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Bose 1800 series 1 : I did it AGAIN

dshoaf said:
I wouldn't recommend that just yet - he's not finished rebuilding it yet! :smoke:

Thierry, it is great to have guys who will document their work so well. I know you are a true mentor for others to follow.

Cheers,

David
Click to expand...

Thanks David, nope, for sure I won't toggle ON yet :D

There are still a lot of items on my To Do list, one of them is to replace the input jack sockets. The original ones are so badly corroded that they'll never return to service.

One may ask why oh why don't you install RCA phono sockets instead of those outdated 1/4" telephone jacks ?
Reason is simple : as you may know the 1800 can be operated either in the classic 2 channel configuration (stereo) or as a 1 kilowatt / 8 ohms mono amplifier (and believe me, then that baby rocks).
This is achieved by inverting the input signal phase on channel 2 using a 1/4" stereo input socket and connecting speaker wire between both positive output - blue and red - terminals of the 1800.
Of course this cannot be done when using an RCA socket which by definition has only 2 contact points. That's the reason why I stick to the good old telephone jacks.

Thierry
 
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Hi,

The story goes on with some cosmetic details. Restoration process goes slowly but I will not surrender !



One speaker terminal washer was broken, repaired it...

P1160107.JPG


Scratched lettering on the back panel, fixed this too

P1160112.JPG

P1160114.JPG


As mentionned, the input jack sockets had rotten away :
P1160122.JPG


Devil hides into details !

P1160123.JPG


Issue solved.
One socket is mono and the other is stereo, wiring them needs some attention because of the phase inverting configuration for mono operation.
I made some paint marks to help remembering where goes each wire :D

P1160118.JPG

P1160125.JPG

P1160132.JPG
 
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onwardjames said:
Very nice work, Thierry!
Click to expand...

Thanks.

I have started reassembly :
- heatsinks
- new capacitors
- new capacitors clamps
- cleaned and checked wiring harness
- new rectifier bridge
- new soft-start resistor.

It begins to look like a real 1800 rather than a wreck :yes:

P1160136.JPG


Refurbished front panel is awaiting for refitting...

P1160104.JPG
 
Some mechanical reassembly with the front panel being refitted with renovated screws. All parts are original, I had a tough work bringing them back to "almost looking as new" condition: each screw was thorouglhy brushed to remove the crust and then received a rust converter coat, then left alone for drying for a week.

P1160141.JPG


With top cover on.

P1160145.JPG


Just as a reminder this what it was looking like a few weeks ago :

P1150942.JPG
 
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Thanks,

I realize that my pictures are far too big, they won't fit into the screen.

Monster pics, just as the 1800 is a monster amp :D

Thierry
 
I love looking at your work, Thierry! It's too bad I only found it at the end. You do such beautiful work and such a great job documenting it for us. An inspiration to us all.

Wow!
 
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I had some fun with a measurement session today, I guess it may be of interest to the forum as very few people published measured specifications for these babies, including Bose themselves. Full report can be viewed here (in french, but figures don't need to be translated) http://audiolalies.blogspot.fr/2014/06/amplificator.html

Power measurement done with 1KHz sine wave, 1,5V RMS at the amplifier inputs. Mains voltage : 234V.

Two channels in service, 8 ohms load 339W RMS per channel before clipping

Pout_8ohms_2.jpg


One channel in service, 8 ohms load 376W RMS before clipping

Pout_8ohms_1.jpg



Two channels in service, 4 ohms load : 645W RMS per channel before clipping

Pout_4ohms.jpg


  • THD : 0.025%
  • intermodulation : 0.15%
  • Frequency response 20Hz/20KHz : +0.4dB, -0.8dB

FR.jpg
 
Truly amazing restoration job on one of the best if not the best Bose product ever manufactured. This is the Lazarus amplifier, back from the grave. Like new again!
 
KentTeffeteller said:
Truly amazing restoration job on one of the best if not the best Bose product ever manufactured. This is the Lazarus amplifier, back from the grave. Like new again!
Click to expand...

Thanks !

I just couldn't stand the idea of seeing it going to the junkyard, which is what the owner intended to do and also why I gave him twice the amount he was asking for.

Thierry
 
Thierry said:
I had some fun with a measurement session today, I guess it may be of interest to the forum as very few people published measured specifications for these babies, including Bose themselves.
.....
Power measurement done with 1KHz sine wave, 1,5V RMS at the amplifier inputs. Mains voltage : 234V.
.....
Click to expand...

When you measured the power into 4 ohms, did you recheck the mains voltage? With that kind of power, it is quite likely that the mains would sag with the additional load.
 
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