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Old 12th Dec 2018, 4:33 pm   #1
CesarLG
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Default Kleinempfänger with lots of hum

Hello! I hace just replaced the electrolytic caps of 4uF and the radio has a very noisy hum even without antenna
I have also replaced the 0.9uF with a 1uF polyester cap
Resistors seem to be fine. Which value are them? 2w?
What do you think
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Old 12th Dec 2018, 4:47 pm   #2
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Default Re: Kleinempfänger with lots of hum

Did you fit the new caps the right way round?
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Old 12th Dec 2018, 5:17 pm   #3
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Default Re: Kleinempfänger with lots of hum

Dried out filter capacitors? That's what it seems like to me. They are only 4uf, but it looks like the speaker is the field coil type that also serves as a choke smoother.
Not a bad little radio as far as looks go and as simple as it gets electronically. No RF stage LW/MW with reaction & only one audio stage.
The VCL11 is a double triode & the audio side must have quite a lot of gain. Was it specifically made for this radio and no other?
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Old 12th Dec 2018, 6:25 pm   #4
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Default Re: Kleinempfänger with lots of hum

I am going to try this 4uF because I think that this hum comes from the AC
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Old 12th Dec 2018, 9:08 pm   #5
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Default Re: Kleinempfänger with lots of hum

I have tried this 4uF ones and it is the same noise
Also ferrites on the feed line
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Old 12th Dec 2018, 9:15 pm   #6
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Default Re: Kleinempfänger with lots of hum

Are you sure the capacitors have been fitted correctly - I had the same problem with my Kleinempanger, and had managed to swap two connections on the smoothing circuit - result was a lot of hum!
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Old 12th Dec 2018, 9:53 pm   #7
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Default Re: Kleinempfänger with lots of hum

Seconded. It's not immediately obvious which way round the smoothing capacitors should be connected in these sets. If in doubt the OP should connect a meter set to DC Volts across each smoother in turn and check that it reads the right way round.
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Old 12th Dec 2018, 10:46 pm   #8
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Default Re: Kleinempfänger with lots of hum

Hello!

How come I have the same issue if I used a non polarized capacitor like the one i showed? Of isit possible that it has a little polarity?
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Old 12th Dec 2018, 10:55 pm   #9
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Default Re: Kleinempfänger with lots of hum

Also the connection points of the "-ve" sides of the HT reservoir and filter capacitors matters as well, eg: they must not be connected together to a common point.

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Old 13th Dec 2018, 1:00 am   #10
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Default Re: Kleinempfänger with lots of hum

Hi,
I think you will find this is not mains hum at all, and has nothing to do with HT smoothing!
I had exactly the same issue on the VE301W I've been working on. Yours sounds exactly the same. My 4 & 2 mfd caps tested perfectly and indeed there was not much ripple on the HT when viewed on a 'scope. Adding extra smoothing made no difference at all. The caps on the VE301 are not polarised.

All the noise was being generated by the first valve. What was left of the metalising was not being grounded. Wrapping the valve in foil got rid of most of the hum and careful adjustment of the hum balancing pot got rid of nearly all the rest.

The output valve, being directly heated, operates immediately. The first valve, having a cathode, takes a while to warm up. Mine hums loudly until the first valve starts to operate and then it quietens down.
Also in mine, the 5 low value tubular capacitors needed replacing as they were very leaky.

I don't have the DKE38 circuit to hand so I don't know how similar the circuit is to the VE301 so don't know how much of the above applies.

Good luck
All the best
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Old 13th Dec 2018, 3:25 am   #11
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Default Re: Kleinempfänger with lots of hum

Very different to your set Nick,the circuit is found easily by googling for it and it is AC/DC chassis with a combined valve comprising an indirectly heated triode detector/beam Tetrode output design,this valve is not metalised. There is the familiar high impedence speaker and no output transformer.
The smoothing caps really have to be the first items to exclude with certainty in order to narrow this down and corner the fault.
I am sure posts no. 2,6 7 & 9 offer very good advice and would really help.
One last thought before getting into bed after a very long day-make sure any workshop flourescent lights in the vicinity are switched off!!! you would not be the first person to experience this non fault hum

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Old 13th Dec 2018, 11:36 am   #12
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Default Re: Kleinempfänger with lots of hum

Quote:
Originally Posted by VT FUSE View Post
Very different to your set Nick,the circuit is found easily by googling for it and it is AC/DC chassis with a combined valve comprising an indirectly heated triode detector/beam Tetrode output design,this valve is not metalised. There is the familiar high impedence speaker and no output transformer.
That's true! I should have done my research before posting I've just had a very interesting read about the DKE38 on 'antiqueradio'. That's much more what I would expect from a utilitarian radio- Paxolin chassis, cardboard capacitor cases, compressed paper speaker rather than metal. Also very few components and no mains transformer. The VE301 certainly was not built 'cheap'!

The two valves used must have had 55V heaters which must have been very unusual. I've heard the VY2 can suffer O/C heater.

I still stand by my first sentence above though, I still don't think it's mains hum! (I'm very happy to be proved wrong- I often am!) It sounds more like the sound you get when you put your finger on the grid of a valve. The VCL11 valve would appear to be metalised, so could still be an issue.

Your point about fluorescent lighting is good- that was causing me problems and it was a while before I thought to turn the light over the bench off!

All the best
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Old 13th Dec 2018, 9:40 pm   #13
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Default Re: Kleinempfänger with lots of hum

I have checked polarity and it is fine. I just looked at the 0.9uF cap and from it both electrolytic caps are on the negative side so it is fine.
I still have hum. I have also got it running on 150v and the hum is the same.
I have ordered a new VCL 11 tube...
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Old 14th Dec 2018, 8:51 am   #14
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Default Re: Kleinempfänger with lots of hum

I am having a look at the whole circuit and it is weird the connection made on a resistor. It is suspicious that there is a broken connection on the potentiometer
Can somebody confirm that the connection is fine where it is or it should be on the red spot ai show on the attachment?
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Old 14th Dec 2018, 11:16 am   #15
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Default Re: Kleinempfänger with lots of hum

There were many different makers of these and every one did things a bit differently. However it should look roughly like this one. It looks to me that there is a wire missing on yours. BTW that's not a potentiometer, its a variable capacitor.
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Old 14th Dec 2018, 11:53 am   #16
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Default Re: Kleinempfänger with lots of hum

The OP should compare the wiring of his set with the circuit diagram.
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