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12AX7 - 12AX7A - 12AX7WA - ECC83 - ECC803S - E83CC - CV4004 -

CV492 - 6681 - 6057 - M8137 - 5751  (click for NOS 5751 tubes)

Descriptions of 12ax7 Vacuum tube types and variants:

ECC83: This European nomenclature for 12AX7 vacuum tube.

ECC803/ECC803S/E83CC: This "premium" version of European made 12AX7 vacuum tube.

The "S" on the ECC803S indicates "select" and are usually gold pin. These are usually found on

Telefunken brand tubes and a very rare Radiotron ecc803S vacuum tube from the Philips factory in Australia, and on Siemens 12ax7 variant tubes.

12ax7:   Original version of the 12ax7 vacuum tube. Early production was manufactured in the USA by Tung Sol, RCA,

Sylvania, GE etc. The earliest 12ax7 vacuum tubes have larger plates. The 12ax7 version without an "A" suffix is to be used

only in parallel filament circuits, so do not use these in a “series” circuit. This is an unusual problem to run into as they are

normally found in TV sets. The best way to tell if your circuit is a series circuit is by examining all of the vacuum tubes and

looking at the voltages (voltages other than 6 and 12 volts). If all tubes in your circuit start with 6 or 12

(except for 5 Volt rectifiers) , then it is a parallel.

12ax7a: Can be used in series or parallel circuits. Many manufacturers marked 12AX7's as 12ax7 without the “A” suffix

well into the 60's and 70's, but these are most often 12AX7A's marked as 12AX7.

12AD7: Non-microphonic/low hum version of the 12AX7 vacuum tube made by Sylvania.  Great for audio applications that

uses the 12AX7 vacuum tube.

12DT7, 12DM7, 12DF7: Special quality low noise/low microphonic versions of the 12AX7 vacuum tube.  Usually branded as 

Westinghouse or Raytheon.

7025: Hifi low noise version of the 12AX7 vacuum tube with all other specifications being the same as 12AX7.

Tubes marked with both 12AX7 and 7025 are usually low noise vacuum tubes as well.

5751: Military version/drop in replacement for the 12AX7 vacuum tube, but is actually different. The 5751 vacuum

tube has identical plate resistance to the 12AX7, but the gain is 70 compared to 100 for the 12AX7 vacuum tube.

Early production 5751 vacuum tubes have extra thick mica spacers (often three know as triple mica) and extra support

rods to minimize microphonic response. Many 5751 vacuum tubes also have matched triode units.

7729: CBS made industrial vacuum tube with gold pins for special applications requiring reliability and low noise/low

microphonics.

6681: The mobile version of 12AX7 vacuum tube.  Usually these are the same as a regular 12ax7 vacuum tube which have

been tested and screened to perform well in circuits with large variations in  filament voltage. 

7058: Same as a 12AX7 vacuum tube with a 13.5 volt non-tapped filament.  Can be used in circuits which do not utilize the

6.3V filament tap. Performance is same as regular 12ax7 vacuum tube.

Suggestions on our best sounding IN STOCK 12ax7 vacuum tubes to buy now :

• Mullard CV4004: Very LOW noise, immaculate detail, wonderful warmth and articulation
• Philips Heerlen Holland 12ax7 (labeled as Philips, Amperex, GE, etc):
• Incredible liveliness and 3
• dimensional sound, beautiful
• vocal quality mids!!
• Siemens E83CC Munich : Special quality design, transparent, with amazing clarity, detail, resolution,
• and high end extension!
• All made in Munich Germany 1977-1979
• Tungsram CV492: Perfect for guitar amps ( this is my personal favorite!)
• Very very open with amazing top end and balanced all the way through!
• Sounds beautiful when pushed. Recommended for Train wreck amplifiers. Back In Stock!!!
• GE JG 12ax7: Excellent value, warm nice detail and an articulation which is unmatched for the money!
• Telefunken smooth or ribbed plate 12AX7: Incredibly high resolution tubes! 
• Known for their detailed clarity and extension in the high end range!
• PRE-War Yugo made 12ax7-  "I love the Ei 12AX7 tubes of old, they were hands down the best sounding pre-amp tubes.” 
• Dr. Z   Owner/Creator Z Amplification. Various Brandings such as Siemens, Audio Research, Lorenz, etc CV492 (see below)

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