JJ 12AX7 / ECC83S V1

TT Selection: V1 - Low Noise
This tube is selected for sensitive input stages (V1)

Electro-Harmonix has released a low noise, low microphonic version of the 12AX7 that meets all specifications required for the tube to be designated 7025. The original 7025 tube was a 12AX7 that was tested and selected for the lowest noise and microphonics for use in the critical first preamp stages of amplifiers where noise and microphonics could be an issue. In order to ensure that the 7025 specification is consistently met, Electro-Harmonix has redesigned the structure of the 12AX7 and has implemented construction techniques to ensure the absolute lowest noise and microphonics possible. In all samples tested, noise and microphonics could not be detected.

The Electro-Harmonix 7025EH has a mid-range that gives clarity and definition to the sound and a smooth top end for warmth and balance. With these characteristics, along with the exceptionally low noise and low microphonics, the Electro-Harmonix 7025EH will work equally well in vintage and modern high-gain guitar amplifiers, as well as sensitive phono preamps.

Bias probe for indirect measurement of quiescent bias current of a tube. The adapter is inserted between the tube and the socket and gets connected to a standard voltmeter (not included). Pay attention to the quality of the measuring device and sufficiently charged batteries!

The quiescent current is measured indirectly via a precision resistor integrated in the adapter. The advantages of this measuring method are harmless voltages at the measuring plugs, which are in the mV range, as well as short ways for the current, since it does not need to be fed through the measuring device (common practice with many measuring adapters of Far Eastern production). As a result, there is no risk of oscillations of the amplifier which can lead to possible damage of the tubes or the amplifier itself.

Note: This adapter cannot be used when additional tube brackets are installed. These must be removed before using the measurement adapter and reattached after the measurement is complete.

Procedure for the measurement

Determine the resistance of the adapter, including the measuring leads. To do this, connect the adapter to the meter, but do not plug it between the tubes and the amplifier, yet. Select the measuring range “Ohm” on the meter and note the measured value, e.g. 1,1 ohms.

For the final measurement insert the adapter between the tube and the currentless amplifier and connect it to the meter, select the measuring range mV and switch on the amplifier. When the amplifier has reached a stable operating condition, read the value in mV from the meter and calculate the quiescent current based on Ohm's law.

Example:
measured voltage = 47 mV, resistance of the adapter = 1,1 ohms.
Formula (I = U / R) or in this case:
bias current (in A) = measured value (voltage in V) / measured value (resistance in ohm)
0.047V / 1.1 ohms = 0.042A or 42mA respectively

For the calculation of the correct bias current as well as further information on the bias measurement, please refer to further documents or the bias setting instructions in the info area, as well as the manual of the amplifier itself.

This measuring adapter is suitable for all EL34, 6L6, 6550, KT88, 6V6, 6CA7 and other tubes with the same pin layout.

Attention high Voltage! Measurements and work on tube amplifiers should only be carried out by qualified persons.

2 tubes, matched as pair

Premium power beam tetrode continuing in the Tung-Sol legacy. The ultimate in musical tone and smooth overdrive, STR delivers the sound that established Tung-Sol as the benchmark of quality.
Faithful re-issue of the original Tung-Sol STR, built to the same “Special Tube Request” specs of amp manufacturers of the 60s.

Files

• Datasheet

 

TT Selection: V1 - Low Noise
This tube is selected for sensitive input stages (V1)

ECC82 / 12AU7 medium gain pre-amplifying double triode.
Provides a very smooth sound with well-defined tones suitable for audio and guitar amplifiers.

Files:

• Datasheet

6 tubes, matched as sextet

Very credible 6550 so far.
We recommend this 6550 for bass amps which are working with 6550 tubes, especially Ampegs.

Files:

• Datasheet

4 tubes, matched as quad

EL34 II has fuller low mids and low end but does not lose headroom in the high end. Stronger than regular JJ EL34 but not as aggressive as the JJ E34L.

Typical Characteristics

• Ua = 250 V
• Ug3 = 0 V
• Ug2 = 265 V
• Ug1 = -13,5 V
• Ia = 100 mA
• Ig2 = 14,9 mA
• S = 11 mA/V
• Ri = 15 kΩ
• μg2/g1 = 11

Limiting Values

• Ua0 = 2000 V
• Ua = 800 V
• Wa(max) = 25 W
• Ug20 = 800 V
• Ug2 = 450 V
• Wg2(max) = 8 W
• Ik = 150 mA
• Uk/f = 100 V
• Rk/f = 20 kΩ

Files:

• Datasheet

2 tubes, matched as pair

Standard EL34 made by JJ with a smooth and dizzy sound.

Limiting Values:

• Ua0: 2000 V
• Ua: 800 V
• Wa(max): 25 W
• Ug20: 800 V
• Ug2: 450 V
• Wg2(max): 8 W
• Ik: 150 mA
• Uk/f: 100 V
• Rk/f: 20 kΩ

Files:

• Datasheet