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Old 9th June 2014, 09:44 AM   #1
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Default 2SC3281/2SA1302 what amp?

I have two pairs of the original Toshiba transistors still on the hefty heatsink ( they check out as good) and the original Pioneer transformer with 75v 0v 75v secondaries.The original amp came out of a skip and had a tree growing through the centre.So no chance of restoration.

What simple amp can I build using these basic building blocks? Have looked here and at ESP but can,t find anything that exactly fits the bill. Of course I don't need to use to use the 75v transformer. Having read the data sheets for the above transistors, it appears they are capable of handling up to 200v on the collector/emitters with a possible OP of 150w. I have several hefty transformers capable of delivering this or can wind my own.

I've built a few valve amps and several simple solid state amps so not a complete beginner. Any suggestions most welcome, thanks for looking,Andy.
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Old 9th June 2014, 01:02 PM   #2
AndrewT is offline AndrewT  Scotland
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2pairs and 75-0-75Vac transformer is not compatible.
A 35-0-35Vac or 30-0-35Vac transformer is compatible with a 1pair output stage (2pair in a stereo amplifier).

1pair of 150W transistors is good for 70W to 80W, driving a speaker.
It could also drive a resistor to 150W, but that is not too good for music reproduction.
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Last edited by AndrewT; 9th June 2014 at 01:05 PM.
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Old 9th June 2014, 01:18 PM   #3
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You will need spares in reserve for the day when something goes wrong. Maybe you're lucky but you'll sure be mad if you couldn't get more of this Toshiba unobtanium for when the worst happens. Don't experiment with those transistors - set the amplifier up to work properly with easily replaced MJL3281/MJL1302 types for starters and then fit the original parts if that's what you want.

2 pairs however, is only enough for say an 80W/8 ohm amplifier and that would be covered by twin power rails of around +/-45V. There are any number of designs here, fitting that sort of description but then question is, what sort of design, complexity, cost and quality are you expecting?
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Old 9th June 2014, 01:52 PM   #4
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These are very standard (and good) transistors. Used in a lot of amplifiers of the mid 80s to 90s. You can use them in pretty much any design.
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Old 9th June 2014, 02:23 PM   #5
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Thanks for your replies. I think the 75v 0v 75v transformer should be saved for another project, as it is daft to get the amp to fit the PSU. Most of the simple designs of amplifiers I,ve looked at so far, that are proven run on around +/_ 30v.
Like ESP's Project 3.

I don't really need a 150w amp for home use- 60w is more than enough and will power my Mission 720's or 730's.

As to complexity,cost etc, A simple class A amp is what I,m after with a low component count. As to cost, I'm on a low budget but have a good stash of caps,resistors etc.Writting this post has focused my thoughts somewhat so I,ll leave building a 100w + amp for another day.

Andy.
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Old 9th June 2014, 02:43 PM   #6
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Quote:
Originally Posted by Welcome View Post
These are very standard (and good) transistors. Used in a lot of amplifiers of the mid 80s to 90s. You can use them in pretty much any design.
IIRC, they were inside the Yamaha AX-900 (4 pairs) delivering 130W (into 8 Ohms)

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Old 9th June 2014, 03:59 PM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Dr Wobble View Post
.............. A simple class A amp is what I,m after with a low component count. ............
You can't get that with 4 transistors, unless you aim for 5W to 10W of maximum power output.
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Old 9th June 2014, 04:01 PM   #8
AndrewT is offline AndrewT  Scotland
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Karl's pic shows 71V capacitors. The maximum transformer voltage for those will be ~40Vac.
45-0-45Vac will overvoltage 71V caps.
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Old 9th June 2014, 09:54 PM   #9
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Quote:
Originally Posted by AndrewT View Post
Karl's pic shows 71V capacitors. The maximum transformer voltage for those will be ~40Vac.
45-0-45Vac will overvoltage 71V caps.
Hi Andrew,

I was curious about the secondaries VAC of that massive encapsulated transformer (weights about 18 pounds the transformar alone) and, although the SM is available, it doesn't show the voltages... Any idea?

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Old 9th June 2014, 11:18 PM   #10
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Originally Posted by Welcome View Post
..You can use them in pretty much any design.
These are original Toshiba 2SC3281/A1302. You can only buy fakes of these at an acceptable price. They were EOL in 1999 and are now collectable or very expensive if genuine because some believe there is nothing as good as these for audio power transistors, even now.
That's why you don't throw them into any test or experimental project with a risk of blowing the only genuine ones you have or are ever likely to have again.
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