In 1960, the writing was on the wall: Tubes were being bested in every area by transistors, which did not require heater power, did not generate as much heat, and were a tiny fraction of the size. GE's engineers made an interesting decision: To give tubes one more shot in the war with transistors, and push off the inevitable end of the vacuum path for a few more years.

What GE did was combine multiple common tube types into "fat" tubes—as many as four in a single glass envelope, all heated from the same filament. The idea was to reduce the amount of power required to heat the tubes and the space they required on the circuit board, as well as the associated costs of multiple sockets. In a very crude way, GE was applying the concept of integrated circuits to tubes, and if solid-state technlogy had not advanced as quickly as it did in the first half of the 1960s, the Compactron idea might have been developed further, with even more tubes in a single envelope, with perhaps resistors and capacitors to implement resistance coupling networks for amplifiers. We'll never know, but Robert Casey has an interesting page speculating on a sort of "super-Compactron" implementing all tubes required for an "All-American Five" table radio in a single envelope. This was never done, but it would certainly have been possible.

In truth, Compactrons (first announced by GE in 1960) were designed almost completely for the color TV market. Table radios and Hi-Fi equipment represented much simpler design challenges for electrical engineers. (Some high-end Scott AM/FM tuners used Compactron tubes, but not many.) Color TVs are tough nuts to crack in many respects, and the transistors of the time (1960) were not quite as good as tubes, especially for high-voltage and VHF/UHF circuits. So GE's engineers took a look at the various elements of Color TV circuitry, and started combining compatible tube elements into single glass bottles.

The result is the catalog of Compactron tubes we know today. A good example is the 6AF11, a three-tube portmanteau consisting of a high-mu triode for AGC keyer service, a medium-mu triode for sync separator service, and a sharp-cutoff pentode for video amplifier service. The 6T9 is a hi-mu triode and power pentode combo representing the entire audio section of a simple TV set. (There was no stereo sound in TV technology at that time.) These sound very application-specific, but they're still just tubes, and they can be used for lots more than the TV circuits that they were designed for. The 6T9, for example, can work at RF frequencies up to 30 MHz, and there are a number of circuits using it for simple amateur radio CW transmitters, with the triode acting as a crystal oscillator and the power pentode as a 5W RF power amplifier. The 6AF11 is used in a popular regenerative all-band receiver circuit designed at GE and published in Popular Electronics in 1963.

The catalog of available devices grew over the first half of the 1960s. I have a PDF of the 1962 list from GE, as well as the much larger 1964 list. I don't know when new devices ceased to be added, but I do see that the 6Z10 (basically a complete TV audio section from discriminator to power audio amp) was not present in the 1964 list. I'm guessing that new tubes may have been added to the Compactron lineup as late as 1970, especially sweep tubes and series-string variants of 6V types.

This idea of stuffing three or more active devices in a single envelope was not completely new. There is a battery tube, the 1D8-GT, which combines a diode, triode, and power pentode into a single bottle. The 1D8 has been around since 1939, and there is a less common 3V filament version called the 3D8. It enabled the creation of cheap 3-tube AM BCB superhets, a good example of which was published in the September 1940 issue of Popular Science. A 1A7 pentagrid converter feeds a 1A5 IF amplifier, which then pumps the IF signal into the 1D8's diode and then its 2-stage audio amplifier. The venerable Rufus P. Turner published an article in the October 1955 Popular Electronics called "1-Tube Wallop," which used a 1D8 to combine a diode BCB AM detector with a two-stage speaker audio amp. Other (and I think far better) 1D8 circuits are discussed here and here.

Compactron tubes are available in huge numbers, and quite cheap, for this reason: They were manufactured in huge numbers right before the bottom fell out of the tube market. Immense quantities survived, and now you can get extremely useful tubes like the 6AF11 and the 6T9 for a couple of bucks each, which is a fraction of what they cost (in inflation-adjusted dollars) in 1963.

Is This Really a Win?

So. Is stuffing as many tubes as possible in one glass bottle really a win? I think so, but there are a couple of downsides to using Compactrons in hobby projects:

6T9 audio amplifier under construction

Compactron Tube Listing

In the table below is a list of all the generally useful 6V and 12V filament Compactron tubes that I know about. I'm omitting most of the Compactrons with odd series-string filament voltages (8V, 15V, 17V, 21V, 33V, etc.) because they require more fooling around to use, and if it's only the filament voltage that's different, you can use the non-filament specs for the 6V version. (I am listing a few that have no 6V or 12V filament versions.) I'm also omitting some of the tubes that are extremely specific to color TV service, like shunt regulators, just to avoid cluttering up the list with devices that hobbyists are not likely to use. There are a handful of types that I am omitting because I can't find good online data for them; oddly enough, the much-loved 6KE6 sweep tube is one of these.

One thing to keep in mind is that Compactrons were designed to have very rugged filaments, and can be operated at +-20% of their rated voltage. In other words, an 11-volt Compactron or a 13-volt Compactron can both be run with 12.6VAC on the filaments. The 11V tube may run a little hot, but unless you have an enclosed cabinet full of them I don't think it'll be an issue.

Links to tube data are (mostly) to the wonderful NJ7P Tube Data Site. A (PDF) at the end of a tube description is a link to a PDF of the tube's full data sheet, which generally contains characteristic curves for the device. (Keep in mind that these are page scans and are often very large files, sometimes over 1 MB.) The PDF data sheets are (mostly) from Frank Philipse's tube data sheet pages. Tubes for which no links are present are Compactrons that I know exist (generally by finding them in tube-tester data books) but for which I have not yet found data online.

If you know of any other useful 6V or 12V Compactron tubes not listed here, please let me know!

6AC9 12GN Dual Diode + Pentode
6AC10 12FE Hi-Mu Triple Triode
6AD10 12EZ Sharp-Cutoff Pentode + 10W Beam-Power Pentode
6AF10 12GX Dissimilar Twin Pentode
6AF11 12DP Hi-Mu + Medium-Mu Triode + Sharp Cutoff Pentode (PDF)
6AG9 12HE Medium-Mu Triode + Sharp-Cutoff Pentode
6AG10 12GT Gated Twin Hexode
6AG11 12DA Twin Diode + Twin Hi-Mu Triode (PDF)
6AH9 12HJ Medium-Mu Triode + Sharp-Cutoff Pentode
6AK9 12GZ Medium-Mu Triode + Hi-Mu Triode + Pentode
6AK10 12FE Triple Medium-Mu Triode
6AL9 12HE Medium-Mu Triode + Pentode
6AL11 12BU Sharp Cutoff Pentode + Beam Power Pentode
6AR11 12DM Semi-remote Cutoff Twin Pentode
6AS11 12DP Hi-Mu Triode + Medium-Mu Triode + Sharp Cutoff Pentode
6AV11 12BY Medium-Mu Triple Triode
6AY11 12DA Twin Diode + Twin Hi-Mu Triode
6B10 12BF Medium-Mu Twin Triode + Twin Diode
6BA11 12ER Medium-Mu Triode + Twin Pentode
6BD11 12DP Hi-Mu Triode + Medium-Mu Triode + Sharp Cutoff Pentode
6BF11 12EZ Sharp-Cutoff Pentode + 10W Beam-Power Pentode
6BH11 12FP Twin Medium-Mu Triode + Sharp Cutoff Pentode
6BK11 12BY Triple Triode
6BN11 12GF Sharp-Cutoff Twin Pentode
6BV11 12HB Dual Sharp-Cutoff Pentode
6BW11 12HD Twin Sharp-Cutoff Pentode
6BY11 12EZ Sharp-Cutoff Pentode + 10W Beam-Power Pentode
6C10 12BQ Hi-Mu Triple Triode
6CA11 12HN Dissimilar Dual Triode + Pentode
6D10 12BQ Hi-Mu Triple Triode (All Sections Identical)
6FJ7 12BM Medium-Mu Twin Triode
6FM7 12EJ Low-Mu Triode + Hi-Mu Triode
6FY7 12EO Low-Mu Triode + Hi-Mu Triode
6G11 12BU Sharp Cutoff Pentode + Beam Power Pentode
6GA7 12EB Diode + Pentode
6GE5 12BJ 18W Beam-Power Pentode (Sweep Tube)
6GF5 12BJ 9W Beam-Power Pentode (Sweep Tube)
6GV5 12DR 18W Beam-Power Pentode (Sweep Tube)
6GY5 12DR 18W Beam-Power Pentode (Sweep Tube)
6HB5 12BJ 18W Beam-Power Pentode (Sweep Tube)
6HD5 12ES 24W Beam-Power Pentode (Sweep Tube)
6HE5 12EY 12W Beam Power Pentode (Sweep Tube)
6HE7 12FS Diode + Pentode
6HF5 12FB 28W Beam-Power Pentode (Sweep Tube)
6HJ5 12FL 24W Beam-Power Pentode (Sweep Tube)
6HS5 12GY 30W Beam-Power Triode
6HV5A 12GY 35W Hi-Mu Beam-Power Triode
6HZ5 12GY 35W Hi-Mu Beam Power Triode
6J10 12BT Gated-Beam Discriminator + 10W Beam Power Pentode
6J11 12BW Twin Pentode
6JA5 12EV 19W Beam-Power Pentode (Sweep Tube)
6JB5 12EY 15W Beam-Power Pentode
6JC5 12EV 19W Beam-Power Pentode
6JH5 12JE 35W Hi-Mu Beam Power Triode
6JK5 12JE 35W Hi-Mu Beam Power Triode
6JM6 12FJ 18W Beam-Power Pentode (Sweep Tube)
6JN6 12FK 18W Beam-Power Pentode (Sweep Tube)
6JS6C 12FY 30W Beam-Power Pentode (Sweep Tube)
6JZ6 12GD 18W Beam-Power Pentode (Sweep Tube)
6JZ8 12DZ Medium-Mu Triode + Beam Power Pentode
6KD6 12GW 33W Beam-Power Pentode (Sweep Tube)
6KN6 12GU 30W Beam-Power Pentode (Sweep Tube)
6K11 12BY Medium-Mu Triode + Twin Hi-Mu Triode
6LB6 12GJ 30W Beam-Power Pentode (Sweep Tube)
6LF6 12GW 40W Beam-Power Pentode (Sweep Tube)
6LG6 12HL 28W Beam-Power Pentode (Sweep Tube)
6LR6 12FY 30W Beam-Power Pentode (Sweep Tube)
6LU8 12DZ Medium-Mu Triode + Beam Power Pentode
6M11 12CA Twin Hi-Mu Triode + Sharp Cutoff Pentode
6MF8 12DZ Hi-Mu Triode + Beam Power Pentode
6MJ8 12HG Medium-Mu Triple Triode
6MN8 12HU Hi-Mu Triple Triode
6MY8 12DZ Medium-Mu Triode + Pentode
6Q11 12BY Twin Hi-Mu Triode + Medium-Mu Triode
6T9 12FM Hi-Mu Triode + 12W Beam Power Pentode
6T10 12EZ Sharp-Cutoff Pentode + 10W Beam-Power Pentode
6U10 12FE Twin Medium-Mu Triodes + Hi-Mu Triode
6Y10 12EZ Dissimilar Dual Pentode
6Z10 12BT Gated-Beam Discriminator + 10W Beam Power Pentode
12AC10A 12FE Except for filament voltage, identical to 6AC10
12AE10 12EZ Sharp-Cutoff Pentode + 10W Beam-Power Pentode
12AL11 12BU Except for filament voltage, identical to 6AL11
12BF11 12EZ Except for filament voltage, identical to 6BF11
12BV11 12HB Except for filament voltage, identical to 6BV11
12HE7 12FS Except for filament voltage, identical to 6HE7
12JF5 12JH
17.5W Beam Power Pentode (Sweep Tube) (PDF)
12JN6 12FK Except for filament voltage, identical to 6JN6
12JS6 12FY
30W Beam-Power Pentode (Sweep Tube); see 6JS6C
12JZ8 12DZ
Except for filament voltage, identical to 6JZ8
12G11 12BU Except for filament voltage, identical to 6G11
12GE5 12BJ Except for filament voltage, identical to 6GE5

12T10 12EZ Except for filament voltage, identical to 6T10
Dual Triode + 7W Beam Power Pentode (PDF)
5890 12J Remote-Cutoff Pentode Regulator
7984 12EU 46W RF Beam-Power Pentode



33W Beam-Power Pentode. Heater 13VAC/DC @ 400ma

Probably identical to 6LF6

There is also a photoconductive sensor cell manufactured (circa 1963) by GE in a Compactron envelope. It's type Z-2946, and what little I know about it is here. If you ever run across a data sheet, please let me know. I have heard that there are a couple of fluorescent indicator ("magic eye") tubes on the Compactron base, but have not confirmed this.

Compactron tube sockets (both solder tab and printed circuit types) are reasonably common at Antique Electronic Supply and on eBay.

"9-Pin Compactrons": Novars and Magnovals

Every so often I hear talk of "9-pin Compactrons." Technically those don't exist; all Compactron tubes have 12 pins. However, in 1962 RCA introduced a line of tubes called Novar. These are all-glass tubes with nine .038" (1.2mm) pins on a base larger than that of the familiar 9-pin miniature. RCA introduced them for use in audio equipment, and the motivation may have been to create a larger base and bulb for greater power dissipation. Most of the Novars I've seen have been power pentodes like the 7868, or color TV rectifiers.

There's something to careful of with Novar tubes. A very similar line was introduced in Europe at about the same time. These were called Magnoval tubes, and they have nine pins on the same diameter circle. However, and crucially, Magnoval tubes have larger pins, at .046" (1.27mm). If you plug a Magnoval tube into a Novar socket, the larger pins will damage the pin contacts on the socket. You can wreck the socket of a late-era tube tester by trying to test a Magnoval in the Novar socket. Before you test what you think is a Novar tube, put a mic or a digital caliper on those pins!

There were not as many Novar tubes as Compactrons, and they were never very popular. Sockets are more difficult to find, though I've seen them online. Sellers sometimes claim that a single socket will work for both Novar and Magnoval, but that's not true. The larger Magnoval pins will damage any socket designed for Novar tubes, and Novar tubes will rattle around in any socket designed for Magnoval pins.

Safety Issues for High-Voltage Tubes

It's important to say right here up front: The voltages you must use in Compactron tube work can kill you. Years ago, the dangers of high voltage were common knowledge among electronics people, because high voltage was present in virtually everything you could call "electronic." However, over the past forty years, semiconductor technology operating at 12V or less has taken over hobby electronics. We've gotten very used to poking at circuit lashups with our bare fingers to try and spot bad solder joints or to detect overheating components. To stay alive, you're going to have to learn a whole new set of techniques, and work by them religiously:

Drawing Your Own Tube Schematics with Visio

If you modify published tube circuits before you build them, it's always a good idea to redraw them so you don't forget how the circuit on the bench differs from the one in that old article in QST. There's a very nice drawing program called Visio (now owned by Microsoft) that I've been using to draw schematics for over ten years now. Older versions can be had on eBay for as little as $20, and in fact the version I use—Visio 2000—is now six years old and still perfectly useful. (The latest versions require product activation, which I cannot abide, but in truth there's little in the newest Visio versions that isn't in Visio 2000. Just don't use Visio 1.0.)

I created a stencil file full of tube pinouts, including all the common tube types (dual diode, triode, tetrode, pentode, and so on) and all you need to do is drag them off the stencil and start connecting the leads. (Visio comes with stencils for all the common components like resistors, capacitors, and inductors.)

You can download the stencil file here. It has stencils for the several earlier versions of Visio, but the Visio 5 stencil works fine with Visio 2000 and later versions.

Compactron Tube Material on the Web

Compactron Projects in Books and Magazines

This list of articles and citations were all originally published in print books and magazines, but a very few have been scanned and mounted on the Web. You can find some of these publications on eBay, or on the used book services like ABE Books.