12AX7A preamp tubes - ribbed vs smooth plate

"4 12AT7 tubes. no clue what they do Beyond rectify"

Your amp is SS rectified, not tubed.

2nd gain stage/phase splitter? Just guessing.

It's a mono block amplifier with 8 KT 88 and 6 small tubes (  4 rectifier, 2 preamp).

I assume the "2 preamp" tubes are the amps input tubes or driver tubes?

. . . ohhh, so they are MC9011s? I just did a cursory read on them--interesting amps.  Anyway, Mac is calling the two 12AX7s the signal tubes for the amp.  Which is not what I would call a "preamp tube"  (I would call a preamp tube a tube in the preamp) but I guess it doesn't matter what you call it.

I wonder what the 12AT7s are for?  Inputs or drivers into the ss section?

OP

I’m 75, until last year, I thought rectifiers were rectifiers, nothing to do with the sound.

My friend had a new Phono Preamp built by .... she included new 'broken in' tubes as well as some spare used tubes.

We listened here, changed tubes, small subtle differences, ’prefer’ not ’better’ differences.

changed rectifier, holy smokes was I surprised how easy it was to hear the difference. ’better’ was obvious.

@elliottbnewcombjr Im also under the impression that a rectifier is a rectifier, so now I’m curious as to what you have found by switching rectifier tubes and what your are now using that make the difference. I have McIntosh MC30s and have been using NOS RCAs. Let me know. Thanks.