Monitor 3, Acoustat Monitor Three Repair in USA

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Charles F. Rouh2004-06-12 20:34

Can anyone provide me with a source, in the USA, who can repair my Acoustat Monitor Three Servo Charge Amplifiers? Both amplifiers are blowing the 5 Amp/250 volt fuses when they are powered on. Thanks in advance, Charles F. Rouh, Georgetown, Texas USA

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Mike Savuto2004-06-20 10:41

Charles, If the 5amp fuses fail when the high voltage circuit is powered up there are several things that can cause it. In our phone conversation you aid that there was no evidence of a tube failure or that any of the resistors in the area of the tubes have failed, so it is most likely in the high voltage power supply. In that area the most frequent cause is shorting of the high voltage transformer, next is the failure of the high voltage diodes, finally the 1uf 3kv capacitors (the gray or silver metal cans next to the big transformer) can short as well. The transformer can be tested by desoldering one of the high voltage leads (red or yellow) from it\'s location, tape over the exposed lead with electrical tape so that it can\'t make contact with anything else, replace the 5amp fuse and plug the amp in. When the hv section tries to power back up, if the fuse blows again, the transformer is shorted and needs to be replaced. If not, the problem is one of the other two items. You can measure the capacitors with a volt meter to see if any of them are shorted (measure just a few ohms instead ofmillions) after removing the wire connection that goes between the two capacitors. Nuts are used to hold the wires in place on older amps, or on newer amps you will need to desolder one of the leads from one of the two capacitors to do this measurement. I have been told by someone whom I trust that 25yrs is about the average life span for capacitors (we have experienced two such failures recently) and these are subjected to high voltages so I expect that this may become a more common problem. (We are now having 1uf 3kv polypropylene replacements built for us which are better sounding and will be providing a .01uf 3kv bypass capacitor for them as well.) If neither of those are bad then I would suspect the diodes in the high voltage doubler circuit. I have many of the diodes test OK when they were really bad and that is because of the fact that testing them with a DVM is just not enough. I just replace them. I have never heard of two amps failing at the same time before. That leads me to believe you had a large surge in the a/c, but that is only a guess. Michael Savuto Analogue Associates, LLC

Thad Seeberger2005-07-29 00:50

I have had this problem on both my amps numerous times. Once the transformer was shorted and I bought a replacement from Sounds Like New in FL. I have had the HV diodes fail numerous times, I fabricated my own HV diode stack using around 15 1N4007\'s in series and then balancing each one with 10 meg resistors across each, this works excellent and in my opinion much beefier. I finally found out what was blowing the diodes after this fix. One of the power resistors (10k if I remember correctly)in the 6HB5 bias circuit was intermittantly arcing causing what I believe is the tube to run away severely stressing the rectifier circuit. I replaced all the power resistors with a much better one and have never had the problem again. Thad Seeberger Newport News VA

Don Gold2010-08-17 18:33

Does anyone know of a source for a power transformer for the Acoustat Monitor. The servo charged Amp. The amp blew a G.E. 6HB5 and my Guru tells me that I need a new power transformer. Number on the transformer is 2008380. It is T1 on the schematic. It's the big transformer on top. It is believed to be 2500 volts AC with 40 ma current.
Any help would be appreciated.

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