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Thread: Altec 9475a preamps

  1. #1
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    Altec 9475a preamps

    anyone here ever worked with theses?

    Altec 9475a preamps

  2. #2
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    I designed the 9475. It is an updated Langevin AM-16. Has wider freq. resp and less distortion. Also same ckt. was put in special package for MA BELL to use in repeater units. Had octal base like vacuum tubes. This was in 63 when ALTEC had the AUDIO CONTROL DIV. Schematics same as AM-16, just better xfmrs. ALTEC's Peerless xfmr div would not make the xfmrs. The eng dept said that it would not work. A company in Santa Ana , ROBOT COIL built them.

  3. #3
    Sal Vito is offline Gold Club Member (1000+ posts)
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    Originally posted by JOHN_HALL1:
    <STRONG>I designed the 9475. It is an updated Langevin AM-16. Has wider freq. resp and less distortion. Also same ckt. was put in special package for MA BELL to use in repeater units. Had octal base like vacuum tubes. This was in 63 when ALTEC had the AUDIO CONTROL DIV. Schematics same as AM-16, just better xfmrs. ALTEC's Peerless xfmr div would not make the xfmrs. The eng dept said that it would not work. A company in Santa Ana , ROBOT COIL built them.</STRONG>
    John,

    Thanks for responding

    BTW: did you have anything to do with the original AM16? Just curious...
    Sal Vito
    The Man of Sound
    salvito@hotmail.com
    312-409-0176

  4. #4
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    thanks for the reply!

    il check into those langevin things...

    cause i just bought 2 altec 9475a and coulnt find anything on these...i guess ill be more lucky with the langevin model

    also....was 500$ bucks a good deal for a pair of these in perfect shape + power supply?

  5. #5
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    Thats a good deal. Would have bought them if I had known about it. There was a wireing error in the early power supplies. Measure the 60Hz noise. If you can see it on the 5mv range of the scope, there is a mod. that will eleminate it. I did design the AM-16 in 62. My budget was $4,700.00. I also designed both power supplies. The waffle iron heat sink was made from a casting of a commercial waffle iron co. Both supplies wery made with C core lams. Very small mag. field.

  6. #6
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    Default 9475a

    HI,

    Apologies if youve seen this before but I accidentally replied to the wrong thread.

    I recently purchased a 9745a module as well but unfortunately am having problems with it, is this the right place to troubleshoot? Ill try my luck...

    Did you have any luck with yours tuxedoma?

    I mainly want to check that the power supply I bought (a straight up 24v dc supply from the electronics store) is the right one . Im getting buzz and the 22 ohm resistor keeps burning up! Ive replaced the two transistors in heatsink (output transistors?) and the power caps but still get awful buzz and no input. I fear something may be terribly wrong! Im hoping its not transformer trouble the 22ohm resistor seems to be hanging in there but can't be sure.

    any tips would be great, I really don't want this to become a paper weight! Thanks for your information as well John, its fantastic to have the actual designer on the forum!


    Cheers

    Tim

  7. #7
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    Default Altec 9475

    If the power supply is same design as used in computers it will cause noise. Use an analogue supply. POWER ONE makes several types. The international version is best as it has a humbucking xfmr. and can't be used to degausse casettes like most supplies. When you replace the xsistors, replace all of them. Use 2N2484 instead of 2n930's and use 2n2219 for the output stage.
    If the amp has been stored for a long time the electrolytic is probably bad. It will measure ok with an ohmmeter. But will draw enough I at turn on to pop the 22 ohm res. As a caution to anyone fireing up an old piece of equipment, use a variac and bring up the ac power slowly. Electrolytics need to be formed. When idle for a long time they form at 0 Volts.

  8. #8
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    Default 9475a

    Thanks John ,

    Ill see what I can do about another supply, thing is though that I am getting no input signal as well and the buzz is really big!

    One or two more q's if thats ok...

    firstly I noticed that the langevin am16 schematic seems a little different to the one I have for the 9475a (u mentiooned it was basically the same schematic with different transformers) one main thing is that the negative of the power supply is meant to be grounded at one point on the langevin but on the altec schematic I have it is connected to pin 15 (and goes thru the circuit ) (+ve to pin 11 -ve to pin 15). Am I neglecting to ground it properly somewhere?

    I was wondering if youd mind if I posted the schematic up to see if it looks right ? I think it is but it actually has no label on it and came with the module itself, it seems to match the module.

    Another thing is Ive replaced the filter caps already but wondered if maybe the other caps in the circuit could be causing power problems, I am a bit loath to replaced any caps that might be in the audio chain with inferior sounding ones. I also noticed that a diode seems to be conducting both ways
    so Ill replace that as well.



    Ill definitely look in to replacing all transistors not just the heatsunk ones.

    Thanks again

    Tim

  9. #9
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    Default Altec Pre

    Yes send schematic. I can't find mine. Replace caps in audio path with Panasonic non polorized parts. They are listed in the DIGI-KEY cat.. The diode in v+ is called idiot proof function. That way if someone reverses p/s connections it doesn't damage the amp. Use reg. electro's for p/s filter.

  10. #10
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    Default Schematic

    Thanks John Ill expriement with replacing the other caps to see if it helps. Im in Australia so no digikey but we have Dick Smiths and Jaycar.

    here is the schematic,

    If you could tell me if it looks
    good that'd be great. I have a feeling Im missing a ground point somewhere but not sure ...perhaps diodes are made for 3am dabblers like myself with too much solder lead in the air.

    Im looking forward to getting this up and running though! Were these the first altec discrete pre?

    Tim
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