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In Reply to: RE: Mac tube question posted by mcgjohn@yahoo.com on February 2, 2017 at 09:31:09:
"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?
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Follow Ups
- RE: Mac tube question - Palustris 12:54:28 02/02/17 (3)
- RE: Mac tube question - Awe-d-o-file 06:34:39 02/03/17 (2)
- Maybe we should help the OP learn why tubes are where they are - airtime 07:05:06 02/03/17 (1)
- RE: Maybe we should help the OP learn why tubes are where they are - Awe-d-o-file 14:48:37 02/03/17 (0)
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