Cyrus 2 Amplifier - 2SC1775A + 2SA872A Equivalent/Replacements? - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 12th February 2010, 01:12 AM   #1
diyAudio Member
 
bleachershane's Avatar
 
Join Date: Jun 2008
Location: Glasgow, Scotland
Default 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/data...or/mXuquxx.pdf and here http://www.datasheetcatalog.org/data...r/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
  Reply With Quote
Old 12th February 2010, 08:43 AM   #2
wahab is offline wahab  Algeria
diyAudio Member
 
Join Date: Nov 2009
Location: algeria/france
Quote:
Originally Posted by bleachershane View Post
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/data...or/mXuquxx.pdf and here http://www.datasheetcatalog.org/data...r/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...
  Reply With Quote
Old 12th February 2010, 09:25 AM   #3
diyAudio Member
 
sumaudioguy's Avatar
 
Join Date: Jan 2010
Location: Midwest U.S.A.
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.
  Reply With Quote
Old 12th February 2010, 09:45 AM   #4
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
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.
  Reply With Quote
Old 12th February 2010, 09:49 AM   #5
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
Quote:
Originally Posted by sumaudioguy View Post
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.
  Reply With Quote
Old 12th February 2010, 09:56 AM   #6
diyAudio Member
 
sumaudioguy's Avatar
 
Join Date: Jan 2010
Location: Midwest U.S.A.
Quote:
Originally Posted by jaycee View Post
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
  Reply With Quote
Old 12th February 2010, 10:36 AM   #7
diyAudio Member
 
bleachershane's Avatar
 
Join Date: Jun 2008
Location: Glasgow, Scotland
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/buv4...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?
  Reply With Quote
Old 12th February 2010, 12:49 PM   #8
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
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.
  Reply With Quote
Old 12th February 2010, 07:07 PM   #9
diyAudio Member
 
bleachershane's Avatar
 
Join Date: Jun 2008
Location: Glasgow, Scotland
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?
  Reply With Quote
Old 12th February 2010, 07:33 PM   #10
diyAudio Member
 
sumaudioguy's Avatar
 
Join Date: Jan 2010
Location: Midwest U.S.A.
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.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Cyrus III intergrated amplifier Ashraf Solid State 5 1st December 2009 07:45 PM
Cyrus 3 Amplifier Component Mistakes? hexagonsun Solid State 10 1st December 2009 07:34 PM
KTC-3200GR or 2SC1775A-EF needed jeffshort2000 Swap Meet 1 24th February 2009 07:01 PM
WTB Cyrus 1 or Cyrus 2 amplifier monstertrucker Swap Meet 0 20th November 2008 01:04 AM
Cyrus 1 amplifier problem elaar Solid State 2 28th September 2006 10:56 PM


New To Site? Need Help?

All times are GMT. The time now is 12:45 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2