History of the AA5
(All American 5ive) AM tube radio

Click here >]:::|- for a schematic diagram of the AA5 AM radio using miniature tubes.
Foreign to AA5 or audio tube sub list. Military to AA5 or audio tube sub list.

Possibly the longest lived consumer electronic product design was the five tube "AC/DC" AM radio. Virtually every household had at least a few over the years. These radios were low cost, and one expensive item designed out was the power transformer. Thus the series heater string, and using the powerline directly rectified for B+ power. No power transformer also made it possible for smaller and lighter sets to be made.

----- (This portion quoted from an article published in the Michigan Antique Radio Club newsletter by John Reinicke)

In the 20's the crystal set and then the Tuned Radio Frequency, or TRF, set would provide adequate performance. The complexity and cost of the Superhet receiver was simply not required. As a result, the Superhet design appeared only in the most expensive receivers. See a brief description of the Superheterodyne radio. In the 30's, the situation rapidly changed. Radio had enjoyed explosive growth and the number of transmitters on the air exceeded the selectivity of the TRf sets. The 30's also saw an extraordinary economic circumstance and the manufacturers of radios realized the need to produce low cost, high performance, receivers. It was now evident the only design that would provide adequate performance was the Superhet. In order to reduce the number of tubes required to support the Superhet, manufacturers designed multipurpose tubes. In April 1933, RCA introduced the 2A7. The 2A7 was the first pentagrid converter which combined the functions of Rf amplifier, mixer, and oscillator in a single envelope. This tube could then be used with a pentode as an If amplifier, a combination diode-triode as a detector-first audio amplifier and a audio power amplifier to make a complete receiver. Add to this a rectifier to power the set and you have a high performance receiver with but 5 tubes. To further improve the receiver, a remote cut off pentode could be used in the If amplifier so the If amplifier could be used as a part of the automatic volume control circuit. The tube line up for this 5 tube receiver would then be: 2A7, Rf amplifier, converter; 58, Remote cut off pentode, If amplifier; 55, Diode-triode, Detector-first audio; 59, Audio output; and 80 for a rectifier. This arrangement uses 2.5 volt filaments and therefore required the use of a power transformer. This was the prototype "All American Five."

1934 saw the introduction of the 6A7 and a whole series of 6 volt tubes to go with it. It was now possible to build an automobile radio or to combine with a 25Z5 rectifier to build a set without a power transformer. (See the March 1990 Chronicle article, Ballast). With the elimination of the power transformer, it was now possible to have a truly low cost, high performance receiver. There are those who argue the series filament version became the classic all American Five.

(end quote) -----

The tube heaters were wired in series, sometimes with a "ballast" resistance added to make the total voltage drop across the entire string add up to that of the powerline, around 120V. All the tubes needed to have the same heater requirement for this to work. All tubes had indirectly heated cathodes.

Early versions of the five tube radio used the same small signal tubes (RF, IF, non-power audio) as transformer sets used. Tubes like 6A7, 6D6, 75, 6F7 and newer ones like 6SK7, 6SQ7. And an extra "tuning eye" 6E5 tube if desired (- George Gonzalez). All these had 300 ma heaters. To make an "AC/DC" radio, you would just need specially designed audio output and rectifier tubes. Like the 43, 25L6, 25Z5 and 25Z6. That would be only two new tubes to be developed (per radio chassis design) to make an AC/DC set. These had higher voltage heaters, but the same current (300mA) as the small signal tubes above. Power handling tubes like audio outputs and rectifiers need bigger cathodes and more heater power to operate. If current is the limiting design factor, increase the voltage to get more heater power.

But all the heaters in a series string in the above didn't add up to enough voltage to be fed directly off the powerline. So some sort of additional voltage dropping resistance was used. Either a power resistor, "ballast tube" or resistive wire in the power cord was used. I don't know if anyone used a power resistor housed in a "wall wart" (calculator charger style) power plug.

One of the above mentioned rectifier tubes, the 25Z6, is a pair of diodes, used in a voltage double circuit. This gets you a B+ of around 250 - 300 volts. Might make "translating" a design from a power transformer design to a "hot chassis" design. Not "AC/DC", voltage doublers won't work off of a DC supply.

Later on, to reduce waste heat in ballast tubes or resistors, the 150 ma tubes were developed. By this time, the 5 tube AC/DC radio was a popular product, so it was worth while to create new tube designs. Basically, the 6V, 300mA heater signal tubes had their heaters replaced with ones that needed 12V at 150mA. "Tuning eye" tubes at 150 mA heater for consumer radios did exist. There's the 6AB5 / 6N5. Heater of 6.3V @ 150ma. And the 1629, heater of 12.6V @ 150ma. But they were rarely used. The Airline model 93WG602B used the 6AB5. But the common 150ma AA5 tubes used the same power as the 300ma AA5 tubes. And the 25L6 became a 50L6 the same way, 2x voltage, 1/2 current. A new design overall was the rectifier tube, the 35Z5, with a tap on the heater to operate a pilot light. And the total added up to the powerline voltage, so no wasted heater string current thru a dropping ballast. Saved 18 watts of power that used to be 18 watts of heat to get rid of. And conserved some energy, but noone worried about that until the mid seventies. It looks like this occurred in about 1940. All these were octal socket tubes. Loktal versions appeared at about the same time, also.

Brief superheterodyne description

So much for the heaters for now. Early sets were TRF's (tuned radio frequency) that just amplified the radio station's carrier frequency, detected it down to audio, and amplified it. This design would need to have 3 or so LC circuits that would "track" each other as you tuned across the band. And with gain stages between, you had to be careful that the amplified signal at the detector didn't leak back into the antenna, or else you'd hear yourself instead of a signal. Later on, the superheterodyne radio was invented, and is still the preferred architecture for modern radio receivers. A basic superhet receives the radio station with an antenna LC circuit, heterodynes it with a supersonic (thus "superheterodyne") locally generated frequency, and the difference of the station carrier frequency and the local oscillator would be the intermediate frequency (IF). After this conversion, a narrow fixed bandwidth and frequency gain stage was designed to amplify the signal. Easier to design such a stage instead of a TRF circuit of the same gain. It also helps that leakage form the IF won't be "heard" by the front end antenna LC circuit, because it's a way different frequency. Special frequency changing tubes were developed to generate and mix the local oscillator frequency with the radio station carrier to generate the IF. The 6A7, 6A8, and 6SA7, and later the 12SA7 are "pentagrid" converter tubes for this purpose.

Tubes with variable gain were used in IF amp stages, so automatic volume control (AVC) could be done. Decrease the gain on strong stations so you don't get blasted out when tuning from a weaker station, and also avoid distortion overload from the strong station. Tubes like 6K7, 6D6, 6SK7, and later 12SK7 were variable gain tubes. Usually called "remote cutoff" pentodes, as the tube wouldn't linearly cutoff current flow like a constant gain tube ("sharp cutoff") would. Yes, these remote cutoff tubes would not be usable in an audio amp, but these tubes lived in IF strips, where only a narrow bandwidth of frequencies were to be amplified, and harmonic distortion products fell outside the bandwidth of the output IF filter, and were thus ignored. The audio detector tube would also measure the signal level, and thus could be fed back to the remote cutoff pentode IF tube. And also to any variable gain tubes at the front end of the radio. The audio detector diode was arranged to create more negative voltage for strong signals, and more negative voltage reduces the gain of the remote cutoff tubes.

Once the audio is detected, it needs to be power amplified to drive a speaker at reasonable volume levels. A triode signal gain stage feeds the power tube, to generate about 1 watt of audio power to the speaker. The audio bandwidth is narrower than modern hi-fi stereos. And the speaker was fairly efficient, so not much power was needed. To a casual listener, if you limit the low frequencies and the highs at the same time, the listener won't really notice. The extreme example of this is the telephone, 300 to 3000 Hz. AA5 radios do about 150 to 5000 Hz. Hi-Fi stereos do about 20 to 20000 Hz.

The five tube AM radio didn't much vary after the 150 mA heater tubes were introduced around 1940 or so. Those were the octal series of tubes. The 12SA7 converter, 12SK7 IF amp, 12SQ7 audio detector and signal amp, 50L6 audio power, and 35Z5 rectifier. Just after WW2, the miniature 7 pin tubes were introduced. Miniature tubes were used in the war, but didn't hit the consumer market until after. The 12BE6 converter, 12BA6 IF amp, 12AT6 audio detector and signal amp, 50B5 audio power, and 35W4 rectifier. The 50B5 had its plate next to the heater, but that made for too much voltage between these pins and uL and similar safety agencies didn't like this. The 50C5 was a rearrangement of the pinout to solve this safety concern (- George Gonzalez.) Another variation, the "loktal" tube, had its own versions of these, 14Q7, 14A7, 14B7, 50A5, and 35Y4, respective functions. By this time, the AA5 acquired its designation, the "All American 5" from ww2 surplus tube dealers who sold to hobbyists (- Doug Houston). You sometimes find AA5 radios using a mix of octals and loktals, or octals and mini's. Doug MacDonald tells of an AA5 that used a mix of octals, loktals and mini's. A Philco 81-122, using 7A8, 12BA6, 14B6, 50L6 and 35Z5. Most likely reason for this grouping of tubes was what they could purchase enough of inexpensively to make radios at the time.

The last version of the AA5 tube line-up was the 100 mA heater string, introduced in the early sixties. Saved an extra 6 watts of heater power, but the tubes took a little longer to warm up, and the audio output power was a bit less. The signal handling tubes were 18V at 100 mA heaters, so those used the same amount of power as the 12V tubes on the heaters. All had the same pinouts as the 150 mA versions. But these had slight differences with the 150 mA tubes, so they were assigned their own designations instead of being called 18BE6 or 18BA6. They were: 18FX6 converter, 18FW6 IF amp, 18FY6 audio detector and signal amp, 32ET5 or 34GD5 audio power, and 36AM3 rectifier (which the RCA tube manual (RC24) says cannot be used to operate a pilot light, but the Sylvania tube manual (1968) says it can operate a pilot light). As you can see, the audio out tube had less heater power than the 50V at 150 mA version had to heat the cathode, thus less audio power output. Also the rectifier was also had less heater power, but the audio stage drawing less current allowed a less current capable rectifier to be used.

A compactron tube version was in development, but turned out it would have cost more to make than the miniature 7 pin tubes already out. See Electronics World Oct 1960 article page 48 and page 49 on these. A radio would have used 2 tubes, a converter/ IF pentode tube "40xx10" (my guess at a likely tube number had it went into production) and a detector/audio driver & output/rectifier "70xx11". 100 ma heaters. The 56R9, a compactron triode and power pentode, is listed in the 1973 edition of GE's "Essential Characteristics" manual, page 212. With a heater current of 150mA, this may have been to be an "AA5" compactron. See a web page of an AM radio I built using compactrons. After you make a few tens of millions of something, you find ways of squeezing the cost to a bare minimum, which is usually just a bit more than the cost of raw materials.

Sub-miniature tubes were used by the military, but were too expensive to make for use in AA5 type radios. See my web page for speculation on how such a radio might have taken shape.

The end of the AA5 radio was in the early 1970's, as stocks of tubes and related parts were depleted by manufacturers and sellers. By then, many were made in Japan, and Japanese AA5 tubes were also made in Japan used by American radio and TV manufacturers. After that, solid state radios, many using a high voltage audio output resistor and thus were also "hot chassis", became the preferred technology.

   ALL AMERICAN FIVE - TUBE COMPLEMENT  (list by John Reinicke)

                        1st Audio    OUTPUT

    2A7       58        55           59        80        1933

    6A7       39/44     75           42                  1934
              78                     43        25Z5      300 mA heaters 

    1A6       1A4       1B5          33

    6A8       6S7       6Q7          6K6       5Y3       1935
    6K8       6K7                                        First octal 

                                     6L6       6X5       1937

    6SA7      6SK7      6SQ7                             1939
    12A8      12K7      12Q7         35L6      35Z4      150 mA heaters
    7A8       7B7       7C6          35A5      35Z3      First Loktal
              7A7       7B6                              sockets
    1A7       1A4       1H5          3Q5

    12SA7     12SK7     12SQ7        50L6      35Z5      1940
    1R5       1T4       1U5          1S4                 First Miniature
                                     1T5                 sockets

    1LA6      1LG5      1LD5         1LA4      117Z3

    12BE6     12BA6     12AV6        50B5      35W4      1946
                        12AT6        50C5
    14B8      14A7      14B6         50A5      35Y4

    12GA6     12EA6     12FM6                            mid to late 50's
    12AD6     12AC6     12AJ6                            12V B+ tubes for
    12AG6     12AF6     12FK6                            car radios, same
    12FA6     12BL6     12AE6                            pinouts as their
    12EG6     12DZ6     12FT6                            AA5 counterparts
              12CN5     12EL6                            different pinouts

    18FX6     18FW6     18FY6        32ET5     36AM3     early '60's
              18GD6                  34GD5               100 mA heaters
    26D6      26A6      26C6                             Military tubes
              26CG6     26BK6                            70 ma heaters

    56R9      150 mA compactron triode/ power pentode tube, early '70's?

GE compactrons never released:
   "40xx10" converter/IF  "70xx11" detector/audio driver & output/rectifier
    100ma heaters  See Electronics World Oct 1960 article page 48 and
    page 49 on these.

Foreign types replacable by AA5 or audio types:

	foreign	American

	foreign	American
	1C1	1R5
	1F3	1T4
	1H33	1R5
	1P10	3S4
	1P11	3V4
	6B32	6AL5
	6BC32	6AV6
	6D2	6AL5
	6F31	6BA6
	6F33	6AS6
	6H31	6BE6
	6L13	12AX7
	6P15	6BQ5
	6R-HH2	6BS8
	10PL12	50BM8
	12BC32	12AV6
	12F31	12BA6
	12H31	12BE6
	13D2	6SN7
	19M-R9	18FW6A
	19M-R10	18GD6
	A2900	12AT7
	B36	12SN7
	B65	6SN7
	B152	12AT7
	B309	12AT7
	B329	12AU7
	B339	12AX7A
	B739	12AT7
	B749	12AU7A
	B759	12AX7A
	CC81E	12AT7WC
	CV133	6C4
	CV452	6AT6
	CV453	6BE6
	CV454	6BA6
	CV455	12AT7
	CV491	12AU7A
	CV492	12AX7A
	CV537	12SA7
	CV538	12SA7GT
	CV543	12SK7
	CV544	12SK7GT
	CV546	12SQ7
	CV547	12SQ7GT
	CV551	25L6GT
	CV552	25L6
	CV561	35L6
	CV568	35Z5GT
	CV571	50L6GT
	CV586	6L6GT
	CV609	42
	CV614	75
	CV782	1R5
	CV852	6C4
	CV925	12SN7GTA
	CV1075	6L6GC
	CV1286	6L6
	CV1287	25L6GT
	CV1928	12BA6
	CV1947	6L6GC
	CV1948	6L6
	CV1959	50C5
	CV1961	12AU6
	CV1966	6SA7
	CV1967	6SA7GT
	CV1981	6SK7
	CV1982	6SK7GT
	CV1988	6SN7GT
	CV1990	6SQ7
	CV1991	6SQ7GT
	CV2007	12AU7A
	CV2016	12AT7
	CV2024	6BE6
	CV2026	6BA6
	CV2526	6AV6
	CV2527	6BA7
	CV2534	50L6GT
	CV3508	12AT7WA
	CV4004	12AX7A
	CV4012	6BE6
	CV4029	5902
	CV4058	6C4WA
	CV5037	6BA6W
	CV5212 	12AT7
	CV5358	6DJ8
	CV8069	6BQ5
	CV8154	12AT7
	CV8155	12AU7A
	CV8156	12AX7A
	CV8201	6BE6
	CV8202	6BA6
	CV8221	12AU7A
	CV8222	12AX7A
	D152	6AL5
	D2M9	6AL5
	D717	6AL5
	D77	6AL5
	DAF92	1U5
	DD6	6AL5
	DF60	5678
	DF62	1AD4
	DF904	1U4
	DF91	1T4
	DH77	6AT6
	DK91	1R5
	DL37	6L6GT
	E81CC	12AT7WC
	E99F	6BJ6
	E2157	12AT7
	E2163	12AU7A
	E2164	12AX7A
	E81CC	12AT7, 6201
	E82CC	12AU7
	EAA91 	6AL5
	EBC90	6AT6
	EBC91	6AV6
	EC90	6C4
	ECC186	12AU7
	ECC70	12AT7WC
	ECC82	12AU7A
	ECC83	12AX7A
	ECC88	6DJ8
	ECC801	12AT7W
	ECC802	6189
	ECC803	12AX7A
	ECC863	12AX7A
	EF72	5840
	EF730	5636
	EF732	5840, 5901
	EF734	6205
	EF93	6BA6
	EK90	6BE6
	EL37	6L6GC
	EL71	5902
	EL84	6BQ5
	EZ4	6C4
	HAA91	12AL5
	HABC80	19T8
	HBC80	19T8A
	HBC90	12AT6
	HBC91	12AV6
	HCC85	17EW8 
	HF93	12BA6
	HF94	12AU6
	HK90	12BE6
	HL92	50C5
	HL94	35C5
	HM04	6BE6
	HY90	35W4
	KT32	25L6GT, 25W6
	KT71	50L6GT
	KT88	6550
	L77	6C4
	LN119	50BM8
	M8121	5840
	M8136	6189
	M8137	12AX7A
	M8162	12AT7WC
	N308	25E5
	N709	6BQ5
	OBC3	12SQ7
	OSW3104	6SA7
	OSW3105	6SQ7
	OSW3111	6SK7
	PM04	6BA6
	QA2406	12AT7WC
	QB309	12AT7
	QL77	6C4
	QS2406	12AT7WC
	UF89	12AD6
	UCL82	50BM8
	W17	1T4
	W727	6BA6
	X17	1R5
	X77	6BE6
	X107	18FX6
	X727	6BE6


Mil to AA5 or audio types:

	VT33	33
	VT49	39/44
	VT58	58
	VT54	34
	VT75	75
	VT78	78
	VT80	89
	VT86	6K7
	VT92	6Q7
	VT103	6SQ7
	VT104 	12SQ7
	VT115	6L6
	VT117	6SK7
	VT131	12SK7
	VT150	6SA7
	VT161	12SA7
	VT173	1T4
	VT174	3S4
	VT199	6SS7
	VT201	25L6
	VT209	12SG7
	VT211	6SG7
	VT231	6SN7
	VT264	3Q4
	VT288	12SH7
	1622	6L6
	5749	6BA6
	5750	6BE6
	5881	6L6GT
	6046	25L6GT
	6057	12AX7
	6060	12AT7
	6100	6C4
	6137	6SK7
	6189	12AU7
	6201	12AT7WC
	6662	6BJ6
	6679	12AT7
	6680	12AU7
	6681	12AX7
	7025	12AX7
	7036	6BE6
	7320	6BQ5
	7581	6L6
	8426A	12AU6

NOTE: Not all subs will work in all circuits!