Sumo Nine Plus output transistor replacement - Sanken 2SC1831

[Tone Meister]

A friend wants to bring over an early (1987?) Sumo Nine Plus amplifier with blown outputs. According to him, the original chips are the obsolete Sanken 2SC1831. I've had no luck sourcing a suitable replacement or finding the early version of the schematic. The later model of the Nine Plus uses NEC 2SD555 chips, which are also obsolete.

What would be a suitable replacement for the original Sanken 2SC1831? Attached is the schematic for the later version of the amplifier.

Thanks in advance.

-Stan

 

[llwhtt]

My last couple of visits to James Bongiorno's place was all about the SUMO NINE, there are NO replacements, period. That's right from the horse's mouth. Sanken pretty much made them for him and his SUMO GOLD. The later NINE+ has drivers so normal output transistors could be used, MJ21194s would be great here.

If you look for replacements you'll end up with Darlingtons, no good. The 2SC1831s are called super betas and that's what allowed the LF353 front end to drive the outputs by itself.

So if it is a NINE+ go ahead and use MJ21194s. The bias on the PLUS is set by removing one of the fuses, connecting a DMM set to amps, and adjusting the pots, keeping them even, for 1 amp. I'm not a big fan for the "keeping them even" but that's how it's done. On the regular NINE you need a distortion analyzer with a balanced input to set the bias.

If his NINE+ used the 2SC1831s that was after James left SUMO and not correct according to him. Beancounters.

I have schematics for all three versions.

Craig

 

[Tone Meister]

Thanks for your reply Craig. Truth is, I don't have the amp in front of me yet, but I do know it is an earlier version with the Sanken 2SC1831s in it. I had narrowed down my search to the MJ21194s as well, but I wanted to be sure before we took the plunge for 20 of those puppies.

BTW, how will the MJ21194s stack up against the original Sankens soundwise? My buddy is concerned that any replacements won't sound as good.

I'm not a solid state guy, actually I'm not even a tech. I'm just a hobbyist with a grasp of the basics and a decent electronics workbench. I'd appreciate any help with the Sumo amp, including a copy of the schematic.

Thanks again

 

[llwhtt]

Once you get the amp in front of you look for the TIP31C (TO220 case) driver transistors, two per channel. If those are there it's a PLUS. A far as sounding the same it's either the "new" sound, if there is a new sound, or silence. The dual opamp should be an LF412.

Go to the ON Semi site, sign up as whatever and you'll be able to buy them for about half price.

Craig

 

[Tone Meister]

Went to the On Semi site and wasn't able to find where to sign up.

 

[Tone Meister]

The amp is a Nine Plus, according to my buddy who's owned it since 1987.

 

[llwhtt]

Near the top center of the home page there is "MyON", click that and register. Might have make up a business name, "Joe Schmo Audio Repair" or whatever floats your boat.

Craig

 

[Tone Meister]

That was a good lead Craig, thanks.

 

[Tone Meister]

Craig,
The 2SC1831 is a Darlington, so can you explain how the MG21194 is a suitable substitute in this amp?

 

[Capt Grogg]

super beta, not darlington

 

[llwhtt]

NO, the 2SC1831 is NOT a Darlington, the subs come up as Darlingtons but it is a Super Beta, current gain is similar to a Darlington.

The original SUMO NINE used the 2SC1831s driven by opamp only, the 2SC1831s had enough gain to be able to do that.

The SUMO NINE PLUS has an opamp, drivers and outputs. The opamp (LF412) does not have enough current gain for normal transistors (2SD555 or MJ21194) so the driver (TIP31C) was added. The driver and outputs are in a Darlington configuration.

It seems that your friend has the oddball version of the NINE, drivers and the super betas. I am pretty sure James told me that was NOT his idea. I do have the schematic for that one but need to scan it for you.

Craig

 

[Tone Meister]

I don't know which version he has yet. He gave me the year he bought it and ID'd the SC1831s. He isn't bringing the amp until the weekend, so I have asked him to look inside the case for those TIP31 drivers you mentioned so we can nail down the version he has.

 

[llwhtt]

It's going to boil down to this, drivers good, no drivers bad. If no drivers and depending how many 2SC1831s are bad just removing the bad ones and making sure outputs are distributed evenly might get it back up and running but at less current capability, no 4 Ohm loads. We'll have to wait and see.

Craig

SUMO made both the NINE and NINE + concurrently, though the NINE came first. I traded an Andromeda I for my NINE over 20 years ago.

 

[a.wayne]

Is it worth fixing .... ?

 

[llwhtt]

I'm trying to keep all of my GAS and SUMO stuff alive, at least the Bongiorno stuff. I went through three Athena pre amps before I got a good one, that was back in the late 80s, it was NOT designed by JB. IMHO the stuff after James left was just not the same either electronically and mechanically. Many amps after James were MOSFET designs, he didn't do MOSFETS.

If all he needs is $50 worth of transistors it's well worth it.

Craig

 

[Tone Meister]

... If all he needs is $50 worth of transistors it's well worth it.

Craig

I agree and I plan to draw the line at the drivers and outputs. If the amp is smoked when I get in there I am less inclined to try to repair it. In fact, I want to be sure that transistors will fix it before ordering a single part.

 

[llwhtt]

I guess there are some disagreements on the SanKen 2SC1831 as being a Darlington or not a Darlington. In my Japanese substitution manual SanKen's replacement for the 2SC1831 is a 2SC4131. It's NOT a Darlington either but it's also not a TO-3 case it's a TO-3P, won't work without some mods.

Craig

 

[llwhtt]

James Bongiorno used to hang out on the SAETalk forum, there he answered some questions about the NINE and the 2SC1831. James never had a problem suggesting replacement components for obsolete devices but the 2SC1831 was one where he very adamant about, there are NO replacements.

Craig

 

[llwhtt]

OK, here's the story of this particular version of the NINE+. The NINE+ was originally designed to use the NEC 2SD555, an expensive transistor. AFTER James sold the company the beancounters didn't want to purchase those expensive xsistors so the circuit was "bastardized", James' word, to use the 2SC1831 of which they had 1000s.

So for this amp to live on it needs to be un"bastardized" and the MJ21194s fitted. There are several components in the bias circuit that need to be removed and replaced with the much simpler bias circuit. Also the output emitter resistors need to be replaced, from .51 Ohms to .2 Ohms. The peak current resistor, R38 looks to 1K in this version, needs to be 120 Ohms in the normal PLUS. The fan appears to be a DC fan instead of the usual AC fan, that shouldn't matter a bit.


Craig

 

[Tone Meister]

... So for this amp to live on it needs to be un"bastardized" and the MJ21194s fitted. There are several components in the bias circuit that need to be removed and replaced with the much simpler bias circuit. Also the output emitter resistors need to be replaced, from .51 Ohms to .2 Ohms. The peak current resistor, R38 looks to 1K in this version, needs to be 120 Ohms in the normal PLUS. The fan appears to be a DC fan instead of the usual AC fan, that shouldn't matter a bit.


Craig

That sounds daunting, at least on paper and begs the questions: does anyone have these circuit changes documented or can we mark up a schematic with the required changes? With the right guidance, I'm confident I could perform the work, but I'd need documentation of those changes before I'd want to dig too deep.