inside the radiogram. Does anyone have any ideas of things it might be, or things to check from these symptoms?

Regards,

Michael
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Old 5th Nov 2018, 6:17 pm   #23
Edward Huggins
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Default Re: Reviving Radio in old German Radiogram

This suggests the amplifier section is faulty and is likely to mean you will get no sounds from the Tuner section either. Try a contact cleaner on the piano keys and actuate them.
If no joy, you will need to signal trace the circuit. Best starting with the amplifier section first. But before you do this, we need to know what confidence/experience you have to work on the circuitry within the chassis of this, especially when it's powered up?
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Old 7th Nov 2018, 8:10 pm   #24
beachboybuff
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Default Re: Reviving Radio in old German Radiogram

Hello Edward,

By Tuner section, do you mean the Radio output, as this appears to be working faultlessly. Problems only start when radiogram is switched to the phono input. I don't have a whole lot of experience with working on this sort of thing, although I'm no stranger to wiring plugs, soldering, etc. I like to think that I would be fine working on circuitry when powered up, and that I won't do anything daft.

Regards,

Michael
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Old 8th Nov 2018, 11:37 am   #25
Edward Huggins
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Default Re: Reviving Radio in old German Radiogram

Ah I see, so the Radio (Tuner) does function well and you now say you are getting a good output via both the amplifiers? Then the fault may well be in the switching that selects the phono/gram input or faulty connections back to the pick up cartridge. Again, I suggest you signal trace starting at the pick up cartridge connecting pins, then working backwards to the phono switching. At this stage we have not yet established if the cartridge is still working.
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Old 8th Nov 2018, 6:57 pm   #26
brightsparkey
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Default Re: Reviving Radio in old German Radiogram

Just checking - the replacement cartridge is a ceramic pickup, not a magnetic one? Magnetic cartridges wont work at all as they only put out a few mV of signal instead of volts.

Kevin.
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Old 9th Nov 2018, 2:09 pm   #27
beachboybuff
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Default Re: Reviving Radio in old German Radiogram

I had suspected that it is not a cartridge issue, as there is no change in symptoms when cartridge is on or off. There is no audible feedback when touching the bare wires that the cartridge would connect to when switched to phono input, which I would have thought there would be (possibly wrongly). Edward, I will look into signal tracing as you have suggested, although I do not yet have a signal generator/tracer.
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Old 9th Nov 2018, 3:28 pm   #28
brightsparkey
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Default Re: Reviving Radio in old German Radiogram

On my Dual changer, at least, the cartridge is only connected once the needle is down, to prevent a bump when it lands being heard. Don't know if this is common. It maybe you have to lower the needle towards the platter before its put in circuit.

Kevin.
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Old 9th Nov 2018, 5:21 pm   #29
ms660
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Default Re: Reviving Radio in old German Radiogram

If the problem is narrowed down to the receiver and cleaning the switch contacts doesn't sort it out do a hum injection test with a meter probe, the gram input on the schematic in the link that was posted is socket III, socket II is ground and socket I is the radio signal output for a tape recorder etc. The switch contacts in the circuit and the switch layout drawing are shown with the receiver switched to the Off (Aus) position, the switch layout drawing is as viewed from above, both MW and LW buttons have to be engaged for the gram input to be selected.

As an aid (if needed) here's the signal flow path from the gram socket in the schematic through the switch contacts (numbers given) when the gram function is selected:

Socket III >> switch contacts 64--65>>switch contacts 49--50>>switch contacts 18--17.

Lawrence.
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Old 12th Nov 2018, 11:30 pm   #30
beachboybuff
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Default Re: Reviving Radio in old German Radiogram

Thank you for your help everyone. I have arranged to borrow some equipment soon, and will carry out signal tracing and switch cleaning and report back after that.

Kevin, I did try lowering the arm down, but nothing appears to happen any different. I can't see any mechanism that would detect when the arm was up or down either.

Thanks again,

Michael
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