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Trace Elliot RAH600SMX, outputs were replaced incorrectly
Trace Elliot RAH600SMX, outputs were replaced incorrectly
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Old 11th June 2018, 11:10 PM   #1
PsychoM is offline PsychoM  Belgium
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Default Trace Elliot RAH600SMX, outputs were replaced incorrectly

I have this 2x300W bass amplifier on my bench, bought as 'not working'.

The outputs have been changed obviously, at the moment it has 2x2SK176 and 2xSJ50 on each side. These are not direct complements. 2 K176s are original Hitachi, all 6 others are DSI (a brand that specializes in obsolete components).

I do not know what was originally in there, I have found a Trace Elliot schematic with BUZ900-BUZ905 in it, but that might be a different revision (schematic seems identical though).

Anyway, are there any dangers running this kind of configuration? I'm afraid there might be some DC offset as Vgs is different? Im also quite sure the transistors haven't been matched, they are used without a source resistor, should that lead to current balancing issues?

Keep in mind, this is a heavy duty bass amp. It should therefore not be very hifi, but it should be very rugged.

Would you keep this config, or change everything to BUZ900/905?

Cheers,
Olivier

Schematisch in attachment.
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Old 11th June 2018, 11:19 PM   #2
MAAC0 is offline MAAC0  Portugal
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I like the non-existent DC protection. Well it has a fan and relay. 4700uF also seems low for 300W. And if You ever put it in service, please exchange that XLR connector for a Speakon one. What's the rail Voltage ?
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Old 12th June 2018, 06:35 AM   #3
PsychoM is offline PsychoM  Belgium
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Quote:
Originally Posted by MAAC0 View Post
I like the non-existent DC protection. Well it has a fan and relay. 4700uF also seems low for 300W. And if You ever put it in service, please exchange that XLR connector for a Speakon one. What's the rail Voltage ?
Rail is +-70V I believe.
Like I said, it's not a hifi design. I have had 50watt amps with 10mF of cap, but this one only has 10mF for 2x300W. I can get pics tonight.
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Old 12th June 2018, 09:27 AM   #4
JMFahey is offline JMFahey  Argentina
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AFAIK thereīs only one Lateral Mosfet manufacturer left: PLC/Exicon in UK.
They make and sell spare MosFet dies (the 6 x 6mm silicon chips thenselves) who are bought by others, encapsulated, and given their own brand.
So *today*, all fresh BUZ, many 2SK/SJ and others "are all the same inside".
So go straight to PLC and get what you need, they do sell straight to the Public and for very reasonable prices.
Their own brand is Exicon .

VERY good stuff , and quite reasonable price, donīt know why Amp manufacturers donīt start using those MosFets again.
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Old 12th June 2018, 09:58 AM   #5
Enzo is offline Enzo  United States
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No guarantee a steady supply will continue to be available.
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Old 12th June 2018, 10:04 AM   #6
Enzo is offline Enzo  United States
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The schematic you posted calls out the parts. See the "50" and "135" next to the parts? J50 and K135 were original. (2SJ50, 2SK135)

I recall those as being common Trace transistors back in the 1980s.
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Old 12th June 2018, 10:02 PM   #7
PsychoM is offline PsychoM  Belgium
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Hi, thanks guys!

I will take a look at what Exicon offers.

By the way, the schematic I posted has a parts list with BUZ900/905 in it, but as Enzo says , the numbers next to the symbols probably point to 2SK135 and 2SJ50. These last are probably what used to be in here.

I'll call around to see who stocks any of these. Getting them from Darnell/RS Iis possible but I'll need to find a middle man

Anyway, here are some pics. Overall, I'm not too impressed. It looks like manual work (apparently "Julian" and "Andy" built this one), even original soldering. Also PCB traces aren't of the greatest quality and like MAAC0 said, there is no DC protection (there is a fuse, but surely something better was available in early 90s..).
Components are of good quality, but then again this used to be a very expensive amplifier. Even now it fetches 500 dollars in good condition.
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Old 13th June 2018, 10:39 PM   #8
MAAC0 is offline MAAC0  Portugal
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1200W with 4*100W transistors from 2SK135 datasheet ??. 70V at 4Ohm it's 17.5A, datasheet says 7A. Weird.
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Old 14th June 2018, 03:03 PM   #9
PsychoM is offline PsychoM  Belgium
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Quote:
Originally Posted by MAAC0 View Post
1200W with 4*100W transistors from 2SK135 datasheet ??. 70V at 4Ohm it's 17.5A, datasheet says 7A. Weird.
Forget the 1200 Watts, thats marketing gibberish. It is 2x300 watts RMS using 2x 2 K135-J50 pairs. So about 6A peak per transistor
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Old 14th June 2018, 04:39 PM   #10
anti is offline anti  Slovakia
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2 x 300W rms is dangerously close to 1200W peak. So it's not "all lies" there.

But what is it? "False" or "misleading" advertising?
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