NAD.. did I already kill it?

Discussion in 'Amps and Cabs [BG]' started by mattysaurus, Jul 6, 2019.


  1. mattysaurus

    mattysaurus

    Mar 21, 2019
    Found another old amp at a yard sale today. Harmony, solid state, 12” speaker, model 7022W. Cheaply made, maybe from the early 70s, but for a buck, why not?

    Just plugged it in and turned it on. Figured it wasn’t the best idea but eh. To my surprise it turned on. Hooked up a guitar... played for a hot second, made a distressed sound, and turned off.

    I figure the filter caps are bad, but did I do any major damage just now? Not too concerned since I only spent a buck on it and it’s not valuable, but I wanted to tinker.
     
  2. BogeyBass

    BogeyBass Inactive

    Sep 14, 2010
    Well if you wanted to tinker.
    Needs repair now lol

    Could be million guesses.
    Might been sold with known issue.

    Anywhere from simple bad loose components or jacks.

    Output device failure
    Or yes leaky old caps. Peeving of the bridge rectifier or blowing fuses from high current draw

    Start with obvious visual checks and ohm readings / diode check on output devices, driver transistors, bias transistor. bridge rec etc etc. Ohm readings / voltage test with transformer isolated from circuit.
    Bad input jacks , output jacks bad grounds case corrosion / connections.

    Literally millions of guesses
     
    jamro217 likes this.
  3. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Don't be so sure the filter caps are bad, that's just a wild guess that's about as accurate as saying R37 is bad without knowing what R37 is or what it does.

    Do you have any experience with electronics, what test equipment do you have?
     
  4. mattysaurus

    mattysaurus

    Mar 21, 2019
    I should clarify that it didn’t turn off. It just died. Power, then no power.

    Woof, opened up the (very cheap) back. Speaker woofer is completely ripped. Not much in the way of shielding. Pretty simple circuit board... green pcb but the traces are all done by hand.

    Everything is so cheap on this thing that I’m not sure it’s even worth messing with. I was hoping I’d at least get a speaker out of it but even that is bad, and I can’t even find a schematic of it online.
     
    Last edited: Jul 6, 2019
  5. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Likely it's not worth even a modest amount of effort unfortunately.
     
  6. Foz

    Foz

    Jul 26, 2008
    Jax FL USA
    Find a lady mannequin leg and make a lamp.
     
  7. mattysaurus

    mattysaurus

    Mar 21, 2019
    Kinda how I’m feeling. This was clearly a very budget model. It almost looks like a speaker cabinet, cheap chipboard and all. Is it even worth taking out the transformer and saving it for another project?
     
  8. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Only if you have a project that might use that particular voltage and type.
     
  9. Sounds like you got your dollars worth of entertainment from the thing already. Hey, at least it wasn't thousands of dollars and died during the first song of the SuperBowl halftime show.
     
    pappabass, Ellery, Giraffe and 2 others like this.
  10. Element Zero

    Element Zero Supporting Member

    Dec 14, 2016
    California
    “Electric sex” in the window. Classic.
     
    2tonic likes this.
  11. Savagehenry

    Savagehenry Supporting Member

    Apr 1, 2017
    Northern Illinois
    Would a computer monitor fit in it? Cut a hole in the top and make a planter? LOTS of threads here about alternate uses for old equipment that blew my admittedly simple mind.
     
  12. farace

    farace Supporting Member

    Jul 9, 2016
    Connecticut USA
    I am admittedly not a tech, but I've poked around inside an amp that seems similar to what you describe, and it was truly alarming due to the corners cut and the resulting lack of safety. I forget exactly what I had, might have been a Harmony, or a Kent, or God-knows-what, but some third- or fourth-tier guitar maker's name on it. The most alarming thing was that it had a two-prong cord, and one leg was screwed right to the chassis. So you had a 50-50 chance when you plugged it in of the chassis--and the ground of the input jack--being hot. IIRC there wasn't even a fuse. Basically seemed like death in a box. I got rid of that in a hurry.
     
    Wasnex, 2tonic and Giraffe like this.
  13. cableguy

    cableguy

    Jun 4, 2009
    North Bend, WA
    Be sure to check the flux capacitor.....
     
  14. two fingers

    two fingers Opinionated blowhard. But not mad about it. Gold Supporting Member

    Feb 7, 2005
    Eastern NC USA
    Or just dump a bucket of ohms in there. Shake it for one minute. It'll be good as new. :thumbsup:
     
    LowActionHero, 2tonic and cableguy like this.
  15. 2tonic

    2tonic

    Dec 22, 2015
    "Light and Harmony for all" ;)
     
  16. iagtrplyr

    iagtrplyr Supporting Member

    Apr 1, 2013
    Clinton, IA
    You could have your own garage sale and slap a fifty cent sticker on it that says “half price.”
     
    Ellery and squidtastic like this.
  17. R37 is definitely bad. Nothing named R37 could ever be good. If you come up with a new product, don’t call it R37, unless it is junk.

    OP - check the R37 to see if it failed. If the amp has one, it’s likely the cause of your problem.
     
    AudioTaper and agedhorse like this.
  18. stringthrough

    stringthrough Supporting Member

    Gut it and make it into a picture frame
     
  19. Sell it for $2 and double your money.
     
  20. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    Guess you'll have to settle for the free 61 B-15 you snagged a couple weeks ago :D
     
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
    Aug 5, 2021

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