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Bose 1801 power amp restore/recap

Richs_Trains

Richs_Trains

Well-Known Member
Hello all,

I post mostly in the Marantz forum as I have recapped about 20 Marantz units, but an old friend who seems to have more equipment than he can deal with has offered to give me a Bose 1801 power amp (250 watts per channel and 26 TO3 outputs!) that is in working condition. I have no experience with this unit and want to make sure that it is up to date and ready to work for another 40 years. There seems to be extensive posts regarding this unit, and favorable reviews, but I did not find any rebuilt threads. Anyone who is familiar with this equipment, I would appreciate advice and recommendations as to what I should check and replace to bring this unit up to 100% operation. There is a kit on the auction site that I am considering, but the seller has some bad reviews on AK for his "new" replacement pots that seem to fail quite often due to poor quality. I should have this unit tomorrow, but since it weighs 82 lbs, I may have to find a different bench then the one that I normally use before I open it up. Any advice and help would be much appreciated! Thank-you, Rich
 
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Trying to remember the one I did....

One main filter cap in mine exploded shortly after I replaced it. Like literally. Big “bang” in the garbage. So be sure to replace those.

Zeners and caps obviously, and I off mounted the bias trimmers so I could access them with the amp put together.
One of my driver boards was pretty burnt, and I think that’s common but I can’t remember a fix or if it just is what it is.
 
Be carefull with the service manual. There are a lot of error . On mine i've change all capacitor and all resistors.
 
lapomm said:
Be carefull with the service manual.
Click to expand...
ivandezande said:
One of my driver boards was pretty burnt
Click to expand...

Well, I got it today, power cord has pretty much lost it's outer cover although the internal wires appear to be okay. I am almost afraid to power this beast up, is a 100 watt bulb sufficient on the DBT to keep from blowing up my house? I have not taken anything apart yet, but from reading the SM is appears the outputs are not actually mounted to the heat sinks but rather mounted to a plate attached to the external heat sinks with the six screws and when you pull the amp boards the outputs come out with it and the heat sinks remain? Also, the bias is adjusted by disconnecting one of the filter caps and measuring between the disconnected wire and the filter cap and you can only have one amp board connected at a time when setting the bias?
 
Richs_Trains said:
Well, I got it today, power cord has pretty much lost it's outer cover although the internal wires appear to be okay. I am almost afraid to power this beast up, is a 100 watt bulb sufficient on the DBT to keep from blowing up my house? I have not taken anything apart yet, but from reading the SM is appears the outputs are not actually mounted to the heat sinks but rather mounted to a plate attached to the external heat sinks with the six screws and when you pull the amp boards the outputs come out with it and the heat sinks remain? Also, the bias is adjusted by disconnecting one of the filter caps and measuring between the disconnected wire and the filter cap and you can only have one amp board connected at a time when setting the bias?
Click to expand...
100W is good. Yes, you have to unscrew the driver boards from the main heatsinks. Pretty straightforward. And yes to the bias, you're measuring each channels current draw.
 
I have a Bose 1801 with one of The capacitors blown the one that sits in the centre of the amplifier 18,000 uf 10 vdc are there any exact replacements for this capacitor or do I have to find some thing else and where can I find these items
Thanks Dan
 
Danbose1801 said:
I have a Bose 1801 with one of The capacitors blown the one that sits in the centre of the amplifier 18,000 uf 10 vdc are there any exact replacements for this capacitor or do I have to find some thing else and where can I find these items
Thanks Dan
Click to expand...
Digikey or Mouser, go find em.
I would recommend just filtering the 3” diameter and 100V rating, you’ll probably need to go up in capacitance.
 
Danbose1801 said:
I have a Bose 1801 with one of The capacitors blown the one that sits in the centre of the amplifier 18,000 uf 10 vdc are there any exact replacements for this capacitor or do I have to find some thing else and where can I find these items
Thanks Dan
Click to expand...
Dan, I ordered a kit to rebuild the amp and it provided a nippon chem com 18,000uf 63 v for the center cap and nippon chem com 15,000uf 100v for the filter caps. Rich
 
Richs_Trains did your original centre cap have four leads coming out of it the 18,000 UF10 V DC and you’ve now switched it to a two terminal capacitor was there a circuit board that you had to add on top of that capacitor or did it already have one. Mine does not have that circuitboard and I’m trying to locate one

Thanks Dan
 
Danbose1801 said:
Richs_Trains did your original centre cap have four leads coming out of it the 18,000 UF10 V DC and you’ve now switched it to a two terminal capacitor was there a circuit board that you had to add on top of that capacitor or did it already have one. Mine does not have that circuitboard and I’m trying to locate one
Click to expand...
Dan, I am pretty sure (I have not done the recap on mine yet) that two of the terminals on the original cap are just connection points and not part of the internal workings of the cap. Hopefully, someone with more experience will weigh in and confirm this. I have purchased new caps for other units that had 4 terminals and only two were valid connections the other two terminals were there to add stability when soldered to the PC board. Of course this cap is mounted vertically, but since my rebuild kit came with this two terminal cap, I am fairly confident that only two terminals of the original are actually valid. Rich
 
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