Hi all i have managed to locate a schematic for my stageline sta 750 from this forum & thanks,
but iam unable to locate some of the transistors from my usual suppliers
so was hoping that some kind person out there
could help with some substitutes
they are
2sd667
2sb647
2sc1815
2sa1837
2sc4793
2sd669a
all assistance is greatly appreciated
also can someone suggest a good semiconductor equivalent book available in the uk.
regards Bobcat
but iam unable to locate some of the transistors from my usual suppliers
so was hoping that some kind person out there
could help with some substitutes
they are
2sd667
2sb647
2sc1815
2sa1837
2sc4793
2sd669a
all assistance is greatly appreciated
also can someone suggest a good semiconductor equivalent book available in the uk.
regards Bobcat
Well this is good for most data sheets,
Datasheet catalog for integrated circuits, diodes, triacs, and other semiconductors, view
As to books... T.D. Towers was the one to have.
Amazon.co.uk: towers transistor selector
don't know the last edition though and the web has kind of made all these obsolete.
2sd667/2sb647 are complementary pair... can't think of anything common in that package as equivalents, you will have to search the catalogues. MJE340/350 are a common choice TO126 package but only 0.5 amp rating... is it enough for your application ?
2SC1815 is general purpose... they are in everything and should be easily available, BC546 is fine, as is 2N5551 etc, but the pinouts are different. Anything will work for these as long as it's rated similarly.
2SA1837/2SC4793 are another complementary pair... high voltage TO220 package. Can't think of anything similar off hand.
2SD669... again is 0.5 amp enough... MJE 340 again.
I'll have a think 🙂
Datasheet catalog for integrated circuits, diodes, triacs, and other semiconductors, view
As to books... T.D. Towers was the one to have.
Amazon.co.uk: towers transistor selector
don't know the last edition though and the web has kind of made all these obsolete.
2sd667/2sb647 are complementary pair... can't think of anything common in that package as equivalents, you will have to search the catalogues. MJE340/350 are a common choice TO126 package but only 0.5 amp rating... is it enough for your application ?
2SC1815 is general purpose... they are in everything and should be easily available, BC546 is fine, as is 2N5551 etc, but the pinouts are different. Anything will work for these as long as it's rated similarly.
2SA1837/2SC4793 are another complementary pair... high voltage TO220 package. Can't think of anything similar off hand.
2SD669... again is 0.5 amp enough... MJE 340 again.
I'll have a think 🙂
2sd669ac is a 1.5A device with hFE>100 @ Ic=150mA and 20W <=40Vce
You will struggle to source an equivalent. Which parameters are absolutely necessary and which can be relaxed?
You will struggle to source an equivalent. Which parameters are absolutely necessary and which can be relaxed?
The 2SD667/2SB647 are used in supply voltage regulator circuits in the Harman-Kardon HK1400 (and possibly HK1200 HiFi Amplifiers, where they are used to provide stabilised +20.5 &-20.5 v. rails for the preamplifier circuits. A quite conventional Transistor assisted zener circuit is used for this purpose, which is supplied with + & -40v from bridge rectifier D20. I need to source a 2SD667 (& possibly 2SB647) or eqivalents for this circuit, and would guess that transistors rated at 30-40v(Vce) and ca 0.5A Max would be more than adequate. If they were in TO-92MOD packages fitting them would be easier, though an alternative package type could be used. Does anyone have any suggestions as to either a source from which to buy the original types, or suitable alternative types. I have a load of transistors of various types, mainly European BCxxx devices, so maybe I can find suitable ones in my parts 'stock'. Is it advisable to replace both transistors with a closely matched pair? The 2SB647 checks out OK, but the 2SD667 is seriously leaky between all 3 terminals, though I've no idea what caused it to fail.
I'm assuming no heatsinks are used. If so then BD139/140 should be suitable. Pretty much anything will be OK for duty such as this as long as its rated accordingly. Even TIP41/42 as long as there is room and all these will have much increased reliability being larger and able to dissipate the heat better.
I wouldn't give it a second thought, just replace them. No matching or anything like that is required.
I wouldn't give it a second thought, just replace them. No matching or anything like that is required.
I did think of using something like TIP31/32, Mooly, although the originals are TO-92MOD rather than TIP case style. Earlier today I fitted a MPSA42 to replace the failed 2SD667, with a temporary 33 ohm resistor in series with the collector, pending getting some 22ohm fusible types. I was getting 36v at the collector of the replacement transistor, but 0v at both the base and emitter. The associated zener diode checks out OK, but I haven't yet checked other peripheral components.
The obsolete Hitachi types (2SD667,9 etc.) are all presently common Ebay copy types and I think it would be best to begin there, oddly enough. I've had good results over several 100 ea. lots so far with those copies.
2SC1815 could be any low noise, small signal NPN. KSC1845 is an improved high voltage type or perhaps BC550 or any of its many similar low noise BC types will replace it, allowing for the different pinouts of euro BC types and checking Vceo rating is adequate. The Toshiba drivers you can get as Unisonic copies from Profusion PLC. You won't find all those types or close substitutes in one big traditional suppliers catalogue though.
2SC1815 could be any low noise, small signal NPN. KSC1845 is an improved high voltage type or perhaps BC550 or any of its many similar low noise BC types will replace it, allowing for the different pinouts of euro BC types and checking Vceo rating is adequate. The Toshiba drivers you can get as Unisonic copies from Profusion PLC. You won't find all those types or close substitutes in one big traditional suppliers catalogue though.
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Most of your reply, Ian, relates to the original post, rather than to my comments/questions concerning the HK1400, in whick, AFAIK at this stage, all the preamplifier devices downstream of the voltage regulator circuits are OK, but I may look on eBay to see if clones of the2SD667 & 2SB647 are avaliable, although I can see no reason why an MPSA42 could not be used as the series pass transistor in this case.
It would help to see the circuit but having zero volts on the base suggests a basic problem somewhere. 36V on the collector suggests no current is being drawn from the supply. So where has the base voltage gone ?
The circuits of both the positive and negative voltage regulators are standard series pass transistor assisted zener types, Mooly. I have the diagrams, which came from HiFi Engine, so I'm not sure that I should scan them & post them on here.
Just do a clear image of the relevant part of the circuit (use Windows sniping tool or equivalent 🙂) and post that. No need to scan anything.
I haven't carried out any further checks since my previous post, Mooly, but if R557 were o/c or high resistance, or C528 was leaky, this could cause the fault. I visually ckecked that I'd wired in the MPSA42 correctly earlier this afternoon, since it's pinouts differ from those of the 2SD667, but no wiring error there. I have in the meantime ordered a pair of the original type transistors from eBay, so may fit the new '667 when I receive it, and after checking for other faults
R557 if open would give your symptom as would the cap being short or very leaky (unlikely to be the cap).
Is the -20 volt rail OK ?
If you remove the transistor you should have 20 volts across the zener. The negative rail supply is a mirror image of the positive although the two are totally separate in operation with no interaction between the two possible.
Is the -20 volt rail OK ?
If you remove the transistor you should have 20 volts across the zener. The negative rail supply is a mirror image of the positive although the two are totally separate in operation with no interaction between the two possible.
The -20v rail is OK as of when I was last working on the amplifier. It may well be Monday or Tuesday before I can get back to it, when I will check R557 and the printed circiut tracks to which it connects.
Many genuine obsolete parts are still available from B+D Enterprises: B+D Enterprises - Home page Unfortunately, sometimes prices are high. Chinese copies are much cheaper and usually work well.
cheers,
cheers,
The 2SD667/2SB647 pair I ordered from an eBay seller should arrive during the coming week, so perhaps I'll at any rate replace the MPSA42 with a '667, although, as I must have hundreds of transistors of various types, including several new MPSA42s bought from CPC a few years back, I was hoping to use a device from my parts stock, rather than getting something in specifically for this job. After all that series pass circuit is nothing out of the ordinary, and, although I havn't measured the current consumption of the negative half of the associated preamp. circuits, I wouldn't have expected either half to draw more than maybe 50mA at most. I could be wrong, though, bearing in mind that the pass transistors are rated at 1A max.
For small, 10-300mA supplies or cap multipliers, I've been using BC327/337 or BC328/338 for longer than I can remember. The dissipation limits are about the same for any TO92 package but it's the ability to withstand short term abuse that can make these higher max. current rated types a good idea.
On a larger scale, the 2SD667/B647 are likely the same chip as the the bigger 2SD669/B649, perhaps in the same way as BC639/640 are to BD139/140. There is some extra latitude in those types, when loads are variable and the gear perhaps subject to abuse, like a lot of DIY projects.
On a larger scale, the 2SD667/B647 are likely the same chip as the the bigger 2SD669/B649, perhaps in the same way as BC639/640 are to BD139/140. There is some extra latitude in those types, when loads are variable and the gear perhaps subject to abuse, like a lot of DIY projects.
This afternoon, I checked the components around Q519 only to find that the zener diode D503 was s/c. I don't have a 22v zener to hand, so the job is once more put on hold whilst I source bothe the diode and a 22 ohm fusible resistor. Who would have thought that such a simple circuit could cause so many problems??
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