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Recently finished PP amps

Posted by SteveBrown (A) on November 18, 2009 at 16:28:23

Well, here is my adaptation on Allen Wright's PP-1c amps (I call them 1.5's). I don't know how to post multiple pics in one thread, so sorry about that. Everyone ends with a description of "how it sounds", let me start by saying: best PP amp I've ever heard. I had a friend down this weekend who has spent most of his life in the music biz in one way or another, he agreed. Everything about these is just wonderful. I'm comparing them right now to some SE 300b's amps. The B's have a richer, warmer feel, but not the frequency extension, pace or seperation in the instruments that the Wright amp does. Here are some construction details:

POWER SUPPLY: Used recycled PTs from Fisher 500c receivers. These are nice in that there are two 6.3v winding and a bias winding. The bias winding gives me -29v after rectification and filter. The B+ (out of a v-doubler) gives me 415v. I used a 320mh choke after the doubler caps. The B2 supply is filtered by 1.5k R and a 60uf oil cap, then a 100k bleeder.

CASCODE DRIVER: Uses 6N6P's running at 16ma per side. My B2 is 377v. I changed the voltage divider (from that shown in the PP-1 schematic) to the upper grid to give me 116v using 150k and 330k. The upper tube plate resistor is 8.2k and has a v-drop of 131v. I used a Pimm Self Biased CCS in the tail, which is adjustable and allows me to dial in the operation nicely.

OUTPUT: I used paralleled two 10M45S CCS in the tail of the cathodes, with a 10ohm resistor between the CCS and each cathode (EL34 at the moment). I made this adjustable by putting a fixed Rk on the first 10M45S and a pot (1k paralleled 100ohm) on the second 10M45S. I'm running the EL34s at 60ma each.

OUTPUT TRANSFORMER: Is a 10k a-a unit a friend gave me, it is apparently a Peerless clone. Sounds MUCH BETTER than the Fisher 7k iron I was using.

CONSTRUCTION: Overall I used Tektronix ceramic terminal strips and construction techniques. I used silver 26ga wire of most non-PS connections and stranded copper teflon wire for the PS and ground stuff.

QUESTIONS: Happy to answer any questions, "yeah-buts", etc...

SUMMARY: Outstanding amp, happy to audition if you're in the Tulsa area!

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Parts Connexion

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