hellaboogie
New member
What's your favorite ECC81 / 12AT7 for phase inverter and also for gain stages
T
TrueTone500
Banned
New member
Use 5751 for a PI tube, not 12AT7.
stephen sawall
SEMI ERECT MEMBER
12AX7 in a lot of amps are not interchangeable 12AT7 and many other tubes. In this case because a 12AT7 draws double the current of a 12AX7. When switching tubes in amps that are not designed to use a variety of tubes be very careful that the tube will not cause damage to the amp.
This is a list of common tubes that fit within the parameters of a 12AX7....
12AX7
This is the original version of this tube. The earliest ones were all made in the USA by the usual manufacturers like RCA, Sylvania, GE and Tung Sol. Very early ones have rather large size plates. The "plain" version without the "A" suffix can only be used in parallel filament circuits, not series, unless the filament circuit is DC powered.
12AX7A
This later version has improved noise specs, mostly due to the improved filament design and can be used in series or parallel AC or DC filament circuits. Many manufacturers produced plain 12AX7's well into the 60's and 70's, but many of those could be 12AX7A's marked 12AX7. Current production noisy or untested tubes are often labeled 12AX7 while tested and selected ones are usually designated 12AX7A.
7025
This is the "hi fi" low noise version of the 12AX7. All other specifications are the same as 12AX7. Tubes marked with 12AX7 and 7025 both should be low noise, too.
ECC83
This is the European equivalent to 12AX7
ECC803, ECC803S E83CC
This is the "premium" version of the European 12AX7. The "S" on the ECC803S means "select" version. These are usually found on Telefunken brand tubes.
5751
This is the "milspec" version of the 12AX7, but is also slightly different. The 5751 has the same plate resistance as the 12AX7, but the gain factor is only 70 compared to 100 for the 12AX7. The 12AT7 also has a gain factor of 70, but since its plate resistance is lower, it draws more plate current than the 5751 and 12AX7, making it less suitable for use in low current high gain stages. The older "real" 5751's have extra thick mica spacers and extra support rods to minimize microphonics.
6681
Mobile version of the standard 12AX7. These are usually standard 12AX7's which have been specially tested to assure they will perform well in circuits with 20% variation in filament voltage. Amperex Holland 6681s are a great example of this tube, and very well suited for use in guitar amps.
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As mentioned above a 5751 might be what you want / A 12AT7 is also rated at about 70% of a 12AX7. 12AX7 rates at 100, 12AT7 rates at 70. All the rating are a average.... I have seen 12AX7's that rate as high as 135 and low of 70.
This is a list of common tubes that fit within the parameters of a 12AX7....
12AX7
This is the original version of this tube. The earliest ones were all made in the USA by the usual manufacturers like RCA, Sylvania, GE and Tung Sol. Very early ones have rather large size plates. The "plain" version without the "A" suffix can only be used in parallel filament circuits, not series, unless the filament circuit is DC powered.
12AX7A
This later version has improved noise specs, mostly due to the improved filament design and can be used in series or parallel AC or DC filament circuits. Many manufacturers produced plain 12AX7's well into the 60's and 70's, but many of those could be 12AX7A's marked 12AX7. Current production noisy or untested tubes are often labeled 12AX7 while tested and selected ones are usually designated 12AX7A.
7025
This is the "hi fi" low noise version of the 12AX7. All other specifications are the same as 12AX7. Tubes marked with 12AX7 and 7025 both should be low noise, too.
ECC83
This is the European equivalent to 12AX7
ECC803, ECC803S E83CC
This is the "premium" version of the European 12AX7. The "S" on the ECC803S means "select" version. These are usually found on Telefunken brand tubes.
5751
This is the "milspec" version of the 12AX7, but is also slightly different. The 5751 has the same plate resistance as the 12AX7, but the gain factor is only 70 compared to 100 for the 12AX7. The 12AT7 also has a gain factor of 70, but since its plate resistance is lower, it draws more plate current than the 5751 and 12AX7, making it less suitable for use in low current high gain stages. The older "real" 5751's have extra thick mica spacers and extra support rods to minimize microphonics.
6681
Mobile version of the standard 12AX7. These are usually standard 12AX7's which have been specially tested to assure they will perform well in circuits with 20% variation in filament voltage. Amperex Holland 6681s are a great example of this tube, and very well suited for use in guitar amps.
......................................................................................................
As mentioned above a 5751 might be what you want / A 12AT7 is also rated at about 70% of a 12AX7. 12AX7 rates at 100, 12AT7 rates at 70. All the rating are a average.... I have seen 12AX7's that rate as high as 135 and low of 70.
2
2tallmusic
Member
TrueTone500":2yscxfd0 said:
I'd say this depends very much on the amp. Consider e.g. older Fender amps.
2
2tallmusic
Member
hellaboogie":2t8r3x0f said:
I use a Telefunken ECC81 in the PI of my Rivera.
blackba
Well-known member
I highly recommend the Mullard cv4024, I use those in my fender amps, great tubes. They run are $30 a pop, so they are not outrageously priced for a nos tubes.
