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I see many opinions regarding the sonic effect or lack thereof of driver tubes in amps; some say not too important, others that they make a huge difference in sound. What effect do the 12AT7 tubes in a Mac MC 275 have; insignificant so long as quiet, rather important, or huge?
My MC 275 IV came from Audio Classics with new KT 88's labeled McIntosh but look to be JJ's. The 12AX7's I personally installed are JJ's that have been "cryo-gentrified" up to black diamond Telefunken status, "up from the ranks", as it were. Pace Jim McShane, I like them in pre-amp apps (ARC 8.) The AT7's are the ones from Audio Classics and are a mixed bag, one is clearly a JJ but the others have two wavy (not Waverly) wafers on top, and a short plate atop a bottom wafer, all 4 labeled McIntosh. Sorry, I can't seem to put a picture here.
If I replace the AT 7's, what sonic effect should I expect? What would be a good replacement?
Also, which has more sonic effect, the AX 7's or the AT 7's?
Thanks in advance for any advice.
LowIQ
Follow Ups:
tubes make a difference. As to which and in what application I think that's a bit personal as opposed to black and white. AT7's are cheaper so try some good ones IMO. The more you try of all the tubes the more you'll know.
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
would agree.
Also sub'ing in a 12at7 for the ax will reduce overall gain a bit, and should lower neg feedback a bit at the same time.
May have a larger effect doing this experiment on the first input tube though than on the driver tube.
have fun.
"Also sub'ing in a 12at7 for the ax will reduce overall gain a bit, and should lower neg feedback a bit at the same time."
This is a common misconception and unfortunately it continues to be repeated.
Tubes are not like light bulbs; you can not simply substitute one type for another. Each vacuum tube type is specified to have a transconductance, plate resistance and amplification factor when operated within specific conditions. These conditions are a function of the ancillary components that define the operating point of the tube. To operate properly the tube needs a specific plate voltage, plate resistor, bias voltage and bias resistor or it will not operate in the most linear region of the plate curves with the lowest noise and distortion.
The engineer that designed the circuit selected the tube type for a reason and he then insured that the tube was operating under the conditions which would provide the lowest distortion and the proper voltage gain for the circuit in which it operates. If one substitutes a different tube than the engineer specified you will creating a random and unknown filter or a noise generator. You might like the sound of the filter you create or you might not; but it will not be hifi and it will not be the circuit that some engineer spent considerable time and research to refine.
So, yes, you can substitute any tube with a 9A base connection into any other socket with a 9A base connection and the circuit will not be damaged and the tube won't melt in a conflagration; but why would you ignore the engineer's exacting work to create a random filter?
Good post. I laughed at the tubes are not light bulbs. I'm gonna use that.
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
Whaaaa! I've been screwing in new LED tubes all day for nothing!
No really, I think the OP wants to know what the difference between 12AT7 and 12AX7's do in his amp. It's good to see he's at least interested but we should direct him on how and why those tubes are where they are.
I'm not sure if it is the OP or a responder the amp uses both types of tubes and other small driver tubes too. AK has more folk willing to take time and explain stuff than here too.
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
nt
I didnt think the OP wanted to sub. The amp takes both tubes and others. Schematic at link. You probably already knew and were only addressing subbing.
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
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