The cheapskates inexpensive John Linsley Hood Class A from 1969

Discussion in 'DIY Discussion' started by JMRead, Jun 15, 2020.

  1. JMRead

    JMRead

    Joined:
    Jun 15, 2020
    Messages:
    3
    Likes Received:
    1
    Hello all,

    I'd made a couple of chip amps 3876 (3875 with a mute) and a couple of years ago a 3886. Always at the back of my mind was the JLH1969. After loads of searches on the web and finding so much conflicting information I decided to go back to the source. This is a link to it: https://drive.google.com/file/d/1p5k4YgTPAYa-aCtt6DpfE6CCekHOhV6k/view?usp=sharing it's the complete cleaned up version not a dog eared photo copy. The one on the Class A site is incomplete, no photographs, sadly.

    My first concern was heat sinks so I looked at what JLH did;
    [​IMG]
    Two 100 x 120mm finned heat sinks with two MJ480's on each one and in a metal box, I couldn't find anything similar.

    I did find these though 100 high x 146 wide x 22 high
    [​IMG]

    From a nice man in Herefordshire: https://futureeden.co.uk/collection...inium-heatsink-t-series-profile-a-86mm-x-22mm I sprayed them with heat resistant paint and baked them in the oven at Gas Mk5 for one hour.

    More soon

    Cheers - J
     
    JMRead, Jun 15, 2020
    #1
    1. Advertisements

  2. JMRead

    JMRead

    Joined:
    Jun 15, 2020
    Messages:
    3
    Likes Received:
    1
    Hello all,

    The output transistors that JLH used are no longer available, fortunately one year after the article he said that 2N1711 and 2N3055 would be an OK match. I would be unable to fit the 2N3055's to my heat sinks so I chose the 'plastic' versions TIP3055.
    [​IMG]

    The box is 17" long 12" wide and 4" deep, not including the heat sinks, I like to be able to change stuff easily I made my 3876 and 3886 on wooden sub assemblies. The heat sinks hang from some Aluminium angle which in turn are supported on some treated roofing lath, really strong stuff. The plywood is 5.5 mm I bought a 4ft x 2ft piece from the local DIY shop.

    I drilled the heat sinks 2.5mm and tapped them M3, I realised after that it would have been just as easy to drill a couple of 3.5mm holes from the front with a clearance area drilled for the nuts, before I painted them and used nuts and bolts. I then countersunk the holes slightly with a drill held in my hand to take off the drill burr and then smoothed it off with some wet and dry paper. I polished the heat sink surface with some Brasso, the TIP3055's are insulated with some silicon pads and the 'sticktion' effect is quite strong, they are quite difficult to remove.

    Cheers - Jim

    Even more soon
     
    JMRead, Jun 20, 2020
    #2
    Sergeauckland likes this.
    1. Advertisements

  3. JMRead

    Sergeauckland

    Joined:
    May 31, 2012
    Messages:
    100
    Likes Received:
    4
    Location:
    Suffolk
    Hi J,

    Any further progress, pics etc? Back in 1972 or thereabouts, a colleague made a pair of JLH Class A amps which he used with his Tannoy Lancasters. I spent a happy evening playing around with them, comparing them to a pair of Quad IIs. Since then, I've often thought of building a pair, just for the fun of doing it, but as I have amplifiers like others have mice, and can't think of any use for them, I've never gotten round to it. Even now in lockdown, I have other things I'm playing with, like making an LED PPM, and restoring a Goldring GL75, and I've just finished servicing a Ferrograph 631 I've had for years. That 631 is another thing I have no use for, except nostalgia as a friend gave it to me, and we both enjoyed it when at University together in the late 1960s.

    Next repair will be my Sony SQD2020 Quadraphonic decoder, which has failed on both front channels. I'm hoping it's trivial, as original parts aren't available, although with the exception of the mechanical items, just about everything should be standard or near equivalents.

    S.
     
    Sergeauckland, Nov 5, 2020
    #3
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.