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cyrus 1 output transistor question. push-pull?
cyrus 1 output transistor question. push-pull?
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Old 9th December 2017, 08:10 PM   #21
randombeliefs is offline randombeliefs  United Kingdom
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Originally Posted by ohdsp View Post
I believe the Cyrus PT7 (Cyrus One and early Two) is the BUV28 and the PT77 (later Cyrus Two) are BUV48.

If the BUV48 fits your version it will work; even if the device is bigger than the original.
that's brilliant thanks so much
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Old 9th December 2017, 08:13 PM   #22
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Originally Posted by randombeliefs View Post
would BUV48A work ? can't seem to find 13009.
In a word, no. It is a switching transistor for smps use.
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Old 9th December 2017, 08:15 PM   #23
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Originally Posted by JonSnell Electronic View Post
In a word, no. It is a switching transistor for smps use.
The original PT7/PT77 parts are (supposed) to be switching transistors, as weird as it may be.
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Old 9th December 2017, 08:26 PM   #24
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Originally Posted by ohdsp View Post
The original PT7/PT77 parts are (supposed) to be switching transistors, as weird as it may be.
If it were class D they would be perfect but it's not.
The Hfe is too low to be of any use, as all power switching transistors are and I doubt they would fit 1000Volt transistors for a little amplifier like this.
Any of the many power transistors that use a TO3p body should do if the Hfe is over 50. 2SC5200 comes instantly to mind. Cheap and reliable.
Check the drivers.
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Old 9th December 2017, 08:29 PM   #25
randombeliefs is offline randombeliefs  United Kingdom
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Originally Posted by JonSnell Electronic View Post
If it were class D they would be perfect but it's not.
The Hfe is too low to be of any use, as all power switching transistors are and I doubt they would fit 1000Volt transistors for a little amplifier like this.
Any of the many power transistors that use a TO3p body should do if the Hfe is over 50. 2SC5200 comes instantly to mind. Cheap and reliable.
Check the drivers.
I also had a look at these

http://cpc.farnell.com/on-semiconduc...264/dp/SC06820

any idea where the driver transistors are on the board ?
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Old 9th December 2017, 08:32 PM   #26
randombeliefs is offline randombeliefs  United Kingdom
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Originally Posted by ohdsp View Post
The original PT7/PT77 parts are (supposed) to be switching transistors, as weird as it may be.
I also had a look at these

http://cpc.farnell.com/on-semiconduc...264/dp/SC06820

any idea where the driver transistors are on the board ?

so , although cyrus pt7 were switching transistors , i don't need to use switching transistors?
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Old 9th December 2017, 08:33 PM   #27
ohdsp is offline ohdsp
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Quote:
Originally Posted by JonSnell Electronic View Post
If it were class D they would be perfect but it's not.
The Hfe is too low to be of any use, as all power switching transistors are and I doubt they would fit 1000Volt transistors for a little amplifier like this.
Any of the many power transistors that use a TO3p body should do if the Hfe is over 50. 2SC5200 comes instantly to mind. Cheap and reliable.
Check the drivers.
If you search the internet you will see the the PT7 is BUV28, a switching device, and the PT77 is the BUV48/BUV48A, also a switching device.

Yes the Hfe is low, but that would probably explain why the original Zetex drive transistors, which have pretty low ratings, are prone to failure.

I have Cyrus One's running better spec'd switching devices, with no issues. Driving 4 ohm loads such as B&W CM10's and Dynaudio Emit M20's; they sound incredible for such a "low power" amplifier. And nothing has gone bang.
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Last edited by ohdsp; 9th December 2017 at 08:44 PM.
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Old 9th December 2017, 08:44 PM   #28
randombeliefs is offline randombeliefs  United Kingdom
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Originally Posted by ohdsp View Post
If you search the internet you will see the the PT7 is BUV28, a switching device, and the PT77 is the BUV48/BUV48A, also a switching device.

Yes the Hfe is low, but that would probably explain why the original Zetex drive transistors, which have pretty low ratings, are prone to failure.

I have Cyrus One's running better spec'd switching devices, with no issues. Driving 4 ohm loads such as B&W CM10's and Dynaudio Emit M20's; they sound incredible for such a "low power" amplifier. And nothing has gone bang.
I have Cyrus One's running better spec'd switching devices, with no issues. Driving 4 ohm loads such as B&W CM10's and Dynaudio Emir M20's; they sound incredible for such a "low power" amplifier. And nothing has gone bang.

what "better spec'd switching device did you choose ?
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Old 9th December 2017, 08:51 PM   #29
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As in the previous post, the STW13009 (TO-247) in one, and FJP13009 (TO-220) in an earlier model.

The drive transistors I used are the MJE243 and MJE253 as specified by Cyrus in the later versions. Fitting these in an earlier model designed for Zetex parts requires some creative lead bending!
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Old 9th December 2017, 08:53 PM   #30
randombeliefs is offline randombeliefs  United Kingdom
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Originally Posted by ohdsp View Post
As in the previous post, the STW13009 (TO-247) in one, and FJP13009 (TO-220) in an earlier model.

The drive transistors I used are the MJE243 and MJE253 as specified by Cyrus in the later versions. Fitting these in an earlier model designed for Zetex parts requires some creative lead bending!
thanks very much !
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