can anyone explain this amplifier? Audio Telex 2sa500B - diyAudio
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Old 10th October 2012, 08:37 PM   #1
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Default can anyone explain this amplifier? Audio Telex 2sa500B

Hi
Just got a hand on a pair of these. dirt cheap.
Its for PA application but given the prodigous amount of heat sink, transistors TIPC (20 each amplifier) and a output coupling amplifier makes me wonder can it be modified to hifi or SQ use.

If we look at schematic it has two wings of single ended TIP35C coupled with an output transformer probably step up . so for hifi can we modify like swaping primary to secondary and increasing bias to sort of run it in class A????

It would be very intersting if any suggestion can be provided to make it a diy hifi.
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File Type: pdf Audio-Telex-SA500B-Service-Information.pdf (216.0 KB, 62 views)
File Type: pdf SA250B-SA500B-Manual.pdf (234.4 KB, 33 views)
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Old 10th October 2012, 08:45 PM   #2
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here is the detailed schematic.
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File Type: pdf schematic.pdf (216.0 KB, 115 views)
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Old 17th November 2015, 12:08 AM   #3
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Hi muddasirwaheedmalik, I know it's been a while, but did you manage to convert these to Hifi use? I was just given a 50W amp with the same topology, & it's got me scratching my head....
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Old 17th November 2015, 02:31 AM   #4
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for those who like a challenge... the topology of this amp is direct coupled non differential preamp, phase splitters transformer coupled to the output stages, which are single ended darlingtons, each side feeding a common output transformer, which has the primary CT connected to earth. Single power supply. - bit of a throwback it seems...
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Old 17th November 2015, 04:55 AM   #5
JMFahey is offline JMFahey  Argentina
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You can't convert these, way too specialized.

Large PA type amplifiers, designed for high power from low voltage *single* supply (so you can OT avoid the output transformer) , mainly so on emergencies they can be run from 2 or 3 car batteries in series.

That said, I don't think they sound *bad* , specially to listen to loud Rock and similar stuff.
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Old 17th November 2015, 05:26 AM   #6
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I think the emphasis here is for minimum cost reliability, repairability and use anywhere around the globe. Even the instructions are written for someone with weak English comprehension. 24V DC operation is another indicator of the applications in mind. There are deliberate choices for a small parts inventory of cheap and widely available semis too, I think. All the same, for a ca.1990 product, I agree that it does seem a throwback design approach.

Even with a direct coupled 4 ohm output, Hi-Fi, it definitely won't be and I expect that trying to use the amplifier for anything more than voice and muzak would be a waste of time. The topology is interesting though - I would not miss the chance to breadboard something simple and small like this then mess with it, if you are keen to learn more about amplifier design and gain some wider experience than the usual circuits we fall back on.
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Old 17th November 2015, 08:47 AM   #7
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You might also like to look at Quad 50e for a related design.
http://quad-hifi.info/public/quad_50e_d%5B1738%5D.pdf
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Old 17th November 2015, 09:23 AM   #8
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It has similarities to early Crest power amplifiers. They were dreadful!
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Old 17th November 2015, 09:51 AM   #9
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Thanks guys, I'll try it out as a guitar amp as is, then scavenge it for the case & power trannie I think... cheers
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