Designs — Tubelab SSE — Tubes and Applications

Beginner

Assembly Manual • Schematic • Parts List • Tubes and Applications • Design • Simulations

At the time this manual was written, the Tubelab SSE has only been tested as a stand alone single ended amplifier. I have not used it in other applications yet. Since it was designed for stand alone amplifier use, this manual only covers this application.

I have built and tested a few different amplifier configurations that all share the same basic design. It is recommended that you duplicate one of these designs if this is your first amplifier, or you want to copy a known good design. Even if you use one of the standard configurations you should expect some variation from my measured values because of tube and line voltage variation.

The Most Popular SSE Design

About 95% of the Tubelab SSE's ever built were made this way. It is a well tested and proven combination. If this is your first amp build, this is the best place to start. The amp runs with a B+ of around 450 volts using 5K ohm output transformers and can be run in triode or ultralinear mode. All of the popular output tubes can be used.

Power Transformer:

The primary winding should match the line (mains) voltage available at your location. A universal (multi winding or multi tapped winding) primary can be used if it supports your line voltage.

The high voltage secondary should be 700 to 750 VCT (350-0-350) to (375-0-375) it should be rated for at least 175 mA DC output. An 800 VCT (400-0-400) transformer will result in too much B+ voltage and should NOT be used. This winding MUST have a center tap.

The rectifier filament winding should be 5 VAC at at least 2 amps. If a 5U4 or 5R4 rectifier is used this winding must be at least 3 amps. A center tap on this winding is OK, but it will not be used.

The main filament winding should be 6.3 VAC at at least 5 amps. A center tap on this winding is OK, but it will not be used.

The transformer may have additional windings or a bias tap. These will not be used.

For builders in the USA, Canada, or other 120 volt 60HZ countries the following transformers have been used:

  • Allied 6K7VG
  • Hammond 274BX
  • Edcor XPWR035.

Many builders outside the USA have used the Hammond 374BX. It is a universal primary design and can be used in the US or just about anywhere in the world. Many builders feel that Hammond's 300 series transformers exhibit higher build quality than the 200 series. There are likely other transformers available to builders in other countries that I don't know about. If it matches the requirements listed above, it should work. Edcor lists a clone of the Hammond 374BX called an XPWR059. 120/240 primary, 375-0-375 @ 175 ma, 50V @ 50 mA, 6.3V CT @ 6A, and 5V CT @ 3 A. I have not tried it though.

Output Transformers:

The OPT is the most critical component in any tube amplifier, and one that is not likely to be upgraded later. The ability of an OPT to reproduce low frequencies is directly related to its size. There are plenty of different types of output transformers available for tube amplifiers. The prices go from $15 USD each to well over $500 USD each. How do you choose? First let me state the requirements:

The Tubelab SSE is a single ended amplifier. The output transformer MUST be designed to work in a single ended amplifier. A push pull transformer will NOT work. Severe distortion will result. The ideal primary impedance for this design is 5K ohms. The secondary impedance should match your speaker impedance. The transformer should be rated to handle the power produced by this amplifier. This could be as low as 5 watts in triode mode, or as high as 15 watts in UL (Ultralinear) mode. The output transformer must have a UL mode tap if you intend to use UL.

The performance of an output transformer is generally related to its size and therefore cost. It will have the biggest effect on the sound quality in the amplifier. I usually recommend that you start with the best transformers that the budget allows even if it means using cheaper tubes. You will upgrade the tubes later, probably not the transformers. See this page for more info.

The small OPT's in the 1 to 2 pound (weight) range will generally exhibit distortion on heavy bass notes. They may be OK if your speakers do not reproduce these frequencies, OR you use an active subwoofer. The small Edcors sound fairly good on my Yamaha NS-10's since their 7 inch woofers can't do much below 70 Hz. Popular transformers in this range are the Edcor XSE15-8-5K and the Hammond 125CSE. I have used both of these, and they work well within their limitations. I prefer the Edcor and it is cheaper. The Edcor has a UL tap, but is available in a single output impedance only (either 4 or 8 ohms). The Hammond has multiple output taps, but NO UL tap (triode mode only).

Both Edcor and Hammond have larger versions of these transformers. The Hammond 125ESE and the Edcor GXSE series have been used by SSE builders who report good results, but I have not tried either of them.

There are several transformers in the 5 to 7 pound range. These are probably the best choice for most builders. A transformer of this size can deliver full solid bass through a big speaker, without compromising the high frequencies, IF it is properly designed AND built. I have used these with good results. The One Electron UBT2, a custom "10 watt" Electra - Print, and an older "Transcendar" I got from Ebay. The Transcendar transformers that I used are no longer made. They were surplus "left over from a production run" I bought a pair and liked them so well that I bought 10 more pairs. There are still Transcendars available on Ebay. Several SSE builders have used them with good results. Electra-Print still makes very good transformers, but they are considerably more expensive than when I got them. The One Electrons are available from Antique Electronics Supply. I have used a pair of "Eastern Audio " transformers that are also common on Ebay. The pair that I have are 600 ohm for another project. They are rated at "50 watts", this is a joke, they are 8 to 10 watt transformers. The build quality is slightly worse than any of the others that I mention, but might be OK if the price is cheap enough. There are dozens of transformers in this size range that I have not tried.

There are also larger transformers available. I have tried the Hammond 1628SEA and the Edcor CXSE25-8-5K. The Hammond is huge at 11 pounds. It will produce full powered bass down to 20 Hz. It will also roll off some of the high frequencies and cost about a watt of output power. It makes bass that can be heard INSIDE the house across the street when connected to my 15 inch OB speakers. This is unreal for a SE amp. The big Hammond does not do well when connected to super high efficiency speakers. The Edcor is smaller than the Hammond at 9 pounds. It gives up very little in the big bass department, but offers serious improvements in the efficiency and high frequency department. I liked the big Edcor so much that I stole it from my SSE for use in a 300B powered Tubelab SE. These are very good transformers and may be cheaper than some of the smaller units. Keep in mind that both of these are BIG and HEAVY, verify chassis fitment and strength!

Other Considerations:

Several users have had problems with the FRED diodes from IXYS. I have noticed that the old ones (3 years ago or older) will live forever, but the newer production diodes are prone to failure. This has to do with their "avalanche performance" which was not specified on the IXYS parts. I no longer recommend IXYS diodes. I have been using Fairchild Semiconductor ISL9R8120P2 without issue, but Fairchild may be eliminating this part. Mouser has 5000 of them in stock. Understand that these diodes are only required if you want the solid state diode option and may be omitted. Simply leave them out if you only want to use a tube rectifier.

I advise adding an inrush current limiter in series with the line (mains) power input to the amplifier. This small component acts like a 120 ohm resistor when it is cold (initial turn on) and gradually reduces to about 2 ohms as it warms up. This greatly reduces the surge that occurs when the amp is turned on. This makes life far easier on the tubes and capacitors. Some users also add another in series with the center tap on the high voltage winding on the power transformer (red - yellow wire). This reduces the surge experienced by the rectifier tube as it warms up. The SSE runs the 5AR4 close to the maximum surge rating, and many new production tubes (especially JJ) are not up to the task. I use the CL-90 from GE sensing. it is DigiKey number KC009L-ND

Computer Simulations

If you already have transformers from another project I have included these amplifier simulations done with TubeCad SEamp Cad to give you an idea of where to start. Choose an output tube, and find the appropriate table. Then find the B+ voltage and load impedance that most closely matches the transformers that you have. You can then choose a cathode resistor value for a given amount of tube dissipation. The power output, distortion and damping factor values are also given. Keep in mind that these are just computer simulations based on a typical vintage vacuum tube.

Power Output Simulations for EL34
Tube Type B+ voltage Load Z Vp Vk Rk Ik Diss (idle) Pwr Out Dist - 2nd Dist 3rd DF
EL34 500 5000 485 43 560 77 34 7.58 7.8 0.5 4.44
EL34 500 5000 486 44 620 71 32 7.67 8.3 0.5 4.3
EL34 500 5000 487 45 680 66 29 7.76 8.8 0.4 4.17
EL34 500 5000 488 45 750 61 27 7.81 9.5 0.3 4.04
EL34 500 5000 489 46 820 56 25 7.87 10.1 0.3 3.92
EL34 500 5000 490 47 910 52 23 7.49 10.7 0.1 3.79
EL34 500 3000 493 44 620 72 33 10.6 12.3 0 3.13
EL34 500 3000 494 45 680 67 31 10.6 13.3 0.1 3.04
EL34 500 3000 494 46 750 61 29 9.98 14.1 0.3 2.94
EL34 500 3000 495 47 820 57 27 9.89 15.4 0.5 2.86
EL34 500 3000 495 47 910 52 24 9.66 16.9 0.8 2.76
EL34 450 5000 435 37 470 79 32 6.29 7.1 0.5 4.59
EL34 450 5000 435 38 510 74 30 6.1 7.2 0.5 4.47
EL34 450 5000 436 38 560 69 28 6.23 7.7 0.4 4.35
EL34 450 5000 437 39 620 63 26 6.33 8.2 0.4 4.21
EL34 450 5000 438 40 680 59 24 6.44 8.8 0.4 4.09
EL34 450 5000 439 41 750 54 22 6.17 9.1 0.2 3.97
EL34 450 3000 442 38 470 81 33 8.57 9.7 0.3 3.35
EL34 450 3000 443 39 510 76 31 8.71 10.4 0.2 3.26
EL34 450 3000 443 39 560 70 29 8.78 11.3 0.1 3.17
EL34 450 3000 444 40 620 64 27 8.32 11.9 0.1 3.07
EL34 450 3000 444 41 680 60 25 8.32 13 0.2 2.98
EL34 450 3000 445 41 750 55 23 8.26 14.3 0.4 2.89
EL34 400 5000 382 30 330 92 33 4.62 5.7 0.5 4.96
EL34 400 5000 383 31 360 86 31 4.49 5.8 0.4 4.85
EL34 400 5000 384 32 390 81 29 4.68 6.1 0.5 4.74
EL34 400 5000 385 32 430 75 27 4.84 6.5 0.5 4.61
EL34 400 5000 386 33 470 70 25 4.69 6.6 0.4 4.49
EL34 400 5000 387 34 510 66 24 4.86 7 0.4 4.39
EL34 400 3000 391 31 330 94 35 6.96 7.8 0.4 3.63
EL34 400 3000 392 32 360 88 32 6.7 8 0.4 3.55
EL34 400 3000 392 32 390 83 30 6.93 8.6 0.4 3.47
EL34 400 3000 393 33 430 77 28 6.63 8.9 0.2 3.37
EL34 400 3000 393 34 470 71 26 6.79 9.6 0.2 3.28
EL34 400 3000 394 34 510 67 25 6.94 10.4 0.1 3.2
EL34 350 5000 329 24 220 107 33 3.03 4.5 0.4 5.37
EL34 350 5000 330 24 240 101 31 3.23 4.8 0.5 5.26
EL34 350 5000 332 25 270 93 29 3.4 5 0.5 5.11
EL34 350 5000 333 26 300 86 26.5 3.28 5.1 0.4 4.98
EL34 350 5000 334 26 330 80 25 3.46 5.4 0.4 4.86
EL34 350 5000 335 27 360 75 23 3.36 5.5 0.4 4.75
EL34 350 5000 336 28 390 71 22 3.54 5.8 0.4 4.65
EL34 350 5000 337 28 430 65 20 3.7 6.2 0.4 4.52
EL34 350 5000 338 29 470 61 19 3.58 6.3 0.3 4.41
EL34 350 3000 340 24 220 111 35 4.78 5.9 0.4 3.95
EL34 350 3000 340 25 240 104 33 5.04 6.3 0.5 3.86
EL34 350 3000 341 26 270 95 30 4.82 6.5 0.4 3.75
EL34 350 3000 342 27 300 88 28 5.02 7 0.4 3.65
EL34 350 3000 342 27 330 82 26 5.23 7.5 0.4 3.55
EL34 350 3000 343 27 360 77 25 5.04 7.7 0.3 3.47
EL34 350 3000 343 28 390 72 23 5.26 8.4 0.3 3.39
EL34 350 3000 344 29 430 68 21 5.03 8.7 0.2 3.3
EL34 350 3000 344 29 470 62 20 5.19 9.5 0.1 3.22

Power Output Simulations for 6L6GC
Tube Type B+ voltage Load Z Vp Vk Rk Ik Diss (idle) Pwr Out Dist - 2nd Dist 3rd DF
6L6GC 500 5000 486 41 560 73 33 5.23 7.5 0.5 3.24
6L6GC 500 5000 487 42 620 68 31 5.24 7.9 0.5 3.16
6L6GC 500 5000 488 43 680 64 29 5.28 8.4 0.5 3.08
6L6GC 500 5000 488 44 750 59 27 5.28 8.9 0.4 3
6L6GC 500 5000 489 45 820 55 25 5.29 9.4 0.4 2.94
6L6GC 500 3000 493 42 560 74 35 6.52 10.2 0.4 2.39
6L6GC 500 3000 494 43 620 69 32 6.47 10.9 0.4 2.34
6L6GC 500 3000 494 44 680 64 30 6.45 11.6 0.4 2.29
6L6GC 500 3000 494 45 750 60 28 6.39 12.3 0.3 2.23
6L6GC 500 3000 495 46 820 56 26 6.35 13.1 0.3 2.19
6L6GC 450 5000 434 34 430 79 32 3.69 6 0.5 3.42
6L6GC 450 5000 435 35 470 74 30 3.78 6.4 0.5 3.35
6L6GC 450 5000 436 36 510 70 29 3.88 6.7 0.5 3.28
6L6GC 450 5000 437 37 560 66 27 3.95 7.1 0.4 3.21
6L6GC 450 5000 438 38 620 61 25 3.99 7.5 0.4 3.13
6L6GC 450 5000 439 39 680 57 23 4.04 8 0.4 3.06
6L6GC 450 3000 442 35 430 80 34 5 8.4 0.5 2.52
6L6GC 450 3000 443 35 470 76 32 5.41 9.2 0.5 2.47
6L6GC 450 3000 443 36 510 71 30 5.16 9.4 0.4 2.42
6L6GC 450 3000 444 37 560 67 28 5.19 10 0.4 2.37
6L6GC 450 3000 444 38 620 62 26 5.2 10.7 0.4 2.32
6L6GC 450 3000 445 39 680 58 24 5.21 11.4 0.4 2.27
6L6GC 400 5000 381 25 270 94 34 2.46 4.6 0.5 3.73
6L6GC 400 5000 383 27 300 88 32 2.57 4.8 0.5 3.65
6L6GC 400 5000 384 27 330 83 30 2.68 5.1 0.5 3.58
6L6GC 400 5000 384 28 360 79 28 2.79 5.4 0.5 3.51
6L6GC 400 5000 385 29 390 75 27 2.91 5.7 0.5 3.45
6L6GC 400 5000 386 30 430 70 25 3 6 0.5 3.37
6L6GC 400 3000 391 26 270 97 36 3.51 6.1 0.5 2.74
6L6GC 400 3000 391 27 300 91 34 3.62 6.6 0.5 2.68
6L6GC 400 3000 392 28 330 85 32 3.74 7 0.5 2.63
6L6GC 400 3000 392 29 360 80 30 3.58 7.1 0.4 2.58
6L6GC 400 3000 393 30 390 76 28 3.71 7.6 0.4 2.54
6L6GC 400 3000 393 31 430 71 26 3.79 8.1 0.4 2.49
6L6GC 350 5000 330 19 180 103 32 1.41 3.5 0.4 3.95
6L6GC 350 5000 331 20 200 97 31 1.52 3.7 0.4 3.88
6L6GC 350 5000 332 20 220 92 29 1.64 4 0.4 3.81
6L6GC 350 5000 333 21 240 88 28 1.76 4.2 0.5 3.75
6L6GC 350 5000 334 22 270 82 26 1.86 4.5 0.5 3.67
6L6GC 350 5000 335 23 300 77 24 1.78 4.5 0.4 3.59
6L6GC 350 5000 336 24 330 72 23 1.88 4.8 0.4 3.52
6L6GC 350 5000 336 25 360 68 22 1.99 5.1 0.4 3.46
6L6GC 350 3000 340 19 180 107 35 2.12 4.6 0.4 2.9
6L6GC 350 3000 341 20 200 101 33 2.26 4.9 0.5 2.85
6L6GC 350 3000 341 21 220 95 31 2.17 4.9 0.4 2.8
6L6GC 350 3000 342 22 240 90 29 2.31 5.3 0.4 2.75
6L6GC 350 3000 342 23 270 84 27 2.42 5.7 0.4 2.7
6L6GC 350 3000 343 24 300 79 26 2.53 6.2 0.4 2.64
6L6GC 350 3000 343 24 330 74 24 2.65 6.6 0.4 2.59
6L6GC 350 3000 343 25 360 70 23 2.77 7.1 0.5 2.55
6L6GC 350 3000 344 26 390 66 22 2.66 7.2 0.4 2.51

Power Output Simulations for KT88
Tube Type B+ voltage Load Z Vp Vk Rk Ik Diss (idle) Pwr Out Dist - 2nd Dist 3rd DF
KT88 500 5000 480 43 430 100 44 6.29 4.8 0.3 4.44
KT88 500 5000 482 44 470 93 41 6.44 5.1 0.3 4.34
KT88 500 5000 483 45 510 88 39 6.58 5.3 0.3 4.25
KT88 500 5000 484 46 560 82 36 6.69 5.6 0.3 4.14
KT88 500 5000 485 47 620 76 33 6.77 6 0.2 4.03
KT88 500 5000 486 48 680 70 31 6.85 6.4 0.2 3.93
KT88 500 5000 487 49 750 65 29 6.9 6.8 0.1 3.82
KT88 500 3000 490 44 430 102 46 9.42 6.9 0.2 3.25
KT88 500 3000 491 45 470 95 43 9.08 7.3 0.1 3.17
KT88 500 3000 492 46 510 90 41 9.19 7.8 0.1 3.1
KT88 500 3000 492 46 560 83 38 9.22 8.4 0.1 3.03
KT88 500 3000 493 48 620 77 35 9.18 9.2 0.2 2.95
KT88 500 3000 493 48 680 71 33 9.15 10 0.4 2.87
KT88 500 3000 494 49 750 66 30 8.69 10.7 0.6 2.79
KT88 450 5000 429 36 330 109 43 4.66 4.1 0.3 4.63
KT88 450 5000 430 37 360 102 40 4.82 4.3 0.3 4.53
KT88 450 5000 431 38 390 96 38 4.99 4.5 0.3 4.45
KT88 450 5000 432 39 430 90 36 5.12 4.7 0.3 4.34
KT88 450 5000 433 39 470 84 33 5.26 5 0.3 4.25
KT88 450 5000 434 40 510 79 31 5.41 5.3 0.3 4.16
KT88 450 5000 436 41 560 73 29 5.24 5.4 0.2 4.06
KT88 450 3000 440 37 330 111 45 6.83 5.6 0.3 3.39
KT88 450 3000 440 38 360 105 43 7.01 6 0.2 3.32
KT88 450 3000 441 38 390 98 40 7.19 6.3 0.2 3.25
KT88 450 3000 441 39 430 91 37 7.3 6.8 0.2 3.18
KT88 450 3000 442 40 470 85 35 7.42 7.3 0.1 3.11
KT88 450 3000 442 41 510 80 33 7.16 7.6 0 3.04
KT88 450 3000 443 42 560 75 31 7.23 8.2 0.1 2.97
KT88 400 5000 375 28 220 126 44 3.03 3.3 0.3 4.92
KT88 400 5000 376 29 240 119 42 3.2 3.4 0.3 4.84
KT88 400 5000 378 30 270 110 39 3.33 3.6 0.3 4.72
KT88 400 5000 380 31 300 102 36 3.48 3.8 0.3 4.62
KT88 400 5000 381 32 330 96 34 3.62 3.9 0.3 4.52
KT88 400 5000 382 32 360 90 32 3.78 4.2 0.3 4.43
KT88 400 5000 383 33 390 85 30 3.93 4.4 0.3 4.3
KT88 400 3000 388 30 240 123 45 4.83 4.5 0.3 3.55
KT88 400 3000 389 31 270 114 41 4.99 4.8 0.3 3.46
KT88 400 3000 390 32 300 105 38 5.15 5.1 0.3 3.38
KT88 400 3000 391 33 330 98 36 5.32 5.5 0.2 3.31
KT88 400 3000 391 33 360 92 34 5.49 5.9 0.2 3.24
KT88 400 3000 392 34 390 87 32 5.64 6.3 0.2 3.18
KT88 400 3000 392 35 430 81 29 5.45 6.5 0.1 3.11
KT88 350 5000 323 21 150 138 42 1.79 2.6 0.3 5.14
KT88 350 5000 324 21 160 133 40 1.95 2.8 0.3 5.08
KT88 350 5000 325 22 180 124 38 2.08 2.9 0.3 4.98
KT88 350 5000 327 23 200 116 35 2.23 3 0.3 4.89
KT88 350 5000 328 24 220 109 33 2.37 3.2 0.3 4.8
KT88 350 5000 330 25 240 103 32 2.32 3.2 0.3 4.72
KT88 350 5000 331 26 270 96 29 2.44 3.4 0.3 4.61
KT88 350 3000 337 22 160 139 44 3.06 3.5 0.3 3.74
KT88 350 3000 338 23 180 129 41 3.24 3.7 0.3 3.66
KT88 350 3000 339 24 200 120 38 3.43 4 0.3 3.59
KT88 350 3000 339 25 220 113 36 3.33 4 0.3 3.52
KT88 350 3000 340 26 240 107 34 3.52 4.3 0.3 3.46
KT88 350 3000 341 27 270 99 31 3.67 4.6 0.2 3.38
KT88 350 3000 341 28 300 92 29 3.83 5 0.2 3.3

Power Output Simulations for 6V6GT
Tube Type B+ voltage Load Z Vp Vk Rk Ik Diss (idle) Pwr Out Dist - 2nd Dist 3rd DF
6V6GT 375 6000 368 25 680 37 13 2.02 4.4 0.2 2.84
6V6GT 375 6000 368 26 750 35 12 2.11 5 0.3 2.78
6V6GT 375 6000 369 27 820 33 11 2.05 5.3 0.4 2.74
6V6GT 375 6000 369 28 910 30 10 2.12 6 0.5 2.68
6V6GT 375 6000 370 28 1000 28 10 2.19 6.7 0.7 2.63
6V6GT 350 6000 342 22 560 40 13 1.64 3.7 0.1 2.92
6V6GT 350 6000 343 23 620 37 12 1.73 4.1 0.2 2.86
6V6GT 350 6000 343 24 680 35 11 1.68 4.3 0.2 2.81
6V6GT 350 6000 344 24 750 32 10 1.77 4.9 0.3 2.76
6V6GT 350 6000 344 25 820 30 10 1.86 5.4 0.4 2.71
6V6GT 325 6000 317 19 430 44 13 1.16 2.8 0 3.02
6V6GT 325 6000 317 20 470 41 12 1.26 3.1 0.1 2.97
6V6GT 325 6000 318 20 510 39 12 1.37 3.4 0.1 2.93
6V6GT 325 6000 318 21 560 37 11 1.33 3.5 0.1 2.88
6V6GT 325 6000 319 21 620 34 10 1.42 4 0.2 2.83
6V6GT 325 6000 319 22 680 32 10 1.38 4.2 0.2 2.78
6V6GT 300 6000 292 16 360 45 12 0.937 2.4 0 3.06
6V6GT 300 6000 292 17 390 43 12 0.919 2.5 0 3.02
6V6GT 300 6000 292 17 430 40 11 1.01 2.8 0 2.98
6V6GT 300 6000 293 18 470 38 10 0.989 2.9 0.1 2.93