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Old 24th December 2003, 03:01 AM   #21
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Actually the Bose amplifier module was manufactured by BGW Systems. I met Brian Wachner back about 1974 and he mentioned they were manufacturing the 1801 module but assembly of the 1801 was done at Bose. He didn't mention if BGW did the design work but I'd bet they did. To me it closley resembled the BGW "Arc Welders Special" the Model 1500 which was also a very band limited amp. I replaced almost all of those modules in all the 1801's that Midwest sold or had in stock when I worked in their service department.

Interestingly when I worked at Midwest Hi-Fi (left there in late 1974 before Kevin was there but I already knew him) the Chicago Oak Street Store manager was shot and killed by burglers one week day. The main thing they made off with was a Bose 1801 power one knows how they lugged it out of there amongst all the pedestrians that normally crowd that part of Chicago. Hardly a getaway..more like a lugaway.

Mark Gulbrandsen
Salt Lake City
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Old 24th December 2003, 03:12 AM   #22
AJT is offline AJT  Philippines
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reminds me of the BGW 750....uses 2n3772's output trannies...
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Old 24th December 2003, 03:28 AM   #23
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Yea, exactly!! I used tons of those amps in Cinema applications and they were virtually indestructable. The Sensurround films proved that one out. They did have one problem later on with a difference in metals reacting with the pins of the output devices and the solder joints opening up...a metalurgy problem so to say. hat was in a certain run of 750's. Brian Wachner was a wondeful forword thinking engineer that designed a great cooling system and the Crowbar shutdown as well. He was a really nice guy too. To his testament thousands of 7500T's and 750's are still in daily use in Cinemas all over the world. BGW recently filed for Bankruptcy and was aquired by Amplifier Technologies of Montebello, CA..... who ever they are......?... I'm not into the home theatre market much.

The DC300's used 2N3772's as well but those amps were not nearly as indestructable as the BGW's were. Phase linear used the Delco DTS 410's which were developed for NASA and the moon programs. See attached photo of the Color Sequential Camera that sent back the first color TV from the moon and its Delco DTS transistors!
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Old 24th December 2003, 04:49 AM   #24
AJT is offline AJT  Philippines
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still have the audio magazine article describing this amp, it came out february 1975, same time the magazine published the FTC regulations on power amp ratings disclosure!!!!
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Old 24th December 2003, 07:06 AM   #25
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That schematic straight from the RCA semiconductor manual and is a full working design.

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Old 3rd January 2004, 10:25 AM   #26
HKC is offline HKC  Hong Kong
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Default Another Amp Schematic

This schematic looks very similar to the one "Quintessence" used on their top model power amp back in the mid of 70'.
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Old 20th April 2007, 04:25 PM   #27
Saulf is offline Saulf  United States
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Default Quitessence Schematic

Hi: I have the Quintessence Group Poweramp II and the matching preamp. Looking at the innards I can tell you that the schematic posted earlier does not match the power amp circuit. I would be very interested in finding out more about my equipment and if someone knows the whereabouts of Barry Thornton I would love to talk to him! Does anybody have the schematics for these? I recently had some crossover distortion in the right channel. I cranked up the bias until it went away. I have no idea how to set it up electrically. It does not seem to have the classic current-source bias circuit. The preamp is also very interesting. It has a hand-wired perfboard phono-stage with what appear to be 9 op-amp chips. I wonder if this was one of the prototypes. Both are wonderful souding and the PA has strong tight bass.

Thank You and BR,

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Old 21st April 2007, 06:00 PM   #28
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I would be amazed if this amplifier sounded good by even standards of its day.

The BGWs and Crown DC300 were reliable. I think this was there only good attribute.

I remember (mid 1970s) replacing a modified Dyna 150 in my father' stereo system (for additional tweaks) and replacing it with a DC300. My teenage sister who didn't know I had made any changes at all and was my no means an "audiophile" called me up to complain.

She told me the stereo sounded like crap and that something must be broken. I fixed it by replacing the DC300. It was only "broken" because it was a DC300.

I remember the Bose amp physically, but I don't remember how well it worked. I have never heard a good quasi comp amplifier. Maybe its possible but reasonable PNPs have been available for 30 years, so I don't see the point. I am not a fan of common emitter output stages, a quasi comp is half common collector - half common emitter.

A old RCA transistor manual is a fun book to have, but I wouldn't use it as a source of inspiration.

Al Clark
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