Seven Pin Medium Base Twin Triode in a Sylvania 6A6 Carton, Consistent With a 6A6, Unmarked Glass
- 3 photos
Never used. The original pack has been opened, or the quantity was split off a full reel or tube. Leads are original and unclipped.
New old stock, open stock on the grading scaleSend the quantity you need. You get a quote back with shipping before anything is charged.
Videos
Filmed on the bench. Sound is stripped from product clips.
- 0:02
The carton is the original Sylvania 6A6 box, teal and black with the S in triangle logo.
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The pin circle and the molded base ring are both visible here alongside the carton.
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A transition frame from the clip with nothing of the tube or carton in focus.
- 0:02
Close enough to read the 6A6 type number on the cream band without any doubt.
Specifications
| Specification | Value |
|---|---|
| Identification | |
| Part number | 9V4JS2MK |
| Manufacturer | Not recorded |
| Condition | New old stock, open stock |
| Date code | Not recorded |
| Package | Seven pin, base style to be confirmed |
| Country of origin | Not recorded |
| Family | Not recorded |
| Stock number | 9V4JS2MK |
| This item | |
| Type marking on glass | None legible |
| Pin count | 7 |
| Base style | Must be read from the tube. Miniature B7G and medium seven pin UX7 are both seven pin patterns and are not interchangeable |
| Base observed in the photographs | Black molded base with projecting metal pins, seven pin medium pattern |
| Envelope observed | Shouldered ST style glass |
| Consistency with the carton | The base and envelope are both consistent with a genuine 6A6. This is NOT a B7G miniature. |
| Carton | |
| Carton brand | Sylvania |
| Carton type marking | 6A6 |
| 6A6 reference data, from the carton marking, not verified for this tube | |
| Function | Twin triode power amplifier, class B push pull output, or class A driver with the sections paralleled |
| Base | Seven pin medium, American UX7, catalogued as U7B |
| Envelope | ST shape glass with a molded base |
| Heater voltage | 6.3V |
| Heater current | 0.8A |
| Amplification factor | 35 |
| Equivalents | 6N7 is the electrically identical octal version. Type 53 is the same design on a 2.5 volt filament |
| Miniature version | None. The 6A6 was never produced as a seven pin miniature |
About this part
An unmarked seven pin receiving tube supplied in a Sylvania carton printed 6A6. The tube carries no legible type number, so its identity rests on the box alone, and a box is weak evidence.
The important detail is what a 6A6 actually is. The 6A6 is a twin triode power amplifier built for class B push pull output and usable as a class A driver, electrically the same as the later octal 6N7 and derived from the 2.5 volt type 53. It has a 6.3 volt, 0.8 ampere indirectly heated cathode, an amplification factor near 35, an ST shape glass envelope, and a seven pin medium base, the old American UX7 pattern with a molded base keyed by two oversize heater pins.
So a count of seven pins does not contradict the carton by itself. What does contradict it is the base style. A 6A6 is not, and never was, a seven pin miniature. If the tube in this box is a B7G miniature, meaning all glass with the pins sealed straight through the bottom and no molded base, then it cannot be a 6A6 and the carton has been reused. Reused cartons are ordinary in old stock. Treat the tube as unidentified until you read it or test it.
Questions about this part
Is this tube a 6A6?
Unverified. The carton says 6A6. The tube carries no legible marking. Those are two different claims and only the first one is established.
Can a seven pin miniature tube be a 6A6?
No. The 6A6 uses the seven pin medium base, an ST shape glass envelope with a molded base and pins projecting from it. A seven pin miniature, B7G, is all glass with wire pins sealed directly through the bottom. If this tube is a B7G miniature it is definitely not a 6A6, whatever the box says.
The 6A6 has seven pins, so why is the match still in doubt?
Because two entirely different seven pin bases exist. Medium seven pin, which is what a 6A6 uses, and seven pin miniature B7G, which is smaller and physically incompatible. Counting pins does not settle it. You have to look at whether there is a molded base.
If the tube is not a 6A6, what does that mean?
Most likely a reused carton. Old stock cartons get emptied and refilled for storage, and tubes originally shipped in bulk trays often end up in whatever box was on the shelf. It is common enough that a box match is never treated as identification on its own.
How would I confirm what this actually is?
Look at the base first: molded base with projecting pins, or bare glass with wire pins. Then look for printing or an etched code on the glass. Then put it on a tube tester with the correct socket.
What would a genuine 6A6 be used for?
It was designed for the class B push pull output stage of AC operated receivers, and it works as a class A driver with both triode sections in parallel. Restorers also use it where a 6N7 circuit calls for the earlier base.
Is a 6N7 a direct substitute for a 6A6?
Electrically the two are the same design. Mechanically they are not interchangeable, since the 6N7 is octal and the 6A6 is seven pin medium. You would need an adapter or a socket change.
Is the carton itself worth anything?
Original Sylvania cartons have collector value in their own right, and that value does not depend on the contents. That is stated here only so the two are not confused with each other.