, low supply voltage

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Fitzroy Wellington2008-09-16 19:54

I own a pair of acoustat 8s that i acquired from a friend. the left half of one of the speakers does not play very loudly simply because the supply to the panels from the 500megohm resistor drops down to 800 or 900v once the panel wires (HV supply and audio), are connected. please note that on its own the interface produces a robust 4.8kv; CAN YOU HELP? Thanks.

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Andy Szabo2008-09-16 23:44

That\'s a fairly unusual problem! Since you have a total of four interfaces with your Model 8\'s, I would suggest you try one of the other interfaces on that panel set (they are interchangeable). If it works ok with another interface, then you know the problem is with the original interface. If the problem exists no matter which interface you use, then the problem is in the panels. If you determine the problem is in the interface, and since it produces proper voltage unloaded, my first suspicion would be the 500-megohm resistor. It may have failed to a much higher value, or opened entirely. I\'ve seen these same resistors for sale on eBay, so finding a replacement should not be too difficult. Although less likely, you could have a failed capacitor in the voltage multiplier. If the problem is in the panels, I have much less advice to offer, since that would be a virtually unheard-of problem. But, there is a first time for everything! My first suspicion would be a break or a short circuit in the connecting wires. This can only be determined by removing the grille sock and doing a physical inspection of the wires. I can\'t really imagine a scenario of how the panel itself could pull-down the bias voltage, unless some physical, conductive object was lodged in between the diaphragm and the stator grids, and was actually cutting through the wire insulation of the grid. Pretty unlikely! So, my best guess would be a problem with the interface. Please do write again if you need further advice. And congratulations on owning a very rare, top-of-the-line Acoustat Model Eight. I have no idea how many Model 8\'s were produced, but my guess would be in the range of only 25 pairs, maybe even less!

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