Single Ended 6BX7

Here we have a very special little amplifier, a true Goliath-slayer and the very embodiment of what I think are best choices in a modern tube amplifier build. This is a single ended 6BX7 amplifier, driven by the 6SL7 and built on a salvaged Columbia chassis with a custom solid bronze top plate and a transformer set harvested from a vintage Sansui amplifier. A modern circuit built around a quality but low cost tube set and using quality vintage parts. This is not a flashy tabloid amp of the week, this is a modest and understated appliance, but what a sound it makes.

The 6BX7 is a tube that I don't think has gotten nearly the attention it deserves. This is a close cousin of the 6SN7 and was used in TV sets in the 60’s and 70’s. It’s a very linear tube, and in my experience, now in both push pull and single ended configurations, this little gem is quite a performer as an audio output tube.

Making a watt or two of power, this is a low output amplifier for sure, and as such it demands high efficiency speakers to really open up and reveal it’s magic tricks, but paired to the right speaker (in this case the Lii F18 and the Visaton B200) this amplifier has a presence factor that is out of this world good. Images and voices just leap out of the speaker; plucked strings are vivid and larger than life. So many of the little nuanced details and sound cues that I’m familiar with in my favorite program material are more convincingly in the room and in real space than with almost any piece of gear I’ve owned to date. But tone and warmth and a sense of drive and pace are all there too. This little amp is a music maker! Well recorded live acoustic music like Matt the Electrician’s Got Your Back is a delight to listen to on the Lii F18 baffles with this amp, everyone is life-sized and you are sitting right there among them. The applause at the end reveals the cavernous space in the recording. That kind of effect is addictive!

Much of the sound of this little 6BX7 amp is similar (in memory anyway) to the Jeremy Fix SE 6SN7 amp I once owned, another small, simple and elegant build using a small output dual triode. That amp also created a superb imagery soundscape. I let the Fix 6SN7 go years ago, and have regretted it a number of times. I’m not letting this sound out of my hands again! In my years in this hobby, I’ve only seen a few amps built around the 6BX7, but if you find one this tube is really worth a look. These are superb performers.

Small and modest, this little amp is one of the very best imaging, “you are there” musical machines that I have had so far! I think the 6BX7 is a tube that has a lot to offer those with sensitive speakers.

6SL7 drivers mean a wide variety of choices, but prices are climbing on this tube type. Luckily there are now a number of modern versions from all of the Asian brands, some of which I hope to try soon in this beautiful little amplifier.

Sansui branded transformer set is likely Tamura iron and of the very best 60’s Japanese quality. A really sweet transformer set here.

Lamp cord power cable on one of the best sounding amps I’ve ever owned…sort of calls the notion of boutique power cables into question. Likewise, these are some of the most generic speaker binding posts available. But they seem to deliver the goods without any difficulty.

The solid bronze top plate is a nice touch on this amplifier.

Here is the 6BX7, an unassuming little dual triode, but quite a powerhouse image and tone machine.