Super rare 1962 NOS MULLARD ecc83 CV4004 M8137 12ax7 wa e83cc BOX PLATE MILITARY specs Mitcham factory

Here is a rare opportunity to get a superb box plate Mullard ecc83, CV4004 type M8137 like, a special military low noise, low microphony military version of ecc83 12ax7. Rare large ring getter version and marbled glass.

Test results 108 %   112 %

This tube has been made in the special quality Mullard factory of Mitcham in Great Britain in 1962, the second week of August.  Old shield logo.

Code (641) R2H2

Note, I had to use a magnifying glass to be sure of the code because it's partially rubbed. But no ambiguity on the R Mullard Mitcham code.

It has been fully tested and revealed super strong and  well balanced, within 4 % , so perfect for demanding stereo purpose, or deluxe phase inverter.

An ideal tube for high end hifi for example or recording studio devices.

Perfect condition, sold as new or very few use.

Highly sought after by the most regarding audiophiles and professional recording studios. Often mentioned as one of the best ecc83 12ax7 type ever made.
Ruggedized ecc83 type. Superb and totally unique construction with its well known box plate. This one has halo getter, copper getter post and non copper rods . Nice copper foils are used as wires as you can see in photos, superb.

Extended frequency range and more linear than any other Mullard type. Very detailed and upfront "3D" sound with the legendary British Mullard smoothness and harmonics.
Would recommended this tube in pro audio equipment especially in recording studio where the complete integrity of signal must be kept with just the right amount of a great tube flavour.
For mastering tube devices or mic preamp for exemple, this  Mullard CV4004 box plate  is perfect.

This tube is also loved by many guitar players and can be experimented in many different slots of the amp. One of the best , but expensive .... I admit...  phase inverter.

TIPS :p Please note it this tube reacts a lot at what is given to him (it appears more to me than most of tube) . And depending on the guitar pickups impedance it can gives quite different tones. Why probably a lot of poeple did not like that tube in guitar as much as more traditional Blackburn Mullard I61 I63 ecc83 model. It is an excellent guitar or musical instrument tubes . But it sometimes need some try to get the best of it, in term of slot placement in the amp or impedance " feeding " For exemple the sound can be VERY different with a high impedance single coil pickup direct to the tube in V1 or if a buffered pedal is place between

Those military cv4004 box plate  are made to last very very long,
I also applied lower voltage on the heater keeping all other parameters the same and relative emission show a super healthy tube ! Wich means a VERY long life left !
                       

I COMBINE SHIPPING ,

 SO PLEASE HAVE A LOOK AT MY OTHER INTEMS AND SAVE .

Shipping price includes full insurance and tracking

These tubes has been tested for

Heater filament test: Short circuit
Heater filament test: Open circuit
Heater filament test: Tolerance check
Heater cathode insulation: Leakage
Heater cathode insulation: Short Circuit
Tests for heater current abnormalities
Amplification factor
Voltage gain
Power gain
Screen grid test
Mutual conductance test
Dual test for double triodes
Emission
Inter electrode leakage
Inter electrode short circuit
Flash-over (arc detection, high voltage breakdown)
Gas ionisation test

with a first tester

and then with a second tester ( Jackson 648S ) for

Leakage

Filament

Circuit

Shorts

Plate

Life test...

The Jackson 648. It is definitely one of my favorite tube testers. While it does not employ a mutual conductance test circuit, it does use an advanced emission circuit that applies separate element voltages to each tube element, and separate load circuits are also used. “These voltages and loads have been carefully selected for each tube to meet most ideally the normal operating condition of the tube.” (Source: 1950 Jackson catalog.)

In my experience, the Jackson circuitry is very effective, and often will surprise you with accuracy that approaches Hickok’s coveted “mutual conductance” test method. ( Source tubesound web site.)

I do my best to test and describe the tubes the best I can.

Note that test results may vary from one tester to an other so this must be taken as an indication, although my jackson is regulary tested for calibration.

 Photos are part of the description you get what you see.

Private sale so no guarantee or return please.

But if any problem (never happened yet ) please contact me first.

Thank you for your interest.