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Old 7th Sep 2016, 2:01 am   #1
lloydwells
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Default Volksempfanger (Siemens) VE301W mains hum.

I have just totally stripped this set down to chassis and built it back up again. If anyone has one of these sets you'll be aware that the caps, well most of them, are in a big tar filled brick in the middle of the underside of the chassis. I have replaced all the caps in this tin box, however I'm getting really bad hum. This starts as soon as the set is turned on. I have managed to about halve how bad it was, by connecting an external 2.2uf cap in place of the one in the can. I think this might be a capacitor quality issue, so I'm after some advice of what would be the best performing replacements for the 2uf and 4uf caps that sit in the HT line.
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Old 7th Sep 2016, 10:21 am   #2
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Default Re: Volksempfanger (Siemens) VE301W mains hum.

If it starts as soon as the radio is turned on and before the HT has risen then it is probably mechanical hum from the mains transformer but keep in mind the valves are directly heated so have a short warm up time.

These sets are designed for 220V operation, are you reducing the mains voltage for this? Polyester film capacitors will give the best performance but I doubt it will make any difference and it probably always hummed a bit. You can short out the intervalve transformer secondary to confirm it is from the output valve.
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Old 7th Sep 2016, 10:27 am   #3
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Default Re: Volksempfanger (Siemens) VE301W mains hum.

If the valves are indirectly heated, then the instant hum is little to do with capacitors. I would look at transformer vibration.

Edit
Beaten to the draw!
Take out the rectifier. Does it still hum?

Last edited by TrevorG3VLF; 7th Sep 2016 at 10:34 am.
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Old 7th Sep 2016, 8:31 pm   #4
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Default Re: Volksempfanger (Siemens) VE301W mains hum.

No rectifier equals no hum
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Old 7th Sep 2016, 8:40 pm   #5
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Default Re: Volksempfanger (Siemens) VE301W mains hum.

Remove the chassis from the cabinet to confirm it's mechanical noise. The fix depends on construction of the mains transformer. There may be bolts that can clamp the laminations tighter. You could add rubber grommets to stop transfer of vibration from the chassis to the cabinet.
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Old 7th Sep 2016, 9:00 pm   #6
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Default Re: Volksempfanger (Siemens) VE301W mains hum.

If it was mechanical why would changing a cap have made a deal of difference ? I'll freely admit I re-capped the whole block with cheapish yellow perils there are two caps in the HT line a 2uf now replaced by the external slightly posher cap and a 4uf as yet the replacement for this hasn't been replaced.I do have slightly more voltage on some test points on the chassis bit nothing above 20v
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Old 7th Sep 2016, 9:13 pm   #7
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Default Re: Volksempfanger (Siemens) VE301W mains hum.

I could not see the diagram clearly but a valve appears to be indirectly heated. Is this so?
The low voltage heater/filament winding looks to be centre tapped to earth. If the connection is offset, this could give massive hum.
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Old 7th Sep 2016, 10:55 pm   #8
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Default Re: Volksempfanger (Siemens) VE301W mains hum.

Sorry, misread your no rectifier no hum.

Capacitor types are unlikely to be the issue and the yellow caps will be better than the original paper ones. I agree with Trevor that the humbuck for the filament is the first thing to look at but I would also suggest you get the AC down to 220V which you can do with a small 240V to 15V transformer wired out of phase as a bucking transformer.
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Old 8th Sep 2016, 1:35 pm   #9
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Default Re: Volksempfanger (Siemens) VE301W mains hum.

Hopefully these will upload.
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Old 8th Sep 2016, 1:36 pm   #10
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Default Re: Volksempfanger (Siemens) VE301W mains hum.

That's the diagrams for it the layout ones rather a handy thing but a little off in places.
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Old 8th Sep 2016, 2:29 pm   #11
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Default Re: Volksempfanger (Siemens) VE301W mains hum.

It's the item marked H that we are interested in. It shows in the layout to the left of the REN904 socket. Old HMV sets used a wirewound resistor with a moving wiper for the earth. The set would not work if it had failed completely, but it might have lost continuity to one end connection or it may be possible to adjust it for minimum hum?

A few minor drawing errors like the REN904 has no heater! (it is indirectly heated)
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Old 8th Sep 2016, 6:43 pm   #12
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Default Re: Volksempfanger (Siemens) VE301W mains hum.

I follow that, my Ekco 313AC uses the same sort of thing so ill check it.
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Old 8th Sep 2016, 7:58 pm   #13
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Default Re: Volksempfanger (Siemens) VE301W mains hum.

Was the hum present before you rebuilt the set or didn't you try? These sets were about as cheap and nasty as it gets and always hummed a bit. For a start try the obvious things like making sure you haven't made any mistakes replacing the capacitors. As mentioned above, make sure the hum bucker is correctly adjusted. Here's another link which includes a circuit diagram with the missing heater connections:http://www.oldradio.de/wiki/index.ph...%A4nger_VE301W
Google translate will translate it for you if necessary.
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Old 8th Sep 2016, 10:57 pm   #14
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Default Re: Volksempfanger (Siemens) VE301W mains hum.

I read German very well years of repairing German cars. It did have a good hum before being rebuilt it was less bad post rebuild but as the original 2uf cap was basically powder that's not surprising. The point of these sets was to be cheap and nasty I also have the DKE38 the even cheaper and nastier German peoples set both of them are actually surprisingly good performers in terms of picking up stations though I don't use them often as the Ekco is my preferred set for listening to radio Cumbria.
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