6SN7 Push-PullThird build with valves. I wanted to check out some other preamp alternatives to the 18 Watt but didn't want to butcher my 18 Watts Unleashed build. It wasn't set up for experimentation and is a keeper anyway. Also I was happy for this new amp to be a couple of watts for home use only. The DennisF 1.8W with a 12AU7 output stage captured my interest and I'd known about the AX84 2W P-P and 4-4-0 for some time. With no price difference between a 12AU7 and 6SN7 and very similar characteristics, I was keen to build an experimenter's chassis based around a 6SN7 output stage. I wanted to build a number of the 18W preamps including normal channel and the Superlite TMB, maybe a plexi, as well as a mini JCM-800 and the 4-4-0. With the success of the quadrupler power supply in the Unleashed For Harp, I was keen to see if I could use only one transformer with an octupler for this lower power amp, and if there was any way to power the heaters as well as the HT off the same transformer. I simulated the unbalanced octupler circuit shown below, which generated about 310V and placed the reference tapping of the PT secondary around 88V. A 30V/1A transformer would have enough to power the whole amp. And if the transformer was wired with the 30V tap as the reference and the 0V tap as the supply into the octupler circuit, then the 24V tap would be a 6.3V heater supply, and the 17.5V tap would be a 12.6V heater supply. The 88V heater elevation was higher than normal but within the specs of what the valves could handle. The 6SN7 output stage needs around 20k plate-plate impedance. The 5W 100V line P.A. transformer was suitable, giving 20k plate-plate for an 8ohm speaker. I made up a chassis in the same way I'd done for the 18 Watts Unleashed and the Unleashed For Harp. Polished aluminium, etched logo power light, four sides screwed together in the corners, laser printed overhead transparency artwork sandwiched with clear acrylic panels - all very time consuming. Tag strips were laid out for flexibility and three preamp sockets were included. Firstly I wired up an 18 Watt lite version of the normal channel. I wanted to test and tweak this side by side with my 18 Watts Unleashed. Once it was as close as I could get it, then I could change the preamps knowing that the phase inverter and output stage were right. The circuit needed some changes as the PI signal was overloading the 6SN7 grids way too much. The 6SN7 biased around 10V on the cathode, where my 18W EL84's are around 13V. Changing the PA grid resistors to ground from 470k to 100k loaded the PI enough to drop the output to where it needed to be for the 6SN7. After that the 6SN7 1.8W and my 18W normal channel looked very similar on the bench with the test signal, and also sounded very similar with a guitar plugged in. There was a noticeable difference in the sound of the triodes vs. pentodes, but it definately captured the vibe of the 18 Watt. Keen to explore the higher gain territory, I then changed the preamp to a Superlite TMB, then the whole amp to a mini JCM-800, then a 4-4-0. As the gain went up, the triode sound became more noticeable. The Superlite TMB sounded good but just a little rough. The mini JCM-800 was a bit harsh when cranked. The 4-4-0 was a failure because I wasn't running the right voltages at different points in the amp, and the 6SN7 was still cathode biased. It didn't perform like the sound clips on the AX84 website. I'm sure one built properly would be great, but by then all I could notice was the sound of the triode output stage and I was loosing interest in the 6SN7 push-pull alternative. This amp was then put aside while I searched for a small power pentode alternative. That led to the 2 Pot Screamer amp with subminiature valves, and the 6SN7 amp was gutted for its power transformer and some screws.
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There has been some recent discussion here of octal preamp tubes. There are several boutique guitar amps using these tubes. The octal preamp tubes I am familar with were used in tweed Fenders and many other vintage tube amps. Can I solicit some opinions from anyone who has tried any octal preamp tubes?
Guitar Amp 6sn7 Sound Effects
The 6SJ7 is a pentode preamp tube that was used in the first Fender Champ. Many of these have a metal envelope, but glass bottle ones are available. Phil recently mentioned using one in a tube pedal. In the Angela Instruments online tube list, Steve compares the tone with the EF86. Sort of interesting and he has NOS 6SJ7's for $8. I wasn't able to find any new production for this tube. Has anyone out there tried this tube? Can you recommend a particular brand for tone or sturdiness?
Buy New 1 Matched Pair PSVANE 6SN7-SE HiFi AMP Vacuume Tube Re 6SN7 CV181 6N8PA: Tubes. 1 Matched Pair Shuguang Natural Sound Vacuum tube 6SN7-T 6N8P/6SN7/6H8C/CV181 1 offer from $169.99. #1,037 in Guitar Amplifier Tubes #65,332 in Music Recording Equipment: Date First Available October 29, 2019. Boutique amp enthusiasts will probably like this feature since the 6SN7 tubes are older and may have more of a vintage amp sound. Fortunately, the 6SN7 is still easy to acquire. This amp has been 'tuned' for good sound, the bias settings of all of the tube stages were tweaked while a guitar was plugged in. The Sound King is a super responsive and lively guitar tube amplifier with the natural presence and musical resonance of an acoustic instrument. The pure joy of experiencing the electric guitar in this way is enhanced by an unusual range of clean and distorted sounds, a wide frequency spectrum and inspiring tone voicing options, while retaining lively dynamics across the entire output volume.
Guitar Amp 6sn7 Sound Bar
- A valve audio amplifier or vacuum tube audio amplifier (United States) is a valve amplifier used for sound reinforcement, sound recording and reproduction. Until the invention of solid state devices such as the transistor, all electronic amplification was produced by valve (tube) amplifiers. While solid-state devices prevail in most audio amplifiers today, valve audio amplifiers are still.
- I found the Rayethon or Magnavox ones used in the B15 Ampegs to be some nice tube. And those make great guitar amps,with a little tweaking. Look at alot of the older gibson amps too,they used the some single triode octals and the twin triode octals. The 7199 or a real one is getting expensive. The sunn amps used those, then replaced them with.
The 6SL7 is a high Mu (amplification factor of 70) twin triode. It was used in the early Princton and Bassman. This would seem to be an excellent candidate considering it's gain but it has a reputation for being noisy. Can anyone confirm that? There seems to be only one modern version available.
The rest of the tweed Fenders used the 6SC7 twin triode(amplification factor 70). No modern versions are being made. Also has a reputation for being noisy. Anyone using these in a homebrew?
The 6SN7 twin triode(amplification factor 20) is the octal preamp tube most people seem to be using despite it's low gain. It is said to be quieter than the other octal twin triodes and is used in many tube hi-fi amps. There are several modern versions of this tube available also. Does anyone have an idea which are the quietest and how they sound?
I am also interested in trying the 7199 in a preamp. This is a 9 pin miniature tube not an octal, but it is interesting. It has a pentode and a triode in a single bottle like the ECL82 and ECL86. But the pentode section is not a power amp like those other tubes. It is a preamp pentode. So the pentode section could be used at the input and cascaded to the triode section either before, or after, the tone controls. Should have plenty of gain. Anyone tried this tube in a preamp?
markd
