Substitutions

    When it comes to magic eye tubes, I have found substitution to be very common.  The following is a list of possible instances or reasons for a repair person to use a substitute:

Some eye tubes are very expensive and
can be replaced with a cheaper substitute
The person who repaired the set just happened
to have a certain tube lying around
The actual performance of the set is not
inhibited by a less or more sensitive tube
A poorly written substitution manual did not
explain the actual differences in the tubes.

    Unfortunately, the lack of detailed information available combined with confusing numbering systems and descrepancies or contradictions between different substitution manuals has made this page and the task of creating it, to put it simply, a mess.  When I realized this, I decided to check the tubes I have against the manuals.  The best statement I can make is that there are very few magic eye tubes with exact substitutes.  I have tried to compile here a practical reference based upon details of any substitution. The organization of this page isn't great, but it has much more information than the average substitution guide.  Suggestion: Use the Find feature of your browser to find the tube you are interested in learning about.

Notes on numbering systems

    Note that it is very common for a tube to be stamped with two numbers.  For example: 6G5/6U5; 6DA5/EM81; 6AB5/6N5.  Naturally, a tube labeled 6G5/6U5 could be replaced with either a 6U5 or a 6G5.  For simplicity purposes, I have listed all numbers individually here.  Important: tubes accompanied by the symbol are foreign types even though they appear in standard EIA tube numbering format.

    Usually the filament voltage on most tubes with numbers in EIA format is referred to by the first digit(s) of the tube number.  If you have a 2E5 and a 6E5, the only electrical characteristic that differs between the two tubes is the filament voltage and current.  Changing the filament supply would allow you to use one in place of the other, respectively.  This applies to all magic eye tubes that are American  types.  With European types, the first letter designates the filament characteristics.  An EM80 has the same electrical characteristics (excluding filament supply) as a UM80, and once again, changing the filament supply would allow for substitution.  There are major exceptions for foreign types:  The EM4 is electrically equivalent to the 6CD7/EM34, but has a P-type base.  The UM4, Which I originally thought was the 12 volt equivalent of the EM4, has an octal base.  The EM35 and the UM35 do not even share the same pinout.

    While letters such as G, GT, GC, etc. after the tube number of an American tube type would usually refer to the glass envelope of the tube, letters following the number of a magic eye tube can and usually indicate a totally different tube.  There are many foreign tubes such as 6E5C, 6E5D, 6E5GT ,6E5M, and 6E5P, some of which barely resemble the American 6E5 and will undoubtedly not work as a substitute.  Foreign types 6U5G and 6G5G have octal bases among other differences to the American 6U5 and 6G5.

1M3, 1N3, DM70, and, DM71, and 1M1 are all electrically equivalent.  The 1M3 & DM70 have long leads (typ. 3cm), and the 1M1, 1N3 & DM71 have short leads (typ. 5mm). Caution!  If you bend the leads, do so at least 3mm away from the glass seal.  If you solder the leads, do so at least 5mm away from the glass seal.  I recommend a socket for these.  (an 8 pin DIP or TO-5 IC socket works well.) Other substitutes: CV2980, Y25.
The 2E5 and 2G5 have no exact substitutes.  They may be substituted for each other, however replacing a 2E5 with the 2G5 will result in less sensitivity, and replacing a 2G5 with the 2E5 will result in more sensitivity.  If the filament transformer can provide an extra amp, a 4.7 ohm, 5 watt resistor in series with the filament makes the 2E5 a good replacement for the 6E5, and the 2G5 a replacement for a 6G5, 6H5, or 6U5.
The 6AB5 and 6N5 are exact substitutes.   Because these were primarily designed for farm sets, The filament current and plate voltage are lower than on other tubes with the same base.  If your filaments are parallel wired and your filament transformer or battery can supply the extra 150 milliamps, a 6G5, 6H5, or 6U5 could be substituted and provide very close sensitivity.   If the 6G5, 6H5, or 6U5 has been used for a substantial amount of time at the 250 volts it is rated for, it may appear very dim at the typical 125 volt supply for the 6AB5 or 6N5.  The 6AB5 or 6N5 is generally less than half the cost of the 6G5, 6H5, or 6U5, which makes this substitute impractical.  Other substitute: CV843
The 6AL7GT and CV3707 are exact substitutes.  The display pattern of the 6AL7GT and CV3707 is unlike that of any other magic eye tube (see the patterns section of this site), having three independent control vanes.   This and the fact that they are rather inexpensive makes it useless to bother finding a substitute for.   Unlike most magic eyes, the 6AL7GT will become less illuminated with an increase in signal as opposed to more illuminated.
The 6AF6 and CV847 are exact substitutes.  The 6AD6 and 6AF6 are not exact substitutes, but can usually be substituted for each other with very little difference in sensitivity, however, the 6AD6 was designed for a slightly higher plate voltage, and was also designed for a 135 shadow angle opposed to the typical  100.  I have successfully used the 6AF6 in place of a 6AD6 without noticeable difference in the sensitivity or shadow angle.
The 6BR5, 6E1p, and EM80 are exact substitutes.  The 6DA5 and EM81 are exact substitutes.  Although very close electrically, there is a visual difference in the display pattern.  The 6BR5 & EM80 have two shadows while the 6DA5 & EM81 have only one (see the patterns section of this site).  Other possible substitutes for the EM80: 65ME, CV1352.  Other possible substitute for the EM81: CV5055.
The 6DG7 and EM85 are exact substitutes.  Although the  6DA5 and EM81 appear similar physically and electrically, the base wiring is different.  An EM85-E is electrically equivalent to the 6DG7 and EM85 electrically, but the physical display of the EM85-E is similar to that of the 6FG6 or 6HU6 (see the patterns section of this site).  The 19DG7 and UM85 are exact substitutes.

The 6CD7, EM34, CV394, 6M2, and 64ME are exact substitutes.
The EM4 is electrically equivalent to the above numbers, but has the German P8A locking base.  Other possible substitute for the EM4: CV1434.

The 6E5, CV239, CV1906, HF3110, and OSW3110 are exact substitutes.
Replacing the 6E5 with a 6G5, 6H5, or 6U5 would result in less sensitivity.  Replacing with a 6AB5 or 6N5 would require lowering the plate voltage to at most 135 volts, preferably 100 volts to obtain the same sensitivity as the 6E5, and would require a parallel filament circuit to accompany the lower power consumption of the 6AB5 or 6N5.

Let's talk about the 6E5 for a moment, as it was the first magic eye produced, sold, is gradually becoming harder to get, and creates a great deal of confusion in terms of the large number of suffix iterations for it.

As it becomes harder to get, I find that using a readily available adapter for an abundant and inexpensive  1629 tube can be used as a replacement provided there is a parallel filament circuit. The adapter not only configures the pins properly for the octal base of the 1629, but also uses a half wave voltage doubler to obtain the 12.6 volts for the filament of the 1629.  With a little rewiring, a couple diodes and capacitors, and an octal socket, you can retrofit the radio or device yourself.

Regarding suffix iterations, I will explain them one at a time here:
The Russian 6E5C , which is often referred to as the 6E5S once translated into english, has an octal base and has nearly identical electrical characteristics as the American 6E5.  In recent years, the 6E5C has become increasingly available from several former Soviet states and is nearly half the cost of a US made 6E5, making it my personal choice for simple, inexpensive set reconfiguration or for projects.
The 6E5D, made by Toyo of Japan, has the same electrical characteristics, socket, and pinout as the 6E5, allowing them to be directly interchanged, but the 6E5D is extremely rare and has a red bezel replacing the filament shield.  See the pictures section of this site for a view of the 6E5D.
The 6E5GT has an octal base and has nearly identical electrical characteristics as the American 6E5.  It is not as easily obtainable as the 6E5C, however.  I have seen the 6E5GT listed as a direct substitute for the 6X6 on more than one occasion in both tube manuals and on other websites, which does work, but it should be noted that the display patterns are different, as the 6X6 found in many DeForest and Rogers sets was a dual vane indicator,while the 6E5GT is a single vane indicator.  It should also be noted that if the 6X6 is substituted for the 6E5GT, it probably will not work due to pinout differences, as the cathode element of the triode portion of the 6X6 is independent from the cathode element of the display portion where the 6E5GT has a common cathode.
The 6E5M is equivalent to the 6ME5 and are 7 pin miniature Japanese tubes.  See the pictures section of this site for a size comparison of the 6ME5 and the 6E5.
The 6E5MT is another 7 pin miniature Japanese tube with an off-center control vane and is equivalent to the 6ME2, also Japanese.  See the patterns section of this site for a visual explanation of the off-center control vane.
The 6E5P is equivalent to the 6ME4 and are more 7 pin miniature Japanese tubes with unique displays.
The 6E5W is equivalent to the 6Z-E1 and are Japanese tubes that can be interchanged with the 6E5.  Consider them to be a 6E5 with two connected control vanes.

The 6T5 Has no exact substitutes.  Replacing with a 6G5, 6H5, or 6U5 would be equivalent functionally, however the display pattern of the 6T5 is one of a kind (see the patterns section of this site), having a full annular shadow that varies in  diameter, as opposed to the common "angle" shadow. The rarity of this tube makes it extremely costly (if you can find one).  Many sets that originally contained a 6T5 now have a 6G5, 6H5, 6U5, 6E5, 6N5, or a like type, except for those that have been impeccably restored.

The 6ME5 and 6ME10 can be substituted for each other, however the target of the 6ME5 is rated for 180 volts while the 6ME10 is designed for a low target voltage of 100 volts.  Although the numbers is in standard EIA format, these are foreign tubes, of Japanese origin.  The sensitivity of the 6ME5 is similar to that of a 6E5 with a target voltage of about 120V.  See the pictures section of this site for a size comparison.

The 6FG6, 6E3p, EM84, EM840, and CV5434 are exact substitutes.  The 6HU6, EM87, and CV10407 are exact substitutes.  The 6FG6 and 6HU6 along with their substitutes may be interchanged, however the 6FG6 has less sensitivity, and requires slightly less filament current.
The 6G5, 6H5, 6U5, CV504, and VT98 are exact substitutes.   Replacing with a 6E5 would result in higher sensitivity and may close even with weak signals.  Adjustment may be necessary.   Replacing with a 6AB5 or 6N5 would also result in higher sensitivity and requires lowering the target voltage from the typical 250 volts to 135 volts.  A parallel filament circuit is also required since the filament current of the 6AB5 or 6N5 is half that of the 6G5, 6H5, or 6U5.  A 6T5 could be used as a substitute, but is rather expensive and different visually, having a full annular shadow as opposed to the common "angle" shadow (see the patterns section of this site).
The 1629, VT138, and CV1756 are exact substitutes.  The low cost and abundance of JAN surplus makes it impractical to bother substituting some other tube for these, and also makes it an attractive tube as a solution for substitution where authenticity is not an issue.  Had a center tap been added to the filament as was done with the 12AX7, 12AU7, etc., this tube would have been perfect for universal applications and substitutions.  An adapter can be made or bought for a 1629 tube to be used as a substitute for a 6E5 and others provided there is a parallel filament circuit.  The adapter not only configures the pins properly for the octal base of the 1629, but also uses a half wave voltage doubler to obtain the 12.6 volts for the filament of the 1629.  With a little rewiring, a couple diodes and capacitors, you can modify the set yourself.
The 19BR5 and UM80 are exact substitutes.  The 19DA5 and UM81 are exact substitutes.  Although very close electrically, there is a visual difference in the display pattern.  The 19BR5 & UM80 have two shadows while the 19DA5 & UM81 have only one (see the patterns section of this site).   Other possible substitute for the UM80: Y119
The19FG6 and 19HU6 may be interchanged, however the 19FG6 has less sensitivity, and requires slightly less filament current.  The 19FG6 and the UM84 are exact substitutes.  The 19HU6 and the UM87 are exact substitutes.
The EM31 and CV1077 are exact substitutes.  Types AW6, E1180, and V177 are possible other substitutes, but I have seen physical differences in pictures of the AW6.

The 6U5G and 6G5G are exact substitutes.  They are European tubes with octal bases and are electrically equivalent to the american 6U5 and 6G5.  Other substitutes for the 6U5G and 6G5G include the 41P103, VI103, Y63, CV2747, and 6M1.

The 6G-E12 and 6G-E12A have no exact substitutes.  They may be substituted for each other and are electrically equivalent, however the display patterns are very different.
The Y63, CV1103, and NR69 are exact substitutes.  The Y61 is electrically equivalent to the Y63, the only difference is the straight glass envelope of the Y61 versus the shoulder type of the Y63.  The Y64 is equivalent to the Y63 except that it is designed to be operated at lower target voltages, down to 80 volts.
The 6977, CV5412, CV6094, and DM160 are exact substitutes.
The Y65, 31P51, and CV51 are exact substitutes.
The 4678, CV2942, ED78, EM1, ME6, ME6S, TK606, TV6, and U6-CAT are exact substitutes.
The 41ME, AD77, AM1, CV1412, ME4, ME4S, TH1, TK406, and TV4 are exact substitutes.
The 6GX8 and EAM86 are exact substitutes.  There are no other substitutes for this tube.
The AW5, CV1359, CV3565, and ME41 are exact substitutes.