Glad it was a good find sum, and also glad that they're a suitable substitute!
I understand that they're a bit slower, seems those original transistors were pretty well specced as was stated in this thread before! But like you said I don't think it will be an issue.
Thanks for the suggestion of that website, who'd have thought anyone was still selling these! Shame it's an American site, just not worth having them imported to me in the UK though with the added costs...
I understand that they're a bit slower, seems those original transistors were pretty well specced as was stated in this thread before! But like you said I don't think it will be an issue.
Thanks for the suggestion of that website, who'd have thought anyone was still selling these! Shame it's an American site, just not worth having them imported to me in the UK though with the added costs...
You'll probably find that almost all low noise transistors in TO92 format have vanished over the last 10 years or so. In fact, that's true for most through-hole components that don't require separate heatsinks. KSA992/KSC1845 from Fairchild are drop-in replacements for 2SA992/2SC1845 and 2SA970/2SC2240. Buy them while they and Fairchild as an independent manufacturer themselves, are still in production.
These parts are splashed around on every serious low noise amplifier project here because there are few options that combine exemplary low noise with good Vceo that don't involve risky NOS parts, fakes, poor substitutes or high cost.
These parts are splashed around on every serious low noise amplifier project here because there are few options that combine exemplary low noise with good Vceo that don't involve risky NOS parts, fakes, poor substitutes or high cost.
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Still available from the UK supplier Cricklewood
CCTV Camera Systems and DVRs from Cricklewood Electronics
CCTV Camera Systems and DVRs from Cricklewood Electronics
thank you for the fast reply! i will try the metioned transistors. is it possible to use them in any possition of the cyrus2 issue7 where there were previously 2SC1775A or 2SA872A types?
best regards
paul
since i live in austria i'd prefer a distributor that is available here, but thank you anyway...
best regards
paul
Each application has its own demands but if the maximum current, voltage and dissipation ratings aren't less than the original parts, they should be fine as general replacements. The Hitachi/Renesas pair are rated for only 50mA Ic so I don't think there will be any problems, even though it seems unusual to use such low rated transistors in the voltage amplifier and for general purposes in any medium power amplifier.
I would not systematically replace semiconductors because they are old or no longer look pristine, though. Other than a few known problem parts, transistors don't deteriorate like electrolytic capacitors and there is no reason to replace them unless they have failed due to other faults. "If it ain't broke, don't fix it".
I would not systematically replace semiconductors because they are old or no longer look pristine, though. Other than a few known problem parts, transistors don't deteriorate like electrolytic capacitors and there is no reason to replace them unless they have failed due to other faults. "If it ain't broke, don't fix it".
Do you have the correct part numbers there? Q39/40 are actually PT7 power transistors in the output stage, bolted to the heatsink. There are 2 pairs of those in parallel in each channel and if any have failed, you need to check all 4 plus the drivers Q33/34 and Q37/38 plus pre-drivers Q27/28 and 29/30.
The bias, or Vbe multiplier transistors are actually Q25/26 and if these are what you mean, there is no need for special transistors as almost any NPN transistor will work fine in that low voltage role. BC549, 550 etc would be quite OK replacing 2SC1775, if not for their pin arrangement of C-B-E. A Japanese transistor pin arrangement of E-C-B would be simplest to fit and 2SC1815 copies are cheap and widely available if you have no other parts to choose from. In that role, there is no need to replace the same transistor in the working channel.
Please advise the actual part(s) that has failed, assuming you measured either a C-E short or no 0.7V Vbe etc.
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Cyrus 2 Manual - Stereo Integrated Amplifier - HiFi Engine
Thanks for the issue number, it certainly helps to know this.
The driver and pre-driver transistors listed are in the output stage with the output transistors, numbered as they appear in issue six which is more common. You are right that the Vbe multipliers are Q39 at least - which is all my schematic for issue 7 shows. In fact, the output stage is quite different in issue 7 - it has only 1 pair of output transistors and current limiters Q35 and Q37 have been added for protection.
You can ignore the first paragraph in post #29 but the same comments in paragraph 2 now apply to Q39/40, as you refer.
Therefore, in the case of bias controller Q39, you would also test Q19 and Q25 for shorted C-E and/or no B-E diode voltage (about 0.7V as suggested).
Thanks for the issue number, it certainly helps to know this.
The driver and pre-driver transistors listed are in the output stage with the output transistors, numbered as they appear in issue six which is more common. You are right that the Vbe multipliers are Q39 at least - which is all my schematic for issue 7 shows. In fact, the output stage is quite different in issue 7 - it has only 1 pair of output transistors and current limiters Q35 and Q37 have been added for protection.
You can ignore the first paragraph in post #29 but the same comments in paragraph 2 now apply to Q39/40, as you refer.
Where BJTs are direct coupled in a cascade such as emitter followers, cascoded or series connected, simple logic says the current to cause failure had to come from and go somewhere and if that is via other transistors, they need to be tested too but not necessarily replaced. The output stage has a lot of heavier current paths and a few failure modes which makes it impossible to predict what will fail each time the output is shorted etc. Often, other components fail too and you need to ensure you found them all, even if it appears to work after the obvious fault is repaired.
Therefore, in the case of bias controller Q39, you would also test Q19 and Q25 for shorted C-E and/or no B-E diode voltage (about 0.7V as suggested).
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so i mesured every transistor and came to the conclusion that its not the bias transistors. the problem were the driver transistors mje253 and 254 and the output transistors. i changed these for both channels and now everything works fine and the bias current is right.
i also recapped the whole thing (all bipolar transistors now nichicon muse bp and all polarized ones changed to panasonic fm). the difference in sound is amazing. some of the old caps already started falling apart.
only problem is, that now i have a very small humm on both channels and when the record player is playing you can here it very very silent even if the volume is totally down and also if i change the input selector to cd or tuner.
i'm not sure if it has been the same before, because its really very silent...
any hints, or should i start a new thread?
thank you very much for the support so far!!!!
best regards
paul
i also recapped the whole thing (all bipolar transistors now nichicon muse bp and all polarized ones changed to panasonic fm). the difference in sound is amazing. some of the old caps already started falling apart.
only problem is, that now i have a very small humm on both channels and when the record player is playing you can here it very very silent even if the volume is totally down and also if i change the input selector to cd or tuner.
i'm not sure if it has been the same before, because its really very silent...
any hints, or should i start a new thread?
thank you very much for the support so far!!!!
best regards
paul
I'd be very surprised if your Cyrus 2 had a wiring fault that is causing the hum.
Can you fit a pair of shorting RCA plugs to the (selected ON) input and measure the output Hum + Noise on the 199.9Vac scale of your DMM and also measure the output offset on the 199.9mVdc scale?
That's your first 4 measurements. There's more to follow.
Can you fit a pair of shorting RCA plugs to the (selected ON) input and measure the output Hum + Noise on the 199.9Vac scale of your DMM and also measure the output offset on the 199.9mVdc scale?
That's your first 4 measurements. There's more to follow.
Hi Paul,
I have some to spare.If you are interested please pm me.
2SA872A/2SC1775A
2SA970/2SC2240
kSA992/kSC1845
2SA1209/2SC2911 are available.
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I made a - for me - quite useful image. its basically an overlay of the copperlayer with the upper layer. with this its easier to locate the solder points when you want to recap from the downside...
maybe is it somebody else of use.... if somebody needs the original files just contact me....
best regards
p
Hello, I have an Cyrus two amp, issue 7 which i have been making some repair to.
I have changed both the PT77 to BUV48A, the MJE243/253 is changed to the same. And the 2SA872A/2SC1775A I have changed with the KSA1381/KSC3503.
I have trouble getting the alignment of the amp correct now. The channel plays, but with distortion. Could anyone here help me in the right direction?
I have changed both the PT77 to BUV48A, the MJE243/253 is changed to the same. And the 2SA872A/2SC1775A I have changed with the KSA1381/KSC3503.
I have trouble getting the alignment of the amp correct now. The channel plays, but with distortion. Could anyone here help me in the right direction?
Cyrus amps...
Thanks for making / posting this image (saved). I have already recapped / completely updated my Cyrus 1. I have often thought about (modifying it) making way to use (a homemade) PSX. This image will be helpful, in future efforts. In many ways this image surpasses the actual service manual, in its usefulness.
FWIW, I used all Nichicon Gold Tunes [the MUSE were too big...] and used all MUSE BP. ~and~ every cap now has a film bypass. This amp sounds amazing... (unfamiliar) people would 'argue that', but it has the sound of my more exotic gear... almost sounds like the best gear that I own, on the right (90+ db sensitivity) speakers.
It is among the best amps that I have experienced driving my Quad ESL57, I can almost say, "I like it better than tubes" as it handles the complex admittance curve of the 57s.
Thanks for making / posting this image (saved). I have already recapped / completely updated my Cyrus 1. I have often thought about (modifying it) making way to use (a homemade) PSX. This image will be helpful, in future efforts. In many ways this image surpasses the actual service manual, in its usefulness.
FWIW, I used all Nichicon Gold Tunes [the MUSE were too big...] and used all MUSE BP. ~and~ every cap now has a film bypass. This amp sounds amazing... (unfamiliar) people would 'argue that', but it has the sound of my more exotic gear... almost sounds like the best gear that I own, on the right (90+ db sensitivity) speakers.
It is among the best amps that I have experienced driving my Quad ESL57, I can almost say, "I like it better than tubes" as it handles the complex admittance curve of the 57s.