Single-driver pentode test data
Last update: 8/10/03, added 6C45p-e and 6SN7 cascade for comparison
I've been running a few tests on some reasonably high-Gm pentodes, in pentode and triode mode. These are tubes that you could use as a single-tube driver for an SET, for example.
I've pretty much gone through all the likely suspects from my tube boxes. Most of the tubes I had can all be obtained for under $10.00, some (like the 12HL7) for as little as $0.70!
I've also tested a whole lot of tubes that were graciously loaned to me by others to test. Many thanks to Don Johnson, Joezef Tulinski and Tom Bavis in the US, Grame Smithson in New Zealand, and Nic Wilshire in the UK.
I tried to pick a reasonable operating point for the tests, based on the tube curves, and some trial and error. No guarantees that these are the best op points for these tubes. I also didn't play with screen voltage - I used either 75 or 150, depending on what I could get away with from a dissipation standpoint (normally, running close to the limits seems to work the best). I also used a limited set of cathode bias resistors (26, 52, 100, 220, 330 ohms) and plate supply voltages (300 - 400 volts).
Note that the operating point may be limited by either of the plate or screen dissipation limits, or in come cases by maximum voltage ratings. I may have pushed the limits a little in some cases. Hopefully this info will point you in a direction, and then you can go and make more detailed measurements and find the ideal operating point.
Also, in general I only tested one tube. There's a lot of tube-tube variation in high Gm tubes, so keep in mind that you may see variations of 10-20% or even more.
I've now added some comparisons: the 6C45p-e, at a number of operating points, with resistor load and CCS. It compares quite favorably with many of the pentodes.
I also tested a 6SN7 cascade driver, like the one used in the Reichert 300B. Interesting comparison. This is a well-regarded amplifier.
Definitions:
Gm is datasheet Gm (transconductance) in mA/V
Pa(max) is maximum rated plate dissipation
Pg2(max) is max rated screen grid dissipation
B+ is supply voltage in volts
Vp is plate voltage in volts
Vg2 is screen voltage in volts
Rk is cathode resistor in ohms (unbypassed)
Ip is plate current in mA (this also includes the screen current in triode mode)
Pa is plate dissipation in watts
Ig2 is screen current in mA
Pg2 is screen dissipation in watts
Rl is load resistance in ohms
5% THD Vo is the output voltage in V RMS at 5% THD
10V THD is the THD at 10V RMS out
Gain is... voltage gain!
Click on the tube type for a GIF file of the FFT spectrum at 10V RMS out
Tube | Gm | Pa(max) | Pg2(max) | B+ | Vp | Vg2 | Rk | Ip | Pa | Ig2 | Pg2 | Rl | 5% THD Vo | 10V THD | Gain |
Triode mode, CCS load - note Ip is the CCS current and includes the sum of "real" plate current and screen current | |||||||||||||||
12HG7 small RCA | 32 | 10 | 1 | 400 | 175 | Triode | 50 | 35 | 5.1 | 6 | 1.05 | CCS | 121 | 0.04 | 43 |
12HG7 large RCA | 32 | 10 | 1 | 400 | 227 | Triode | 50 | 35 | 6.6 | 6 | 1.36 | CCS | 103 | 0.11 | 50 |
12GN7/12HG7A GE | 36 | 11.5 | 1.5 | 400 | 205 | Triode | 100 | 35 | 5.7 | 7 | 1.44 | CCS | 118 | 0.05 | 39 |
11HM7 GE | 30 | 7 | 1 | 400 | 200 | Triode | 100 | 35 | 6.0 | 5 | 1.00 | CCS | 124 | 0.05 | 42 |
12HL7 RCA | 21 | 10 | 1 | 400 | 149 | Triode | 100 | 35 | 4.2 | 7 | 1.04 | CCS | 88 | 0.08 | 29 |
6688 RCA | 16.5 | 3 | 0.9 | 400 | 120 | Triode | 50 | 18 | 1.6 | 4.5 | 0.54 | CCS | 61 | 0.17 | 43 |
6197 RCA | 11 | 7.5 | 2.5 | 400 | 219 | Triode | 150 | 35 | 6.2 | 6.5 | 1.42 | CCS | 121 | 0.12 | 24 |
6CL6 Sylvania | 11 | 7.5 | 1.7 | 400 | 192 | Triode | 150 | 35 | 5.5 | 6.5 | 1.25 | CCS | 94 | 0.22 | 19 |
6EJ7/EF184 RCA (Amperex) | 15 | 2.5 | 0.9 | 300 | 148 | Triode | 220 | 18 | 1.9 | 5.5 | 0.81 | CCS | 76 | 0.09 | 61 |
8077/7054 RCA | 11.5 | 5 | 1 | 400 | 184 | Triode | 100 | 35 | 5.3 | 6 | 1.10 | CCS | 117 | 0.18 | 28 |
12BY7A/12BV7/12DQ7 GE | 12 | 6.5 | 1.2 | 400 | 197 | Triode | 100 | 35 | 5.7 | 6 | 1.18 | CCS | 92 | 0.08 | 28 |
D3A (Telefunken) | 35 | 4.2 | 1 | 400 | 167 | Triode | 52 | 26 | 3.2 | 6.7 | 1.12 | CCS | 94 | 0.04 | 70 |
CV4045 (RK) | 13 | 12 | 2.5 | 400 | 147 | Triode | 52 | 50 | 6.6 | 5.3 | 0.78 | CCS | 55 | 0.07 | 27 |
SV83 (Svetlana) | 15 | 12 | 1.5 | 400 | 175 | Triode | 220 | 50 | 7.5 | 7.4 | 1.30 | CCS | 86 | 0.13 | 23 |
6CW5/EL86 RCA | 11 | 14 | 2.1 | 400 | 142 | Triode | 220 | 50 | 6.4 | 5 | 0.71 | CCS | ?? | 0.49 | 7.4 |
6686/E81L Amperex | 11 | 4.5 | 1.2 | 400 | 210 | Triode | 100 | 26 | 4.1 | 6.3 | 1.32 | CCS | 95 | 0.18 | 48 |
7788/E810F RCA (Amperex) | 50 | 5 | 1 | 400 | 166 | Triode | 100 | 26 | 3.8 | 3.3 | 0.55 | CCS | 103 | 0.13 | 47 |
6JC6 Sylvania | 15 | 2.5 | 0.6 | 400 | 170 | Triode | 100 | 18 | 2.3 | 4.3 | 0.73 | CCS | 85 | 0.15 | 60 |
PL802 | 40 | 6 | 2.5 | 400 | 207 | Triode | 52 | 35 | 6.1 | 5.6 | 1.16 | CCS | 119 | 0.05 | 69 |
6HF8 Amperex (pentode sect.) | 12.5 | 5 | 1.1 | 400 | 170 | Triode | 150 | 26 | 3.4 | 5.9 | 1.00 | CCS | 91 | 0.21 | 22 |
6EB8 Sylvania (pentode sect.) | 12.5 | 5 | 1.1 | 400 | 222 | Triode | 100 | 26 | 4.8 | 4.6 | 1.02 | CCS | 119 | 0.17 | 30 |
8608 Amperex | 45 | 10 | 1.5 | 400 | 158 | Triode | 100 | 50 | 7.2 | 4.7 | 0.74 | CCS | 102 | 0.03 | 29 |
8233 GE (E55L) | 45 | 10 | 1.5 | 400 | 162 | Triode | 100 | 50 | 7.3 | 4.9 | 0.79 | CCS | 97 | 0.08 | 28 |
6AG7 RCA | 11 | 9 | 1.5 | 400 | 197 | Triode | 150 | 35 | 5.6 | 6.4 | 1.26 | CCS | 58 | 0.14 | 21 |
6EH5 Sylvania | 14.6 | 5.5 | 2 | 400 | 187 | Triode | 330 | 35 | 5.5 | 5.6 | 1.05 | CCS | ?? | 0.15 | 11 |
Tube | Gm | Pa(max) | Pg2(max) | B+ | Vp | Vg2 | Rk | Ip | Pa | Ig2 | Pg2 | Rl | 5% THD Vo | 10V THD | Gain |
Triode mode | |||||||||||||||
12HG7 small RCA | 32 | 10 | 1 | 400 | 207 | Triode | 52 | 40.8 | 8.4 | 7.5 | 1.55 | 4000 | 102 | 0.22 | 23 |
12HG7 large RCA | 32 | 10 | 1 | 400 | 198 | Triode | 52 | 41.7 | 8.3 | 8.8 | 1.74 | 4000 | 84 | 0.17 | 24 |
12GN7/12HG7A GE | 36 | 11.5 | 1.5 | 400 | 178 | Triode | 52 | 45.5 | 8.1 | 10 | 1.78 | 4000 | 78 | 0.32 | 22 |
11HM7 GE | 30 | 7 | 1 | 400 | 183 | Triode | 52 | 46.3 | 8.5 | 8 | 1.46 | 4000 | 83 | 0.19 | 24 |
12HL7 RCA | 21 | 10 | 1 | 400 | 104 | Triode | 52 | 30.0 | 3.1 | 7 | 0.73 | 8000 | 46 | 0.17 | 22 |
6688 RCA | 16.5 | 3 | 0.9 | 300 | 128 | Triode | 52 | 17.5 | 2.2 | 4 | 0.51 | 8000 | 56 | 0.45 | 29 |
6197 RCA | 11 | 7.5 | 2.5 | 400 | 288 | Triode | 100 | 8.0 | 2.3 | 6 | 1.73 | 8000 | 59 | 0.35 | 16 |
6CL6 Sylvania | 11 | 7.5 | 1.7 | 400 | 136 | Triode | 100 | 27.0 | 3.7 | 6 | 0.82 | 8000 | 44 | 0.61 | 14 |
6EJ7/EF184 RCA (Amperex) | 15 | 2.5 | 0.9 | 300 | 164 | Triode | 220 | 8.3 | 1.4 | 3 | 0.49 | 12000 | 81 | 0.33 | 24 |
8077/7054 RCA | 11.5 | 5 | 1 | 400 | 155 | Triode | 100 | 25.6 | 4.0 | 5 | 0.78 | 8000 | 69 | 0.39 | 18 |
12BY7A/12BV7/12DQ7 GE | 12 | 6.5 | 1.2 | 400 | 168 | Triode | 100 | 24.0 | 4.0 | 5 | 0.84 | 8000 | 62 | 0.25 | 17 |
D3A (Telefunken) | 35 | 4.2 | 1 | 400 | 168 | Triode | 52 | 22.4 | 3.8 | 6.6 | 1.11 | 8000 | 84 | 0.16 | 42 |
CV4045 (RK) | 13 | 12 | 2.5 | 400 | 196 | Triode | 52 | 44.4 | 8.7 | 6.6 | 1.29 | 4000 | 38 | 0.29 | 14 |
SV83 (Svetlana) | 15 | 12 | 1.5 | 400 | 189 | Triode | 220 | 44.8 | 8.5 | 8 | 1.51 | 4000 | 71 | 0.32 | 13 |
6CW5/EL86 RCA | 11 | 14 | 2.1 | 400 | 170 | Triode | 220 | 52.5 | 8.9 | 5 | 0.85 | 4000 | ?? | 0.74 | 5 |
6686/E81L Amperex | 11 | 4.5 | 1.2 | 400 | 191 | Triode | 100 | 20.4 | 3.9 | 5.7 | 1.09 | 8000 | 69 | 0.19 | 20 |
7788/E810F RCA (Amperex) | 50 | 5 | 1 | 400 | 165 | Triode | 100 | 26.0 | 4.3 | 3.4 | 0.56 | 8000 | 90 | 0.32 | 28 |
6JC6 Sylvania | 15 | 2.5 | 0.6 | 400 | 147 | Triode | 100 | 13.1 | 1.9 | 3.8 | 0.56 | 15000 | 62 | 0.29 | 37 |
PL802 | 40 | 6 | 2.5 | 400 | 176 | Triode | 52 | 23.3 | 4.1 | 4.7 | 0.83 | 8000 | 85 | 0.26 | 41 |
6HF8 Amperex (pentode sect.) | 12.5 | 5 | 1.1 | 400 | 166 | Triode | 220 | 23.5 | 3.9 | 5.8 | 0.96 | 8000 | ?? | 0.42 | 12 |
6EB8 Sylvania (pentode sect.) | 12.5 | 5 | 1.1 | 400 | 214 | Triode | 220 | 19.8 | 4.2 | 3.5 | 0.75 | 8000 | ?? | 0.45 | 12 |
8608 Amperex | 45 | 10 | 1.5 | 400 | 134 | Triode | 52 | 60.0 | 8.0 | 6.5 | 0.87 | 4000 | 69 | 0.04 | 19 |
8233 GE (E55L) | 45 | 10 | 1.5 | 400 | 138 | Triode | 52 | 58.8 | 8.1 | 6.7 | 0.92 | 4000 | 58 | 0.1 | 19 |
6AG7 RCA | 11 | 9 | 1.5 | 400 | 187 | Triode | 220 | 22.0 | 4.1 | 4.6 | 0.86 | 8000 | ?? | 0.35 | 11 |
6EH5 Sylvania | 14.6 | 5.5 | 2 | 400 | 163 | Triode | 330 | 24.7 | 4.0 | 4.9 | 0.80 | 8000 | ?? | 0.32 | 7 |
Tube | Gm | Pa(max) | Pg2(max) | B+ | Vp | Vg2 | Rk | Ip | Pa | Ig2 | Pg2 | Rl | 5% THD Vo | 10V THD | Gain |
Pentode mode | |||||||||||||||
12HG7 small RCA | 32 | 10 | 1 | 400 | 275 | 150 | 50 | 31.3 | 8.6 | 4 | 0.60 | 4000 | 85 | 0.29 | 39 |
12HG7 large RCA | 32 | 10 | 1 | 400 | 260 | 150 | 50 | 35.0 | 9.1 | 5 | 0.75 | 4000 | 93 | 0.13 | 37 |
12GN7/12HG7A GE | 36 | 11.5 | 1.5 | 400 | 238 | 150 | 50 | 40.5 | 9.6 | 5 | 0.75 | 4000 | 104 | 0.08 | 40 |
11HM7 GE | 30 | 7 | 1 | 400 | 245 | 150 | 50 | 38.8 | 9.5 | 5 | 0.75 | 4000 | 101 | 0.09 | 40 |
12HL7 RCA | 21 | 10 | 1 | 400 | 207 | 75 | 50 | 24.1 | 5.0 | 4 | 0.30 | 8000 | 116 | 0.08 | 61 |
6688 RCA | 16.5 | 3 | 0.9 | 300 | 130 | 150 | 50 | 21.3 | 2.8 | 5 | 0.75 | 8000 | 70 | 0.07 | 54 |
6197 RCA | 11 | 7.5 | 2.5 | 400 | 288 | 150 | 100 | 14.0 | 4.0 | 5 | 0.75 | 8000 | 64 | 0.25 | 18 |
6CL6 Sylvania | 11 | 7.5 | 1.7 | 400 | 166 | 150 | 100 | 29.3 | 4.9 | 7 | 1.05 | 8000 | 80 | 0.06 | 29 |
6EJ7/EF184 RCA (Amperex) | 15 | 2.5 | 0.9 | 300 | 164 | 150 | 220 | 11.3 | 1.9 | 3 | 0.45 | 12000 | 58 | 0.34 | 27 |
8077/7054 RCA | 11.5 | 5 | 1 | 400 | 180 | 150 | 100 | 27.5 | 5.0 | 5 | 0.75 | 8000 | 111 | 0.03 | 35 |
12BY7A/12BV7/12DQ7 GE | 12 | 6.5 | 1.2 | 400 | 168 | 150 | 100 | 29.0 | 4.9 | 5 | 0.75 | 8000 | 109 | 0.23 | 32 |
D3A (Telefunken) | 35 | 4.2 | 1 | 300 | 143 | 150 | 52 | 19.6 | 2.8 | 6 | 0.90 | 8000 | 78 | 0.15 | 69 |
CV4045 (RK) | 13 | 12 | 2.5 | 400 | 253 | 150 | 52 | 36.8 | 9.3 | 3.8 | 0.57 | 4000 | 63 | 0.48 | 24 |
SV83 (Svetlana) | 15 | 12 | 1.5 | 400 | 254 | 150 | 220 | 36.5 | 9.3 | 5.5 | 0.83 | 4000 | 89 | 0.42 | 24 |
6CW5/EL86 RCA | 11 | 14 | 2.1 | 400 | 200 | 150 | 220 | 50.0 | 10.0 | 4.2 | 0.63 | 4000 | ?? | 0.14 | 9.2 |
6686/E81L Amperex | 11 | 4.5 | 1.2 | 400 | 270 | 150 | 100 | 16.3 | 4.4 | 4.3 | 0.65 | 8000 | 78 | 0.44 | 33 |
7788/E810F RCA (Amperex) | 50 | 5 | 1 | 400 | 206 | 150 | 100 | 24.3 | 5.0 | 3 | 0.45 | 8000 | 114 | 0.32 | 52 |
6JC6 Sylvania | 15 | 2.5 | 0.6 | 350 | 156 | 150 | 100 | 12.9 | 2.0 | 3.8 | 0.57 | 15000 | 92 | 0.27 | 65 |
PL802 | 40 | 6 | 2.5 | 300 | 185 | 150 | 26 | 28.8 | 5.3 | 5.6 | 0.84 | 4000 | 82 | 0.11 | 61 |
6HF8 Amperex (pentode sect.) | 12.5 | 5 | 1.1 | 400 | 170 | 150 | 100 | 28.8 | 4.9 | 7.1 | 1.07 | 8000 | 109 | 0.04 | 33 |
6EB8 Sylvania (pentode sect.) | 12.5 | 5 | 1.1 | 400 | 200 | 150 | 100 | 25.0 | 5.0 | 4.2 | 0.63 | 8000 | 125 | 0.04 | 35 |
8608 Amperex | 45 | 10 | 1.5 | 400 | 252 | 75 | 52 | 37.0 | 9.3 | 2.8 | 0.21 | 4000 | 95 | 0.23 | 46 |
8608 Amperex | 45 | 10 | 1.5 | 400 | 235 | 150 | 100 | 41.3 | 9.7 | 2.7 | 0.41 | 4000 | 116 | 0.63 | 28 |
8233 GE (E55L) | 45 | 10 | 1.5 | 400 | 252 | 75 | 52 | 37.0 | 9.3 | 2.8 | 0.21 | 4000 | 94 | 0.17 | 45 |
8233 GE (E55L) | 45 | 10 | 1.5 | 400 | 238 | 150 | 100 | 40.5 | 9.6 | 4.1 | 0.62 | 4000 | 116 | 0.08 | 27 |
6AG7 RCA | 11 | 9 | 1.5 | 400 | 221 | 150 | 150 | 22.4 | 4.9 | 4.4 | 0.66 | 8000 | 102 | 0.32 | 23 |
6EH5 Sylvania | 14.6 | 5.5 | 2 | 400 | 194 | 75 | 100 | 25.8 | 5.0 | 4 | 0.30 | 8000 | 119 | 0.11 | 30 |
Tube | Gm | Pa(max) | Pg2(max) | B+ | Vp | Vg2 | Rk | Ip | Pa | Ig2 | Pg2 | Rl | 5% THD Vo | 10V THD | Gain | ||
Comparisons | |||||||||||||||||
6C45p-e | 45 | 7.8 | NA | 400 | 166 | NA | 200 | 11.7 | 1.9 | NA | NA | 20000 | 116 | 0.28 | 23 | ||
6C45p-e (cathode bypassed) | 45 | 7.8 | NA | 400 | 166 | NA | 200 | 11.7 | 1.9 | NA | NA | 20000 | 107 | 0.36 | 34 | ||
6C45p-e | 45 | 7.8 | NA | 400 | 167 | NA | 100 | 23.3 | 3.9 | NA | NA | 10000 | 113 | 0.26 | 25 | ||
6C45p-e (cathode bypassed) | 45 | 7.8 | NA | 400 | 167 | NA | 100 | 23.3 | 3.9 | NA | NA | 10000 | 109 | 0.39 | 35 | ||
6C45p-e | 45 | 7.8 | NA | 400 | 200 | NA | 52 | 50.0 | 10.0 | NA | NA | 4000 | 112 | 0.29 | 23 | ||
6C45p-e (cathode bypassed) | 45 | 7.8 | NA | 400 | 200 | NA | 52 | 50.0 | 10.0 | NA | NA | 4000 | 103 | 0.41 | 34 | ||
6C45p-e CCS | 45 | 7.8 | NA | 400 | 194 | NA | 100 | 35.0 | 6.8 | NA | NA | CCS | 119 | 0.07 | 41 | ||
6C45p-e CCS | 45 | 7.8 | NA | 400 | 156 | NA | 220 | 10.0 | 1.6 | NA | NA | CCS | 126 | 0.12 | 35 | ||
6C45p-e CCS | 45 | 7.8 | NA | 400 | 194 | NA | 52 | 45.0 | 8.7 | NA | NA | CCS | 131 | 0.07 | 40 | ||
6SN7 cascade (Reichert) | 400 | 70 | 1.6 | 110 |
You can download the whole thing as a PDF file or Excel spreadsheet below in the full PDF file below...
PDF file of results (LARGE 1.46M PDF file)
Excel spreadsheet of the data (892k .XLS file)