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Old 19th Sep 2020, 9:16 pm   #16
barrymagrec
Octode
 
Join Date: Dec 2017
Location: Morden, Surrey, UK.
Posts: 1,552
Default Re: PX4 substitutions

Quote:
Originally Posted by barretter View Post
Quote:
Originally Posted by barrymagrec View Post
In the original Williamson amplifier book there was a version for PX4s as well as the more familiar KT66 version.

They were to all intents and purposes identical. I changed my PX4 version to the KT66 type after an unfortunate accident involving a leaky garage roof and the mains transformer, the replacement had no 4 volt windings.
What do you mean by "the original Williamson amplifier book"? DTN Williamson wrote several articles for "Wireless World" which were later gathered together as a pamphlet entitled "The Williamson amplifier" but nowhere in it is there a design for his amplifier using PX4s. He does mention the PX25 but dismisses it in favour of the KT66. There was a design for a push-pull PX4 amplifier in a "Wireless World" article in 1943 but that wasn't by Williamson.
There were quite a few variations on the PX4 by other British valve manufacturers but I doubt if they are any more available or cheaper than the original.
There is an earlier book than the one usually seen - I have a copy in my loft somewhere but I can`t find it - I seem to remember it was called something like "High quality sound reproduction" by DTN Williamson and published by GEC.
It contains , from memory, PX4 and KT66 versions of the classic amplifer, an AC/DC unit using KT33c, Tuners for both the AM and FM experimental VHF broadcasts, a preamp with a huge number of different disc EQs and a puff piece about the merits of the GEC matal cone loudspeaker.

I was given the book and amplifier by my Uncle, who used it to build the PX4 amplifier in the early fifties, possibly because of better availibility of PX4s at the GPO.
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