I have a Sphinx Project 18 amplifier which is missing the output FETs.
Originally they are 2SA1302 / 2SC3281
Is there a good direct replacement (other than MJL1302/3281) for those available today? Where?
At first, I was planning to convert the amplifier for 2SJ201/2SK1530 but then decided to choose the easy way.
By the way, I used search and someone suggests using 2SA1943/2SC5200, but is that really a drop-in replacement? If so, which would sound better, this or MJL?
Oh, and the output stage design can be found on this doc on page 7 https://www.google.fi/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&uact=8&ved=0CFAQFjAG&url=http%3A%2F%2Fwww.transparentsound.com%2Fsphinx%2Fpj18designmanual.pdf&ei=K7B4U6SNNvT64QTb7YGABw&usg=AFQjCNGh4_r9FBhcS5ErWLg4EZJFZVFGHA&sig2=wVIyXG7iwo7ZS-f6DVFxBw&bvm=bv.66917471,d.bGE
Originally they are 2SA1302 / 2SC3281
Is there a good direct replacement (other than MJL1302/3281) for those available today? Where?
At first, I was planning to convert the amplifier for 2SJ201/2SK1530 but then decided to choose the easy way.
By the way, I used search and someone suggests using 2SA1943/2SC5200, but is that really a drop-in replacement? If so, which would sound better, this or MJL?
Oh, and the output stage design can be found on this doc on page 7 https://www.google.fi/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&uact=8&ved=0CFAQFjAG&url=http%3A%2F%2Fwww.transparentsound.com%2Fsphinx%2Fpj18designmanual.pdf&ei=K7B4U6SNNvT64QTb7YGABw&usg=AFQjCNGh4_r9FBhcS5ErWLg4EZJFZVFGHA&sig2=wVIyXG7iwo7ZS-f6DVFxBw&bvm=bv.66917471,d.bGE
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The original bipolar transistors were obsolete around 15 years ago. Just as you can read from the similar part numbers of the On-Semi clones, MJL1302 and MJL3281 were and still are, the preferred replacement parts.
However, On Semi have expanded this type range with additional packages like TOP3 and also higher voltage versions for use in large amplifiers. Hence you also have related types like MJL0281, 4281, NJW series etc. which may also be suitable according to the specification of your amplifier.
Any seller of power transistors will stock or obtain these popular products. Digi-Key, Mouser, Profusion, Farnell, RS and any local Scandinavian and German parts distribution companies will also be able to supply.
2SA1943/C5200 are not equivalent in that they are for lower voltage and dissipation. They also do not have the legendary gain linearity of the original Toshiba types. In this multiple device design, it would also be necessary to use more components to match the power rating of the design. Not recommended IMHO.
Please note that if transistors failed and were removed, other parts could also have been burned in the event. The drivers (the preceding components) could also be damaged as could others further back. If you simply replace the outputs, there is no guarantee of success or that the new parts will not also disappear in smoke.
In any case, when a new assembly or fitting replacement parts, always initially use a current limiting device such as a variac or bulb limiter (an incandescent lamp of 60W or so) in line with the mains power to the amplifier (safely wired and with mains quality insulation too!)
If you search this bulb limiter or bulb tester item here, you will find a full description, but it's a light bulb, in series with the live or active mains lead, in simple terms. If it remains glowing when nothing is connected to the amplifier other than power, there is a problem and this device is all that's preventing smoke by restricting current to the bulb's own rating. If the glow settles to dim, you can then remove and adjust the idling current according the manual specification and likely all will be OK.
However, On Semi have expanded this type range with additional packages like TOP3 and also higher voltage versions for use in large amplifiers. Hence you also have related types like MJL0281, 4281, NJW series etc. which may also be suitable according to the specification of your amplifier.
Any seller of power transistors will stock or obtain these popular products. Digi-Key, Mouser, Profusion, Farnell, RS and any local Scandinavian and German parts distribution companies will also be able to supply.
2SA1943/C5200 are not equivalent in that they are for lower voltage and dissipation. They also do not have the legendary gain linearity of the original Toshiba types. In this multiple device design, it would also be necessary to use more components to match the power rating of the design. Not recommended IMHO.
Please note that if transistors failed and were removed, other parts could also have been burned in the event. The drivers (the preceding components) could also be damaged as could others further back. If you simply replace the outputs, there is no guarantee of success or that the new parts will not also disappear in smoke.
In any case, when a new assembly or fitting replacement parts, always initially use a current limiting device such as a variac or bulb limiter (an incandescent lamp of 60W or so) in line with the mains power to the amplifier (safely wired and with mains quality insulation too!)
If you search this bulb limiter or bulb tester item here, you will find a full description, but it's a light bulb, in series with the live or active mains lead, in simple terms. If it remains glowing when nothing is connected to the amplifier other than power, there is a problem and this device is all that's preventing smoke by restricting current to the bulb's own rating. If the glow settles to dim, you can then remove and adjust the idling current according the manual specification and likely all will be OK.
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2sa/c are BJTs, not mosFETs.
Which were originally fitted?
Any of the MJxx281/x302 can replace the 2sa3281/1302.
Are they fitted as parallel pairs? If so then you need to measure and select matched pairs.
You can test the amplifier without the output devices.
There is on the Forum a description and sch of the temporary connections required to carry out this test. It proves the earlier devices are working, or not working, and saves blowing up the new outputs.
Which were originally fitted?
Any of the MJxx281/x302 can replace the 2sa3281/1302.
Are they fitted as parallel pairs? If so then you need to measure and select matched pairs.
You can test the amplifier without the output devices.
There is on the Forum a description and sch of the temporary connections required to carry out this test. It proves the earlier devices are working, or not working, and saves blowing up the new outputs.
I bought this amplifier in parts, the amplifier board (which includes everything - main power supplies, and all the amplifier circuitry on one board) was never used and had most of the parts installed from the factory, excluding the output FETs, drivers, few capacitors, and some relays. The output FETs in the original design are 2sa1032/2sc3281.
I already replaced all the PSU capacitor beacuse they have been laying around since 1998 and didn't want to blow them on first startup.
This shows the configuration.. I guess I need to match them.
I tried to search but no luck.. I would like to do all the testing just to be sure even though there should not be anything broken.
I decided to use these MJL equivalents since I can easily find them
Thanks! This will be useful advice
If you read the article linked in the OP, you'll see this amplifier was an unfinished conversion project (Project 18) from BJT to Mosfet. i.e the Mosfet drivers were to be changed from Mosfet to BJT and the output devices from BJT to Mosfet. (yeah, one of those crazy projects
)The original BJT parts are were removed for the conversion long ago, by a previous owner but the specified parts are also obsolete now. Does that make sense?
Here's a link to a few threads on limiters: http://www.diyaudio.com/forums/equipment-tools/252386-bulb-limiter-testing.html
By the way, when matching those 2SA1302 / 2SC3281 in this design, do I need to match each pair or each quartet or both? How close and on which terms, hFE or something else?
Those outputs each have their own base and emitter resistors. They don't have to be matched.
Hi everyone, quicl google search brought me to this thread. I am fixing a Creast Audio 8001 power amp that has the 2SA1302 / 2SC3281 in the output stage. 11 pair of them in total.
I started with buying them on ebay. Prices seem fine so I went for it. Later I started doing some research onto the subject became aware of fake transistors. Soon the ones from ebay arrived from china. Opened one of them up and turns out they are fake. Later bough some other seller which they looked better in the inside but he die was still almost only just the quarter of the original Toshiba, decided not to install them. Little afraid, the amp is capable of delivering 750w each side at 8 ohm so i want to make sure I will install something that will be able to handle the 120volts rail and produce the 750w without blowing up. I see the MJL1302 and MJL3281 that was recommended by Ian here available at CPC and considering to going for them. There is only 5 pairs that are needed to be replaced in the amp the other 6 pairs tested fine. Question:
Can I mix these? Cani leave the original pairs that work in the amp and replace the broken ones with the MJL1302 and MJL3281 ones ? Shall I instead replace all output transistors with the MJL1302 and MJL3281 ones Including the ones that are fine ? Can i mix the original ones with the replacement ones? The obvious pro is the cost saving. Are there any cons to mix the two types ?
Else read about the current limiter bulb here. would i need to have as large as possible power bulbs in series with the main ? This amp takes a lot of power, would I one two 100w bulbs in parallel put in serious in the mains for instance ?
Thanks in advance
I started with buying them on ebay. Prices seem fine so I went for it. Later I started doing some research onto the subject became aware of fake transistors. Soon the ones from ebay arrived from china. Opened one of them up and turns out they are fake. Later bough some other seller which they looked better in the inside but he die was still almost only just the quarter of the original Toshiba, decided not to install them. Little afraid, the amp is capable of delivering 750w each side at 8 ohm so i want to make sure I will install something that will be able to handle the 120volts rail and produce the 750w without blowing up. I see the MJL1302 and MJL3281 that was recommended by Ian here available at CPC and considering to going for them. There is only 5 pairs that are needed to be replaced in the amp the other 6 pairs tested fine. Question:
Can I mix these? Cani leave the original pairs that work in the amp and replace the broken ones with the MJL1302 and MJL3281 ones ? Shall I instead replace all output transistors with the MJL1302 and MJL3281 ones Including the ones that are fine ? Can i mix the original ones with the replacement ones? The obvious pro is the cost saving. Are there any cons to mix the two types ?
Else read about the current limiter bulb here. would i need to have as large as possible power bulbs in series with the main ? This amp takes a lot of power, would I one two 100w bulbs in parallel put in serious in the mains for instance ?
Thanks in advance
Hi,
The Onsemi equivalents for these devices work very well. As rugged as the originals and better SOA which gives you good headroom.
I would suggest replacing all the devices. It will not be a good idea to mix old and new pairs in the same design due to different knee characteristics.
The light bulb needs to be used with the amplifier disconnected, to check if the mains circuit is working properly. You have a positive result if the bulb briefly glows as the reservoir caps charge up, and then the bulb should go out. It is not recommended to use it on an amplifier unless you are starting from scratch, i.e with the bias set all the way down to zero.
If you are doing a full bias reset then yes, you need a bulb but a 60W bulb is better than a 200W bulb. You want a higher starting resistance - the 200W bulb will offer so little of it that even in fault conditions it might not light up.
The Onsemi equivalents for these devices work very well. As rugged as the originals and better SOA which gives you good headroom.
I would suggest replacing all the devices. It will not be a good idea to mix old and new pairs in the same design due to different knee characteristics.
The light bulb needs to be used with the amplifier disconnected, to check if the mains circuit is working properly. You have a positive result if the bulb briefly glows as the reservoir caps charge up, and then the bulb should go out. It is not recommended to use it on an amplifier unless you are starting from scratch, i.e with the bias set all the way down to zero.
If you are doing a full bias reset then yes, you need a bulb but a 60W bulb is better than a 200W bulb. You want a higher starting resistance - the 200W bulb will offer so little of it that even in fault conditions it might not light up.
Hi Sangram, thanks for the swift reply!
"The light bulb needs to be used with the amplifier disconnected, to check if the mains circuit is working properly" - Do i understand correctly that what you mean is that the current limiter is only needed to test the power supply unit ?
I though it is needed for limiting the current in a case when there is a fault condition the output stage, with this not allowing components burning out in the output stage.
Are you suggesting that if the bias potenciometer is at minimum than there is no risk of damage even when there is a fault in the output stage ? A shorted output transistor even ?
So the following steps would need to take place after replacing the known faulty parts:
- testing the amp with output stage not connected to rail voltage with current limiter - if no fault found moving to next step
- testing the amp with output stages back on rail and bias at minimum. When increasing bias what will I bee looking for ? How will i know there is a fault or the amp safe to operate?
Lastly just one more question. CPC only have 7 pieces of one of the MJL3281AG Mouser has none. What other online shops are recommended apart form these too ?
"The light bulb needs to be used with the amplifier disconnected, to check if the mains circuit is working properly" - Do i understand correctly that what you mean is that the current limiter is only needed to test the power supply unit ?
I though it is needed for limiting the current in a case when there is a fault condition the output stage, with this not allowing components burning out in the output stage.
Are you suggesting that if the bias potenciometer is at minimum than there is no risk of damage even when there is a fault in the output stage ? A shorted output transistor even ?
So the following steps would need to take place after replacing the known faulty parts:
- testing the amp with output stage not connected to rail voltage with current limiter - if no fault found moving to next step
- testing the amp with output stages back on rail and bias at minimum. When increasing bias what will I bee looking for ? How will i know there is a fault or the amp safe to operate?
Lastly just one more question. CPC only have 7 pieces of one of the MJL3281AG Mouser has none. What other online shops are recommended apart form these too ?
If you have an output stage that has a fault, and you have replaced the faulty parts, you will have to set bias pots at minimum if you desire to check the output stage using a light bulb.
Usually a fused supply is used for this test, or low-wattage 10R resistors inserted in the supply leads. The light bulb is not the correct test for this kind of fault condition, as it will not allow you to set the bias (after which you will anyway need to test it, with the aforementioned 10R resistors).
Usually a fused supply is used for this test, or low-wattage 10R resistors inserted in the supply leads. The light bulb is not the correct test for this kind of fault condition, as it will not allow you to set the bias (after which you will anyway need to test it, with the aforementioned 10R resistors).
Hi guys, thanks for your answers ! Very useful Sangram, thank you !
I read on other threads/ on the net the Digikey is famous of selling fake transistors, not sure how much is that true. Any opinion on this ? nfsgame?
Also, i ve read the serivce manual which recommends tests using a variac. Ive been looking around to get one but can not really decide what level of current handling this variac would need to be able to do.
Acording to the brouchure I found online, the 120v version has:
1.6 amps drawn at idle
21.8 amp at one third power
37.5 max
so at 230volts this would be 18.7amp. As the serive manual mentions test conditions where the amp needs to be driven onto clipping I suppose i need a variac that handles all the 18.7 amps?
How important is the variac ? I d raher just go ahead with Sangram's suggestion with the resistors in the rail's to protect the output devices its seems more cost effective than investing in a variac. Would a low-wattage mean 5w for instance in this context ? 2w perhaps ?
I read on other threads/ on the net the Digikey is famous of selling fake transistors, not sure how much is that true. Any opinion on this ? nfsgame?
Also, i ve read the serivce manual which recommends tests using a variac. Ive been looking around to get one but can not really decide what level of current handling this variac would need to be able to do.
Acording to the brouchure I found online, the 120v version has:
1.6 amps drawn at idle
21.8 amp at one third power
37.5 max
so at 230volts this would be 18.7amp. As the serive manual mentions test conditions where the amp needs to be driven onto clipping I suppose i need a variac that handles all the 18.7 amps?
How important is the variac ? I d raher just go ahead with Sangram's suggestion with the resistors in the rail's to protect the output devices its seems more cost effective than investing in a variac. Would a low-wattage mean 5w for instance in this context ? 2w perhaps ?
Digi-Key selling fake parts? I would think your source of information to be fake instead.
Forget the variac, use the Dim bulb tester instead
Do the math on power dissipation for any resistor value you select, base it on the idle current. Once you establish the circuits are operating properly, these limiters are not needed anymore
Forget the variac, use the Dim bulb tester instead
Do the math on power dissipation for any resistor value you select, base it on the idle current. Once you establish the circuits are operating properly, these limiters are not needed anymore
I second that , I have bought fets directly from the USA and they aren't fakes , please show some evidence of this and please tell the US military as well as Congress .
I had fakes from China with proper die size ( 5x5mm) but fake nevertheless betas linearity very far from specs
Definitely source of info here is the issue. None of the official authorized distributors will ever risk to sell anything of unknown origin. And for the last 20 years I never had any issues with parts from them, unlike ebay or aliexpreess sourced parts. So this
is just outright lies.
after at least two congressional hearings in the past about chinese fakes in military equipment I think he is quite seriousNot sure are you serious or not.😉
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