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Old 21st Sep 2018, 9:25 am   #1
vampyretim
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Default BUP40 transistor replacement for Quad II

Hi,

I'm repairing a modern quad II. The Kt66's on one channel have failed and drawn a current that has fried a lot of components in the power supply and the output stage. It has also taken out the solid state phono preamp which has a BUP40 transistor across it's supply voltage. I can't seem to find a replacement BUP40 anywhere! Does anyone have one? Or can someone point me in the right direction?

I've successfully repaired the valve side of things, all output valves have been replaced with matched pairs and I have repaired the rest of the damage. The rest of the amp sounds great. It would seem ironic that it's the modern circuit that I'm having difficulty finding parts for.

Any help much appreciated.

Many thanks,
Tim.
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Old 21st Sep 2018, 10:21 am   #2
Craig Sawyers
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Default Re: BUP40 transistor replacement for Quad II

Try contacting Quad service, which is still in Huntingdon.

Craig
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Old 21st Sep 2018, 10:38 am   #3
Herald1360
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Default Re: BUP40 transistor replacement for Quad II

It looks like a PNP power transistor.

Probably not too difficult to sub.

https://alltransistors.com/transisto...ansistor=30043

Beware- apparent datasheet is for BUP400, an IGBT!
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Last edited by Herald1360; 21st Sep 2018 at 10:50 am. Reason: Corrections
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Old 22nd Sep 2018, 6:45 pm   #4
Chris55000
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Default Re: BUP40 transistor replacement for Quad II

Hi!

https://pdf1.alldatasheet.com/datash...ISC/BUP40.html

It's not easy to substitute because of the relatively high hFE and wide hFE range quoted, but see how you get on with the readily available BD140-16 first!

Chris Williams
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Old 26th Sep 2018, 9:42 am   #5
vampyretim
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Default Re: BUP40 transistor replacement for Quad II

Thanks Chris.
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Old 29th Sep 2018, 11:37 am   #6
SteveCG
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Default Re: BUP40 transistor replacement for Quad II

vampypetim - a quick thought. I thought modern Quad IIs used KT88 valves and not the KT66s (you mention in your opening post)used in the original 1950s design. Perhaps I'm wrong on this!

Last edited by SteveCG; 29th Sep 2018 at 11:38 am. Reason: Added info
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Old 29th Sep 2018, 6:58 pm   #7
JohnM73
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Default Re: BUP40 transistor replacement for Quad II

The current Quad II classic monoblock reproductions still use the KT66 (would love to see how the interior construction compares to the originals), as does the Quad II Classic Integrated. It's the Quad II Forty, Quad II Eighty which use the KT88s:


http://www.quad-hifi.co.uk/product.php?cid=7

Cheers,

John
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Old 2nd Oct 2018, 1:05 pm   #8
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Default Re: BUP40 transistor replacement for Quad II

Thanks, JohnM73, for the clarification.
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Old 2nd Oct 2018, 3:45 pm   #9
GrimJosef
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Default Re: BUP40 transistor replacement for Quad II

Quote:
Originally Posted by JohnM73 View Post
The current Quad II classic monoblock reproductions still use the KT66 (would love to see how the interior construction compares to the originals) ...
Google is your friend - they look like this

https://i.pinimg.com/originals/79/09...dcfe452973.jpg

The connectors have all changed and the wiring is up to modern standards. The circuit is similar but a few details have changed. The KT66 cathode bypass capacitor is now 47uF (was 25uF), the HT reservoir and smoothing capacitors are now larger - 32uF or 47uF I think (were 16uF) and there seems to be a bleed resistor on them which wasn't there originally. The metal-cased coupling capacitors between the EF86s and the KT66s have been replaced by plastic-bodied ones and it's nice to see that the stray capacitance to ground that the original metal case provided has now been replaced by small disc ceramics . There may be additional components around the rectifier - is that a thermistor designed to slow the heater warm-up (some modern KT66s seem to take a long time to warm up) and perhaps there's an inline fuse in the HT output from the rectifier ? Of course it's impossible to tell how the details of the modern transformers compare with the original ones.

Cheers,

GJ
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