Vari-mu / UA 176 questions

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Baltimore

Well-known member
Joined
Nov 19, 2005
Messages
268
Location
Baltimore, MD - the Charm City
I've recently become very interested in Vari-Mu compressors, and I've been looking over the UA 176 schematic (http://waltzingbear.com/Schematics/Urei/UA_176.htm).  The dual diode tube (the 6al5) can be replaced with a pair of silicon diodes, right?  I'm assuming this will give a different response, but I don't mind as I'm not trying to build a clone.

Also, is the interstage transformer necessary? And for that matter, is the 12ax7 really necessary? I've also been looking at the am864 schematic (http://www.waltzingbear.com/Schematics/Misc/AM-864.htm) which is without the interstage and extra tube, and people complain about its insane output levels all the time.

Any help is appreciated!
 
There are pages and pages to be found here about the benefits of an interstage transformer.  Dig around.  PRR, Larrchild, and NewYorkDave did most of the talking. 

The 12AX7 drives the 12BH7, which otherwise would suffer (or benefits, depending on what you want), from having a varying drive impedance as the GR tube shifts around.  And, if you lose it, you have to do away with the feedback loop in the output stage. 

I think the proper topology comparison for what you suggest by losing the 12AX7 would be the GE Unilevel/Collins 356E versus the Gates Stalevel. 
 

Latest posts

Back
Top