OK, I searched the forum on this one, but didn't found anything, so here goes...
Someone threw an AR amplifier in my lap as part of a deal with a pair of AR-speakers I bought.
The amp has a problem in the R channel when output goes over 20%, esp. at lower frequencies and low impedances (4 ohms).
Input is sine on top, output from speker terminal.
Questions:
A: Where can I find a service manual / schematics?
B: Anyone seen this before, clues?
C: Is this amp even worth salvaging?
I have some experience in tube-amps, but less in solid state. Ironically It's rather simple to find documentation on old tube-amps and new solid-states. But in between those...
Someone threw an AR amplifier in my lap as part of a deal with a pair of AR-speakers I bought.
The amp has a problem in the R channel when output goes over 20%, esp. at lower frequencies and low impedances (4 ohms).
An externally hosted image should be here but it was not working when we last tested it.
Input is sine on top, output from speker terminal.
Questions:
A: Where can I find a service manual / schematics?
B: Anyone seen this before, clues?
C: Is this amp even worth salvaging?
I have some experience in tube-amps, but less in solid state. Ironically It's rather simple to find documentation on old tube-amps and new solid-states. But in between those...
I think this was a good quality amplifier for the time; possibly
a quasi-complementary output stage, may have been
direct-coupled.
The Classic Speakers Page (http://www.****nal.net/speakers/)
had schematics, but appears to be completely offline at the
moment.
I'd check power supply first, especially low-voltage supplies
and any regulated supplies. It's been my experience that
electrolytic caps in those supplies are unreliable, going open-
circuit or high impedance.
If the output stage is capacitor-coupled, check those capacitors
as well.
After that, check the driver and output transistors.
a quasi-complementary output stage, may have been
direct-coupled.
The Classic Speakers Page (http://www.****nal.net/speakers/)
had schematics, but appears to be completely offline at the
moment.
I'd check power supply first, especially low-voltage supplies
and any regulated supplies. It's been my experience that
electrolytic caps in those supplies are unreliable, going open-
circuit or high impedance.
If the output stage is capacitor-coupled, check those capacitors
as well.
After that, check the driver and output transistors.
sometimes this helps:
http://web.archive.org
more precisely:
http://web.archive.org/web/*/http://www.****nal.net/speakers/
http://web.archive.org
more precisely:
http://web.archive.org/web/*/http://www.****nal.net/speakers/
ROTFL!... Seriously: I have already 'scanned' that site. The AR amps there are too modern. I have found one copy of a manual at:
W7FG
It was in poor condition and no schematics. I have not yet received it so I can't tell.
Yes, there is a large multicap. Same thing as the old Dynacos; may have to be replaced.
Since it seems to be so har finding data on this one, maybe that is telling the tale? It is rare and should be salvaged?
W7FG
It was in poor condition and no schematics. I have not yet received it so I can't tell.
Yes, there is a large multicap. Same thing as the old Dynacos; may have to be replaced.
Since it seems to be so har finding data on this one, maybe that is telling the tale? It is rare and should be salvaged?
Acoustic Research amplifier
I have the schematics of this ampllfier
and its integrated preamp.
Djk is right, it has an interstage transformer.
It is supplied by a class A push-pull low power stage
(17V power supply) .
The power output stage is a DC coupled
(+/- 39V) push-pull made of NPN bipolarls,
no output coil.
But Djk is wrong, it's certainly worth repairing,
at last just to hear what industry
was able to do before 1970.
For high fidelity purposes, interstage transformer
coupling in solid state ampifiers are very rare,
I only remember two other shematics using this technogy,
which is quite interesting,
one of them was a Rogers amplifier which
sounds very gound with a BBC LS3/5A.
I can scan the schematics and send it to you,
however let me a little while,
because I currently have some computer problems
to solve.
~~~~~~~~~~~ Forr
§§§
I have the schematics of this ampllfier
and its integrated preamp.
Djk is right, it has an interstage transformer.
It is supplied by a class A push-pull low power stage
(17V power supply) .
The power output stage is a DC coupled
(+/- 39V) push-pull made of NPN bipolarls,
no output coil.
But Djk is wrong, it's certainly worth repairing,
at last just to hear what industry
was able to do before 1970.
For high fidelity purposes, interstage transformer
coupling in solid state ampifiers are very rare,
I only remember two other shematics using this technogy,
which is quite interesting,
one of them was a Rogers amplifier which
sounds very gound with a BBC LS3/5A.
I can scan the schematics and send it to you,
however let me a little while,
because I currently have some computer problems
to solve.
~~~~~~~~~~~ Forr
§§§
Just hope the interstage transformer is OK.
I was an AR dealer and service center in the 70s and had to fix a few pieces with bad transformers.
As far as an example of what the state of the art was back then, forget it. In 1966 a McIntosh MA5100 was direct coupled and vastly better. The HK citation 12 was also available.
OTOH, if I won the lotto there are some horrible examples of motorcycles I would love to buy. No one would ever buy a K model Sportster for performance, but there is something cool about them.
I was an AR dealer and service center in the 70s and had to fix a few pieces with bad transformers.
As far as an example of what the state of the art was back then, forget it. In 1966 a McIntosh MA5100 was direct coupled and vastly better. The HK citation 12 was also available.
OTOH, if I won the lotto there are some horrible examples of motorcycles I would love to buy. No one would ever buy a K model Sportster for performance, but there is something cool about them.
Thank you for all inputs! Yes I suspect the caps, it's always the 1:st that goes.
No, I am not doing this (repair of old amps/loudspeakers) to get great sounding equipment! I am in this as a hobby to salvage the herritage of old things and to preserve them as much in their original as possible. Old Dynaco tube amps and Acoustic Research has by chanse become my favourites.
When a project is finished it is great to use, see and feel the equipment of yesterday and also to hear music (vinyls usually) the way it did back then!
When sound is the main issue I turn to completely different equipment.
The AR amp was 'thrown in' as a 'you take it, I don't need it' when I bought a pair of AR 10 PIES (which btw. is as modern as I'll go in this hobby!).
So the original question, 'is it worth salvaging' is answered with a 'yes'. To make it even more so, the original box (with a wood slab in it) came with the amp!
I'll post in this thread when the job's done. That may take a long time, other projects stand in line before this amp!
No, I am not doing this (repair of old amps/loudspeakers) to get great sounding equipment! I am in this as a hobby to salvage the herritage of old things and to preserve them as much in their original as possible. Old Dynaco tube amps and Acoustic Research has by chanse become my favourites.
When a project is finished it is great to use, see and feel the equipment of yesterday and also to hear music (vinyls usually) the way it did back then!
When sound is the main issue I turn to completely different equipment.
The AR amp was 'thrown in' as a 'you take it, I don't need it' when I bought a pair of AR 10 PIES (which btw. is as modern as I'll go in this hobby!).
So the original question, 'is it worth salvaging' is answered with a 'yes'. To make it even more so, the original box (with a wood slab in it) came with the amp!
I'll post in this thread when the job's done. That may take a long time, other projects stand in line before this amp!
AR amp Manuals
http://www.vintageaudiomanuals.com/-A-.htm
This site says they have it.
I still have one of those amps and I used to have the books , but I don't think I could find them.
I bought mine in 1970.
Rob
http://www.vintageaudiomanuals.com/-A-.htm
This site says they have it.
I still have one of those amps and I used to have the books , but I don't think I could find them.
I bought mine in 1970.
Rob
Thank you 'rgruenhaus'.
I have saved the link.
On the AR 10PIES: they are now fixed (new foam) and are working well. Too well... I have to dig into one of my 3a's to find a mechanical problem...
New is also that I installed Sheldon Stokes cap assy into my Dynaco MKIII's. Perfect result! I recommend the kit!
I have saved the link.
On the AR 10PIES: they are now fixed (new foam) and are working well. Too well... I have to dig into one of my 3a's to find a mechanical problem...
New is also that I installed Sheldon Stokes cap assy into my Dynaco MKIII's. Perfect result! I recommend the kit!
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