The 6SN7 Identification Guide

Discussion in 'Headphone Amps (full-size)' started by adhoc, Dec 5, 2006.
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  1. adhoc Contributor
    0. Introduction & preamble

    FEEL FREE TO POST REPLIES TO THIS THREAD!!!

    Found a mistake? Have a suggestion? Got photos you want to share? Send them all to the following email address:

    6sn7gt-at-gmail-dot-com

    (just replace ‘-at-‘ and ‘-dot-‘ with ‘@’ and ‘.’ respectively. DIE, SPAM, DIE!!!)



    While every effort is taken to maintain the accuracy of this thread, mistakes do get through. Please let me know if you find any! Thanks!




    Version history
    1.0 - 05/12/2006 - Original thread set up


    A quick note regarding nomenclature:
    ‘6SN7’ is not an actual tube designation – the earliest designation was ‘6SN7GT’. In this thread, ‘6SN7’ is loosely used as a ‘master term’ to refer to 6SN7GTs, 6SN7GTAs, 6SN7GTBs, 6SN7Ws, etc – in other words, all the available permutations of the 6SN7GT tube. It is interesting to note though that European tube manufacturers sometimes just labeled tubes ‘6SN7’.



    This thread is divided into 6 sections:

    0. Introduction and Preamble (this post)
    1. VT-231s
    2. US-made NOS 6SN7s
    3. 5692s
    4. European NOS 6SN7s
    5. Other non-US NOS 6SN7s


    And so it begins…

    This thread archives the physical construction of popular NOS 6SN7 tubes, with the aim of helping tube buyers make informed purchases. Tube relabeling was indeed common ‘back in the day’, but a tube’s construction will *always* betray its true origins.

    More disturbingly, as the demand for NOS 6SN7s rises, so will the number of unscrupulous sellers counterfeiting tubes with intent to make a quick buck. The information contained here is the best weapon tube lovers can use against such counterfeiters.

    The 6SN7GT tube type was formally registered in 1941 by RCA and Sylvania. The 6SN7GT is an octal base medium-mu (20) [i.e. medium amplification] double-triode tube. It runs on a heater current of 0.6A (@ 6.3V). The 6SN7GT type is essentially two 6J5-type single-triodes within a single envelope.

    The 6SN7GT is the direct descendant of the straight sided 6F8GT. This in turn was a straight-sided glass envelope which descended from the ‘coke-bottle’ shaped 6F8G.

    [Tube nomenclature 101: having a lone ‘G’ designation after the tube type indicated that the tube utilized a ‘shoulder-tube #12’ type glass envelope; the ‘coke-bottle’ shape. A ‘GT’ designation in turn meant that the tube had a straight-sided glass envelope.]

    The 6F8G was a first attempt at placing two 6J5G triodes in a single envelope, but was unpopular due to its unwieldy shape and top grid cap, which necessitated extra connectors.


    6SN7 equivalents

    There are a few direct electrical equivalents of the 6SN7GT, and they are as follows:

    7N7 – short lived loktal base version registered by Sylvania/Raytheon in 1940
    CV1988 – British designation; Civilian Valve #1988. Made by Brimar.
    6N8S – Soviet designation, still in use today
    B65 – metal based tube produced by the Marconi Group of companies
    13D2 – Brimar made ‘industrial’ 6SN7GT (many GE manuals wrongly characterize this tube as having a 12.6V heater.)

    It is useful to note that the following types, namely:

    ECC32
    ECC33
    5692* (see note below)

    …are, contrary to popular belief, not perfect electrical equivalents of the 6SN7 type. Substituting these tubes in place of 6SN7s in your equipment may result in damage.

    *: 5692 types can be run at 6SN7 specifications and function identically even though they were technically not designed to do so (more on that later).

    More commonly, unique nonlinearities in amplification caused by deviation from 6SN7 specifications lend characteristic ‘sounds’ to these tube types. These unique ‘sounds’ in turn are often misconstrued as being ‘better’ – a notable example of this would be how the ECC32 type is often perceived to have ‘better sound’ due to it’s higher gain. The human mind gives preferential attention to louder sounds, and the result of substituting ECC32s in place of 6SN7s is more often than not subjectively perceived to be ‘better’.


    6SN7 variants

    The 6SN7A and 6SN7W were both short-lived designations for 6SN7GTs made to military specifications. Their construction included an additional ‘free-standing’ support post between the micas for greater vibration tolerance. It is likely that there were little, if any, additional selection criteria imposed upon A/W designations that were not already fulfilled by GT specifications. These designations used from (approximately) 1941 to 1945.

    The VT-231 (‘Vacuum Tube #231’) designation was used throughout WWII by the US Army Signal Corps. It should be noted that the term ‘VT-231’ was simply an inventory control number and thus lends no special significance to the tube so labeled. There is a full section devoted to VT-231 and JAN tubes later in this post.

    The 6SN7GTA and GTB versions were introduced in 1950 and 1954 respectively. They have ‘upgraded’ ratings, which are as follows.

    GTA: maximum anode dissipation upgraded to 5W (the GT is rated for 2.5W)
    GTB: identical to the GTA, but with a controlled heater warm up time for use in equipment with 600mA heater strings

    This is significant because it means that a circuit designed around the 6SN7GTA/GTB cannot have 6SN7GTs substituted into it. Substituting a GT in place of a GTA/GTB in your equipment will precipitate its rapid destruction and possibly damage your equipment.

    Tubes labeled 6SN7GTC were made in the late 60s and early 70s. They are electrically identical to 6SN7GTBs but have their glass envelopes replaced by black colored metal envelopes. These tubes were mostly manufactured in South America.


    VT-231s and ‘JAN’ rated 6SN7s

    The VT-231 designation was a military inventory control number, and should be taken as nothing more than that. Assuming identical construction, there is zero difference between a tube labeled VT-231 and a 6SN7GT of the same vintage. A lot of mystique has been built up around VT-231 labeled tubes by tube sellers, and many people mistakenly believe

    ‘JAN’ stands for ‘Joint Army-Navy’, and was meant to indicate that the tubes labeled as such were ‘passed’ for military use. However, no additional criteria that were not already fulfilled by the 6SN7GT specification were known to have been imposed. ‘JAN’ labeled tubes are identical to non-JAN tubes of the same vintage and construction.

    The ‘JAN’ naming convention was always written as follows:

    JAN-<manufacturer>-<tube type>

    Thus examples of JAN ratings would include: JAN-CTL-6SN7GT, JAN-CHS-5U4G, JAN-CRC-6AS7G, etc.

    JAN manufacturer abbreviations:
    CHS – Sylvania
    CHY – Hytron or CBS-Hytron
    CKR – KenRad
    CL – GE
    CRC – RCA
    CRP – Raytheon


    5692 types

    The 5692 was designed by RCA in response to a particular problem involving radar-controlled artillery pieces. Bouts of intense vibration (while firing) were rapidly destroying 6SN7GT types in such equipment. The 5692 was designed to withstand such stress, and has extra rugged construction with features such as an extra top mica, 5 additional freestanding support posts and a low profile. The 5692 was patented in 1948 but not produced till 1951.

    5692 types were advertised as a 6SN7GT substitute that had a vastly extended lifespan – 10,000hours. This outlandish claim, however, falls apart when you examine the recommended operating specifications of the 5692. The 5692’s recommended operating parameters are much lower than those of the 6SN7GT; any 6SN7GT would last far longer (maybe even 10,000hours?) when run at 5692 ratings.

    There are 2 ‘general types’ of 5692s – red bases and brown bases. The red bases in particular may have their color vary from a bright cherry-red to a dark, deep red easily confused with brown.

    Who actually produced 5692s in the USA is a controversial issue amongst tube lovers; here are some of the competing theories:

    -All red base 5692s were made by RCA.
    -All red base 5692s were actually made by GE, but for RCA (explains the high incidence of GE labeled red bases).
    -All brown base 5692s were made by CBS-Hytron.
    -Raytheon made a brown base 5692.
    -Sylvania made a brown base 5692.
    -Westinghouse made a brown base 5692.

    [My opinion, based on personal experience, is that GE made red-based 5692s for RCA, and that CBS-Hytron (earlier) and Sylvania (later) made brown-based 5692s.]

    There is only one known European equivalent of the 5692 type: a Swedish-made brown base version designated either 33S30A or 33S30B.

    In the late 1960s, 6SN7GTBs were often relabeled as 5692s. Remember – if the construction doesn’t include the special features unique to 5692s (mentioned earlier), it isn’t a ‘real’ 5692.

    (Very) rarely, 5692s have been known to be labeled as 6SN7GTBs.


    A note on glass colour (‘smoked’ glass tubes)

    Tubes with black or grey glass were only made en-masse till the early 1950s, after that they become vanishingly rare. What happened?

    The black/grey coat was a carbon/graphite coat, designed to prevent electrons from massing on the glass and exerting an undue influence on tube operation (massed negative charges).

    Whether its eventual disappearance was the result of cost-cutting measures, or the introduction of new glass that was somehow resistant to this electron massing is unknown.


    ** Descriptive terms used in this guide **

    This guide uses descriptive terms liberally. To prevent confusion, they are defined as follows:


    Base: Bases were almost always made of plastic (Bakelite?). Brown bases are usually made of micanol, a ‘low loss’ material – 6SN7s with micanol bases are sometimes designated 6SN7GTY. Rarely, some bases are ‘metal’ – a metal (nickel alloy) strip was wrapped around the glass base of a tube and glued on. These metal strips will corrode if improperly stored and often fall off due to old age. Some tubes produced in the late 1960s to 1980s come with ‘button’ bases – the plastic base is no longer a large cylinder but looks more like a plastic button affixed to the bottom of the tube instead.

    Glass: Almost all 6SN7s have straight sided glass envelopes. Glass may either be ‘smoked’ (blackened or greyed) or clear. Glass envelopes often vary slightly in height even amongst examples of identical construction and vintage, but generally fall into 2 broad categories – ‘tall bottle’ and ‘short bottle’. An extreme example of a tall bottle 6SN7 would be the Sylvania VT-231 while the opposite would be any 5692 tube.

    Getter: More accurately known as ‘getter flashing’. A getter is the silvery coat of pure barium metal deposited on the inside of a tube to ‘get’ (react with) free gas molecules within the tube, which would otherwise interfere with tube operation. A ‘top getter’ is located at the top of the tube, a ‘bottom getter’ is located at the bottom of the tube, and so on and so forth.

    When referring to the getter ‘shape’ we are talking about the ‘getter holder’. The getter holder is a structure within the tube that held the barium metal before it was ‘flashed’ onto the inside surface of the tube. Common getter shapes in 6SN7s include ‘ring’ (also known as ‘O’), ‘D-shaped’, ‘foil’ (looks like a piece of aluminum foil), ‘square’ (a square ring), rectangular (a rectangular ring) or ‘cup’ (looks like an inverted cup).

    Mica: Mica is a naturally obtained mineral, and is used extensively in tube construction due to its ability to withstand high temperatures whilst maintaining its electrically insulative properties.

    Micas are located near the top and bottom of tubes, and are described in terms of their location and shape. An example would be ‘round top mica with rectangular bottom mica’. Descriptors such as ‘round’, ‘rectangular’, ‘square’ and ‘racetrack’ are self-explanatory. A ‘scalloped’ mica is a mica that looks as though a creature has taken a small nibble out of the edge at regular intervals. A ‘spiked’ mica is one that has little spikes extending out. Scalloped and spiked micas can occur with any mica shape.

    Mica spacers: Mica spacers are pieces of mica attached anywhere within the tube that serve to brace the internal construction against the glass to improve its vibration resistance.

    Plate: Plates are more correctly known as ‘anode plates’, and are the large metallic structures that extend between the top and bottom micas. There are always 2 separate plates in 6SN7 tubes. They are described in terms of color and shape. Color is self-explantory – plates are usually either grey or black. Shape is a little more tricky though.

    ‘T-plates’ (also known as ‘box plates’) are plates that have a ‘T’ shaped cross section.

    ‘Triangular plates’ are plates that have a triangular cross section.

    ‘Flat-plates’ are not actually perfectly flat, but have thin and long rectangular cross sections.

    ‘Round-plates’ or ‘oval-plates’ are plates that have a circular or oval cross section.

    ‘Ridged’ (or ‘embossed’) refers to the raised shapes stamped onto the plates. These often have a pattern that looks somewhat like a ladder.

    ‘Smooth’ plates are plates that have no ridging/embossing on them – in other words, perfectly smooth.

    ‘Angled plates’ are plates that are at strange angles to each other – in other words, not directly mirroring each other in placement and orientation.

    ‘Staggered plates’ are flat-plates that are parallel to each other, yet at a ‘funny’ angle when viewed from above, like this: / / or \ \ (as opposed to | | or =)

    Examples of plate descriptions would include ‘black T-plates’, ‘grey staggered flat plates with ladder ridging’, etc.

    Support posts: support posts are additional metal posts that extend between the top and bottom micas and serve to brace the tube internals against vibration.


    [​IMG]
     
    EELawson and Wildcatsare1 like this.
  2. adhoc Contributor
    1. VT-231s

    Hytron
    Hytron was bought by CBS in 1952. Tubes made by Hytron post-1952 have ‘CBS-Hytron’ or plain ‘CBS’ labeling.
    Base: black with white labels
    Glass: clear
    Plates: black, T-plates
    Getter: bottom, rectangular, flashing rarely extends up past plastic base
    Top mica: rectangular
    Other significant features: top and bottom micas are identical


    KenRad
    Base: black, white labels sometimes written in a ‘gothic’ font
    Glass: black (very common) or clear (less common)
    Plates: black, flat with ‘ladder’ ridging, ‘staggered’ arrangement
    Getter: bottom, flashing extending up to 1/3 of the way up tube
    Top mica: rectangular with 3 spikes on both shorter sides
    Other significant features: line of small holes down longitudinal midline of top mica. Protruding grid posts and plate anchors on top mica have distinctive ‘staggered’ pattern.


    ‘National Union’
    National Union never made a tube labeled 'VT-231'. However, National Union did make a JAN-rated 6SN7GT (JAN-CNU-6SN7GT). These came in 2 flavors – (earlier) grey glass and (later) black glass. Check the US-made 6SN7GT section for more on National Union 6SN7GTs.


    RCA
    Base: black with silver labels
    Glass: grey extending right from base to near the top, usually opaque
    Plates: black (difficult to see except with a very strong torchlight)
    Getter: bottom, flashing extending up past plastic base
    Top mica: round
    Other significant features: 2 stabilising rectangular mica ‘ears’ on either side of round top mica. Mica ears often ‘scratch’ out trails in the grey glass.


    Raytheon version 1 (T-plates)
    Earliest known version of VT-231
    Base: black with orange-yellow labels
    Glass: clear
    Plates: black, T-plates
    Getter: bottom, flashing rarely extending up past plastic base
    Top mica: racetrack shaped with 4 spikes coming off either shorter side
    Other significant features: bottom mica identical to top mica. No support rods.


    Raytheon version 2 (Flat plates)
    Chronologically, the next version of Raytheon VT-231s.
    Base: black with orange-yellow labels
    Glass: clear
    Plates: black, flat with ‘ladder’ ridging.
    Getter: bottom, flashing rarely extending up past plastic base
    Top mica: racetrack shaped with 4 spikes coming off either shorter side
    Other significant features: Bottom mica identical to top mica. 2 metal supporting rods between top and bottom micas. 2 supporting rods are ‘free-standing’ and are not attached to anything aside from the two micas.


    Raytheon version 3
    Unknown vintage. Rare.
    Base: black with orange-yellow labels
    Glass: clear
    Plates: black, flat with ‘ladder’ ridging.
    Getter: bottom, flashing rarely extending up past plastic base
    Top mica: racetrack shaped with 4 spikes coming off either shorter side
    Other significant features: 2 ‘free’ copper support posts. Bottom mica identical to top mica. Top mica has ‘spring-loading’ of plates (black U-shaped structures)


    Sylvania
    Base: black, white labels (rarely yellow)
    Glass: clear
    Plates: black, T-plates
    Getter: bottom, foil, flashing extending up to 1/3 of the way up tube
    Top mica: rectangular
    Other significant features: micas may appear whitish. Bottom mica may be slightly smaller than top mica.


    TungSol
    Base: black, white labels
    Glass: black glass extending from bottom of tube to ¾ up
    Plates: round plates, ‘keyhole’ appearance when viewed from above
    Getter: bottom, foil, very hard to see
    Top mica: round with small spikes on opposite sides (earlier; 19??-42) or oval (later; 1942-46)
    Other significant features: spring-loading of plates (U-shaped structures) on top mica. U-shaped structures may face same or opposite directions. Tubes with oval micas have long thin metal pieces affixed to the opposite edges of their micas to brace them against the inside of the glass. Oval mica tubes have the bottom mica identical to the top mica, sans metal bracers.
     
    Wildcatsare1 likes this.
  3. adhoc Contributor
    2. US-made NOS 6SN7s

    CBS / CBS-HYTRON / HYTRON 6SN7GT
    Also JAN-CHY-6SN7GT
    Tubes marked “Hytron” came first, followed by “CBS-Hytron”, then lastly by plain “CBS”. The construction between these 3 tubes appears identical.

    Base: black, white (Hytron, CBS-Hytron) or red (CBS) print
    Glass: clear, tall-bottle always
    Plates: black, T-plates, 2 holes per plate
    Getter: bottom, square, flashing rarely extends past plastic base
    Top mica: rectangular
    Other significant features: bottom mica also rectangular


    CBS 6SN7GTA
    Base: black with red labels
    Glass: clear, midway between tall and short bottle height
    Plates: flat, black
    Getter: ???
    Top mica: racetrack with spiked shorter edges
    Other significant features: bottom mica same shape


    CBS 6SN7GTB
    Base: black with red print, base is slightly shorter
    Glass: clear, short bottle
    Plates: ???
    Getter: side
    Top mica: ???
    Other significant features:


    GE 6SN7GT
    Check the non-US NOS 6SN7 section.


    GE 6SN7GTA
    Made up till around 1955.
    Base: black, white printing
    Glass: clear, has 6SN7GTA etched into it on side, short bottle
    Plates: dark gray (often called black), large flat-plates with ‘ladder’ ridges
    Getter: side, D-getter, flashing covers a circular patch inside tube
    Top mica: round with spiked edges, has 2 anode plate ‘tabs’ per plate on top mica (4 total)
    Other significant features: bottom mica is racetrack shaped


    GE 6SN7GTB
    Often confused with the GE 6SN7GTA.
    Base: black, white printing
    Glass: clear, has 6SN7GTB etched into it on side of glass
    Plates: light gray, large flat-plates with ‘ladder’ ridges
    Getter: side, D-getter, flashing covers a circular patch inside tube
    Top mica: round with spiked edges, has 2 anode plate ‘tabs’ per plate on top mica (4 total)
    Other significant features: bottom mica is racetrack shaped


    KenRad 6SN7GT
    Also JAN-CKR-6SN7GT
    KenRad stood for ‘Kentucky Radio’. KenRad was bought by GE around the mid-1940s and ceased to exist as a brand name by the early 1950s. Military tube boxes from the 1940s are labeled with “KenRad, Division of General Electric Corp”. The construction of this tube is identical to the KenRad VT-231 tube (both clear and black glass).



    National Union (NU) gray glass 6SN7GT
    Also JAN-CNU-6SN7GT
    Earliest 6SN7GT vintage by NU. RCA round mica 6SN7GTs are often relabeled as NU and do look extremely similar. Look to the top mica spacers for confirmation of identity – RCA (rectangular) vs NU (square).

    Base: black with white or silver labels
    Glass: gray. Gray glass extends from base upwards to almost cover the top. Occasionally found as short bottles.
    Plates: gray glass - black, flat-plates
    Getter: bottom,
    Top mica: round, with square mica spacers on opposite sides
    Other significant features: twoU-shaped structures on top mica. Bottom mica identical to top mica.


    National Union (NU) black glass 6SN7GT version #1
    Also JAN-CNU-6SN7GT
    Later vintage. Version 1 – round plates. Tooling similar to 6SL7GT

    Base: black with white or silver labels
    Glass: black. Black glass begins ¼ of the way from base and ends near the top.
    Plates: gray, round plates, circumference of plates larger than that of Tungsol VT-231
    Getter: bottom, foil, flashing rarely extends up past base
    Top mica: circle with spiked edges, spikes come into contact with glass
    Other significant features: Bottom mica identical to top mica. 2 free-standing supporting rods.


    National Union (NU) black glass 6SN7GT version #2
    Also JAN-CNU-6SN7GT
    Later vintage. Version 2 – flat plates, rectangular top mica.

    Base: black with white or silver labels
    Glass: black. Black glass begins ¼ of the way from base and ends near the top.
    Plates: black, flat plates
    Getter: bottom, foil, flashing rarely extends up past base
    Top mica: rectangular with spiked shorter edges that contact glass.
    Other significant features: Bottom mica identical to top mica.


    National Union (NU) black glass 6SN7GT version #3
    Also JAN-CNU-6SN7GT
    Later vintage. Version 3 – flat plates, round top mica.

    Base: black with white or silver labels
    Glass: black. Black glass begins ¼ of the way from base and ends near the top.
    Plates: black, flat plates
    Getter: bottom, rectangular, flashing rarely extends up past base
    Top mica: round with 2 mica spacers
    Other significant features: rectangular with spiked shorter edges that contact glass


    Raytheon 6SN7GT
    Also JAN-CRP-6SN7GT.
    3 versions identical to 3 VT-231 iterations – read Raytheon VT-231 section for details.


    Raytheon 6SN7WGT
    Also JAN-CRP-6SN7WGT
    Base: brown with red or yellow print (red print is earlier)
    Glass: clear
    Plates: black, flat with ‘ladder’ ridging, shiny
    Getter: top, square, flashing may be slightly small
    Top mica: round with 4 ‘umbrella spokes’ extending downwards from edge
    Other significant features: 2 black U-shaped structures on top mica, bottom mica also round


    Raytheon 6SN7GTA
    Base: black
    Glass: clear
    Plates: gray,
    Getter: side getter,
    Top mica: ???
    Other significant features:


    Raytheon 6SN7GTB
    Base: black with yellow print
    Glass: clear, short bottle
    Plates: black, flat with ladder ridging
    Getter: side, D-shaped ‘wrapped’ around plates
    Top mica: round with 2 sides spiked
    Other significant features: bottom mica identical to top mica


    Raytheon Uniline 6SN7GTB
    Base: black with yellow print
    Glass: clear, tall bottle
    Plates: gray, flat with ladder ridging
    Getter: top, ring
    Top mica: racetrack with spiked shorter edges
    Other significant features: bottom mica identical to top mica


    RCA 6SN7GT version #1
    Also JAN-CRC-6SN7GT.
    Earlier vintage. Identical to RCA round mica VT-231 except not labeled ‘VT-231’ but having ‘RCA’ in a circular logo (with a lightning bolt) labeled in silver print on the base. Made till 1949.



    RCA 6SN7GT version #2
    Also JAN-CRC-6SN7GT
    Later vintage - made from 1949 onwards.

    Base: black, silver print, “RCA” in “tall and narrow” script
    Glass: gray, opacity varies; may sometimes be almost transparent – later vintages seem to have less blackening. Glass blackening often starts some distance from tube base (contrast to earlier versions)
    Plates: black, flat with ladder ridging
    Getter: bottom, flashing rarely extends up past base
    Top mica: racetrack shaped (contrast to round mica earlier versions)
    Other significant features: no top mica spacers.


    RCA 6SN7GTY
    Base: light brown micanol, black labels
    Glass: gray
    Plates: blackened (blackening is inconsistent) flat plates
    Getter: bottom, rectangular, flashing rarely extends up past base
    Top mica: racetrack shaped
    Other significant features: bottom mica is racetrack shaped with spiked shorted edges.


    RCA 6SN7GTA
    Base: black, silver labels
    Glass: clear
    Plates: black, large flat plates with ‘ladder’ ridging
    Getter: side, flashing covers a circular patch on the side of the tube.
    Top mica: racetrack
    Other significant features: bottom mica is same as top mica


    RCA 6SN7GTB
    Base: black, silver labels
    Glass: clear
    Plates: black, flat-plates
    Getter: side, small flashing on side
    Top mica: racetrack
    Other significant features: bottom mica same as top mica


    RCA 6SN7GTC
    Base: black plastic
    Glass: no glass. Made of metal
    Plates: unknown
    Getter: unknown
    Top mica: unknown
    Other significant features: made in South America throughout the 70s.


    Sylvania 6SN7GT version #1
    Also JAN-CHS-6SN7GT
    Identical to VT-231s except:
    - Green printing seen on black base; white labels are much rarer.
    - Made in the 1950s.
    - Flat plate versions exist across all year of make (very rare).

    Base: black, green labels, triangular Sylvania logo with ‘lightning bolt’ through logo.
    Glass: clear
    Plates: black, T-plate, (or rarely, flat black plates) with 2 holes per plate
    Getter: bottom, foil, flashing can extend up to 1/3 of way up tube
    Top mica: rectangular, (flat plate versions have round top and bottom micas)
    Other significant features: when seen, date codes are vertically arranged (from top to bottom) ‘YWW’ with Y underlined. Y = last digit of year, WW = week number of year.


    A note on Sylvania Chrome Domes:
    The “Chrome Dome” moniker was first applied to particular early 1950s vintage Sylvania 6SN7GTs by tube enthusiasts. The name came about in response to the tube’s appearance – it had a beautifully shiny top getter flashing that nearly reached the bottom of the tube, obscuring almost all of the internal construction from view.

    These particular 6SN7GTs are extremely rare, and as time passed, people began applying the “Chrome Dome” moniker to many other Sylvania tubes with top getter flashing.

    The following Sylvania tubes are often (incorrectly) called ‘Chrome Domes’:
    6SN7GTA
    6SN7W
    6SN7A
    6SN7WGT
    6SN7WGTA



    Sylvania 6SN7GT version #2 “Chrome Dome”
    Base: black, often unlabeled, sometimes simply labeled “Sylvania”
    Glass: clear
    Plates: black, T-plates
    Getter: top, foil, flashing extends down to cover nearly all of the tube
    Top mica: unknown
    Other significant features: bottom mica rectangular


    Sylvania 6SN7GT 1952 “Bad Boy”
    Also JAN-CHS-6SN7GT
    Made only from late 1951 (‘1-48’ examples seen) to 1952. Differs slightly in construction from ‘regular’ Sylvania rectangular top mica 6SN7GTs. Re-labeled bad boys are known to exist.

    Base: black, green labels marked ‘2-XX’ (where XX is the week of the year)
    Glass: clear
    Plates: black, T-plate with 3 holes per plate
    Getter: bottom, foil, flashing can extend up to 1/3 of way up tube
    Top mica: rectangular with 3 spikes on each of the shorter edges
    Other significant features: bottom mica is rectangular. When seen, date codes are vertically arranged (from top to bottom) ‘YWW’ with Y underlined. Y = last digit of year, WW = week number of year.


    Sylvania 6SN7A / 6SN7W version #1
    Also JAN-CHS-6SN7A/W
    Internal construction seems identical to the Sylvania metal base 6SN7A/W – only differences seem to be the height and base material.

    Base: black plastic with green or yellow print
    Glass: clear, usually short bottle (tall bottle much rarer)
    Plates: black, T-plates, 2 holes per plate
    Getter: top, foil, getter flashing extends almost halfway down tube, foil getter (not usually visible)
    Top mica: round, has 4 ‘umbrella spokes’ extending downwards from edges of mica, U-shaped anode plate extensions (not usually visible) on top of mica
    Other significant features: bottom mica racetrack shaped, a single support post extends between micas


    Sylvania 6SN7A / 6SN7W version #2 “Metal Base”
    Also JAN-CHS-6SN7A/W
    This tube is most often known as the ‘metal base 6SN7W’ – however, examples labeled 6SN7A are known to exist.
    Base: metal with green or yellow print – metal is actually a single flat piece connected at one side to make a cylinder. If removed, ‘remaining’ plastic base looks surprisingly like a ‘button’ base 6SN7GT.

    Glass: clear, always tall bottle
    Plates: black, T-plates, 2 holes per plate
    Getter: top, foil, getter flashing extends almost halfway down tube, foil getter (not usually visible)
    Top mica: round, has 4 ‘umbrella spokes’ extending downwards from edges of mica, U-shaped anode plate extensions (not usually visible) on top of mica
    Other significant features: bottom mica racetrack shaped, a single support post extends between micas


    Sylvania 6SN7WGT
    Also JAN-CHS-6SN7WGT or USN-CHS-6SN7WGTA
    Base: brown with green labels
    Glass: clear, may have faint white labels
    Plates: black T-plates, has 3 holes per plate
    Getter: top, flashing extends about halfway down tube
    Top mica: round, top mica has 4 “umbrella spokes” extending downwards
    Other significant features: bottom mica round. 1 freestanding support post.


    Sylvania 6SN7WGTA version #1
    Also JAN-CHS-6SN7WGTA
    Base: brown, green print
    Glass: clear, may have green print on it
    Plates: angled black T-plates
    Getter: top, ring getter holder
    Top mica: round with a few spikes
    Other significant features: bottom mica identical to top mica


    Sylvania 6SN7WGTA version #2
    Looks similar to the WGT.
    Base: brown, may have green print
    Glass: clear, may have faint white labels
    Plates: black T-plates, has 3 holes per plate
    Getter: top, flashing extends about halfway down tube
    Top mica: round, top mica has 4 “umbrella spokes” extending downwards
    Other significant features: bottom mica round. 1 freestanding support post.


    Sylvania 6SN7GTA
    Base: black with green print
    Glass: clear, short bottle
    Plates: black T-plates, 3 holes per plate
    Getter: top, foil
    Top mica: rectangular with spiked shorter edges
    Other significant features: bottom mica identical to top mica


    Sylvania 6SN7GTB
    Come with many label colors. For dating – red labels are later than green labels are later than yellow labels.
    Base: black, label color varies, not a ‘full’ base
    Glass: clear
    Plates: black, angled T-plates
    Getter: top, ring
    Top mica: round with 2 spiked sides
    Other significant features: bottom mica identical to top mica


    Tungsol 6SN7GT “Round Plate”
    Also JAN-CTL-6SN7GT
    Construction identical to that of Tungsol VT-231. See VT-231 section for details.



    Tungsol 6SN7GT “Mouse Ears”
    Base: black
    Glass: clear
    Plates: earlier vintages had black T-plates, later versions had gray T-plates
    Getter: bottom, flashing rarely extends up past base, square getter holder
    Top mica: rectangular, has 2 distinctive circular mica spacers making contact with the glass on each side (“mouse ears”)
    Other significant features: bottom mica also rectangular


    Tungsol 6SN7WGT
    Also JAN-CTL-6SN7WGT
    Base: brown, base is slightly shorter than most other 6SN7GT, white labels
    Glass: clear
    Plates: angled black T-plates
    Getter: top, D-getter holder
    Top mica: round with spiked edges
    Other significant features: bottom mica identical to top mica


    Tungsol 6SN7WGTA
    Also JAN-CTL-6SN7WGTA
    Construction appears similar to WGT.

    Base: brown, base is slightly shorter than most other 6SN7GT, white labels
    Glass: clear
    Plates: angled black T-plates
    Getter: top, D-getter holder
    Top mica: round with spiked edges
    Other significant features: bottom mica identical to top mica


    Tungsol 6SN7GTB version #1
    Construction appears similar to WGT/WGTA.
    Base: black with white print
    Glass: clear, tall bottle
    Plates: angled black T-plates
    Getter: top, D-getter holder
    Top mica: round with spiked edges
    Other significant features:

    Tungsol 6SN7GTB version #2
    Identical to version #1, except in short bottles rather than tall bottles.


    [​IMG]
     
    EELawson and Wildcatsare1 like this.
  4. adhoc Contributor
    3. 5692s:

    This section is unusual in that the provenance of the tubes contained within it is still a topic up for debate.

    CBS-Hytron ‘Brown Base’ 5692
    Possibly made by Raytheon instead.
    Base: brown
    Glass: clear, short bottle
    Plates: large black flat-plates,
    Getter: top, small getter flashing
    Top mica: dual top mica, round with smooth edges
    Other significant features: bottom mica identical to top micas, 5 extra support posts


    RCA ‘Red Base’ 5692
    Possibly made by RCA.
    Base: red; color varies from bright cherry red to deep burgundy red, labels are white (earlier vintage) or orange (later vintage)
    Glass: clear, short bottle
    Plates: large flat-plates
    Getter: top, small getter flashing
    Top mica:
    Other significant features: bottom mica identical to top micas, 5 extra support posts


    Sylvania 5692
    Base:
    Glass:
    Plates:
    Getter:
    Top mica:
    Other significant features:


    Standard Electric 33S03A/B
    Made in Sweden.
    Base: brown, speckled
    Glass: clear, short bottle
    Plates: large black flat-plates, blackening is inconsistent, one/both plates have numbers ‘scratched’ onto it/them
    Getter: top, small getter flashing
    Top mica: dual top mica, round with spiked edges
    Other significant features: bottom mica identical to top micas, 5 extra support posts


    [​IMG]
     
    Wildcatsare1 likes this.
  5. adhoc Contributor
    4. European NOS 6SN7s

    Amperex 6SN7GTB
    These tubes are likely Russian-made. Be wary of overpaying for them!
    Base: black
    Glass: clear, orange Amperex labeling with globe logo, may have white ‘6SN7GTB’ labeling
    Plates: grey, T-plates
    Getter: bottom, ‘flying saucer’ getter holder, flashing extends a little bit past base, usually more so on one side
    Top mica: rectangular, has ‘spring-loading’ for plates (U-shaped structures)
    Other significant features: bottom mica identical to top mica. micas appear whitish. 2 support rods on either side between both micas.


    STC/Brimar 6SN7GTY / CV1988 (UK)
    Brimar stood for ‘BRItish Made American Range’ and was originally part of STC (Standard Telephone and Cables), which in turn was the British agent of Western Electric. Only Brimar made the CV1988 – known relabels include Cossor, STC, Zaerix, ITT (International Telephone and Telegraph) and Mullard. Sometimes labeled as 6SN7GTY.
    Base: brown, no printing
    Glass: black or clear (less common), if applicable blackening extends up from ¼ from bottom of tube to top, white printing on glass with factory code FE (indicating STC Oldsway production)
    Plates: grey, ‘flattened oval’ cross section
    Getter: bottom, ring getter holder, flashing does not extend past base
    Top mica: round with spiked edges, spikes contact glass, 2 small anode plates extensions extend vertically
    Other significant features: bottom mica round with smooth edges


    Brimar 6SN7GT (UK) version 1
    This tube is identical to the CV1988 except that black bases may be used.
    Base: black or brown (less common) with printing
    Glass: black or clear (less common), if applicable blackening extends up from ¼ from bottom of tube
    Plates: grey, ‘flattened oval’ cross section
    Getter: bottom, ring getter holder, flashing does not extend past base
    Top mica: round with spiked edges, spikes contact glass, 2 small anode plates extensions extend vertically
    Other significant features: bottom mica round with smooth edges


    Brimar 6SN7GT (UK) version 2
    This tube came next chronologically and differs from earlier examples by not having anode plate extensions on the top mica and having a differently shaped getter holder. No black glass examples of this tube have been yet found by the thread author.
    Base: black with printing, printing may be reddish-orange
    Glass: clear
    Plates: grey, ‘flattened oval’ cross section
    Getter: bottom, rectangular getter holder, flashing does not extend past base
    Top mica: round with spiked edges, spikes contact glass
    Other significant features: bottom mica round with smooth edges


    Brimar 6SN7GT (UK) version 3
    Latest vintage. Often found as Cossor relabels. Note the different top mica shape. No black glass examples of this tube have been yet found by the thread author.
    Base: black
    Glass: clear, often with Cossor labels
    Plates: grey, ‘flattened oval’ cross section
    Getter: bottom, rectangular getter holder, flashing does not extend past base
    Top mica: round, smooth edged
    Other significant features: bottom mica identical to top mica


    Brimar 13D2 (UK)
    6SN7GT equivalent produced for industrial use. Extremely rare.
    Base: dark brown, no labels
    Glass: clear, has white labels printed onto it
    Plates: grey flat plates
    Getter: top, on top-most mica (more on that later), dual ring getter – one above each plate
    Top mica: 2 round top micas; top-most mica has smaller diameter than next top mica
    Other significant features: bottom mica round, diameter roughly same as top-most mica


    Cossor 6SN7GT (UK)
    Cossor bought tubes in bulk, and then relabeled them. Tubes labeled ‘Cossor’ have been seen that were made from anyone from RCA to Brimar to Sovtek.


    Fivre 6SN7GT (Italy)
    Fivre stands for ‘Fabbrica Italiana Valvola Radiofonica Elettronica’. Original tube retail boxes are red and black.
    Base: black
    Glass: clear, has a colourful label on it
    Plates: grey
    Getter: bottom,
    Top mica: rectangular with a few ‘spikes’ on either short end
    Other significant features:


    GEC B65 (UK)
    GEC stands for ‘General Electric Company’.
    Base:
    Glass:
    Plates:
    Getter:
    Top mica:
    Other significant features:


    Haltron 6SN7GT
    Haltron bought tubes in bulk, and then relabeled them. Tubes labeled ‘Haltron’ have been seen that were made from anyone from Brimar to Sovtek. Many were also made in eastern-bloc countries.


    Osram B65 (UK)
    Base: metal base with no labels
    Glass: grey glass beginning ¼ of way from base, tube data print on glass
    Plates:
    Getter: bottom, inverted cup, flashing rarely extending up past metal base
    Top mica: round with ‘umbrella spokes’ coming off bottom
    Other significant features: usually has color print ‘Osram’ logo on glass


    MWT B65 (UK)
    MWT stands for ‘Marconi Wireless Telegraph’.
    Base: metal, no labels
    Glass: smoked, has colorful label on it, also may have (fragile) white print
    Plates:
    Getter: bottom, inverted ‘cup’ getter, flashing does not extend much past base
    Top mica: round
    Other significant features:


    Neotron 6SN7 (France)
    Commonly confused with TungSol round plate 6SN7GTs.
    Base: black
    Glass: smoked with orange “Neotron 6SN7” logo, black glass extends from base of tube
    Plates: round
    Getter: bottom
    Top mica: rectangular
    Other significant features: top mica has two rectangular mica ears on it and two large U-shaped structures, (looks similar to Tungsol RP except for top mica shape)


    RFT 6SN7GT (West Germany)
    An extremely unusual tube.
    Base: black, ‘short’ base
    Glass: clear with yellow RFT logo and labels
    Plates: grey, flat with NO ridging and an unusual ‘monolith’ look
    Getter: top, flat disc
    Top mica: NOT mica, but ceramic! round with 2 mica ‘ear’ supports
    Other significant features: bottom ‘mica’ is also made of ceramic, round and has ‘cutouts’ on 2 sides.


    Philips 6SN7GT (Holland)
    Philips Holland had numerous subsidiaries - examples include: Adzam (exclusively an export name), Amperex, Pope (exclusively an export name), Philips Miniwatt, Mullard, Miniwatt, Miniwatt Dario, Radiotechnique, etc. This tube has been known to be relabeled with the following brand names: Pope, Philips Miniwatt, Miniwatt and Mullard.
    Base: black with white labels
    Glass: clear (less common) or grey-black (similar color and luster to pencil lead). If grey-black glass, begins ¼ of way up tube from base and ends near top. May have white print on glass (Mullard).
    Plates: grey, flat with ‘ladder’ ridging
    Getter: bottom, D-shaped, flashing rarely extends past plastic base
    Top mica: racetrack shaped
    Other significant features: bottom mica is racetrack shaped with mica ‘spikes’ coming off shorter sides


    Sicte 6SN7GT (Italy)
    Base: black with orange print
    Glass: clear with a very colorful label
    Plates: grey
    Getter: bottom, flashing extending slightly up past base
    Top mica: rectangular
    Other significant features:


    Sovtek 6SN7GT (Russian)
    Base: black
    Glass: clear, labels in silvery ink
    Plates: grey, T-plates
    Getter: bottom, ‘flying saucer’ getter holder, flashing extends a little bit past base, usually more so on one side
    Top mica: rectangular, has ‘spring-loading’ for plates (U-shaped structures)
    Other significant features: bottom mica identical to top mica. micas appear whitish.


    Telefunken 6SN7GTA (West Germany)
    May be marked ‘Radiotron’ on base.
    Base: black, usually clear of any labels
    Glass: clear, white labels, says ‘Made in West Germany’
    Plates: grey, plates have 2 horizontal ‘holes’ midway in them
    Getter: top, ring, flashing is restricted to topmost portion of tube; does not extend down much
    Top mica: round with scalloped edges
    Other significant features: bottom mica is identical to top. Top of tube glass is obviously less ‘rounded’ than most other 6SN7s.


    Tungsram 6SN7GTY / CV1988 (UK)
    Extremely rare.
    Base: brown
    Glass: black, blackening extends up from ¼ from bottom of tube to top
    Plates:
    Getter:
    Top mica:
    Other significant features:


    Zaerix 6SN7GT
    Zaerix was a company name owned by Z&I Aero, London, England. Zaerix, like Haltron, bought tubes in bulk, and then relabeled them. Tubes labeled ‘Zaerix’ have been seen that were made from anyone from Brimar to Sovtek. Many Zaerix tubes were also made in eastern-bloc countries. Zaerix bought tubes in bulk, tested them to ensure that they were within spec, and then relabeled and supplied them to the UK government and various OEM companies.


    [​IMG]
     
    Wildcatsare1 likes this.
  6. adhoc Contributor
    5. Other non-US NOS 6SN7s

    Due to the relative rarity of these tubes this list is, in particular, not meant to be comprehensive. If you have any information regarding these tubes, please PM me.

    GE 6SN7GT (JAN-CL-6SN7GT)
    Made in Canada
    Base: black, red labels
    Glass: clear
    Plates: black, T-plates
    Getter: bottom, rectangular, flashing rarely extends up past plastic base
    Top mica: rectangular
    Other significant features: bottom mica same shape as top mica. Micas are nearly transparent.


    RCA
    Made in Canada
    Base:
    Glass:
    Plates:
    Getter:
    Top mica: square with 2 rectangular mica ‘ears’ either side,
    Other significant features:


    AWV (Amalgamated Wireless Valve Co.) 6SN7GT
    Made in Australia
    Base:
    Glass:
    Plates:
    Getter:
    Top mica:
    Other significant features:


    Miniwatt 6SN7GT
    Made in Australia
    Base:
    Glass:
    Plates:
    Getter:
    Top mica:
    Other significant features:


    Mullard 6SN7GT
    Made in Australia
    Base:
    Glass:
    Plates:
    Getter:
    Top mica:
    Other significant features:


    Radiotron 6SN7GT
    Made in Australia
    Base:
    Glass:
    Plates:
    Getter:
    Top mica:
    Other significant features:


    Radiotron 6SN7GTA
    Made in Australia
    Base:
    Glass:
    Plates:
    Getter:
    Top mica:
    Other significant features:


    [​IMG]
     
    Wildcatsare1 likes this.
  7. adhoc Contributor
    reserved post #1

    (kept here in case of future additions)
     
  8. adhoc Contributor
    reserved post #2

    (kept here in case of future additions)
     
  9. Frihed89
    It is my understanding that only a small fraction of the Slyvania JAN-CHS-6SN7GTs are "bad boys". Is your description of the JAN-CHS-6SN7GT or the bad boy part of the production run?

    If you are describing the bad boys, then how do the other JAN-CHS-6SN7GTs differ in construction from the bad boys?
     
  10. adhoc Contributor
    Quote:

    Originally Posted by Frihed89 /img/forum/go_quote.gif
    It is my understanding that only a small fraction of the Slyvania JAN-CHS-6SN7GTs are "bad boys". Is your description of the JAN-CHS-6SN7GT or the bad boy part of the production run?

    If you are describing the bad boys, then how do the other JAN-CHS-6SN7GTs differ in construction from the bad boys?




    Hi there -

    Bad Boys were only made in
    - late 1951
    - 1952
    - early 1953

    Thus they will be marked with either
    - '1xx' (late week production numbers only),
    - '2xx' (all 52 weeks of the year) or
    - '3xx' (early week production numbers only)
    date codes.

    They can also be JAN-rated and thus be marked JAN-CHS-6SN7GT.

    For construction details, look to the section on Bad Boys in post #3 and compare against that for 'normal' Syl 6SN7GTs.
     
    Wildcatsare1 likes this.
  11. Rob N Contributor
    I've not seen any metal bases with yellow print.All the ones I've seen have had either black or green print
     
  12. adhoc Contributor
    Quote:

    Originally Posted by Rob N /img/forum/go_quote.gif
    I've not seen any metal bases with yellow print.All the ones I've seen have had either black or green print



    For tubes, never say never. [​IMG]

    [​IMG]

    Granted, this tube isn't labeled 'Sylvania' - but I have seen one Sylvania metal base with yellow labels. Just one. [​IMG] Unfortunately I do not have a photo of that tube. [​IMG]
     
  13. augustwest
    Nice write-up! Extremely interesting reading.

    - augustwest
     
  14. jamato8 Contributor
    I have a friend who worked for RCA and has multiple patents, though he was the inventer and RCA has the patent, on tubes. He designed and got the ball rolling on many tubes. I never thought to ask him about what he may know about the black and grey glass tubes but I will pose this to him. It is funny because many of the "new" circuits using tubes you read about and are brought forth as something just thought of are not. I have brought many of these designs to his attention and he always recognizes them.
     
  15. augustwest
    "I have a friend who worked for RCA and has multiple patents, though he was the inventer and RCA has the patent, on tubes. He designed and got the ball rolling on many tubes. I never thought to ask him about what he may know about the black and grey glass tubes but I will pose this to him."

    It would be great to document the real story from the "old timers" who made the tubes and find out why things were done a certain way. In both the manufacture and marketing methods used. I'm sure they just didn't use black/grey glass because it looked sexier.

    - augustwest
     
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