FS: Stax SRA-3S w/Pro bias output
Nov 20, 2008 at 5:14 PM Thread Starter Post #1 of 2

spritzer

Member of the Trade: Mjölnir Audio
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Click for a larger picture. Stand not included and the headphones are sold separately

For sale is a modified Stax amp which was originally introduced in 1968 is in an amazing condition. It is a versatile little thing and even has a MM phone stage built in along with two other inputs. The amp uses two 6CG7's as output tubes and they are from my 60's Toshiba stash just like the ones that the amp shipped with originally. The SRA-3S is completely stock except I swapped out the output coupling caps with some modern 1kV Wima's and I've also changed the configuration of the amp so one plug is Pro bias and the other one is the stock normal bias. To make the damage to the original amp design minimal I simply tapped into the stock bias voltage before the voltage divider so the output is around 550v so not quite the 580v of the Pro bias standard but close enough. I also left the stock 6-pin Stax connectors in place and simply plugged the center pin of the new Pro socket with a white plastic cap so it only works for 5 pin plugs. It drove a set of Lambdas with authority and it shouldn't have any trouble driving the Sennheiser HE60/90 or the Koss ESP950 either. The amp is configured for 117v only and can not be changed over to 230v. It even comes in it's original box and a copy of the schematic.

Gone on eBay

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