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Author Topic: Bench test a wurlitzer amp  (Read 6443 times)
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Skeleton Man
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« on: May 26, 2009, 05:27:12 pm »

Hi guys,

I'm in the process of repairing the amp (wurlitzer 543 stereo) from my wurlitzer 2600 juke and it's a real pain to pull the amp, change something, put the amp back in, and re-hook 6 different connections!

Does anyone know how I can wire up a test plug to allow me to test the amp on the bench ?

It has a "muting plug" which apparently shorts some contacts and keeps feeding the amp with a flat input voltage or something. I'm wondering if I can rig up a plug to simulate play and non-play mode ?

I asked John at Durfee coin op, but he wasn't able to help with testing (great for parts though!). I haven't tried the guys at victory glass yet.

Chris
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Jim
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« Reply #1 on: May 26, 2009, 06:58:18 pm »

Chris,

I just checked my manual and see there's an electrical schematic for the amp.
PM me if you want this as a PDF that I can email you...
As far as bench testing, you'll need an input signal, just to start, with the correct signal voltage or you may get mixed results...
Does the amp currently function at all...?
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« Reply #2 on: May 27, 2009, 09:01:21 pm »

Hey Jim,

Sure I'll take a PDF..  I have a reprint of the whole manual but an electronic copy of the amp schematic would be great (I've been wanting to scan and enlarge to poster size, pdf saves me pulling the book apart).

As far as does it work - yes, preamp works, power amp is now dead. When I first got the machine it would work perfectly for about 10 minutes, then no sound. One day I tried the machine and no sound, ever since then it has had the same problem. If I hook up the auxillary output from the amp to my home theather, it works great (sounds great too).

I've replaced most of the capacitors with a kit from "jukebox friday night", haven't gotten them all yet, but a couple of big non-polarized ones are done and a bunch of tiny ones that go across signal lines and terminals.  I haven't gotten to those monster "cans" on top of the chassis yet - so this is my next step.

All the tubes glow so I'm assuming they are ok - I replaced all except for 2 of them when I first got it because they were missing. I bought matching pairs of "new old stock" or "working pull", spent about $125 on tubes (versus $260+shipping for a tube kit).

Bench testing would be ideal - the mp3 input and speaker output are what I have on hand, unless someone wants to loan me their signal generator and oscilloscope ?  laugh

Chris
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Jim
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« Reply #3 on: May 28, 2009, 04:06:09 am »

Quote
unless someone wants to loan me their signal generator and oscilloscope ?
I sold my scope a few years back but I think I still have my signal generator... I can't remember where i put it though...

Give me a few days on the schematic as I won't be home for a couple of days...
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« Reply #4 on: May 30, 2009, 11:32:21 pm »

Well I got my answer from The JukeBox List and apparently I need to jumper 2 pairs of pins on the chassis connector. I haven't tried this yet tho.

I did replace one of the 4-in-1 "can" capacitors with 4x electrolytics from the capacitor kit and I once again have sound!  I'm hoping as I replace the rest it will start to sound better (sounds kinda distorted right now)


Chris
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« Reply #5 on: May 31, 2009, 04:01:31 am »

"It's Alive" ! ! !
Good work, Chris ! ! !
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« Reply #6 on: May 31, 2009, 01:26:44 pm »

Thanks Jim  biggrin

Appreciate the pdf too, I was able to find a capacitor I couldn't originally see on the schematic (it was like an ugly duckling hidden over the other side of the circuit).
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