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Old 24th July 2014, 10:34 AM   #11
Mooly is offline Mooly  United Kingdom
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OK For what its worth, I think its worth a go.
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Old 24th July 2014, 10:59 AM   #12
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Looking at the transistors on this and I think I would go for TIP41C and TIP42C for the outputs and probably MJE340 and MJE350 for the drivers.

Look at the TIP 41C attached. You need to be able to mount that on the heatsink. It would need the appropriate insulating kit too (mica/silicon washer and bush).

Also, don't be tempted to buy transistors off ebay, too many fakes and suspect devices around.
Attached Files
File Type: pdf TIP41C.pdf (42.9 KB, 6 views)
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Old 24th July 2014, 11:05 AM   #13
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It will not work

VAs has not enough current to drive MJe 340 or even BD 139 or 140
Bias will be altered like hell and will not work unless modified
Cob is different compensation also needs to be altered
Plus that TIP series is waaaaaaaaay slower than the originals resulting a degrade in the total quality of the amplifier ...
Load resistors for both drivers and outputs will need to be replaced and the all thing will end up to a mess

I can suggest an already tested set of semis if you like that is more "drop in "
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Old 24th July 2014, 11:08 AM   #14
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By all means
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Old 24th July 2014, 11:28 AM   #15
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1) outputs can be C4467 A1694 one drill per transistor and one insulator and its done the physical size of the trs and the pcb pads will fit with no probs The specific transistors have been outsiders which means that are real performers from sanken and seems that these can easily be found dirt cheap and original

2) drivers should be 2Sb560 2SD438 small and very easy to drive also possible to obtain also given as replacements in some other Kenwood similar models ( by Kenwood)

3) Bias will be fine like that and if not altering Re 27 will bring bias in a reasonable adjustable level

4) in some models i have seen some oscillation with this modification and cured it increasing miller cap on the VAS Ce 11 from 22pf to 33

Been trying with Mje150xx series for outputs as these seem to be almost capable to handle the current but it was impossible to drive them the circuit goes to oscillation
Been trying to place 1943 5200 impossible to drive then went to BD 139-140 for drive then impossible to be driven from VAs + oscillation while in all cases bias went to hell

Circuit is too thin and delicate and needs transistors that are easily driven

Kind regards
Sakis
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Old 24th July 2014, 11:37 AM   #16
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Thanks Sakis, its always good to know what devices have successfully been used in the past.

The BD's are marginal on voltage, otherwise they would actually have been my first choice I wondered about the old 2N5551/5401 too although even those are becoming harder to find.

Thanks
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Old 24th July 2014, 11:47 AM   #17
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5401 5551 ? No in Greece we have loads of can find them in any shop

Also i think these are way too small for drivers
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Old 24th July 2014, 01:36 PM   #18
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Quote:
Originally Posted by east electronics View Post
5401 5551 ? No in Greece we have loads of can find them in any shop

Also i think these are way too small for drivers
Hmmm... an old Towers book gives these as 325mw dissipation in free space, the Fairchild data sheet quotes 625mw. Sounds about right Very little different to the 2SD438

It is a problem sometimes knowing what to recommend for these older designs...

I'd still think modern production TIP41C/42C's for outputs would be OK for this and available anywhere. I'm looking back at its little brother in the link I posted earlier, the KA1500.
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Old 24th July 2014, 11:01 PM   #19
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well, i spoke to my local electronics shop today. the only transistors still available are the ones for Qe9 and Qe11, being a 2SA733. i was told there are not even substitutes available for the others.
i hate to think i have to scrap the amp due to my mblooper.
any suggestions guys?
thanks so much,
aidan
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Old 24th July 2014, 11:10 PM   #20
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whoa, go slow guys!
so, originals were
Qe9 2SA733
Qe11 2SC945 (not available)
Qe13 2SC945 (not available)
Qe15 2SA733
Qe17 2SC1735 (not available)
Qe19 2SA850 (not available)
Qe21 2SD588 (not available)
Qe23 2SB618 (not available)

so, where do i spend my hard(ly) earned monies?
do i buy the available 2SA733's, and sub the others, or do i need a whole new line up?
also, should i do both channels?
you guys are great!
aidan

Last edited by Lower Tones; 24th July 2014 at 11:28 PM.
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