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Hi all, just found this site. I'm new to tube amps in general and OTLs in particular.
I have a pair of M60 that I have been listening to for about a week. They came with
6H8C Russian and 6AS7GA General Electric tubes. I also have an older Atma-sphere P2 preamp with transformer outputs. Line and phono stages are all 12AT7s. Pretty sure the 3 in the line stage are supposed to be 12AU7s. The line stage 12AT7s are a combination of new EH and Sylvania tubes. The phono stage has a 3 GE, 2 Mullard ECC81 BVA GB, and 2 I don't know.
It sounds great, and I should probably just leave it alone. None of these tubes seem to be typically recommend, so I wonder what I might be missing. Without going crazy, where should I start to get the most improvement with different tubes?
Those GE 6AS7GAs are not known for reliability!
We recommend the Chinese 12AT7 is it is easier to find low noise/lo microphonics with them. If you are running a high output cartridge its probably no worries.
There are a number of updates available for the P2 with significant performance increases!
Ralph, what is the issue with the GE 6AS7GAs? Can they damage the amps or speakers?
I do have a full set of brand new Chinese 6N13PJ tubes that I was keeping as back up replacements once the GE's eventually go.
My cartridge is high output (4 mV), but I am surprised how far I need to turn up the volume compared to the line stage. Ideally, I would like to take all the tubes and test them, or replace with all new tubes as a baseline starting point.
Which brings me to my next question, how many of you use and own a tube tester?
Seems a little frustrating not knowing what kind of condition the tubes are in, if they are matched or not etc..
Thanks for the link for Joe's tube lore.
I have the Amplitrex tube tester.
I couldn't imagine not having it. It's amazed me how many tubes I've purchased that where 'not' well matched.
The 6AS7GAs won't damage anything but they are known for arcing.
How many tubes are in the phono section? If there is a jumper plug in place the phono gain will be lower.
All the phono tubes are present. The 12AU7s that I ordered finally arrived. The two tubes nearest the front to the right in th P2 were filled with 12AT7s ( the third tube behind these was a 12AU7. I was mistaken when I said it was a 12AT7). I replaced these 2 12AT7s with the new 12AU7s and the gain on the line stage dropped significantly. Gain on the line and phono stages are now more equivalent, in fact, the phono is a little hotter.
Turns out a friend has a tube tester that I can use, saves me having to buy one.
The 6H8C Russian is the same as the 6SN7 as you likely know. For my S-30, I preferred Sylvania, Ken Rads and National Union tubes. The first one in the line seemed to make the most difference followed by the second with the third no being affected really.
Check out Joe's tube lore in the FAQ for his thoughts on various other tubes.
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