Rebuilt of Linsley Hood Mosfet amplifier from Wireless World 1982

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I found in my stock a pair of the original Hitachi Mosfets 2SJ50 and 2SK135 from the '80s and during the lock-down I decided to rebuild the Linsley Hood 80-100 Watt Mosfet amplifier published in the Wireless World magazine in 1982 that I had also built in the '80s.

I designed a new PCB since my original PCBs, as published in the article, were not in good condition.
I also reduced the supply voltage to +/- 35 Vdc because I didn't need more power than 40 Watts / 8 Ω and I used modern components.
To my opinion this amplifier is still very, very good and I was very pleased with the final results.

It was so good that I ordered a pair of Exicon Mosfets, that according to their manufacturer are direct replacement for the Hitachi Mosfets, to built one more amplifier.
In comparison with the Hitachi Mosfets, I think that Exicon mosfets have a little better transparency.

If you are looking for an amplifier to build, I fully recommend it.

Here are some photos of the assembled PCBs.
 

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  • The PCB with the original Hitachi Mosfets.jpg
    The PCB with the original Hitachi Mosfets.jpg
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  • The PCB with the Exicon Mosfets.jpg
    The PCB with the Exicon Mosfets.jpg
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I would hate to see another DIY's hard work for the community's benefit turn up on the global kit market or retail audio market as products for someone else's profit. Don't post the layout or Gerber files - email them to any long-term member who asks...err.. nicely :)
 
I am curious Gdan can you tel me why you picked the earlier ( August 1982 ) version of JLH,s series of mosfet power amplifiers as John updated it later in 1984 and later still ?


I built the 1984 version and later versions including my own variations of it including class A versions as I was so pleased with the openness and clarity of the design.
The 5p compensation capacitor and where it was placed as directly opposed to D.Self,s amplifier design philosophy to me was a revelation at the time and doing many tests presented a very clean 1kHz sine wave and square wave and with the same compensation I was able to up the bandwidth to over 100kHz without any instability.


I like the way you compacted the boards as opposed to some commercial designed PCB,s of his mosfet amps as that is precisely what I did to enable a large bandwidth without HF oscillation and the need to change the Comp. capacitor to a higher value.



I am very glad to see John,s work still being talked about and built .
 
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Joined 2010
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I am curious Gdan can you tel me why you picked the earlier ( August 1982 ) version of JLH,s series of mosfet power amplifiers as John updated it later in 1984 and later still ?


I built the 1984 version and later versions including my own variations of it including class A versions as I was so pleased with the openness and clarity of the design.
The 5p compensation capacitor and where it was placed as directly opposed to D.Self,s amplifier design philosophy to me was a revelation at the time and doing many tests presented a very clean 1kHz sine wave and square wave and with the same compensation I was able to up the bandwidth to over 100kHz without any instability.


I like the way you compacted the boards as opposed to some commercial designed PCB,s of his mosfet amps as that is precisely what I did to enable a large bandwidth without HF oscillation and the need to change the Comp. capacitor to a higher value.



I am very glad to see John,s work still being talked about and built .


It is the first amplifier that I built back in the 80s when I was a student.
Actually from what I remember, this 1982 design was very popular here in Greece.
It is a very good amplifier, very stable. I used the first version for many many years.
I am an admirer of Linsley Hood work.
 
Yes Gdan its the 1984 design probably built using the original PCB,s which if not careful in layout and components could produce slight RF oscillation, that's why I said I built my versions more compact like yours.


Your point is well proven by actual practical means not just theory.
 
I got this amp up and running in my test chassis today.

I have built a lot of amps and must say that the sound of this one is excellent. It is incredibly sweet and tuneful and provides great insight into the music.
I have not detected any of the "mechanical" sound that characterises many amplifiers (however I'm still in the honeymoon period ;) ).