Identify your tube
mC1:
- 17mm long plates.
- Square getter on 2 support posts, aka "cage" getter.
- Copper plate posts.
#f91
Many folks, especially hi-fi-audiophiles prefer this f91 design, to even the mC1, for it's smoother, and more accurate, mid/upper-mid frequency range. Identical design and date code: valve 1: f91 B8D; valve 2: f91 B8D; The f91 is the only Mullard design using a halo getter which incorporates the double 'goalpost' getter support as used in the mC1. Manufactured from July 1957 until early 1959 only. 17mm long plates. Halo getter on 2 support posts (goalpost getter support).
Of all the designs of ecc83, the most golden- and huge- sounding are the 1950's 17mm "long plates". They are also much rarer than the later 13mm "short plates".
However, the plates were shortened in later designs in order to reduce microphony, which all valves exhibit to some degree. Long plates have generally higher levels of microphony, and greater variation too.
Getters and plates are means of gauging a period of time in which an actual tubes was produced.
Plates
Long Black Plate
From 1940~ to 1957~
Long Gray Plate
Around 1957-1959
Short Gray Plate
From 1960~ onwards
Square Plate
The square plate ECC83 is actually a military tube which is built to an even higher standard than the standard ECC83. The square plate ECC83 is usually disguised as a CV4004, CV492, B339, M8137. They were built in the Mitcham factory (date code "R") in the 1950s and later on in the 1980s - after the Blackburn factory (date code "B") has shut down.sourced(link: text: )
Getters
In America
From the oldest to newest:
- Square Getter
- D Getter
- Large O Getter
- Small O getter (from 1964~ onward)
In Europe
From the oldest to newest:
- Foil Getter
- D Getter
- Large O Getter
- Small O Getter
Some says are the best tubes
- RCAs black plate 12AX7 with square D getter, from late 1950.
- Mullard branded IEC Mullard are from late 60s's onwards, and are quite inferior to the early 60's versions.