Hello, I am building an EL519 based amp that uses 12ax7a The base trebel and mid control that im adding uses 12ax7 's. I wanted to know if it made a difference which i used. Im probably getting all the tubes from ebay so if would be better cost wise if i could use as many of the same tubes as possible.
--Tom
--Tom
I believe the original 12AX7 did not have a spiraled heater.
An "A" was just a later "improved" version, as was a 7025 - supposedly a low noise version. Any 12AX__ made in the 60's and onwards will have all of the improvements. You'll often see a single tube labeled "12AX7 12AX7A 7025" on the envelope.
A 6EU7 is a low noise version. They give noise specs in the RCA manual. Whether there is any audible improvement or not is up for debate. It's a cheaper alternative though, and is essentially identical.
An "A" was just a later "improved" version, as was a 7025 - supposedly a low noise version. Any 12AX__ made in the 60's and onwards will have all of the improvements. You'll often see a single tube labeled "12AX7 12AX7A 7025" on the envelope.
A 6EU7 is a low noise version. They give noise specs in the RCA manual. Whether there is any audible improvement or not is up for debate. It's a cheaper alternative though, and is essentially identical.
A
Hi,
Correct.
The 5751 has a lower mu than the 12AX7A so these are NOT equivalent.
NEVER replace a 12AX7(A) and its' equivalents numbers in a phono preamp unless you're sure RIAA correction does not depend on its' characteritic values.
Often low noise was obtained by...lowering mu and selection for noise figures.
In practice you'll see the heater light up (flash) on a non A suffixed small signal tube when power is applied.
It does not make any significant difference in real life though.
Cheers,
Hi,
Correct.
The 5751 has a lower mu than the 12AX7A so these are NOT equivalent.
NEVER replace a 12AX7(A) and its' equivalents numbers in a phono preamp unless you're sure RIAA correction does not depend on its' characteritic values.
Often low noise was obtained by...lowering mu and selection for noise figures.
In practice you'll see the heater light up (flash) on a non A suffixed small signal tube when power is applied.
It does not make any significant difference in real life though.
Cheers,
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