Cyrus 2 Amplifier - 2SC1775A + 2SA872A Equivalent/Replacements?

Beginning work on a Cyrus 2 amplifier and Cyrus PSX power supply I recently acquired.

I have so far found that two of the power transistors on one channel are blown. They were 2x TIP3055. As far as I know these were NOT original parts and at some point must've been put in by someone... The original output transistors were marked in-house by Cyrus as PT77 (this is definitely not a standard transistor number and I must stress for anyone else reading this that the numbers on the bottom of these transistors are most definitely manufacturing date markings! Please stop wasting your time sticking '2SB', '2SA' and '2SC' in front of whatever numbers are on yours!) Through this forum I have found that TIP35C is a good replacement for them as is the MJE340/MJE350 for the driver stage transistors.

Without checking any further transistors or components yet I am also considering replacing the pre-driver transistors. These are proving tricky as they don't seem to exist anymore! They are 2SC1775A (NPN) and 2SA872A (PNP) and the datasheets are available here http://www.datasheetcatalog.org/datasheet/HitachiSemiconductor/mXuquxx.pdf and here http://www.datasheetcatalog.org/datasheet/HitachiSemiconductor/mXyzyuuu.pdf

If anyone can point me in the direction of a correctly specced replacement TO-92 packaged transistor I would be very very grateful! If it's available through Farnell I'll be even more happy (but don't let that last criteria stop you giving your input!)

Thanks ;)
 
Beginning work on a Cyrus 2 amplifier and Cyrus PSX power supply I recently acquired.

I have so far found that two of the power transistors on one channel are blown. They were 2x TIP3055. As far as I know these were NOT original parts and at some point must've been put in by someone... The original output transistors were marked in-house by Cyrus as PT77 (this is definitely not a standard transistor number and I must stress for anyone else reading this that the numbers on the bottom of these transistors are most definitely manufacturing date markings! Please stop wasting your time sticking '2SB', '2SA' and '2SC' in front of whatever numbers are on yours!) Through this forum I have found that TIP35C is a good replacement for them as is the MJE340/MJE350 for the driver stage transistors.

Without checking any further transistors or components yet I am also considering replacing the pre-driver transistors. These are proving tricky as they don't seem to exist anymore! They are 2SC1775A (NPN) and 2SA872A (PNP) and the datasheets are available here http://www.datasheetcatalog.org/datasheet/HitachiSemiconductor/mXuquxx.pdf and here http://www.datasheetcatalog.org/datasheet/HitachiSemiconductor/mXyzyuuu.pdf

If anyone can point me in the direction of a correctly specced replacement TO-92 packaged transistor I would be very very grateful! If it's available through Farnell I'll be even more happy (but don't let that last criteria stop you giving your input!)

Thanks ;)

MJE340/MJE350 are not usable as drivers, their max current
is way too low...linearity will be dreadfull..
TIP are also poor devices..
that said, 2SA872A/2SC1775A are not easily replaceable, as they
are of exceptionnal quality, just check the datasheet..
i just wonder why hitachi did stop their production...
you can use 2SA970/2SC2240 which are slightly less good,
or 2SA992/2SC1845...
anyway, if you stick with the other devices, no need of these
high perfs transistors, crappy mpsa/mpsl can be used, but
they lag far behind...
 
I never get to excited over Hatachi transistors. Cyrus is a great amp. I know the guys that designed it personally but I digress. MJL1302A and MJL3281A will make fine outputs. KSA1220A and KSC2609A would make fine drivers if they fit. Probably would work fine for the predriver also. Does the amp really have 3 current gain stages? No matter. If you do not like that one we have been using 2SA1284 and 2SC3244 for super TO-92 package devices. Those should still be around but maybe not. That amp original transistors were TI and as anyone who knows is kind of a second rate transistor company but at the time of the amp some liked TI better than anything else. Sankens like the 2SA958 and 2SC2168 came along just a little later and are grossly better than anything TI ever had or has even today. These part numbers have been replaced by Sanken with later numbers but do not have the new numbers right at hand.
 
The Cyrus PT77's are really in house marked ST BUV48A transistors.
The original drivers were MJE243/253 which are quite easy to source.

For predriver use, Sanyo's 2SA1208/2SC2910 would work very well indeed.

All of these parts are available from Farnell.
 
I never get to excited over Hatachi transistors. Cyrus is a great amp. I know the guys that designed it personally but I digress. MJL1302A and MJL3281A will make fine outputs. KSA1220A and KSC2609A would make fine drivers if they fit. Probably would work fine for the predriver also. Does the amp really have 3 current gain stages? No matter. If you do not like that one we have been using 2SA1284 and 2SC3244 for super TO-92 package devices. Those should still be around but maybe not. That amp original transistors were TI and as anyone who knows is kind of a second rate transistor company but at the time of the amp some liked TI better than anything else. Sankens like the 2SA958 and 2SC2168 came along just a little later and are grossly better than anything TI ever had or has even today. These part numbers have been replaced by Sanken with later numbers but do not have the new numbers right at hand.

Having heard and simmed this circuit it is an excellent circuit. The triple output stage leads to extremely low THD. The big problem with this circuit is it is very difficult to stabilise, primarily because of the CFP input stage.

I did simulate a copy of this circuit using all Fairchild devices (KSA992/KSC1845, KSA1381/KSC3503 and others) and it performed extremely well - was just tricky to stabilise.
 
The Cyrus PT77's are really in house marked ST BUV48A transistors.
The original drivers were MJE243/253 which are quite easy to source.

For predriver use, Sanyo's 2SA1208/2SC2910 would work very well indeed.

All of these parts are available from Farnell.

He seems to have the right original stuff and a good TO-92 sub. Faster is better for this amp so you may want to consider those Fairchild parts for the driver and outputs available from Mouser.com
 
Wow, thanks for all the input so far, much appreciated!

I'd very much like to hear this amp as intended, I've heard so many good things about it I want to see if it'll outperform my current setup of a Rotel RC-850 Pre-amp (so modded it's barely Rotel anymore...!) and RB-870BX power amp.

So:
PT77 = ST BUV48A (still available at Farnell http://uk.farnell.com/multicomp/buv48a/transistor-npn-to-247/dp/9294139)

MJE243/MJE253 still available (ON SEMICONDUCTOR|MJE243G.|RF Bipolar Transistor | Farnell United Kingdom and ON SEMICONDUCTOR|MJE253G|TRANSISTOR, DUAL, PNP, TO-225 | Farnell United Kingdom)

The original pre-drivers (which are also used in many other positions on the board) are no longer available and suitable replacements 2SA1208/2SC2910 should be fine. 2SA1208 is no longer available from Farnell apparently but the 2SC2910 is still available. When I have some more time late I'll have a look to see if I can find a current supplier of the 2SA1208...

So my new question is... The power and driver transistors, is it worth sticking with the original parts or going with newer parts as suggested by Jaycee etc?

When you said it was hard to stabilise, what problems were you finding and as a relative newbie to these things should I just go the original part route to get the unit working?
 
Profusion stock the Sanyo transistors - I don't know if they sell in small quantities though. The 2SA1209/2SC2911 would also work, these are in a larger TO-126 package though so you would need to check there is room for them to fit. I think the pinout is the same.

The stability problems were with a re-design using all different parts and different compensation, so not really relevant to a repair job.
 
Ahhh so I needn't start panicking about stability issues with my current task!

Profusion do indeed state they stock the 2SA1208 but when you add them to your basket they then tell you they're out of stock! Even if they had them in stock you'd have to buy 50 which is a bit overkill for my needs. Seems like they're becoming a hard part to find but nevertheless there is always eBay for the the 2SA1208... 10 pcs PNP Epitaxial Planar Transistor 2SA1208 A1208 on eBay (end time 11-Mar-10 04:47:00 GMT)
Farnell for the 2SC2910, the MJE243 and MJE253 and eBay once again for the BUV48A at a good price (perhaps too good...?) BUV48A on eBay (end time 17-Feb-10 03:21:07 GMT)

Anyway, so far the outputs, drivers and quiescent transistors are the necessities for now. Going to go for the whole lot of them, even if it was only one channel that went out, just for the sake of not having completely new transistors on one channel and circa 20 year old ones on the other! (Does that make sense?) Here's hoping that all the pre-drivers are intact and undamaged and they can therefore stay as they are. If not I now know what and where my options lie! Can't wait to bring this amp back to life and get a listen!!!

Few more questions... Is Panasonic FM a good contender for a board recap bar the biggest 10000uF reservoir caps?
 
Almost always faster and/or more linear transistor benefit the designs. Sometimes higher gain helps and sometimes lower gain helps depending on the particular design quirks. For emitter follower stages faster has always been a benefit in stability and phase margin.

Simply put, there are better device choices today than in 1979.

Around here and with my circuits the Pansonic FM are "fantastic magic." The 100kHz bandwidth is much better than the caps from 1979 with their 4kHz bandwidth.
 
Thanks for the replacement suggestions! :cool:

We have one channel working (the right channel), getting it to work didn't start too smoothly :(

Doing a few voltage checks at various points the service manual suggested showed most supplies were as they were meant to be. The plus voltage across the Phono/RIAA opamps was a tad off, meant to be +18, was nearer +16... but hell, that's didn't seem too off target... The minus was pretty close to -18. These supplies came from LM317/LM337 respectively.

The quiescent voltage measured on the working channel as the service manual described was/is pretty off at 2mV. The service manual states it should be between 8mV-20mV. The DC offset was well within the stated tolerances. We decided to go ahead and plug in one of our test speakers (the ones you don't mind blowing to smithereens with dodgy amplifiers!)

In they went and the amp went on... BUZZ BUZZ BUZZ... :eek:
Well something wasn't right. The sound coming from the speaker sounded like a rough square wave, intermittently blasting through. Turned the amp off, tried some different speaker cable, same thing. Fuses all remained intact during this.

But then the heat coming off the LM317/LM337 was drawn to my techie mates attention when the heatsink near burnt his arm! :eek: Not good! Alot of the Elna CE-BP capacitors amongst a few others looked ready to pop their lids off in the phono stage circuit... :( Decided to remove power to the phono/RIAA circuit by taking out the two regulators.

Once that was done, the speakers went in again and voila, no LOUD noises! :D Decided to plug in a source and give it a whirl. Big Star "O My Soul" (it's mono!) got first shot. Perfect sound, in fact, even through a knackered pair of JPWs I was quite pretty impressed by the sound! :D

So, having got this far I'm not sure where to go next.
Probably a complete recap first off?
Then to tackle the dodgy phono circuit supplies and see if that cures the buzzing when there is power to that part of the circuit?
THEN comes the tests to see if the known working parts on the right channel work in the previously blown left channel?
If they do all well and good, I'll go ahead and get brand new power and driver transistors :)
If no, well, who wants to buy a mono Cyrus 2 from me? ;);)

We're assuming that the noises heard at first turn on were spikes from the power circuit to the phono circuit dirtying the supplies? Taking out the regulators instantly cured the symptom and like I said, some of the capacitors do look pretty aged to say the least! I have also read in these forums that the capacitors used in the phono circuit had a tendency to be unreliable.

So... a tricky one but hopefully worthwhile to spend some time with?
 
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I think you might be bang on, certainly sounded like intermittant oscillation!

Some success so far, one channel working, one channel faulty and no phono stage, and not even tried the PSX as yet lol Well, one thing at a time eh!
Glad it's got this far anyway, now to find suitable capacitors and some new regulators when I get the chance! Was also considering a separate transformer for the phono stage. If I'm correct, the LM317/LM337s are having to drop approx 22V to get the +/-18V outputs. That seems like a pretty hefty drop, no wonder Cyrus stuck some crummy heatsinks on! They really should've got another secondary from the internal transformer at a lower voltage to power the regulator circuit!
 
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Good thinking jaycee... For the time being it can pretty much stay out of circuit while I get the rest up and running as it should lol
Even if I don't plan to use the phono stage the fault will still bug me until I get to the bottom of it! Shouldn't cost much for some new small value caps and a couple of regs, all so I can hopefully say "AHH, it was THAT!" lol
 
Is there any chance someone could confirm that this > http://www.toshiba.com/taec/components2/Datasheet_Sync//50/6461.pdf
is a suitable replacement for this > http://www.datasheetcatalog.org/datasheet/HitachiSemiconductor/mXwvryv.pdf

Once again for PNP, that this > http://www.datasheetcatalog.org/datasheet/toshiba/962.pdf is a suitable replacement for this > http://www.datasheetcatalog.org/datasheet/HitachiSemiconductor/mXyzyuuu.pdf

Transistor replacement is something I'm not overly clued up with. I've done my best to match up most of the original transistors specs with the possible available replacements. Capacitors, resistors, opamps, I'm fine with... When it comes to transistors there's too many bloody numbers and I'm not sure what I'm supposed to be looking for here lol

If anyone can help, thanks in advance!
 
Is there any chance someone could confirm that this > http://www.toshiba.com/taec/components2/Datasheet_Sync//50/6461.pdf
is a suitable replacement for this > http://www.datasheetcatalog.org/datasheet/HitachiSemiconductor/mXwvryv.pdf

Once again for PNP, that this > http://www.datasheetcatalog.org/datasheet/toshiba/962.pdf is a suitable replacement for this > http://www.datasheetcatalog.org/datasheet/HitachiSemiconductor/mXyzyuuu.pdf

Transistor replacement is something I'm not overly clued up with. I've done my best to match up most of the original transistors specs with the possible available replacements. Capacitors, resistors, opamps, I'm fine with... When it comes to transistors there's too many bloody numbers and I'm not sure what I'm supposed to be looking for here lol

If anyone can help, thanks in advance!


How about the original parts here: Audio and Video, Computer Parts, Batteries, Cable and Wiring at MCM Electronics

I do not think you need the A suffix for that amps. Good find on very linear transistors. Going to add them to my cool transistor list.