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Phase Inverters

1/16/2006 2:58 AM
Evan Phase Inverters
Just wondering what's the most efficient/powerful PI in use. Distortion is OK. Sometimes one prefers minimal tubes.  
At this point I remember the Jan/06 Guitar Player magazine reviewing a cool amp called The Fargen Mini Plex. Just BRILLIANT. Only two preamp tubes.  
2)standard triode into CF which drives two paralleled, single ended output stage.  
The author, Terry Buddingh, who knows his stuff says those two tubes drive the EL34s to maximum power.  
Like the Zendrive reviewed in the same issue, no addition equals no subtraction. Though I did love The Silver Dragon whilst I had one, but it wasn't true bypass and it sounded it.
1/16/2006 8:34 AM
Ray Ivers
I've seen a 12AX7 LTP PI that uses positive and negative feedback to achieve a voltage gain of 200+. Combine this with a 6AS7 or 6DZ7 and you'll have a low-power (maybe 10W or so) push-pull guitar amp with two tubes total. Using a transformer or center-tapped choke as a PI will also allow a minimum of tubes to be used.  
1/16/2006 1:45 PM

The Fargen Miniplex is a parallel SE amplifier per the Fargen website. No PI in that amp.  
1/23/2006 12:43 AM
Arthur B. Interesting use of PFB
I have this to believe it. Got an original schematic?
1/23/2006 1:06 PM

For an amp of similar concept, see in the How-To Section - "Super Single." That amp incorporates the parallel SE output as well as what Fargen calls his decade switch (switched cathode resistor bypass on the first stage). For the parallel first atage, check out something like the Matchless Lightning and for the cathode follower/tonestack circuit, check out the Fender 5F6A or various Marshalls.  
1/23/2006 11:45 PM
Arthur B. Re: Phase Inverters
I was actually referring to the PI, but I'll check out the amp you mentioned.
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