Referring back to message #182, there was a correction published in Wireless World April 1971, bottom of page 180 (World Radio History: Wireless World April 1971):
I did not find any other corrections up to the end of the year.
The Demo version does accept the Sprint file for egra's Blomley PCB but unfortunately the Export, Save and Print functions are disabled in version 6 (the current one on the website).
egra, would you consider uploading the PCB as Gerber? Are they available on any of the PCB maker's websites - PCBway or JLCPCB or whoever?
I re-read most of these posts and did a little research. The BC546 and BC556 are good replacements for the 2n3904 and 2n3906. They are 65v devices with ~300MHz ft. If you don't need the high voltage, BC547 or BC548 with theit matching PNPs (BC557, BC558) are faster. Splitter transistors only have to take half the supply voltage.
Other transistors that need a bit of speed are the output NPN and PNP pair of power transistors. The improvements in manufactoring are telling. In 1972 the 2n3055 was our goto big power transistor (for telephone circuits) but then it had an ft of 10kHz (no typo). I was playing with quasi-complementary Blomley circuits at the time and tried the 2n3055. It nearly worked - you could hear it was wrong, but only just. Blomley is a VERY tolerent circuit. Modern 2n3055s would work fine with an ft of 2.5MHz. The complement of the 2n3055 is the MJ2955. (I'm not seriously suggesting that you use these but they will work fine.) Complementary PNPs were nearly unknown in 1972.
Other transistors that need a bit of speed are the output NPN and PNP pair of power transistors. The improvements in manufactoring are telling. In 1972 the 2n3055 was our goto big power transistor (for telephone circuits) but then it had an ft of 10kHz (no typo). I was playing with quasi-complementary Blomley circuits at the time and tried the 2n3055. It nearly worked - you could hear it was wrong, but only just. Blomley is a VERY tolerent circuit. Modern 2n3055s would work fine with an ft of 2.5MHz. The complement of the 2n3055 is the MJ2955. (I'm not seriously suggesting that you use these but they will work fine.) Complementary PNPs were nearly unknown in 1972.
I have just joined this forum, I used to do a lot of audio electronics design back in the 1970s.
I think I have a photocopy of the full wireless world article on the Peter Blomley PA design somewhere, I tended to keep things like that. It was an interesting idea, but whether practical performance justified its complexity was another matter. The reason I largely gave up designing audio circuits was that it seemed to me there was nothing practical left to gain in quality terms - everything was good enough, for me, snyway.
As a matter of fact, I'm still using the amplifier I finished designing just before my 1st year college exams in early summer 1974.
I think I have a photocopy of the full wireless world article on the Peter Blomley PA design somewhere, I tended to keep things like that. It was an interesting idea, but whether practical performance justified its complexity was another matter. The reason I largely gave up designing audio circuits was that it seemed to me there was nothing practical left to gain in quality terms - everything was good enough, for me, snyway.
As a matter of fact, I'm still using the amplifier I finished designing just before my 1st year college exams in early summer 1974.
A little off-topic; apologies in advance.
I was listening to some music on headphones through my JLH headphone amp and I thought about this comment. My newer JLH headphone amp is an AliExpress version; the DC offset is inclined to drift as it warms up - and it does get quite warm. I wondered if anyone has made a Blomley-type headphone amp, i.e. with signal splitting separate from the amplification stage; would there be any improvement? Would it be as good as a Class-A headphone amp? It should at least be cooler.