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Old 20th August 2006, 07:44 PM   #1
bigphil is offline bigphil  Canada
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Default Looking for amp suggestions

I've tried doing a search already, but all I can find is info on fake transistors.

I have an old pioneer prologic amp, I've tried to fix it but I give up.

I've tested the power supply - still good, and as far as I can tell the main transistors are still good as well (anyone have a sure fire way of testing them?).

I am going to salvage from the amp:
- +-69V supply complete with a big transformer and specialized Pioneer Filter Capacitors at 8200uf. (still good)

- (2) 2sc3281 and (2) 2sa1302 (originals from a pioneer unit - notcounterfiet)

I also have the lower stage original toshiba transistors but I dont know if they are good, so I will need a way to test.

I also have the chassis with a LARGE heatsink that can handle lots of heat.

So if anyone has suggestions on how to easily find out if these transistors are still good, and if they are any suggestions on a power amp I could build with these components. I am open to pretty much anything I was thinking maybe a Class A, but I'd be interested in high output designs as well. Thanks in advance everyone.
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Old 20th August 2006, 07:54 PM   #2
bigphil is offline bigphil  Canada
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forgot to mention they are Toshiba originals.

I also have from the unit:
- A set o f NOBLE dual emitter resistors
- (3) Toshiba A1263 and (3) Toshiba C3180

any chance I could make something decent?
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Old 20th August 2006, 07:58 PM   #3
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Any chance of some pictures of the amp? most importantly of the heatsink.. might help people suggest what you could build with it, I mean Class A gives off a lot of heat, the heatsink may look big but if its the original from the pioneer amp then it may not be big enough for a class A.. What kind of power are you looking to achieve? what impedance speakers are you wanting to drive it with?
Cheers,
Owen
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Old 20th August 2006, 08:08 PM   #4
bigphil is offline bigphil  Canada
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pictures:
Click the image to open in full size.

Click the image to open in full size.


- the mouse is for size comparison

I figured the heat sink would be good for around 10 watts class A (?)
Looking to drive an 8 ohm load.

The original amp was rated to 125 watts (yeah right).
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Old 20th August 2006, 08:35 PM   #5
anatech is offline anatech  Canada
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Hi bigphil,
I think your biggest problem is that the transformer output and transistors / heatsink are mismatched. With lower supply voltages the SymAsym would be good, there's the GEM and a few others around.

You will find that heatsink will get hot at 20 W average heat input. Those fins have poor thermal contact with the mounting plate. Look closely at it. I have thrown most of that type out as next to useless.

I didn't mention Greg Ball's amp because it's a complete kit, not what you asked for.

So keep your eye's peeled for other junk amps for heatsinks and transformers. Your transformer is good for something, so are the outputs and other bits you have.

A transistor tester would be a good thing to build up or buy right now for you.

-Chris
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Old 20th August 2006, 08:58 PM   #6
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Default ..

What is the exact pioneer integrated model ?
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Old 20th August 2006, 09:10 PM   #7
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Default ..

What is the exact pioneer integrated model ?
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Old 20th August 2006, 09:13 PM   #8
bigphil is offline bigphil  Canada
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Default Re: ..

Quote:
Originally posted by anatech
Hi bigphil,
I think your biggest problem is that the transformer output and transistors / heatsink are mismatched. With lower supply voltages the SymAsym would be good, there's the GEM and a few others around.

You will find that heatsink will get hot at 20 W average heat input. Those fins have poor thermal contact with the mounting plate. Look closely at it. I have thrown most of that type out as next to useless.

I didn't mention Greg Ball's amp because it's a complete kit, not what you asked for.

So keep your eye's peeled for other junk amps for heatsinks and transformers. Your transformer is good for something, so are the outputs and other bits you have.

A transistor tester would be a good thing to build up or buy right now for you.

-Chris
Thanks for your suggestions, I will probably just salvage what I can then until I decide more specifically what I'd like. Can you recomment me a good transistor tester?

Quote:
Originally posted by parsecaudio
What is the exact pioneer integrated model ?
It was a pro-logic. I tried fixing it for a long time, but it acts too funny (inconsistent between power-ups) which makes it hard to troubleshoot. It was a VSX-9500S, I have another complete working model and really like the sound - only 0.005% THD.
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Old 20th August 2006, 09:29 PM   #9
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Default Hi bigphil

The Toshiba 2sc3281-2sa1302 are a very good complementary transistors:high FT and good linerarity
.For your pro logic integrated amp,if the power amp stage are similar to the VSX series,it is not a bad amp,but it have a very small open loop bandwihdth.The distortion specified is for middle frequency only,due to decrease of NFB it will increase to high frequencies.A better solution for the output stage can be made.
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Old 20th August 2006, 10:46 PM   #10
anatech is offline anatech  Canada
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Hi bigphil,
Watch for Heatkit testers. You do not need a curve tracer and it takes too long. What you do want is something that measures gain, collector-emitter leakage and collector-base leakage. Analog meters are fine and more than accurate enough.

-Chris
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