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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 27th Feb 2009, 11:07 am   #21
peter_sol
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Default Re: Dansette Major - no sound

Hi
Perhaps the EL84 is low emission.
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Old 27th Mar 2009, 12:55 pm   #22
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Default Re: Dansette Major - no sound

Changed both resistors and I still have the hum. The hum comes on as soon as I switch it on then it gets louder as the amp warms up. The volume control has no effect on the hum and the volume when playing a record is very low, not really enough even for a small room. Any more advice will be gratefully received.
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Old 27th Mar 2009, 1:33 pm   #23
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Default Re: Dansette Major - no sound

Hi Stuart. Check the "earthy" end(the other end from the end the signal is fed in from) of the volume control is actually connected to chassis. Also check continuity of the track(two outer connections of control) and one end to the centre when turned.
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Old 27th Mar 2009, 4:42 pm   #24
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Default Re: Dansette Major - no sound

Tim, thanks for your input. The volume control is earthed OK and one side goes from 0-950K and the other from 950K-0. Could one of the new capacitors have gone already? I have 2 out of the 3 I need so I could replace them again.
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Old 28th Mar 2009, 12:48 am   #25
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Default Re: Dansette Major - no sound

There is no reason for capacitors to 'keep going'!! Electrolytics are fairly reliable and as long as you fit ones of the correct voltage and value and the right way round of course, there is no reason for them to fail.

As the hum is there as soon as you switch on, there can be several causes. If the hum is coming from the speaker as soon as you switch on, this is caused by the mains transformer inducing hum into the output transformer. Most manufacturers position the transformers at right-angles to each other to minimise the effect if they are close together. However, in compact designs this may not be possible so it's a trade-off between minimum hum and convenient positioning. Not much you can do to improve this kind of hum.

If the hum is not coming from the speaker, then it's probably the mains transformer itself. Some transformers do hum. However it can also be caused by a fault (excessive current flow) which will need to be investigated.

Smoothing hum will only be heard once the output valve has warmed up. Assuming the new smoothing capacitors are the correct value and voltage as stated above, it's unlikely to be these components.


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Old 28th Mar 2009, 1:46 pm   #26
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Default Re: Dansette Major - no sound

Rich. Thanks for your input. I got to thinking about earths and realised that one of the brass bolts and stand offs was missing which could be providing an earth. I made a new one, fitted it and the hum has now gone. The only problem now is the volume, the control seems to work OK, the resistance varies from 0-950K, but it only affects the sound coming out in the last few degrees of rotation of the knob. Any ideas?
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Old 28th Mar 2009, 9:05 pm   #27
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Default Re: Dansette Major - no sound

Hi Stuart.

Well at least you are making progress. Glad the hum is now gone. As this is a single valve amplifier, it will not have loads of gain. At best you will get about half a watt. I have no idea of the output of the Ronette cartridge you have but the original type fitted would have been (probably) a BSR TC8H which would probably have something like 300-500mV output. I suspect that the Ronnette will not be as high as that.

However make sure the volume control is connected correctly. Check it for resistance from both ends to the slider and make sure that you get good control. Just thinking that if you have a partial short across the pot somewhere, this will affect it's operation.

If everything is OK and you are sure wiring is correct then it may just be that the output from the cartridge is not high enough. Remember though that these sort of amplifiers are not going to give much volume. From your description of the way the volume control is working, either there is a wiring error or the cartridge does not have enough output.


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Old 28th Mar 2009, 10:17 pm   #28
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Default Re: Dansette Major - no sound

Rich. I sent the Ronette back because I thought it was unsuitable. The original cartridge was a BSR X1H which I have read has an output of 4 volts. I bought a NOS X1HE on eBay and that is now fitted. I have also sent for a Pfanstiehl 126 to try which is supposedly a replacement for the X1H but it is ceramic and I believe they don't have such a high output.
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Old 29th Mar 2009, 10:42 am   #29
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Default Re: Dansette Major - no sound

The BSR X1H would itself have been a replacement (probably). I doubt that the spec said the output was 4 volts!!!! More like 400mV or maybe that was expressed as .4 volts.

I think the X1H is probably still available but I am not well informed on suppliers of these. You could check on the main website (under suppliers) or no doubt, someone on the forum will be able to advise better.


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Old 2nd Apr 2009, 1:11 pm   #30
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Default Re: Dansette Major - no sound

The volume control should be a "log" (logarithmic) type. Check that it hasn't been replaced by a "lin" (linear type). It should have LOG or LIN stamped on it somewhere. If not set the volume control as close as possible to the centre position and measure the resistance from the centre tag to each of the outer tags. You should get vastly different readings. If they're equal a linear control has been fitted.
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