Learning how to substitute transistors

[Roboburger]

I've been here lurking and reading for the last few weeks, hoping to learn more about electronics. I got the basics, but I've reached a point outside my scope today.

I'm refurbing a Luxman R1040, and there's a few shorted transistors. I've been bopping around trying out various Substitution forms on web pages, but I get all kindsa different answers. Here's the skinny:

Q203a is a 2sc1951, it's shorted C-E, and I have no idea which of the many substitutes to use. I was reading this guide on Audio Karma. So Far, I have found potential substitutes in : NTE382, ZTX694B ( is pinout different?), 2sc2230A, KSC2316Y ... Here's a chart of the variables:


What am I looking to Match, or what can be over, or what must be under?
From what I was reading- if there is a compliment pairing with a Transistor- I should be considering hFE highly. I don't think there is in this case. Right..?
Do I gotta keep a tight rein on Dissipation (Pc)? or Collector Current (Ic)?

Anyone got an opinion, or can ya point me to another guide to transistor Subbing?

Thanks!

 

[JohnRoberts]

It kind of looks like almost any of them would work but higher miller capacitance might need to tweak the value of C206 for stability margin.

They all look like they have more voltage and beta than needed, but more is not bad. The higher bandwidth parts (ft) could also impact stability.

maybe try one and see what happens.

JR

 

[Brian Roth]

@Roboburger ....

Nothing specific to add....but you said:

"....I'm refurbing a Luxman R1040, and there's a few shorted transistors....."

Meaning more than one shorted? Which ones, out of curiosity? Shorted from what to what (ie, CE, CB, BE). Only one channel?

In these direct coupled amps "everything affects everything else". <g> One rogue part can cascade and cause other failures. Thus, a new replacement transistor might die because of other failed parts.

Not trying to be a downer here, but I had battles with Crown power amps years ago! <g> In a few, I had to literally desolder many trans. to find something like a leaky junction.

Best of luck!

Bri

PS....as I recall, Luxman amps sounded very nice....and were reliable.

 

[Roboburger]

Thanks, fellas! I just don't wanna screw this up needlesly..

I'm just going through all the transistors on the PCB. The was another failed one- I'll report on what its location was later.

 

[ruffrecords]

Just to add to what Bri said, transistors very rarely fail themselves. Usually something else fails and takes the transistors with them. I would check the electrolytics and for shorted or open resistors.

Cheers

Ian

 

[Brian Roth]

And, it's tough to find "subtle" transistor faults with them in a circuit like this. Crazy/obvious junction faults can be detected in-circuit with a simple VOM.....shorts, opens....but not "leaky' junctions.

Bri

 

[drtechno]

Anyone got an opinion, or can ya point me to another guide to transistor Subbing?

Thanks!

I use the JEDEC Transistor substitute manual.
There are people that have that online plus other substitution databases.
My printed book tells me 2sc1573 , 2sc1518, 2sc1509.

Also, Q204 should be the same gain (hfe), so you are going to have to get a few and match hfe and I would replace the same pair in the other channel so it would match.

 

[Roboburger]

Meaning more than one shorted? Which ones, out of curiosity? Shorted from what to what (ie, CE, CB, BE). Only one channel?

In a few, I had to literally desolder many trans. to find something like a leaky junction.

Best of luck!

Bri

PS....as I recall, Luxman amps sounded very nice....and were reliable.

yes, besides 203, 204 shorted C-E, too- but I have that one on hand- 2SA750

Yeah, I learned that last year on a Carver that you can't just pop out the bad guy and try again-

 

[Di_Sousa]

I'm refurbing a Luxman R1040, and there's a few shorted transistors. I've been bopping around trying out various Substitution forms on web pages, but I get all kindsa different answers. Here's the skinny:

Q203a is a 2sc1951, it's shorted C-E, and I have no idea which of the many substitutes to use. I was reading this guide on Audio Karma. So Far, I have found potential substitutes in : NTE382, ZTX694B ( is pinout different?), 2sc2230A, KSC2316Y

Check out this thread for Transistors cross reference and substitutes.

There's more substitutes and easier to find than the ones you posted:

https://groupdiy.com/threads/useful-transistor-equivalence-cross-reference-websites-list.84850/


I have 2SC2240 transistors in case you need it, I send you for free

 

[Roboburger]

Check out this thread for Transistors cross reference and substitutes.

There's more substitutes and easier to find than the ones you posted:

https://groupdiy.com/threads/useful-transistor-equivalence-cross-reference-websites-list.84850/


I have 2SC2240 transistors in case you need it, I send you for free

Wow! I'd love a pair. Yeah- those specs are a lot closer than anything else. why didn't the other engines return that ??? I'll message you.

 

[Di_Sousa]

Wwhy didn't the other engines return that ??? I'll message you.

The Engines I posted in the thread I linked, are the best ones on the web,
I've tried them all...

For the transistors send me you raddress by PM, and I will send you 2 in a normal letter envelope

 

[Roboburger]

Lol, I can't figure out how to DM someone! I'm going to lunch, I'll figure it out later.

 

[CJ]

Here's what you do. Very simple. You are after four specs.

NPN or PNP
V-ec
I-c
hfe

That is, emitter collector voltage (so the transistor can stand the voltage put out by the power supply)

Maximum collector current, so the transistor can handle the current demand as dictated by the circuit,

And hfe, transistor gain, which is simply the ratio of collector current to base current.


There may be more than on spec for hfe but as JR says, it don't have to be perfect, just ballpark close.

If you want you can build a hfe tester if you have a power supply and a few volt meters.

That way you can pull a working sample from your amplifier and check the gain against the specs to see where they have the transistor graded. Sometimes the transistors will have a suffix on the part number like f g h or a b c which is a result of a screening process.

Or you can take a chance on evilbay for NOS.

Oh, and you should try to match the package type ie; TO. 220 and pinout but sometimes you can work around this on the smaller power level transistors.

Once you meet or beat V and I, all you have to do is match the current gain spec.


Now if you are working on a FM tuner, the process becomes a little trickier.

How do I disable spell checker?

 

[Roboburger]

I use the JEDEC Transistor substitute manual.
There are people that have that online plus other substitution databases.
My printed book tells me 2sc1573 , 2sc1518, 2sc1509.

Also, Q204 should be the same gain (hfe), so you are going to have to get a few and match hfe and I would replace the same pair in the other channel so it would match.

it looks to me that the Voltage of 2sc1518 2sc1509 are too low... Vcb and Vce for the original are 120V. No?

 

[JohnRoberts]

Here's what you do. Very simple. You are after four specs.

NPN or PNP
V-ec
I-c
hfe

That is, emitter collector voltage (so the transistor can stand the voltage put out by the power supply)

Maximum collector current, so the transistor can handle the current demand as dictated by the circuit,

And hfe, transistor gain, which is simply the ratio of collector current to base current.


There may be more than on spec for hfe but as JR says, it don't have to be perfect, just ballpark close.

JR would add, needs to be in the same package and confirm footprint/pin out.

JR

If you want you can build a hfe tester if you have a power supply and a few volt meters.

That way you can pull a working sample from your amplifier and check the gain against the specs to see where they have the transistor graded. Sometimes the transistors will have a suffix on the part number like f g h or a b c which is a result of a screening process.

Or you can take a chance on evilbay for NOS.

Oh, and you should try to match the package type ie; TO. 220 and pinout but sometimes you can work around this on the smaller power level transistors.

Once you meet or beat V and I, all you have to do is match the current gain spec.


Now if you are working on a FM tuner, the process becomes a little trickier.

How do I disable spell checker?

 

[Roboburger]

Thanks everybody. I am hip to the idea that the footprint needs to be the same. Hfe is new to me, so I am gonna make sure to get out the bench Power supply and the multiple voltmeter angle to lean their actual Gain values.

 

[Roboburger]

The Engines I posted in the thread I linked, are the best ones on the web,
I've tried them all...

For the transistors send me you address by PM, and I will send you 2 in a normal letter envelope

It looks like you gotta PM first and then I can reply. I'm too new and don't have access to PMs yet.

 

[Di_Sousa]

Lol, I can't figure out how to DM someone! I'm going to lunch, I'll figure it out later.

1) top right corner , next to your nickname, click the Envelope symbol
2) then click "Start new conversation"

 

[pucho812]

I usually just go into the NTE cross reference and then buy whatever NTE says. I have never had an issue that way

 

[Roboburger]

1) top right corner , next to your nickname, click the Envelope symbol
2) then click "Start new conversation"

View attachment 119788

I found out I was too new. You have to have ten posts for that Start Conversation button to appear. I guess that helps keep spammers from joining and PM'ing the whole database!