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previous: Soren It's a new one for me!Anyon... -- 9/17/2003 7:03 AM View Thread

Re: Transformer Phase Inverter

9/17/2003 3:35 PM
Ray Ivers
Re: Transformer Phase Inverter
I've used an interstage for a phase inverter, into a driver stage and then the output tubes. I think you may be wanting to use it as a phase inverter/driver, though, and no, I've never done that. I have a Fender 400PS that does it, and I've worked on some amps that used it as well (I remember a SS Vox Conqueror that I thought sounded a lot like a tube amp, and possibly a Gibson or two?). If it's done right, I think you'll be happy with the results. Do you plan to try Class AB2 (grid current) operation? I would. :D  
The bass response of a given transformer depends a lot on the impedance of the driver stage, and unless the interstage has lots of primary inductance (it seems many of them don't) you may find this to be an issue depending on how low you want to go. If you're going to use the stock 1987 non-master topology you may want some bass rolloff from the driver, but in a non-master amp I think you might not. Driving a 10k-primary interstage from a tube like a 12AX7 may result in a thinner and more distorted tone than you want (at least from the driver stage), so I would be prepared to try some unusual tubes with this unusual drive method. I would also recommend not using negative feedback in the output stage; I've read warnings from people far more knowledgeable than myself regarding NFB around two transformers being a bad idea.  
That's a cool, simple circuit in your link. In one of my other posts I referred to the 6B4-G as a possible driver tube, but here it's used as the output tube (I guess I'm just a high-power kinda guy). ;)  

Ray Ivers Allied Interstage Partial Specs -- 9/17/2003 11:51 PM
Soren Re: Transformer Phase Inverter -- 9/18/2003 3:43 AM