Wl. KtThank You Ylli ! Will do that in the morning ! Thanks for the comprehensive instructions, can you just clarify what IOW means and what across R47 means. I think Im getting there ! And I think everyone who shares this post will benefit from a great learning curve also ! Thanks to everyone so far who have added their twopenneth worth ! Best Regards Paul
Well it was all going very well, until for some reason while checking the mV over those resistors and the output, the amp decided to switch in the protection circuit and blew the internal fuse.! Hahaha! Will have some replacements fuses on Tuesday! Then spotted ALL those R47 resistors are ZERO Ohms 4W Cement resistors. The output voltages on each channel were showing 27mV on one and 1.9mV on the other channel. Next episode on Tuesday when I get some more fuses. I will crack this though! Haha Best Regards PaulIn other words..... R47 is one of the two parallel emitter resistors. It is the voltage across that resistor.
I mentioned that option in my post.
Curiouser and curiouser.You mentioned you ordered new D200 and D100 transistors? Exactly what transistors and from where did you order them? I would have expected a 'D200' to actually be a 2SD200 and a 'D100' to be a 2SD100. But these do not make sense in your posted circuit. The 2SD200 is a silicon NPN and the 2SD100 is a Germanium NPN transistor with ratings way too low to be used as an output transistor.
Here are the ones Ive ordered as a backup ! NPN and PNP as per the schematic ! The ones installed are marked ST D100 and ST D200 and on the covering spec sheet they are specified as D100/200 (SGS) ! This amp was designed as an audiophile amp which won awards back in 1989 ! Hope this clarifies ! I was only intending to replace these Darlington Transistors if they were the cause, but from all your knowledge so far, that may not have to be the case ! Best Regards PaulHello,
Looking at the schematic the D100 and D200 seem to be darlington transistors.
They have drawn 2 arrows at each.
Is there a logo on the D100 and D200?
This might also help finding replacements.
Yes I believe that is correct ! Dont know how it got drawn incorrectly though ! Checking another of their designed amps and it is drawn correctly on that other diagram ! Well spotted everyone ! I was really lucky to get hold of these diagrams in the first place from someone who use to work fo the company years ago ! Best Regards PaulCuriouser and curiouser.
The D200 should be a PNP (but as pointed out earlier it is drawn with collector and emitter swapped) and the D100 should be NPN.
I have put the D100 and D200 details above ! They were hard to find so hope maybe one day I will be able to use them, if not sooner ! haha ! Best Regards PaulI can't find a D100 or 2sd100.
The D200 should be a 2sd200 http://pdf.datasheetcatalog.com/datasheets/savantic/1267.pdf This is silicon and NPN/
2sd100 substitute https://www.nteinc.com/specs/100to199/pdf/nte102a.pdf
2sd200 substitute https://www.nteinc.com/specs/300to399/pdf/nte389.pdf
Something is WAY off. Could be house numbers.
I do have a Japanease transistor databook, I could try to look there.
What you don't want is a "crash course" in amplifier repair. When I built my version of the Leach Amp (google it), I accidently mirrored the PCB layout. It took me eons to find that mistake. Since the amp is so symetrical, I was able to use the boards by swapping the N-channel devices with the p-channel ones and making two cuts in the PCB to swap the orientation of the bias regulator (Q7 et. al.) in your amp.
I later as a side job repaired audio amplifiers professionally. I took on the shops harder repairs. One amp I repaired (300W/ch_was for a disco where 5 shops refused to repair it before me. Metal film resistors actually melted and became a puddle on the PCB. The guy really wanted it repaired no matter what the cost because the amp was borrowed from a friend or relative.
The speaker terminals were directly shorted by some clown that hooked them up. Excess strands of speaker wire everywhere. I think I also added thump suppression to the amp as well.
Powering up amps with a 100 W incandescent bulb in series is one trick. It acts as a current dependent resistor. If the amp has a short, the lamp will light and limit the current.
Thankyou and noted ! You are absolutely correct the emmitter collector are around the wrong way in D200 on the diagram, but any ideas on a solution ? Thanks Best Regards PaulI don't know what the real scheme you have, but it's not drawn correctly (with a mistake). The D200 transistor is drawn in reverse!
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by Rushi Patel