Came across a NOS tube sale. One of the items on sale is NOS RCA 12AU7 clear tops. I ordered a pair for my M125's as I've read a lot of positive comments about these. Is it better to install them in the front positions, or rear? Or does it even matter? Just looking to get the most out of them.
3 posters
New driver tubes, place in front or rear?
LeGrace- Posts : 389
Join date : 2016-08-07
Location : Ontario, Canada
deepee99- Posts : 2244
Join date : 2012-05-23
Location : Wallace, Idaho
Correct me if I'm wrong (I frequently am!) but the front holes are the voltage amplifier holes (same with the SP-14, and the centre hole on the ST-70s and ST-120s) and will benefit the most from a good tube selection. The rear holes are buffers, and don't care so much.LeGrace wrote:Came across a NOS tube sale. One of the items on sale is NOS RCA 12AU7 clear tops. I ordered a pair for my M125's as I've read a lot of positive comments about these. Is it better to install them in the front positions, or rear? Or does it even matter? Just looking to get the most out of them.
manookjs likes this post
mijohn- Posts : 119
Join date : 2013-06-19
Sorry to correct you Dave, but as far as the SP-14 is concerned the front tubes are one channel and the back are the other. The pair on the left are the gain stage and benefit from the best tube selection, the pair on the right are the buffer stage. But more relative to this thread you are correct about the M-125's. 
deepee99- Posts : 2244
Join date : 2012-05-23
Location : Wallace, Idaho
MiJohn, you're of course right, too. I think of the "front" of the preamp, i.e. the gain stages, as being on the left-most side, and the two buffers on the RH side as you're looking at the amp's front panel. I think in terms of the LH side being actually the front because the circuits run side-by-side (looking from the front).The layout's a bit confusing till you get used to it.mijohn wrote:Sorry to correct you Dave, but as far as the SP-14 is concerned the front tubes are one channel and the back are the other. The pair on the left are the gain stage and benefit from the best tube selection, the pair on the right are the buffer stage. But more relative to this thread you are correct about the M-125's.
mijohn- Posts : 119
Join date : 2013-06-19
Whether it's the front, back, left side or right side , the important thing is you do know which pair of tubes is which! 
LeGrace- Posts : 389
Join date : 2016-08-07
Location : Ontario, Canada
Thanks for the info and technical reasoning!