Updated 16 DEC 2005
12AX7, ECC83, 7025 Tubes - additional information and
response curves and misc tube charts and data
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ECC83 Response Curves
The graph on the left shows the
aspects of ECC83 performance in a
general amplifer - a Fender Twin
Reverb Blackface. This will be
applicable to performance changes
between two types of tubes in most
amplifiers.
The ECC83 has stronger mids and
low, with more pronounced mids than
most of the 12AX7 family of current
tubes. It is less bright on the high
end than current 12AX7R2, R3, and
7025 tubes.
The ECC83 is one of the factors that
make a Marshall sound like a
Marshall in the 1987, 1959, and JTM
45 series as an example.
The BLUE line is the ECC83. The
GREEN line is a reference Sovtek
12AX7WA tube. The 12AX7WA was
chosen as a reference, as this is one
of the most common tubes as
supplied by tube makers today as
stock issue rather than an NOS tube.
ECC83 at a glance
A reference tube has a target of 1.2 millamps, a TC 0f 1600, and a gain of 100. Few tubes made
today can produce these original specifications. It is strongly suggested that you know and trust
your tube vendor, as on most newly made preamp tubes, there is a swing of more than +/- 50% in
any given factory runs within the same batch of the same type! A reference tube has a target of
1.2 millamps, a TC 0f 1600, and a gain of 100. Few tubes made today can produce these original
specifications.
Compared to "spec" for this tube:
Average output = 1.3 milliamps
Average transconductance = 1604
Average gain = 85%
Low output in sample run = 0.9 milliamps
High output in sample run = 1.6 milliamps
Ei 7025 long smooth plate response
curves
These tubes are generally some of the
lowest output tubes in the 12AX7 family.
Their gain is close to par, but gain is
not the same as output, as you have
learned in some of my other writing.
These have a bright high end, the most
bright of any of the 12AX7/ECC83/7025
family. The NOS long plates such as
the RCA's and GE's of the past, were
used in many Fender amps, known for
their bright clear tone.
The BLUE line is the 7025 Ei, and the
GREEN line is the reference Sovtek
12AX7WA. The Ei has less low and mid
response, but comes on stronger in the
mid high and high range. These are
too bright for some tastes in an amp
like a Marshall, when using a Strat or
Tele sort of guitar.
In a Marshall amp with it's input loaded
with pedals, these will get back some of
the lost treble and sparkle as a quick
"fix" for a loaded down front end.
These tend to be more microphonic in
many combo amps, due to a longer
plate structure. This is even more
severe than in the 12AX7R2 (Sovtek
12AX7LPS), which also has a long plate
structure.
The gain on these is higher than a lot
of tubes today, but the current is lower
than most. This sort of means, in a
clean and simple front end (Fender
tweed or tolex era amp, or even plexi
era Marshalls), they will be articulate.
But, in a complex front end amp such
as a Bogner, Mesa, or any hybrid amp,
they may not have the "push" to make it
through all that mass of circuitry.
Be sure you know and trust your
vendor on these. They can sound
great, but can become microphonic in
short order unless well screened by
your tube supplier.
Ei 7025 at a glance
A reference tube has a target of 1.2 millamps, a TC 0f 1600,
and a gain of 100. Few tubes made today can produce these
original specifications. It is strongly suggested that you know
and trust your tube vendor, as on most newly made preamp
tubes, there is a swing of more than +/- 50% in any given
factory runs within the same batch of the same type! A
reference tube has a target of 1.2 millamps, a TC 0f 1600, and
a gain of 100. Few tubes made today can produce these
original specifications.
Compared to "spec" for this tube:
Average output = 0.6 milliamps
Average transconductance = 1064
Average gain = 90%
Low output in sample run = 0.4 milliamps
High output in sample run = 0.7 milliamps
Tube data chart - This may be hard to decipher in it's formatting, so if you have any questions, just
drop me an email from cutting and pasting a particular line, and I will try to get back to you with
some help.
Tube Tolerance Ave output % of mA expected Ave TC (gm) TC % Average gp Average Gain
GE 6072A 1970s Date Code * 2.6% 96% 1710 1750 42/44
GE 6072A Black Plate 1963 * 1.9% 100% 1750 1750 44/44
GE 12AX7WA (1980s) * 8.7% 92% 1520 1600 98/100
GE 5751 (1950s) 2.5% 98% 1190 1200 69/70
JAN/Philips 12AT7WC 1980s * 11.6% 105% 5780 5500 72/70
RCA 12AX7 NOS 1950s-60s 8.8% 99% 1620 1600 100/100
RCA 5751 Black Plate (1950s) * 3.7% 96% 1251 1200 69/70
RCA 7025/12AX7 NOS 1960s * 6.6% 97% 1580 1600 97/100
Telefunken ECC83/12AX7 - diamond base * 11.6% 102% 1680 1600 102/100
RCA 12AU7 NOS Cleartop * 2.1% 96% 2180 2200 18/18
12AX7 Telefunken smooth plate new Dynaco 12.6% 102% 1610 1600 98/100
12AX7/ECC83 Telefunken Diamond Bottom Ribbed Plates * 2.7% 94% 1680 1600 105/100
12AX7 MINIWATT / SUPER RADIOTRON AUSTRALIA 1960s 0.8% 100% 1606 1600 100/100
12AX7 Amperex Bugle Boy Holland LONG PLATE 1950s * (10) 4.4% 112% 1640 1600 105/100
12AX7 AMPEREX BUGLE BOY HOLLAND 1967 * 6.1% 109% 1580 1600 101/100
7025 Amperex Holland orange Globe Logo 1971 7.7% 94% 1690 1600 92/100
CV4004 Brimar 1961 4.5% 92% 1570 1600 91/100
CV4035 / 12AX7 Brimar NOS flying leads 9.8% 108% 1740 1600 112/100
7025 GE ribbed plates 1950s * 2.2% 100% 1610 1600 99/100
7025 GE ribbed plates 1960s 3.7% 100% 1590 1600 102/100
M8137/CV4004/12AX7 Mullard Box Plates * 11.2% 92% 1640 1600 92/100
12AX7 Raytheon black ribbed plates square getter halo 1950s * 5.4% 94% 1520 1600 100/100
JRC-12AX7 RCA Black Plates 1954 * 4.9% 101% 1590 1600 100/100
12AX7A RCA gray ribbed plates 1960's-1970's * 12.6% 93% 1660 1600 96/100
ECC83/12AX7 Siemens long plates early 1960s * 9.9% 95% 1620 1600 104/100
12AX7 Sylvania Gray Plate square getter halo 1958, 1959 * 8.2% 102% 1710 1600 101/100
12AX7R3 Electro Harmonix (10/7/02) 25.0% 95% 1507 94.19% #DIV/0!
12AX7R3 Electro Harmonix (10/29/02) 16.7% 85% 1382 86.38% 0.0162 85.31
12AX7R3 Electro Harmonix (12/12/02) 16.7% 83% 1403 87.69% 0.0161 87.14
12AX7C - Chinese (10/28/02) 25.0% 83% 1461 91.31% 0.0160 91.31
12AX7C - Chinese (12/13/02) 16.7% 92% 1588 99.25% 0.0170 93.41
ECC83 JJ (10/07/02) 33.0% 93% 1467 91.69% #DIV/0!
ECC83 JJ (11/07/02) 66.7% 113% 1664 104.00% 0.0195 85.33
ECC83 JJ (12/13/02) 58.3% 112% 1604 100.25% 0.0189 84.87
12AX7R - Sovtek 12AX7WA 10/7/02 41.7% 78% 1190 74.38% #DIV/0!
12AX7R - Sovtek 12AX7WA - (10/28/02 batch) (note a) 41.7% 88% 1293 80.81% 0.0147 87.96
12AX7R - Sovtek 12AX7WA - (12/13/02 batch) 41.7% 78% 1180 73.75% 0.0137 86.13
12AX7R2 Sovtek LPS (10/7 batch) 50.0% 83% 1469 91.81% #DIV/0!
12AX7R2 Sovtek LPS (10/23 batch) 67.0% 70% 1418 88.63% #DIV/0!
12AX7R2 Sovtek LPS (10/31 batch) 75.0% 83% 1505 94.06% 0.0182 82.69
12AX7R2 Sovtek LPS (12/12 batch) 42.0% 97% 1557 97.31% 0.0186 83.71
7025 - Ei (10/31 batch) 33.3% 87.50% 1419 88.69% 0.0155 91.55
7025 - Ei (12/12 batch) 25.0% 46.67% 1064 66.50% 0.0118 90.17
Svetlana 12AX7 4/8/03 42.0% 72.50% 1369 85.56% 90.66
JJ 12AT7 / ECC81 4/7/03 - output = 8.9/ 10.0 gain = 58.8 / 60.5 TC = 4711 / 5500
GE 6072A 1970s Date Code * 2.6% 96% 1710 1750 42/44
GE 6072A Black Plate 1963 * 1.9% 100% 1750 1750 44/44
GE 12AX7WA (1980s) * 8.7% 92% 1520 1600 98/100
GE 5751 (1950s) 2.5% 98% 1190 1200 69/70
JAN/Philips 12AT7WC 1980s * 11.6% 105% 5780 5500 72/70
RCA 12AX7 NOS 1950s-60s 8.8% 99% 1620 1600 100/100
RCA 5751 Black Plate (1950s) * 3.7% 96% 1251 1200 69/70
RCA 7025/12AX7 NOS 1960s * 6.6% 97% 1580 1600 97/100
Telefunken ECC83/12AX7 - diamond base * 11.6% 102% 1680 1600 102/100
RCA 12AU7 NOS Cleartop * 2.1% 96% 2180 2200 18/18
12AX7 Telefunken smooth plate new Dynaco 12.6% 102% 1610 1600 98/100
12AX7/ECC83 Telefunken Diamond Bottom Ribbed Plates * 2.7% 94% 1680 1600 105/100
12AX7 MINIWATT / SUPER RADIOTRON AUSTRALIA 1960s 0.8% 100% 1606 1600 100/100
12AX7 Amperex Bugle Boy Holland LONG PLATE 1950s * (10) 4.4% 112% 1640 1600 105/100
12AX7 AMPEREX BUGLE BOY HOLLAND 1967 * 6.1% 109% 1580 1600 101/100
7025 Amperex Holland orange Globe Logo 1971 7.7% 94% 1690 1600 92/100
CV4004 Brimar 1961 4.5% 92% 1570 1600 91/100
CV4035 / 12AX7 Brimar NOS flying leads 9.8% 108% 1740 1600 112/100
7025 GE ribbed plates 1950s * 2.2% 100% 1610 1600 99/100
7025 GE ribbed plates 1960s 3.7% 100% 1590 1600 102/100
M8137/CV4004/12AX7 Mullard Box Plates * 11.2% 92% 1640 1600 92/100
12AX7 Raytheon black ribbed plates square getter halo 1950s * 5.4% 94% 1520 1600 100/100
JRC-12AX7 RCA Black Plates 1954 * 4.9% 101% 1590 1600 100/100
12AX7A RCA gray ribbed plates 1960's-1970's * 12.6% 93% 1660 1600 96/100
ECC83/12AX7 Siemens long plates early 1960s * 9.9% 95% 1620 1600 104/100
12AX7 Sylvania Gray Plate square getter halo 1958, 1959 * 8.2% 102% 1710 1600 101/100
Tesla ECC802S 10.9 of 10.6 2153 2200 16 / 17
Tesla ECC82 11.1 of 10.6 2601 2200 18.8 / 17
