Safe to use a 12ax7a in place of a 12ax7 in phono preamp?
- Thread starter hatrack71
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Sure. Just not vice versa. The "a" designation has to do with the filament warm up....
hatrack71
distracted by everything
Excellent and thank you. AKer Billfort hooked me up with a very nice phono stage. I owe him big time!
Gary Kaufman
Well-Known Member
For many tubes the "A" was a controlled warm up, but actually in the 12AX7/12AX7A both were spec'd the same for filament warm-up.
The "A" was spec'd for low noise/hum. I believe there was no spec on the 12AX7, the 12AX7A was spec'd for < 1.8uv rms (as was the 7025).
You should be able to substitute in either direction without causing electrical problems. The 12AX7 "might" be noisier, but then again it might not....
- Gary
The "A" was spec'd for low noise/hum. I believe there was no spec on the 12AX7, the 12AX7A was spec'd for < 1.8uv rms (as was the 7025).
You should be able to substitute in either direction without causing electrical problems. The 12AX7 "might" be noisier, but then again it might not....
- Gary
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Thanks Gary. Learn something here every day....:thmbsp:
Gary Kaufman
Well-Known Member
You've got to love tube "nomenclature" - there are so many crazy inconsistencies. For the 12AU7/12AU7A the "A" version is less microphonic, for 12B4/12B4A the "A" has controlled heater warm up, for the 6L6G/6L6GA the difference is a smaller bulb.
The worse was Western Electric - Western Electric's 350B is a "super" 6L6, but don't try and plug in a 350A (it's more like a 807, wrong base and a plate cap). Actually almost any WE tube is incompatible with other brands, wonder how many folks have thought a 245A is a 45 equivalent (it's a tetrode, not a triode).
- Gary
The worse was Western Electric - Western Electric's 350B is a "super" 6L6, but don't try and plug in a 350A (it's more like a 807, wrong base and a plate cap). Actually almost any WE tube is incompatible with other brands, wonder how many folks have thought a 245A is a 45 equivalent (it's a tetrode, not a triode).
- Gary
The amusing thing is, a 245 is RCA's original designation for the 45. I don't believe it ever sold with an A though.
Related to other suffixies, and stepping way backward in time, you have the UV201 and the UV201A. The UV201 was a 1 amp heater, where the UV201A was a 0.25 amp heater. Then you had the CX301 and CX301A, which was the same thing sporting a Cunningham logo instead of the RCA meatball. Eventually it just became the 01A.
Related to other suffixies, and stepping way backward in time, you have the UV201 and the UV201A. The UV201 was a 1 amp heater, where the UV201A was a 0.25 amp heater. Then you had the CX301 and CX301A, which was the same thing sporting a Cunningham logo instead of the RCA meatball. Eventually it just became the 01A.
Gary Kaufman
Well-Known Member
UV's were short pins, UX were the long pins.
There were UX-201AA, UX-201B and UX201C also.
The list of brands that produced UX-201A's is pretty long, my favorite was "By-Heck".
Also equivalent, DeForest had the 401A, CeCo had the "A", Sears (WLS) had the 2976.
There were UX-201AA, UX-201B and UX201C also.
The list of brands that produced UX-201A's is pretty long, my favorite was "By-Heck".
Also equivalent, DeForest had the 401A, CeCo had the "A", Sears (WLS) had the 2976.
