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squinancy · 6th May 2019, 4:09 pm

Thanks for all the above.
I checked service sheet 1153: the HT decoupling is 2uF.
The HT cap in this set is 2.2uF (400v) which I installed about 12 years ago. I don't think it has dried up.

However, I connected a different speaker. Being a small collector I don't have that many suitable ones readily available. I used a small 4Ω 5W speaker and none of the distortions I mentioned could be heard.

I listened to the "distortion" on the original speaker a bit longer and I can say that it only happens in the lower mid-range. General instrumental music, for instance, is always clear (if a bit flat, which is normal), free from this sound. That solo male tenor or low female voice produces it.

Further, I think that even when this failure of sound occurs, the sound that's meant to be produced is produced flawlessly, but an added high pitch rattling sound, as if a handful of screws (or broken glass) started to dance in or around the speaker, is also heard. When the volume is turned well down - but still audible, the added sound disappears, the same voice, same frequency is heard clearly, without interference.

Does this mean that the speaker is definitely responsible? If so, what kind of a flaw is this? Any hope of repair?

If beyond repair, how easily can a CN429 replacement speaker be obtained? This one says "Type MB5MO, Spec 2864" on the plate behind the speech coil. I googled these codes but not a single hit.

6th May 2019, 4:09 pm	#3
squinancy Retired Dormant Member Join Date: Aug 2007 Location: New Malden, London, UK. Posts: 70	Re: Vidor CN429 Lady Margaret rattling sound Thanks for all the above. I checked service sheet 1153: the HT decoupling is 2uF. The HT cap in this set is 2.2uF (400v) which I installed about 12 years ago. I don't think it has dried up. However, I connected a different speaker. Being a small collector I don't have that many suitable ones readily available. I used a small 4Ω 5W speaker and none of the distortions I mentioned could be heard. I listened to the "distortion" on the original speaker a bit longer and I can say that it only happens in the lower mid-range. General instrumental music, for instance, is always clear (if a bit flat, which is normal), free from this sound. That solo male tenor or low female voice produces it. Further, I think that even when this failure of sound occurs, the sound that's meant to be produced is produced flawlessly, but an added high pitch rattling sound, as if a handful of screws (or broken glass) started to dance in or around the speaker, is also heard. When the volume is turned well down - but still audible, the added sound disappears, the same voice, same frequency is heard clearly, without interference. Does this mean that the speaker is definitely responsible? If so, what kind of a flaw is this? Any hope of repair? If beyond repair, how easily can a CN429 replacement speaker be obtained? This one says "Type MB5MO, Spec 2864" on the plate behind the speech coil. I googled these codes but not a single hit.