Creating a hi-fi quality amplifier (Based on a Goodmans Module 80)

Discussion in 'The Projects Forum' started by r3zafalls, Feb 3, 2014.

  1. r3zafalls

    Thread Starter New Member

    Feb 3, 2014
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    Hello everyone,

    I am new here; I've been looking for a forum for awhile now that can give me some help on various component questions as building circuits is a new hobby for me.
    My main area of interest is applications that involve audio and hi-fi systems especially analog/vintage equipment.

    I got quickly knee deep in the murky quicksand that is breaking things apart and making things when i got hold of an old tired Goodmans module 80 that had a lenco turntable in it which i was mainly interested in at the time it was worth quite a bit on ebay :p .

    I ended up stripping the whole thing down to the left and right amp channels + power supply throwing them into a box (looks more pretty than it sounds) wired up to a alps 50k pot and passive pre switching which gave me the best sounding amp i have ever owned and it cost me next to £30.

    The experience has given me the idea to prototype a amplifier based on the circuit design of the goodmans.

    Its going to be difficult because most of the components used are no longer in production or the values are very hard to find. However I have managed to find their equivalents to the nearest values.

    Namely the transistors were a pain to find. I used http://alltransistors.com to find the equivalents.

    Anyway (I tend to waffle on abit) i have bought most of the components i need there is just one which is puzzling me on both left and right modules theres a clear diode with three bands on it (white, purple, black) and for the life of me i cant find it anywhere for purchase or find its values for equivalents .

    Can anyone help here? Thank you!
     
  2. TANDBERGEREN

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    Jan 20, 2014
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  3. Rolf Zetterberg

    Member

    Sep 20, 2008
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    Are you talking about W11(emitter TR18)?

    Hello Tandbergeren.
    No,it's a silicon affair with MJE2955.
     
  4. r3zafalls

    Thread Starter New Member

    Feb 3, 2014
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    TANDBERGEREN,

    The Goodmans Module 80/90 have an output of 30watts. The 80 was a record deck fm radio combination. The 90 was the same amplifier but did away with the record deck.

    I have bought the manual and schematic sheet but i can't find anything substantial to online which shows the circuit diagrams clearly.


    Rolf Zetterberg,

    Hi,

    Yes i'm talking about the W11 its listed as 1S970 on the component sheet there's a diode that comes up on my search online by that part number but its not the component on the board.

    I've taken a picture of the diode seen at the link below.

    http://i160.photobucket.com/albums/t180/Matterz_00/SERENITY-PC/WP_20140203_009.jpg
     
  5. Rolf Zetterberg

    Member

    Sep 20, 2008
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    That old 1S970 again...
    If you google for this diode,a big 1000V power diode comes up,so something is obviously wrong.
    http://www.vintage-radio.net/forum/showthread.php?t=96571
    The diode in module 80 probably(I can't see any other explanation)works as a stabilizing diode since it draws around 12mA of extra current from the midpoint voltage.Now,since the current drawn by the transistor is far lower than that,the voltage across the diode is more or less constant in spite of the transistor's current varying.It stabilizes the amplifier is my theory.
    Normally there will be a resistor and a capacitor here.
    Try to find a diode that develops a voltage of 0.75V when 12-15mA flows through it.
    Have you measured this voltage on your's?
     
  6. richard.cs

    Member

    Mar 3, 2012
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    I have a module 90 and schematics for it, I seem to remember the output was substantially greater than 30 Watts (90?) but I could be wrong. I spent a while going through it last summer fixing things and updating a few parts.* In it's day it was a good but very expensive piece of electronics and there are places where a 3-shilling part was used when it would have been only marginally better than a resistor.

    I don't have schematics in front of me at the moment but when I get home from work I'll look up W11 and see if I can suggest any alternative parts. It's definately an all-silicon design. It looks from the photo like you've got just the audio amplifier board out, I have a feeling some parts of that took regulated power supplied off of one of the other boards, are you using the goodmans power supply as well? On the 90 it's part of a big PCB with lots of other stuff.

    *It's not rare enough that I'm reluctant to modernise things that make sense - dial lamps that melt their mountings definately had to go.
     
  7. TANDBERGEREN

    Member

    Jan 20, 2014
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    Rated at 35 watts RMS per channel <1% distortion. Frequency response 30 Hz to 20 kHz. Amplifier has same chassis and uses similar circuit to Goodmans Module 80.

    Please look here: http://www.radiomuseum.org/r/goodmans_forty_forty_ch_module80.html

    But that diode puzles me too.
    With a bit of the schematics I could give some input....
     
  8. t06afre

    AAC Fanatic!

    May 11, 2009
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    Did they not use color code Zener diodes back then? My guess is that it may be a zener diode. If the diode is not a goner. You may connect it in series with a resistor say 1 to 1.5K. Then use a variable power supply , and a voltmeter to find the zener voltage. I will guess the white band is the cathode
     
  9. TANDBERGEREN

    Member

    Jan 20, 2014
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    No colourcodes.
    White band is the cathode.

    Could actually be as simple as a ekvivalent to a 1N4148. Lots of equipment from that era had similar diodes wich all was 1N4148 or ekvivalent.

    To connect a powersupply via an 1K5 Ohm resistor to the cathode and try with voltages up to about 40V would most certenly clarify if this is a zener.
    If full voltage still is meassured over the diode, then I would replace it with a 1N4148 IF the one in the amp is broken. If not: Leave it to be there.
     
  10. t06afre

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    Is the board on the picture part of the power supply unit?
     
  11. TANDBERGEREN

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    Jan 20, 2014
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    No. Seems as if it is one of the poweramplifiers.
     
  12. richard.cs

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    Mar 3, 2012
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    That board is the audio amplifier but includes some PSU stuff. It has the rectifiers on that PCB with two huge electrolytics bolted to the PCB nearby. What I can't remember is if that board makes use of the regulated power supplies from elsewhere in the unit.
     
  13. TANDBERGEREN

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    Jan 20, 2014
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    Ah. Got the schematics now.

    The W11 diode is only for reference to setting the constantcurrentregulator TR16 by R105.

    Type diode here is not critical, only a quite standard 1N4007 or 1N4148.

    What is the value of R110? Divide 35V over the value of R110 and You have what current there will flow through that diode.
     
  14. TANDBERGEREN

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    Jan 20, 2014
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    There is only a -15V regulator present there.
    It supplies the FNM-tuner.

    All Audio is powered by the -56V
    And there is at least three "huge" caps there.
    One for the power, and one for each poweramp output.

    Strange placed theese three.
    The one for the power is located lying down near the front.
    The two other cans are located around left power uotput board.
     
    Last edited: Feb 4, 2014
  15. richard.cs

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    Mar 3, 2012
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    I've got my module 90 schematics now, audio driver runs on +/- 29V derived from a centre-tapped 42V winding on the transformer that supplies nothing else. It's pre-amp (which is on the main PCB and used for all sources) runs from the regulated 21V supply (buffered version of the varactor supply) and there's also a regulated 13V for the tuner.

    Is the module 80 different?

    In terms of this mystery diode the numbering is different on the 90 but there are only 3 diodes present per channel, a 30V zener regulating a current source and a dual-diode across the B-E junctions of the output transistors.
     
    Last edited: Feb 4, 2014
  16. TANDBERGEREN

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    Jan 20, 2014
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    Module 80 is a single powersupply unit.
     
  17. TANDBERGEREN

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    Jan 20, 2014
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    The module 90 is a splitpowersupply unit, Module 80 a single power unit.

    Module 90 could actually have been mistaken for a Radionette SM40 in a different cabinet.
    Kind a crossover between SM40 and SM230

    The 80 and the 90 is in no way similar to eachother.

    But at this point I have the schematics for both, and i will look closely in to them to find what we really have here.

    I have also seen those refering to Module 90 as a 70W amp.
    In my oppinion, I would call it a 25W amp /8Ohms, 50W /4Ohms. Max.
    But they both were refferet to as 35/40W by the manufacturer.
     
    Last edited: Feb 4, 2014
  18. TANDBERGEREN

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    Jan 20, 2014
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    Module 90 is probably more like the Goodmans One-Ten, isn't it?
     
  19. TANDBERGEREN

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    Jan 20, 2014
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  20. richard.cs

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    Mar 3, 2012
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