It was well over 20 years ago that I took a couple of handmade amplifiers over to this guy I knew that ran a local store. We had gotten to know each other and gotten talking and he had separates but had never heard a tube amplifier. So I took two over and told him to play with them. What the heck. Have some fun.
He really liked the first one. He had it in his system for a few days and had a great time. Then he took it out of the system and put in the second one. He said that he immediately had to get his guitar out and play along with the music. It was that good.
This one is like that.
I've been wrestling around a bunch of Citation II and Mc60's lately. I'm doing some projects for some local guys. Those are big, heavy units. I get tired of hauling amps like that around so for fun I scratch built a small amplifier. This one is a push pull 6AQ5 unit. I can hold it up with one hand. It's quite a contrast with those big old heavy things. It's brand new. I finished it yesterday.
Small units present different challenges than big units. Big units are really heavy. I'm not a kid. That gets old. Big units tend to have a lot of open space under the chassis though. There's usually a lot of room to work inside those. Small units are more like building a ship in a bottle. Cramped spaces, everything close together, and you're using a hot soldering iron.
It's an exercise that I feel necessary every once in a while to keep my technique. This unit has an upper surface of eight inches by eight inches. It's all hard wired. I don't use circuit boards for any application, ever. The tubes are a quad of 6AQ5, a pair of 6CG7, a single 12AU7, and a 5Y3G rectifier tube. Those are all included. The output transformers are plenty good enough and big enough for 6L6 units. I've used them that way many times. For 6AQ5 they're much larger than needed. They fit so I used them.
The outputs autobias. The phase inverters autobalance There are no adjustments at all for the user to bother with. Nothing to worry over and set wrong. The tube compliment was set by a couple of factors, space, availability, cost to replace, and of course sound. Really, if you're a builder, you should be able to make a superior sounding unit from a large selection of tubes and components. Some seem to like selecting the odd, expensive and obscure tube varieties as if to purport that the rarity of their selections is reflected in the exquisite sound produced.
That's HiFi hogwash. Cost and quality of sound are not necessarily related. With that in mind, I used a 12AU7, in my mind the best input tube ever made while also being among the least expensive, a pair of 6CG7 as phase inverters, electrically identical to the well respected 6SN7 in a nine pin mini envelope which fits much better in a small space, and a set of 6AQ5 running in tetrode mode. The 6AQ5 are similar, though not identical, to the 6V6 outputs. Those are renowned for tonal rightness. These are hardly different when used correctly and much smaller physically.
Smaller is important when space is at a premium.
The rectifier tube is a 5Y3G. It rather dominates the visual space. If the buyer prefers, a regular 5Y3 could be substituted. They're the same tube, just shaped differently. The 5Y3 produces the proper voltages for the 6AQ5. A 5U4 or a 5AR4 would source too much voltage and adversely affect tube life while hardening the sound.
I know there are tube rollers out there. Most builders know that changing a voltage here or there in construction has a far greater effect on realized sound than spending a fortune on fancy tubes. Even so, I've tried to accomodate tube rollers by choosing a tube compliment that's very reasonably priced and extremely available. 6AQ5 are out there for peanuts. You don't need a matched set either. 6CG7 are very available at bargain basement prices too. The most important tube in the amp, the single 12AU7, is very easy to find. There are zillions out there. Used ones cost very little and will last 30 years easily. 12BH7 will work for the first tube as well. Just plug it in if you like that taller look. Essentially it's the same tube.
I've long railed against the lunatic madness of Audio Jewelry. Really, $25,000 for a set of interconnects? Wonder solder where a single solder joint improves everything? $200 for a fuse for Heaven's sake and then you have to consider the "polarity" of the fuse?
My Grandmother used to say "Everybody likes to be a nice guy but nobody wants to be a soft touch". That's Victorian for nobody wants to be a sucker with some other guy laughing at how stupid we are when they cash our big check.
This is Audio, the land of the happily self deluded. I will have none of it. I did however, on this unit use some nice speaker output terminals. They will take the firehose type of speaker wire if you actually think that makes a difference over the smaller gauge wire we normal people use. There is an IEC power cable jack which will accept the loonybin style power cable that some think they need. The fuse however, is a smaller, British style and won't fit the super Beeswax and Phoenix feather included fuses that some are throwing their hard earned cash at these days.
Sorry about the fuse thing but there you have it.
I will include an AC line cord that does everything that the Laws of Physics say it should. If you want to purchase some fancy pants AC line cord that does more than the Laws of Physics say is possible, be my guest.
How does it sound? You thought I'd never get to that, didn't you?
It's glorious. On the workbench I have a dippy little pair of Klipsh punys that don't sound very good with anything. I should ashcan them. With this unit, playing some John Lee Hooker, they rocked out. Yes they did. Getting great sound out of poor speakers isn't easy.
After that I tried something different. It's a 6AQ5 unit. That's 14 or 15 watts a side, tops. I hooked it up to my VMPS Tower II. Those can take 350 watts a speaker. I run two pair which presents a 3 ohm load. The unit is set at 8 ohms output. The speakers can take a combined 1400 watts. I gave them 14 a side and got deep full bass and articulate highs, striking imaging and no stridency whatsoever out of a clean and dead quiet backdrop.
It's currently playing some John Field. Sometimes a little grace and elegance is what you need on a quiet night. That's when you can listen best, when it's quiet and you're in repose. Rocking out is sometimes what you want. That's less demanding in many ways than the tonal correctness that solo piano on a still evening can grant. Simple, uncluttered music is what tells.
Meanwhile, if you have a guitar about, you might just want to get it out and practice a bit because pretty soon you'll want to play along with the music yourself.
Just like that fellow 20 something years ago.
The best buy in HiFi.
Get it or regret it.