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12 Volt Car Radio Tubes |
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By the end of the 1950s the hand writing was on the wall and most engineers and managers knew that tubes were destine to be replaced by transistors. |
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As often happens when an established technology is threatened by a more advanced one, tube engineers began to innovate to meet the threat. |
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The two most visible of these innovations were the compactron and the family of tubes that would operate from a plate supply voltage of 12 volts. |
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Many car radios were made using these tubes for everything except the audio output where a transistor was used. Given time the tube engineers |
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would have found a way to get 2 or 3 watts from a tube with a plate supply of 12 volts. Unfortunately time ran out on them. |
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Listed below is the legacy of a dying industry. But don't play taps just yet. There is still a lot of interest in tubes. |
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A space charge tetrode is biased by applying + 12 volts to grid 1 and the signal to grid 2. An LV tetrode is biased in the conventional way. |
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Signal grid bias is provided by contact potential. A large resistor is connected from the grid to cathode. |
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Heater (H), Filament (F) |
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Type |
Function or Configuration |
H/F |
V |
A |
Other heater voltages |
Plate Dissipation |
Max Plate Voltage |
Gm |
µ |
Rp |
Base |
Notes |
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12AD6 |
Medium mu Triode Duo Diode |
H |
12.6 |
0.15 |
- |
N. A. |
30 |
1000 |
15 |
15 k |
7 Pin Mini |
Two diodes share cathode with Triode. |
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12AJ6 |
Duo Diode Triode |
H |
12.6 |
0.15 |
- |
N. A. |
30 |
1200 |
55 |
45 k |
7 Pin Mini |
Two diodes share cathode with Triode. |
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12DV7 |
Duo Diode Triode |
H |
12.6 CT |
0.15 |
- |
N. A. |
16 |
750 |
14 |
19 k |
9 Pin Mini |
One cathode for the Triode, another for the two Diodes. |
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12EL6 |
Duo Diode Triode |
H |
12.6 |
0.15 |
- |
N. A. |
30 |
1200 |
55 |
45 k |
7 Pin Mini |
Two diodes share cathode with Triode. |
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12FK6 |
Duo Diode Triode |
H |
12.6 |
0.15 |
- |
N. A. |
16 |
1200 |
7.4 |
6200 |
7 Pin Mini |
Two diodes share cathode with Triode. |
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12FM6 |
Duo Diode Triode |
H |
12.6 |
0.15 |
- |
N. A. |
30 |
1300 |
10 |
7700 |
7 Pin Mini |
Two diodes share cathode with Triode. |
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12U7 |
LV Duo Triode |
H |
12.6 CT |
0.15 |
- |
N. A. |
30 |
1600 |
20 |
12.5 k |
9 Pin Mini |
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Heater (H), Filament (F) |
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Type |
Function or configuration |
H/F |
V |
A |
Section Data |
Max Plate Watts |
Max Plate Volts |
Max Screen Volts |
Gm |
Rp |
Base Type |
Notes |
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12AL8 |
Space Charge Tetrode plus Triode |
H |
12.6 |
0.55 |
Pentode |
N. A. |
30 |
16 G1 |
15000 |
480 |
9 pin mini |
Triode u = 13, has separate cathode. |
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Triode |
N. A. |
30 |
- |
1000 |
13 k |
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12DK7 |
LV Tetrode plus 2 Diodes |
H |
12.6 |
0.5 |
N/A |
0.5 |
30 |
30 |
5000 |
4000 |
9 pin mini |
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12DL8 |
Space Charge Tetrode plus 2 Diodes |
H |
12.6 |
0.55 |
N/A |
N. A. |
30 |
16 G1 |
15000 |
480 |
9 pin mini |
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12DS7 |
Space Charge Tetrode plus 2 Diodes |
H |
12.6 |
0.4 |
N/A |
N. A. |
16 |
16 G1 |
16000 |
500 |
9 pin mini |
Diodes and Tetrode have common cathode. |
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12DU7 |
LV Tetrode plus 2 Diodes |
H |
12.6 |
0.25 |
N/A |
N. A. |
16 |
16 |
6200 |
6000 |
9 pin mini |
Diodes and Tetrode have common cathode. |
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12DV8 |
Space Charge Tetrode plus 2 Diodes |
H |
12.6 |
0.375 |
N/A |
N. A. |
16 |
16 G1 |
8500 |
900 |
9 pin mini |
Two diodes have common cathode. Tetrode has separate cathode |
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12DY8 |
LV Tetrode plus Triode |
H |
12.6 |
0.35 |
Tetrode |
N. A. |
16 |
16 |
6000 |
5 k |
9 pin mini |
Separate cathodes. |
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Triode |
N. A. |
16 |
- |
2000 |
10 k |
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12EM6 |
LV Tetrode plus Diode |
H |
12.6 |
0.5 |
N/A |
0.5 |
30 |
30 |
5000 |
4000 |
9 pin mini |
Common cathode. |
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12J8 |
LV Tetrode plus 2 Diodes |
H |
12.6 |
0.325 |
N/A |
N. A. |
30 |
30 |
5500 |
6000 |
9 pin mini |
Two diodes have common cathode. Tetrode has separate cathode |
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12K5 |
Space Charge Tetrode |
H |
12.6 |
0.4 |
N/A |
N. A. |
30 |
16 |
15000 |
480 |
7 pin mini |
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12CN5 |
Sharp Cutoff Pentode |
H |
12.6 |
0.45 |
N/A |
N. A. |
16 |
16 |
3800 |
40 k |
7 pin Mini |
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12CX6 |
Sharp Cutoff Pentode |
H |
12.6 |
0.15 |
N/A |
N. A. |
33 |
33 |
3100 |
40 k |
7 pin Mini |
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12EK6 |
Sharp Cutoff Pentode |
H |
12.6 |
0.19 |
N/A |
N. A. |
16 |
16 |
4200 |
50 k |
7 pin Mini |
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12AC6 |
Remote Cutoff Pentode |
H |
12.6 |
0.15 A |
N/A |
N. A. |
30 |
30 |
750 |
500 k |
7 pin Mini |
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12AF6 |
Remote Cutoff Pentode |
H |
12.6 |
0.15 A |
N/A |
N. A. |
16 |
16 |
1250 |
300 k |
7 pin Mini |
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12BL6 |
Semi-Remote Cutoff Pentode |
H |
12.6 |
0.15 A |
N/A |
N. A. |
30 |
30 |
1350 |
500 k |
7 pin Mini |
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12DZ6 |
Remote Cutoff Pentode |
H |
12.6 |
0.19 A |
N/A |
N. A. |
16 |
16 |
3800 |
25 k |
7 pin Mini |
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12F8 |
Remote Cutoff Pentode Duo Diode |
H |
12.6 |
0.15 |
N/A |
N. A. |
30 |
30 |
1000 |
330 k |
9 pin Mini |
Common cathode. |
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Heater (H), Filament (F) |
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Type |
Function or configuration |
H/F |
V |
A |
Section Data |
Max Plate Voltage (volts) |
Max Screen Voltage (volts) |
Gm |
µ |
Rp |
Base Type |
Notes. |
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12EC8 |
Medium mu Triode Sharp cutoff Pentode |
H |
12.6 |
0.225 |
Triode |
16 |
- |
4700 |
25 |
6 k |
9 pin mini |
Suppressor tied to pentode cathode. |
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Pentode |
16 |
16 |
2000 |
- |
750 k |
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12FR8 |
Diode, Low mu Triode, and Sharp Cutoff Pentode |
H |
12.6 |
0.32 |
Triode |
16 |
- |
1200 |
10 |
8.3 k |
9 pin mini |
Diode plate current = 5 mA. Diode and Triode share a common cathode. Suppressor grid tied to Pentode cathode. |
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Pentode |
16 |
16 |
2700 |
- |
400 k |
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Heater (H), Filament (F) |
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Type |
Function or Configuration |
H/F |
V |
A |
Notes and Comments |
Base Type |
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12AD6 |
Heptode Converter |
H |
12.6 |
0.15 |
This is a 5 grid tube with grids 2 and 4 tied together and brought out to a single pin. Grid 5 is tied to the cathode. Low voltage tube designed for vibrator less car radios. |
7 pin mini |
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12EG6 |
Dual Control Heptode |
H |
12.6 |
0.19 |
This is a 5 grid tube with grids 2 and 4 tied together and brought out to a single pin. Grid 5 is tied to the cathode. Low voltage tube designed for vibrator less car radios. |
7 pin mini |
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The application note indicates that both grids 1 and 3 have remote cutoff characteristics for application of AGC to both grids |
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12FX8 |
Triode Heptode |
H |
12.6 |
0.3 |
Heptode section is a 5 grid tube with grids 2 and 4 tied together and brought out to a single pin. Grid 5 is tied to the cathode. Triode section has mu of 10 and separate cathode. Low voltage tube designed for vibrator less car radios. |
9 pin mini |
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12GA6 |
Heptode Converter |
H |
12.6 |
0.15 |
This is a 5 grid tube with grids 2 and 4 tied together and brought out to a single pin. Grid 5 is tied to the cathode. Low voltage tube designed for vibrator less car radios. |
7 pin mini |
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