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Need help with ARC sp16 and tubes

I found the right channel out completely today for phono source only. Preamp is ARC sp16, 6 12AX7 tubes, 3 phono, 3 other. If I connect phono to a line level input, I get low volume sound in both channels which tells me its the phono section of the pre-amp, not cart or anything upstream.

I have spare 12AX7 tubes to test with one by one sometime soon when I get a chance.

My question is, is it common for 1 channel of a 12AX7 tube to go completely? There is sound in left channel but not sure if 100% or not at this point.

I have heard noise levels increase in the past with the ARC when tubes get weak and need to be replaced but have not experienced a 1 channel out scenario with it before.

Thanks in advance for any insights.
128x128mapman
5 responses Add your response
mapman's avatar
mapman OP
22,197 posts
 
OK, problem solved. It was phono section tube slot 3 gone bad. Replaced that with a spare I have and back in business. Luckily it was not phono slot 1 which takes a more expensive very low noise tube in order to keep things quiet that is harder to replace.

The things we do for tubes....
tobes's avatar
tobes
436 posts
 
03-06-13: Mapman
Luckily it was not phono slot 1 which takes a more expensive very low noise tube in order to keep things quiet that is harder to replace.
Odd you've found that first position to be fussy - I bought my SP16 S/H with the original New Sensor EH tubes that had many years of service and the phono was still remarkably quiet.
While I'm not currently using my SP16 for phono duties, I've found the phono very quiet with commonly available low cost New Sensor 12AX7's. At present I have the Svetlana variant fitted - ~$15ea matched/balanced - with zero noise issues.
mapman's avatar
mapman OP
22,197 posts
 
Tobes, that's good to know.

My current tubes came from ARC about a year back. They shipped me 6 tubes, 1 special low noise (more expensive) for slot 1, which is the one most towards the rear of the three phono tubes to the right looking in from the front.

Knowing that now, I can be smarter moving forward about what tubes are needed to get the job done effectively without overpaying for no reason.

My phono section is very quiet. I have low tolerance for any background noise when listening. My only wish is that I could turn off the phono section separately from the rest to save tube life in that lately I have been lazy and listening mostly to music server digital.
tonywinsc
583 posts
 
I had never looked closely at the SP-16. I looked it up and I was suprised to see that it is very similar internally to my old SP-6b. Like a modern version of it. The SP-6b used 6 12AX7 tubes configured the same way. Based on that, my experience says that you would see a nice improvement with some NOS tubes.
mapman's avatar
mapman OP
22,197 posts
 
Tony,

Thanks for that. I'll keep it in mind.
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