Modern 2SC458 Replacement Strategy

[VA1DER]

I just completed a restoration of a Realistic STA-120B which called for replacing 18 of the notorious Hitachi 2SC458's. Though I try to replace as little as possible in a restoration, I am in the camp that considers this a shoot-on-sight transistor. Replacing this many called for a modern sourcing strategy. There are a lot of threads talking about replacements, but the transistor landscape has changed a bit and some replacements are hard to find.

By modern standards, the different ranks and noise specs of the 2SC458 equate to six different transistor types today. I simplify this a bit by not bothering to differentiate and replace every I find with low noise substitutes.

2SC458	nominal hFE	Replacement	Notes
B	150	Onsemi KSC1815YTA	Noise figure 1dB typical at 10KΩ 1KHz, Rbb not stated
C	240	Rohm 2SCR533PFRA	En = 0.465nV/√Hz, Rbb = 8.65Ω !! But Vbb = 540mV, SOT-89 required through-hole conversion
D	400	Toshiba 2SC2240-BL	Noise figure 2dB max at 10KΩ 1KHz, Rbb not stated, Almost unobtanium now,
D	400	Diodes Inc. ZTX1051A	En = 0.420nV/√Hz, Rbb = 7.84 !!

Onsemi KSC1815YTA:

• Good dual purpose low-ish current and voltage noise.
• Good for low gain replacements or
• Good for the I-V stage in two-stage phono pre-amps when paired with the 2SCR533PFRA
• Available for about 17 cents each at Mouser

Rohm 2SCR533PFRA
This transistor is pure magic and the driving influence for this post. My STA-120B after restoration has noise more than 120dB down from signal with these beauties in the tone amp.
I sourced this originally due to Dick Kleijer's excellent work on ultra low noise transistors.

• OUTSTANDING voltage noise, one of the lowest I've ever seen, but its extremely low Rbb makes it less attractive when current noise dominates.
• Good for medium-gain replacements, most 2SC458LG's in use tend to be in this gain level
• SOT-89 so requires conversion. More on this below.
• Great for tone amp board replacements, or the voltage amp stage in two-stage phono pre-amps.
• Very low junction voltage drop, Vbe = ~540mV. This can lead it to act as if it has more gain in certain topologies.
• Currently marked as NRND, this appears to be due to a simple rebadge where it is being split into the 2SCR533PHZG and 2SCR533P5 for with and without AEC-Q101 (automotive) qual. I have not myself used the replacements as the PFRA is still very available.
• Available for 30 cents to $1 each at mouser depending on quantity

Toshiba 2SC2240-BL

• The previous gold-standard for 2SC458 replacements. Still a good transistor, but becoming increasingly expensive and/or unobtanium
• Good for high-gain replacements
• Ok for medium gain if a good feedback network is in place, but this increases noise
• Genuine ones going for $2+ each, know what you're looking for as 95% of ads are fakes.

Diodes Inc ZTX1051A
HAVE NOT YET USED MYSELF - I've included this as something to look into for those who have no stock of 2SC2240's, based the same work by Dick Kleijer. The 2SCR533PFRA from that list turned out to be the lowest noise transistor I've ever seen.


SOT-89 Conversion
The 2SCR533PFRA has been an almost magic replacement for me, but it does require some work. SOT-89 is not naturally tenable for vintage restorations. I use it with:

• SOT-89 -> .1" / 2.54mm pitch header hole micro-board
• 90˚ .1" / 2.54mm pitch 0.6mm gauge R1 12mm header pins, or
• Straight .05" / 1.27mm pitch 0.4mm gauge 14mm micro-header pins (every second one removed)

(Ali Express links given above are notoriously ephemeral so you may have to search by name or photo)



I use .6mm right angle headers when the through-holes on what I'm working on are large enough. Many aren't quite large enough for .6mm square header pins, so I use .4mm gauge. I can only find long .4mm gauge in .05" pitch and straight, so I pull every second pin when I use these, and then bend it right angles after.


The finished product.

For those who don't do SMT yet, SOT-89 isn't terribly hard to solder if you have a steady hand. I purchased an inexpensive pencil hot air gun and some 63/37 solder paste and it makes short work of it.

 

[ivandezande]

I use KSC1845 and move on with my life and the next project. If any of these 60 year olds actually cared about noise floor, they wouldn’t buy vintage, they’d buy new. They just want it to make sound and look pretty.

I appreciate your research and your drive, but you call out a Realistic. You can use off brand (maybe not perfect replacement) parts in the Kia of vintage audio. It’s ok.

 

[MFRD]

@VA1DER appreciate the writeup, very helpful.

 

[dlucy]

Good writeup. Thanks for making AK even more valuable. A few items to consider:

KSC1815YTA is not a transistor model, not something anyone should be searching for during sourcing. KSC1815 is the model and Y is the grade. TA is the packaging-for-sale format and is irrelevant. Whether someone buys KSC1815Y in "TApe" format or "BUlk" format won't matter (to humans using their hands). So a good recommendation would be "KSC1815" or "KSC1815Y"... without the "TA" or "BU" or other suffix.

KSC1845 is a far better replacement, noise-wise, for all audio signal applications where the current is low. It is far superior to the KSC1815 in these instances. Your tables, data and recommendations would be more complete, more applicable to the typical use of 2SC458 if they included the KSC1845.

The high high current rating (by comparison to the others) of the Rohm 2SCR533PFRA, 3A compared with 10mA and 100mA, makes me very skeptical as to its performance on low current signals... like those in tone circuits you reference and in anything prior to the output stage. All other transistors with good to excellent noise figures tend to have lower and lower current handling figures. Are you saying your comments about how magical this replacement options is are in tone circuits and phono stage circuits?

 

[ConradH]

+1 on KSC1845. It can replace a remarkable number of parts, but is limited to 50 mA. Another useful but lower voltage part is 2N5088. Many old transistors offered a combination of high gain with moderate voltage and current, that didn't exist with available 2N series parts of the time. OTOH, I sometimes wonder if high gain goes along with lower long term reliability. When you find something you like, stock up! A large number of parts I thought would be available forever, like PN2222A, are disappearing fast!

 

[VA1DER]

KSC1815YTA

...is the way it's sourced on Mouser and Digikey. I tend to make parts lists that a novice can simply search for at the source. But your points are very well taken, thank-you!

KSC1845 is a far better replacement, noise-wise, for all audio signal applications where the current is low.

7dB typical NF at 100kΩ Rs is not a compelling low noise use case to me.

Now, Neither the 1845 or the 1815 publishes Ropt, so it's hard to directly compare. But in my experience, if an audio transistor performed better at the far more normally quoted 10KΩ Rs, its data sheet would say so.

[KSC1845] is far superior to the KSC1815 [noise wise]

The data sheets for each would tend to disagree. If there is other data, I'd happily consider it.

I don't normally recommend the KSC1845 as a replacement as it has half the current handling of the 2SC458. People who know what they're doing well enough to know exactly when it's safe to substitute a transistor with half the current handling, those people don't need a post like mine anyway.

The KSC1815 has better (published) noise, an hFE that matches many in-the-wild 2SC458's, and current handling that makes it a drop in replacement without having to think about it (when it's gain-appropriate).

makes me very skeptical as to [the 2SCR533PFRA's] performance on low current signals...

Check out Dick Kleijer's work. All the tests were at low current. I wouldn't have normally given a switching transistor like the 2SCR533 the time of day for this type of thing if it hadn't been for that work. That got me to try it, and when I tried it I was convinced.

When I recently refurbed an STA-120, I first replaced every 2SC458-LG on the tone amp with some of my precious supply of 2SC2240-BL's. Which has a gain very much in the same ballpark as the KSC1845, I'll add. I don't have great noise measurement capability, but tying the tone amp input to ground, turning on the receiver, and ramping up the volume to full is a useful comparative metric to see how much voltage noise is on the output. The improvement after moving to the 2SCR533PFRA was marked. On the order of 7dB.

 

[jheu02]

I notice noone has mentioned the BC550. It is a great low noise high gain transistor, and even has the 100mA Ic. It does have a different pinout, so you need to be careful to make sure of proper insertion, but especially in gear that has transistors inserted in the "triangle" leg configuration, it's no big deal.

 

[bolero]

I was getting noise with KSC1845's in the phono section of a restored Sansui AU-999

Following someone's advice on AK I tried KSC1815's instead & they are fine

I still have the KSC1845's everywhere else: it was just phono for some reason.

 

[tom3]

Deleted.

 

[ivandezande]

I was getting noise with KSC1845's in the phono section of a restored Sansui AU-999

Following someone's advice on AK I tried KSC1815's instead & they are fine

I still have the KSC1845's everywhere else: it was just phono for some reason.

Good point, I’ve had and seen posts about this happening in Marantz 2230/2245/2270. No other units have had that issue for me.

 

[Watthour]

I notice noone has mentioned the BC550.

Good call. That's why I collected a couple thousand of those, since the 458 "outhouse" bipolars were so predominant for quite a while, and I've been in units that had 60+ at a time.

 

[JyriK]

Rohm 2SCR533PFRA
This transistor is pure magic and the driving influence for this post. My STA-120B after restoration has noise more than 120dB down from signal with these beauties in the tone amp.
I sourced this originally due to Dick Kleijer's excellent work on ultra low noise transistors.

But how does it sound? This Rohm transistor has collector output capacitance (Cob) about 7 times higher compared to 2SC458. It certainly affects higher frequencies. Maybe the noise got canceled due to this.

 

[gadget73]

Just for yucks, has anyone taken a noise measurement with KSC1845 or 1815 and compared it with a noise measurement in the same gear with the surface mount transistor? I'm just curious how much difference we're talking about in-circuit vs just straight measurements of a transistor in a test circuit.

 

[mrk229]

I notice noone has mentioned the BC550. It is a great low noise high gain transistor, and even has the 100mA Ic. It does have a different pinout, so you need to be careful to make sure of proper insertion, but especially in gear that has transistors inserted in the "triangle" leg configuration, it's no big deal.

Looks like a nice part as long as you keep in mind it's lower voltage ratings compared to the KSC1845.

EDIT-- @jheu02 pointed out below that the 2SC458 has lower voltage ratings than the BC550. So my point is, well, kind of pointless.
The BC550 should be a good replacement. (watch the pinout)

For reference the 2SC458:
Collector- Emitter Voltage VCEO Max: 30V
Collector- Base Voltage VCBO: 30V
Maximum DC Collector Current: 100mA


KSC1845:
Collector- Emitter Voltage VCEO Max: 120V
Collector- Base Voltage VCBO: 120V
Maximum DC Collector Current: 50mA


BC550:
Collector- Emitter Voltage VCEO Max: 45V
Collector- Base Voltage VCBO: 50V
Maximum DC Collector Current: 100mA

 

[jheu02]

Looks like a nice part as long as you keep in mind it's lower voltage ratings compared to the KSC1845.

Yes, however, the transistor that was being replaced was the 2SC458, which has 30V Ce and Cb ratings IIRC. So, the BC550 has plenty good ratings to replace the C458. Also, I seem to recall that some of the potential noise issues with C1845 were actually due to such high voltage handling WHEN USED is a very much lower circuit.

 

[ConradH]

IMO, noise is usually not an issue on tone boards and such, only phono sections. Not every BJT location needs the lowest noise part. OTOH, I've seen some phono boards where they switch out the eq and put line signals through, so some thought is required. Almost any choice can be better than the '458 because even if the curve family hasn't changed, they seem to get noisy as they get older. Who do we hate? The '458!

 

[dlucy]

...is the way it's sourced on Mouser and Digikey. I tend to make parts lists that a novice can simply search for at the source. But your points are very well taken, thank-you!

The point of my comment was exactly that: to help beginners find the right devices. When you advise someone to search for "KSC1815YTA" and there are no TApe-packaged devices left on Mouser or digikey, those sites will show "out of stock".

If, instead, one searches for "KSC1815", then the site will show all the KSC1815, no matter which packaging format, and therefore beginners are more likely to find compatible devices.

 

[mrk229]

Yes, however, the transistor that was being replaced was the 2SC458, which has 30V Ce and Cb ratings IIRC. So, the BC550 has plenty good ratings to replace the C458. Also, I seem to recall that some of the potential noise issues with C1845 were actually due to such high voltage handling WHEN USED is a very much lower circuit.

Yes indeed you are correct. I will edit and add that to my previous post. #14 Modern 2SC458 Replacement Strategy

 

[bolero]

Good point, I’ve had and seen posts about this happening in Marantz 2230/2245/2270. No other units have had that issue for me.

It was a last-ditch effort: I went thru the whole board, had already replaced most parts, couldn't figure it out.

Luckily I had ordered both 1815 and 1845

 

[jheu02]

Question for those if you who have gone the SMD route with adapter boards or just leads soldered on....

Most datasheets I've seen, the SMD doesn't have the power handling capabilities of the thru hole device. Has this ever become an issue?