3, Interfaces, Rebuilding interfaces

Read more on the Acoustat 3 in our home audio section

Rick Jenkins2004-02-23 22:21

Hello again, Andy. I\'m in the process of rebuilding the interfaces (mk-121C Medallion) of my Model 3\'s. I\'ve located and purchased everything I need for a complete electronic components up-grade....except for the rectifier diodes in the voltage multiplier stage. I\'ve read on this site, of fellow enthusiasts who have up-graded (?) by using microwave oven diodes. I am quite aware there is more to diode selection than just the electrical value; as in the case of the 25G10 (25mA 10kV).

So many manufacturers have been located who can supply diodes of this value. But what is ultimately important is selecting the diode with the correct operating ratings & parameters optimized for this circuit. Specifically,don\'t we need to know: DC blocking voltage, average forward voltage drop, average rectifier forward current, average reverse current, peak surge current, repetitive peak reverse voltage, recovery time....etc!

I\'m not an engineer, so it\'s beyond my ability to correctly make a selection choice. Would you be willing to share with us what you feel to be the most important criteria in selecting this diode? I\'ve owned my Acoustats for almost 20 years now, and although there have been no failures, there is some concern a few parts in the circuit may be drifting out of spec., or, perhaps even reaching the end of their useful life. What do you think? I\'m etching new boards for the multiplier stage, and installing all new parts (once I have new diodes!). This way, I\'ll have the originals for back-up.

This whole project is a labor of love for a wonderful pair of speakers that have served me well for so many years. Thank you for any & all input concerning these diodes, Andy.

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Andy Szabo2004-02-23 22:21

As I have mentioned elsewhere, I DO NOT advocate any changes to the bias power supply, either in terms of component upgrading or changing the design. I think Jim Strickland did a proper job of circuit design and component choice. Remember that the sole purpose of this supply is to provide 5000-volts DC. There is no audio signal flowing through these components, and hence the conventional ”rules” of audio component upgrading do not apply.

I do not know enough about the intricacies of high voltage diode specifications to know if the high-power ”microwave oven” diodes will work in this application. I can say that these parts are physically huge, and it would be difficult to mount them on the original PC board.

Please see my entry under ”Refurbishing - Available Parts” for information on replacement diodes. Since there is a good source for a proper replacement part, there is no need to consider the use of diodes intended for a wholly different application.

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