I don't know how it lost sensitivity because I've only recently bought them. But leaving them plugged in for about 24 hours improved things somewhat and I re-checked the EHT which is below the 6kV -+7% so I think it is mainly a matter of rebuilding the EHT supply. Det good news is that the treble panel is not at fault!
It is quite difficult to measute the EHT with ordinary measuring instruments. You need at least 100 Mohm input resistance. If sensitivity goes up after a few days, and both units are equally load (bass and treble), probably all is good. Sensitivity is about 82 dB/1 W /1m, much less than an average cone speaker.
Hi lcsaszar
- Thanks for your comment. Indeed sensitivity went up after a couple of days, so I'm inclined to conclude as you did that the panels are ok. I measured the EHT with a calibarated electrostatic voltmeter (which used to belong to The Royal British Navy - I found it at a flee-market many years ago but had it calibrated recently).
- Thanks for your comment. Indeed sensitivity went up after a couple of days, so I'm inclined to conclude as you did that the panels are ok. I measured the EHT with a calibarated electrostatic voltmeter (which used to belong to The Royal British Navy - I found it at a flee-market many years ago but had it calibrated recently).
My rebuilt QUADs required about an hour to charge. One leaky bass panel will pull down the EHT supply. Have you tried sequentially disconnecting your bass panels to see if one is loading down the EHT? If you have transparent dust covers--check for white powdery corrosion around the rivets holding your panels together.
j beede.
Thanks for you comments - and yes I checked for the powdery corrosion - and there is none. Now after having been plugged in for several days the "weak" one seems to have smarteded up its ideas and has about the same sensitivity as the other one. So it seems that is was just matter of a slow starter.
Thanks for you comments - and yes I checked for the powdery corrosion - and there is none. Now after having been plugged in for several days the "weak" one seems to have smarteded up its ideas and has about the same sensitivity as the other one. So it seems that is was just matter of a slow starter.
Just acquired a pair of these and that was exactly what was happening to one of them.
After taking them apart to clean etc - i saw corrosion on every rivet in one panel and the HT lead was badly corroded - after further investigation the white cable passing thru the stators was badly corroded !
What causes the corrosion ?
All the others where 100% OK !
Just one bass panel and i disconnected the HT supply to it and the speaker plays great now- so it was for sure pulling down the other good panel.
I need to get this one bass panel refurb'd.
I'm in Vancouver BC.
Does anyone know anyone who could do a good job ?
I'm pretty handy but feeling this might be a delicate job to install a new diaphragm and recoat it etc..
Thanks, Alan.
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