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Old 15th October 2012, 07:10 PM   #1
RS232 is offline RS232  United Kingdom
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Default Building a 1987 power amp

As per title I am planing the build of a 1987 power amp from an article on Elector Electronics magazine.
I'm building it for 2 reasons:
First I know it works because I build it before (when the article came out)
Second I have all the most expensive parts like 1 huge heatsink (400x450mm) that I had cut in 2 today, 1 huge toroid transformer (2kw) with the right output voltage, 4 x 15000uF x 120V capacitors and 18 2sk175/2sj55 pairs of mosfets.
To start the build I have 1 question for now.
What is the best way to attach the TO3 mosfets to the flat heatsink ?
I don't want to use "L" profiles because I want to keep the case as close to Standard as possible (+/- 430mm wide).
Any Ideas ?
This is going to be a slow build because I have a day job and I'm not in a hurry

Ric

Last edited by RS232; 16th October 2012 at 01:02 AM.
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Old 15th October 2012, 07:22 PM   #2
RS232 is offline RS232  United Kingdom
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Default 1987 power amp

This is the heatsink I'm going to use
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Old 16th October 2012, 01:04 AM   #3
RS232 is offline RS232  United Kingdom
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Found the answer to my question on Peter Daniel A75 project
Going to have some machine work done but I was counting with that
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Old 16th October 2012, 06:10 AM   #4
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'Looks wonderful but quite an expensive solution, assuming they are custom milled profiles in lieu of L section ones. If you have access to a machine shop, great but I see some serious cash needed, as one who has had to cost engineering work.
Perhaps you'll also consider fabricating those massive bars from 2 pieces of plate or plate and rectangular bar. That will be a lot simpler and cheaper.
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Old 16th October 2012, 07:00 AM   #5
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Rs232.. Please tell us wich amplifier you are building

Regards mark
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Old 16th October 2012, 10:06 AM   #6
RS232 is offline RS232  United Kingdom
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The name on the article was "1000 watt amplifier" and was published in 1987.
The power of 1000W is the bridged power the rated power was/is 250W 8ohm or 500W 4ohm or 1000W 8ohm in bridge mode.
It uses 4 pairs of 2SK175/2SJ55/channel.
I will post the schematic as soon I sort a few things (soon).

Ric

Last edited by RS232; 16th October 2012 at 10:21 AM.
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Old 16th October 2012, 12:49 PM   #7
wahab is offline wahab  Algeria
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I guess this is this one....

This iteration of their Crescendo amp still use a random stabilization
using the output stage capacitance as a shunt compensation.
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Old 16th October 2012, 03:14 PM   #8
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I will stay around ... and so is thermal runaway ,and oscillation .

That will be an interesting battle to watch .

i cannot offer advice ... but i can only say one thing ... Match very very carefully any semis you are willing to use .stay as close is possible to the original semis ...

If you decide to ventilate the project make sure that the cool air ventilates only the outputs ...even your breath above the drive board will change idle and offset .

Happy regards
sakis
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Old 16th October 2012, 04:04 PM   #9
RS232 is offline RS232  United Kingdom
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Quote:
Originally Posted by wahab View Post
I guess this is this one....

This iteration of their Crescendo amp still use a random stabilization
using the output stage capacitance as a shunt compensation.
So you are saying that the amp is unstable ?
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Old 16th October 2012, 04:08 PM   #10
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yes ...like most of Giesberts projects and approaches ....all of them are hfe depending and suffer from a number of stability issues
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