It figures.
ARC used to be the easiest company to talk to for tech support and now you have to wait,leave a message and hope they call back.This is what happens when scumbag investment firms buy these companies that are profitable and deplete resources such as good staff.Now ARC is part of this huge conglomerate of high end audio companies such as Mcintosh,Marantz,Snell,ARC,and several others. I used to be able to call ARC and get Chris or Leonard on the phone within minutes for a technical issue or parts ID.
Anyway,I'm off on springbreak so if you want to call,I'll be home all week.
ARC used to be the easiest company to talk to for tech support and now you have to wait,leave a message and hope they call back.This is what happens when scumbag investment firms buy these companies that are profitable and deplete resources such as good staff.Now ARC is part of this huge conglomerate of high end audio companies such as Mcintosh,Marantz,Snell,ARC,and several others. I used to be able to call ARC and get Chris or Leonard on the phone within minutes for a technical issue or parts ID.
Anyway,I'm off on springbreak so if you want to call,I'll be home all week.
Just spoke to Calvin. They have no parts that I needed. So my gut feeling to look elsewhere was correct. As to my questions about the correct current draw, and the change to different zeners on Mk II the response was he doesnt know anything about it. It is only proper that AR would want to repair this thing themselves.
Btw: mkI diagram calls for 7 zeners of 47v each, which gives us a reference voltage of 329v. Mk II diagram shows a row of 7 29v zeners. Misprint?
Btw: mkI diagram calls for 7 zeners of 47v each, which gives us a reference voltage of 329v. Mk II diagram shows a row of 7 29v zeners. Misprint?
I am surprised and sorry to hear that it didn't go well with ARC. I called and left a message for Calvin. He returned my call within twenty minutes and had what I needed for a much older amp than yours. If you can get part numbers off the old transistors you might be able to find them yet. Also, be wary of changing those coupling caps. The Relcaps are high quality and sound really good in these amps.
As for the transistors the first thing you should do is remove all the tubes and start checking voltages inside the power supply and the audio section. The voltages will be a bit higher without a load but you should be able to get a good idea of what you have.
And my last bit of advice is don't replace components unless you have a good reason too
It will be very hard to improve on ARC parts and you are more likely to degrade the sound quality than improve it. I would check the power supply voltages and then the audio section without tubes. If you find nothing amiss put the tubes in and try listening to it.
Also, you have a 1 amp and a 1.5 amp fuse correct? At 120 volts that is 120 and 180 watts max for the two sections. If you add up the tube filament current draw at 6.3 or 12.6 volts and the HT voltages and standard current draw for the tubes you can get an approximation for the steady state power for the amp when powered up.
Remember volts times amps = power. There will be other losses but but at leasst you'll be in the ballpark, or not.
As for the transistors the first thing you should do is remove all the tubes and start checking voltages inside the power supply and the audio section. The voltages will be a bit higher without a load but you should be able to get a good idea of what you have.
And my last bit of advice is don't replace components unless you have a good reason too
It will be very hard to improve on ARC parts and you are more likely to degrade the sound quality than improve it. I would check the power supply voltages and then the audio section without tubes. If you find nothing amiss put the tubes in and try listening to it.
Also, you have a 1 amp and a 1.5 amp fuse correct? At 120 volts that is 120 and 180 watts max for the two sections. If you add up the tube filament current draw at 6.3 or 12.6 volts and the HT voltages and standard current draw for the tubes you can get an approximation for the steady state power for the amp when powered up.
Remember volts times amps = power. There will be other losses but but at leasst you'll be in the ballpark, or not.
I apologize, I reread the entire post and found you have missing parts. That will make it difficult! With the ARC manual you will only have the ARC part numbers for those missing parts. I would suggest making a list of the ARC part numbers for the missing parts and then contacting Calvin to get you the manufacturer's original part numbers. If they can't supply the parts they should at least give the numbers so you can find them.
Back to the project
Hi
Back to this after a long break.
Got the PS working. Having problematic readings on V5/6 and V7/8. Cathodes V7/8 (those are the outputs before the main phono coupling caps) read 270v instead of 164v, as do the plates of the V5/6. Turns out the U4 regulator for the V5/6 is putting out only about 2V instead of the spec 32V. Furthermore, it's not getting the 44V from the large MJ413 transistor, which seems to be fed from the U5 regulator (which seems to be fine). A bit confused by all this
))))))))))))))
Hi
Back to this after a long break.
Got the PS working. Having problematic readings on V5/6 and V7/8. Cathodes V7/8 (those are the outputs before the main phono coupling caps) read 270v instead of 164v, as do the plates of the V5/6. Turns out the U4 regulator for the V5/6 is putting out only about 2V instead of the spec 32V. Furthermore, it's not getting the 44V from the large MJ413 transistor, which seems to be fed from the U5 regulator (which seems to be fine). A bit confused by all this
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Finished!
Thanks to all! It is playing, very nicely. I couldn't figure out why the auto-mute is screwed-up, but I just bypassed it and use manual (suggested by all users). Now will try to figure out how to lower the phono gain on it (and may be the line too). Don't need that much gain, I use an MC step-up transformer. At factory settings SP-10 eats tubes for breakfast.
Thanks to all! It is playing, very nicely. I couldn't figure out why the auto-mute is screwed-up, but I just bypassed it and use manual (suggested by all users). Now will try to figure out how to lower the phono gain on it (and may be the line too). Don't need that much gain, I use an MC step-up transformer. At factory settings SP-10 eats tubes for breakfast.
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