Hart JLH find....please help with identity/info!!

[tonewheelkev]

Hart "John Linsley Hood" KIT find....please help with identity/info!!

Came across these Kit Built (?) power amps....and...Oh Boy...the smell!!!
Now in a state of dissembly....each has 4 x Mosfet O/P transistors.

Initially...thought that they'd started life as Stereo Power amps, that had been converted to Mono-Blocks, but now realise this isn't the case.


They certainly are of different vintages, with variations to case cover/front panel.


What appears to be the younger of the two has gold plated binding posts.


Would love to find instruction manual that may have been with the kit, along with any circuit diagrams, and useful service info.


Although my skills are somewhat limited to assembly, (and cleaning) I have the help of a most competent tech, and intend to 'restore' these to drive my main L/R speakers......I understand that although these amps are old (25 to 35 years??)....they are still considered capable today??


So....over to any JLH nutcases out there....hopefully

 

[Mark Tillotson]

Probably a variant of the Hitachi MOSFET circuit - the caps need checking if that old, though may still have life left. The heatsink compound has probably dried out a bit. Looks to have plenty of protection circuitry on the PSU board.

 

[tonewheelkev]

Thanks Mark...searched for "Hitachi MOSFET circuit"....and that just broadens the field for me!!
Think I'm really needing 'baby' steps here...

 

[nautibuoy]

Building one of those kits was my very first foray into DIY Audio - it's a good sounding amp.

 

[Nisbeth]

Quite possible that the schematic is one of these: The Class-A Amplifier Site
but you'll have to do a bit of checking against the PCB to find it I think.

Edit: Looks like it is the "audio design" one - both schematics are there but no more information.

 

[latala]

Nothing like the Hitachi circuit but very high quality
We worth restoring Boy I am getting old I actually purchased one of the very first mosfet
amplifiers Hitachi imported into the UK back in the day
Very nice two
I still use a large Hitachi mosfet in my main setup
Trev

 

[tonewheelkev]

Building one of those kits was my very first foray into DIY Audio - it's a good sounding amp.

Wonderful!!!... What is it please?
Is it possibly the Monoblock (K1100M) that's referred to halfway down the page here, left hand column :


https://www.americanradiohistory.co...ireless-World-1995-11-S-OCR-OCR-Page-0046.pdf

 

[nautibuoy]

You might want to check out Rod Elliott's site;

The Class-A Amplifier Site

it has schematics for the amp and power supply;

http://sound-au.com/tcaas/ETI5-89.gif

http://sound-au.com/tcaas/ETI5-89a.gif

 

[tonewheelkev]

All good fellas!
Nautiboy....Nisbeth had previously had just posted that link a few minutes ago!
.....with you having made one some years ago....I was hoping to get the model number!!!!!??


....Almost there!!!

 

[nautibuoy]

Wonderful!!!... What is it please?

It's the Linsley-Hood 80W Mosfet amp, published in ETI in 1989. IIRC there was an error in the PSU schematic that was published in the magazine but the Hart kit, which is what you have, had resolved this - just saying you might find a discrepancy.

 

[tonewheelkev]

Aaaaghh....thought the Linsley-Hood 80W Mosfet amp, published in ETI in 1989...was a stereo amp??
This is a mono amp....and I have 2!!


I easily get confused!!

 

[nautibuoy]

It may be that the discrepancy is between the 1984 and 1989 articles.

Incidentally, John Linsley-Hood lived only a couple of miles away from me and was very gracious and helpful with my project and the visit I made to his home remains a great memory, mainly because of his help with the amplifier but also because of the way he lit his open coal fire with, essentially, a small flame thrower he had connected to the gas supply!

 

[nautibuoy]

It's definitely the Hart kit of the 80W Mosfet amp; the stereo version just had two amplifier boards stacked above each other - you can still see the mounting holes for the second amp board. It looks as though someone has just added another chassis/PSU - it might even have been an option Hart offered.

 

[nautibuoy]

Anyway, IMO they're worth the expenditure of a little TLC.

 

[nautibuoy]

Another link;

A Paul Kemble web page - JLH mosfet amplifiers.

and here's a picture of the fully-equipped stereo kit;

I built mine without the bells and whistles, just a plain front with a passive ALPS volume control.

 

[nautibuoy]

Gosh, this magazine cover brings back memories...

 

[tonewheelkev]

This is all excellent stuff nautibuoy(finally got spelling right!!)...and many thanks for putting yourself 'out'...as they say!
Interesting too...that you encountered JLH in the way that you did!!


Thanks...and much appreciated!!
Kev/Leeds

 

[ctrlx]

here is a thread on it


JLH Mosfet Power amplifier construction thread


there are others too....

 

[nautibuoy]

No problem Kev.

It looks like the one with the big blue LCR caps was the original as the wires that have been taped off would have connected to the upper amp board.

 

[tonewheelkev]

This is starting to make sense to me now (I think!!)
If I was to populate x2 more of the power amp pcbs....I could progress towards x2 stereo amps here??(Assuming that the PS in each monoblock could handle the extra PCB)


Hhhhmmmnnn!!!!