Converting TO-220 to TO-247 - diyAudio
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Old 23rd July 2007, 03:22 AM   #1
Clipped is offline Clipped  Thailand
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Default Converting TO-220 to TO-247

Is it possible to convert a TO-220 based amp to use TO-247?

provided i can find a way to mount them to a heatsink.

The victim will be an orion 225 digital reference...currently it uses
ST micro BD909/910 (original 2n6688/91) i think the TIP35/36 has similiar ratings by looking at the spec sheet...but i could be wrong.

so would this be a plug and play operation or would i need to change the Base and Emitter resistors also?

thanks
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Old 23rd July 2007, 04:25 PM   #2
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Generally, the alotted space will not allow this conversion.

If the transistors had similar parameters, you would not need to make any changes to the drive circuit.

What's the reason for wanting to do this?
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Old 23rd July 2007, 05:27 PM   #3
djQUAN is offline djQUAN  Philippines
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if that amp uses the mounting bar method of mounting the devices to the heatsink, I think it would involve a bit of mechanical work to fit those big output devices you want to put in.

I'm also curious as to why you want to change to bigger devices.
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Old 23rd July 2007, 06:30 PM   #4
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I did this to a Punch 150 years ago < like 15> a pre HD model that used bipolar outputs the amp is still running. It would pull down a 50 amp HP Harrison power supply I used back then so it was a mean machine after doing the deed but, it had to be forced air cooled to keep it below the over-temp limit.

I remember it well as it pulled over 50 amps at 12 volts easily driving a 4 ohm mono load of dual 12's with mids and tweets in a tri-linear mode setup. Not to shabby for a 150 watt amp don't you think?
the amp is still in a friends car today, and has never had a failure since the one that allowed it to be built up.

If your new to this sort of stuff I cannot recommend you doing this sort of thing. I had extensive equipment at my disposal to use during this youthful expression of tech savy I had back then. I am older now and I just buy the right sized equipment nowadays, it saves time, and money later on down the road
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Old 24th July 2007, 02:37 AM   #5
Clipped is offline Clipped  Thailand
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hi guys,

this is just something ive been wanting to do for a while now, i know the fets in the power supply are good for around 1500 watts with the original fets or similiar...just wanting to try and get the most out of it i guess...that is, if it 'would' be more powerful do to the new transistors.

if im not mistaken the bd909/910 combos are rated at 75 watts and the tip 35/36 at around 125 watts....i cant seem to find bi-polars more powerful...but fets are easy

im trying to pick things up again, a while back i was going to rewind the transformer to 36 volts but never got around to it, so will probably rewind and put the bigger transistors in too....but do one thing at a time so i can take notes.

more than likely i would mount them on the bottom footing of the heatsink that would touch the mounting surface...make a stainless steel shroud mount a fan to it, and elevate it...

it'll probaly be one heck of an ugly monstrosity....or very cool looking.

it would be really cool if i could use TO-3's...lol

i just want to experiment...in the spirit of invention

or would it be easier just to add more transistors?

thanks!

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Old 24th July 2007, 06:59 PM   #6
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Default Power?

Are you trying to get more power out of the amp? Just changing the transistors won't help as the power output of an amp is determined by the power supply. The power supply voltage determines the output power as long as there is enough current capacity to back it up.

Merely going to heavier duty transistors will not give you any more power. And if you figure to run the amp at a lower load impedance with the heavier transistors, if the power supply is not upgraded, all you'll do is overload and kill the power supplies.

Power amp design is a careful set of tradeoffs between amplifer dasign and power supply. Without taking it all into account, you're just going to make it worse. Either less reliable orjust not accomplish anything useful.

I design car amps for a manufacturer in LA and we spend as much time on the power supply as the amp itself.
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