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RE: Audio Research D-76 - advice on biasing

Posted by Dman (A) on January 25, 2010 at 14:44:00

In Reply to: Audio Research D-76 - advice on biasing posted by mark944s2@yahoo.co.uk on January 25, 2010 at 11:41:01:

As an owner/refurbisher of an ARC D-76a, they are a slightly similar in procedure to the older D-76. Do you have a D-76 or D-76a? Just checking!

In either case, the biasing is relatively simple- the 1/4" plug allows one to connect a DVM to it and measure milliamps (PLEASE use an insulated 1/4 plug- not the type that are metal jacketed!). one pot allows the overall bias level to be set, while the other balances between the two 6550s. I'm not sure of the positioning on the D-76 though. The circuit is similar. I set the bias on the D-76A between 45 and 50ma. You really don't need to go much higher (the Manual for the D-76a suggests 55ma, and it has a beefier power supply!). Somewhere between 45 and 50 gives a good average and tube life and decent sound. The 60ma that your manual suggests is rather high, IMHO...

I would suggest that with either amp, you should upgrade all the power supply caps if you haven't already! I did MOST of them, with exception of one or two, and ended up taking out a pair of 6550s within a month of everyday use! turned out that the two I didn't were directly in teh bias circuit! YIKES...

Good luck!

Dman
Analog Junkie

• D-76A vs. D-76   (Open in New Window)

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