Author Topic: NZ Made Alron 4500 Guitar Amp  (Read 1781 times)

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Offline Raff

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NZ Made Alron 4500 Guitar Amp
« on: December 12, 2015, 06:12:19 am »
Hi everyone,

I'm trying to repair a New Zealand made Alron branded guitar amplifier, its dated 1978 on the chassis.

It has 2 MJ802 transistors as the output pair, an OC branded Folded Line reverb box, and is rated at 45 watts output.

Its giving me a bit of grief so I was hoping someone may have a circuit diagram lying around?

The fault is virtually no output at all. Maybe 100 milliwatts if lucky.

I've tried signal tracing but there are some odd circuit design techniques in it that make no sense to me yet.

The power supply is fine, +_ 40 volts, the speaker is fine, all transistors check ok with my meter, the electro caps have either been replaced or check fine.

I've never worked on an amp like this one, it uses a transformer as the phase splitter for the output transistors.

A schematic would make repair so much easier.  :phew:

Thanks,
Raff
 

Offline Shock

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Re: NZ Made Alron 4500 Guitar Amp
« Reply #1 on: December 12, 2015, 01:29:40 pm »
If you want help with the repair side of things it helps to include decent photos and list what troubleshooting equipment you have.

Regarding the schematic good luck on that, the look of these suggests a dirt cheap solid state amp. Could be helpful to know if they really were made there or some company just slapped a name on a Japanese brand.
Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 87V, 117, 27/FM
Oscilloscopes: Rigol DS1054Z, Phillips PM3065
 

Offline Seekonk

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Re: NZ Made Alron 4500 Guitar Amp
« Reply #2 on: December 12, 2015, 02:11:47 pm »
Transformer design like that should be a piece of cake.  If you haven't blown out a speaker, output very near 0V, then the problem is likely the driver transistor to the transformer or circuit before that.  Could be as simple as ghe audio electrolytic feeding the driver transistor.
 

Offline Raff

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Re: NZ Made Alron 4500 Guitar Amp
« Reply #3 on: December 14, 2015, 07:43:06 am »
Well I got the old girl working.

Turns out my scope probes went faulty.

It makes it hard when you have to troubleshoot your troubleshooting equipment before troubleshooting  :palm:

A few old electros replaced, a bit of rewiring and a tidy up and away she goes.

Its actually not a bad little combo, sounds pretty good to my ears anyway.

Thanks,
Raff
 


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