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Old 10th July 2001, 08:52 PM   #1
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Location: Germany, Melle near Osnabrueck
I'm an owner of an old Technics SE-A3 and the powertransistors are broken. The devicetype is
OD503A-Q but these parts are discontinued by
Technics. I have no technical paper about these
devices, my measurement's in the no damaged devices
has shown me hfe are 50-60. Has anyone an idea to
replace the output-transistors which another type.
The Technics/Panasonic technican's told me that there
is no chance, but i don't believe it.
The O/P Stage is running at +75 /-75 Volts and is completely
DC coupled in complementair design. Two drivers drive 4
bipolars at the NPN line and two drive the PNP line.
The transistor's are double type's rated at
+/- 150V and +/- 10/15 Amp. the heatsink is big enough
to mount any other types on it TO-220 - T 200 or so.
I love this amp, he must live on....
could anybody help me ?
best regards Bocky
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Old 11th July 2001, 12:09 AM   #2
grataku is offline grataku  United States
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The amp with the big VU-meters, a classic!
there shouldn't be a problem to get the amp back in business. You said that there are no specs available for the transistors so what does this info pertain to??

-The transistor's are double type's rated at
+/- 150V and +/- 10/15 Amp.-

What do you mean by "double type's"? Maybe PNP-NPN combined into one???

MT-200 (sanken type stuff 2sc2922-2sa1216 etc) will need a lot of room, toshiba has a slightly smaller alternative.
see
http://pdf.toshiba.com/taec/componen.../2sc3281ds.pdf

The "R" gain range device should work for you. You should try to match the transistors before you installing them since they are going to be paralleled. Lars Clausen of LCaudio.com will sell you some matched 2SA1216-2SC2922.
Also, some adjustment may be required to get the DC offset to behave.
Do not forget to check that there are no other broken devices before the power trans. Usually bad things happen for a reason.
If have more detailed questions fell free to ask.


[Edited by grataku on 07-10-2001 at 07:16 PM]
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Old 11th July 2001, 10:16 PM   #3
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Thanks grataku

What do you mean by "double type's"? Maybe PNP-NPN combined into one???

Yes, that's matches exactly what i mean. Excuse me.
What's is the better one, Sanken or Toshiba
that's the question.

The "R" gain range device ...

I couldn't find any dealer in germany
which allows me to order devices in special ranks.
what happens when i order only the typ without ranks ?
Do they deliver me with a lot of different kinds ?
Do you have an distributor adress to order with ranks ?

Lars Clausen of LCaudio.com will sell you some matched 2SA1216-2SC2922...

I'm unable to find this offer, can you give me the exact
link to that offer ?

Also, some adjustment may be required to get the DC offset to behave...

To what value must i adjust ?

best wishes Bocky
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Old 11th July 2001, 10:28 PM   #4
hifi is offline hifi  Sweden
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hello..


check under the components page or call or mail him directly (lars claussen)

/micke
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Old 12th July 2001, 01:16 AM   #5
grataku is offline grataku  United States
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Bocky,
do what hifi told you, send an email to LCaudio, Lars will answer, he's a very nice guy. Are you sure you can fit all those MT-200 devices? They are rather large.

As far as the adjustment go is very much going to be an "experimental" kind of deal, do you have the schematics and instrumentation?
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Old 13th July 2001, 11:34 PM   #6
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Yes, i'm measured out my heatsinks and, yes, it is enough
room for the sanken types.
I have found a dealer ho can deliver me with those types
at range y ( hfe 55-110 ), i have ordered doubled, than
i can match the devices, i hope that's enough or isn't ?
Tell me, what's the best match method ?
Method a la Nelson Pass or is it quiet right to measure only
the hfe ?
I have yet the problem to find a mica insulator, what's better mica, ceramic or kapton ? It must be thin !
But my biggest problem is that i couldn't find the reason
for my broken O/P !!!
Could you give me any tips ? The driver stage should be o.k.
i've checked out any device but couldn't find any failure
could it be, that an driver transistor is half damaged ?
Yes i have an schematic of this amp and an oscilloscope too.
I think it would take a long time to repair them...
greetings Bocky
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Old 14th July 2001, 03:25 AM   #7
grataku is offline grataku  United States
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Bocky,
Great! I would be interested in the Sanken transitor myself, would care to tell me were are you buying them from and how much per trans.? They are 2sa1216 and 2sc2922, right?
The hfe matching is not critical, the internal resistance is what counts! Elliot Sound Products website should also have a "how to" section on matching. Remember to match the NPNs with NPNs NOT the NPNs with PNPs.
Good luck and let me know how is goes.




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Old 22nd July 2001, 05:33 PM   #8
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The trans. cost's 13.45 US$ each, a little expensive maybe.
I'm got them from my hifi dealer near me.
I've matched the trans. with the method of Nelson Pass,
and it looks good, the measurement are 3.97 / 3.98 / 3.99 /
4.03 Volts for the npn and the pnp are a little more different, i think it's o.k. I've mounted them on my heatsink and rewired the pcb connection it looks good.
But i can't finnished, i've no micaplate it's realy hard
to get - nobody knows about MT-200 cases i don't know any dealer to get them. Have no idea. Could anybody help me ?
best regards Bocky
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Old 23rd July 2001, 12:27 AM   #9
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Default Silicon Impregnated Sheet

While I'm not personally a great fan of silicon impregnated thermal insulators; I've been led to believe they do not perform as well as traditional mica, but that could be BS. It is however available as a sheet so you can cut it out to suit whatever size you like, it's a lot less messy to use, and has the dandy property of not being carcinogenic.

Not sure where you are, but check radio spares.

Cheers,

Pete

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Old 23rd July 2001, 08:05 AM   #10
grataku is offline grataku  United States
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I may have some. How many do you need? Contact me privately.
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