Next post – more music! But in the mean time…
THD Electronics, in my opinion, produces some of the better amplifiers available in today’s market. I was a 
Univalve user for quite some time, and never ceased to marvel at its tone and sensitivity. Why don’t I own one now (as of 4/12)? I sold mine to finance the purchase of my Lowden O35. I’d like to get another one some day…
It’s a deceptively simple amp, with volume, treble, bass and attitude controls, a built-in attentuator, high/low voltage switch, and on the back a line out with volume and sensitivity controls in addition to the speaker outs. At 15 watts, it seems like a pip-squeak of an amp, but don’t let that fool you. 15 “tube watts” is quite loud, and can keep up with a band through the right speaker cab.
One of the coolest features of the Univalve, is its ability to accept a variety of tubes, which changes the tone and output of the amp in potentially radical ways! Here’s a partial list of tubes that work with the Univalve:
| Preamp 13D9 5751 5814 5963 5965 6072 6085 6189 6201 6679 6680 6681 7025 7247 7729 7730 12at7 12au7 12av7 12ax7 12ay7 12az7 12bh7 12dw7 E180CC ECC81 ECC82 ECC83 |
Power Amp 350B 1614 1621 1622 5881 5932 5992 6550 7027/7027A (require special adapter) 7189/7189A (needs THD UniYJ adapter or equivalent) 7408 6AK6 (with a Smicz TAD adapter) 6BQ5 (needs THD UniYJ adapter or equivalent) 6CA7 6F6 6F6G 6G6G 6K6GT 6L6/G/GA/GB/GC/WGA/WGB 6V6/G/GT/GTA/GTY 6W6GT 7581A CV509 CV511 CV731 EL34 EL37 EL84 (needs THD UniYJ adapter or equivalent) KT63 KT66 KT77 KT88 KT90 KT100 ZA5306 |
I’ve done a number of comparison recordings in order demonstrate tonal differences in various tube combinations.
6V6GT
The Uni loves 6V6 tubes! They produce a lower output than a EL34 or a 6L6, but the amp really growls and sings with this type. The best tubes are the older “NOS” American and European brands. Here are some clips of my 2 favorites:
Visseaux 6V6GT – France. Great cleans, but turns into a growling monster when pushed. Marshall-like tonality with the right preamp tubes.
[audio:https://www.billvencil.com/wp-content/uploads/2011/04/visseaux6v6gt.mp3|titles=Visseaux 6V6GT]Mazda 6V6GT – France. Darkish tone, lots of depth. Cleans are nice, however, distortion is where this tube shines. Also, the Mazda really works well with a tube overdrive, such as a Tonebone pushing it.
[audio:https://www.billvencil.com/wp-content/uploads/2011/04/visseaux6v6gt.mp3|titles=Mazda 6V6GT]6K6GT
Even lower powered (~4 watts) than the 6V6 types, the 6K6GT works really well with the Univalve. Lo-voltage, of course. A lot of the same flavor as the 6V6, but a slightly lower volume and typically, a lower price!
Visseaux 6K6GT – France. Wonderful cleans; really sings; IMO, the best 6K6 out there. Has an almost “wooden” (in a good way) overtone. Not quite as dirty when overdriven, but you can get it cranking with the higher gain preamp tubes. Sounds great with a Radial Tonebone too!
[audio:https://www.billvencil.com/wp-content/uploads/2011/04/visseaux6k6.mp3|titles=Visseaux 6K6GT]Tung-Sol 6K6GT – haven’t seen too many of these. And they sound pretty daggone great. Less wood than the Visseaux, a little more sparkle. And they overdrive more too.
[audio:https://www.billvencil.com/wp-content/uploads/2011/04/tungsol6k6.mp3|titles=Tung-Sol 6K6GT]6G6G
A wonderful low-powered tube that works in the Uni. Puts out ~2 watts or so, and the Uni runs it somewhat above its spec, so the little guy really cranks! The best ones are the RCA JAN military type. Cheap and pretty easy to find. Here’s a demo:
[audio:https://www.billvencil.com/wp-content/uploads/2011/04/6g6test.mp3|titles=6G6 Demo]6AK6
A 1.1 watt tube that works with an adapter from the now defunct amp company, Smicz. Even all these years later, I think that THD should consider making these adapters. It puts the Univalve into “loud stereo” mode, which is great for living room use. Here are comparions of several different brands:
[audio:https://www.billvencil.com/wp-content/uploads/2011/04/ciftemix.mp3|titles=Cifte] [audio:https://www.billvencil.com/wp-content/uploads/2011/04/gemix.mp3|titles=GE] [audio:https://www.billvencil.com/wp-content/uploads/2011/04/janphillipsmix.mp3|titles=Jan Phillips] [audio:https://www.billvencil.com/wp-content/uploads/2011/04/motorolamix.mp3|titles=Motorola] [audio:https://www.billvencil.com/wp-content/uploads/2011/04/rcamix.mp3|titles=RCA] [audio:https://www.billvencil.com/wp-content/uploads/2011/04/tungsolmix.mp3|titles=Tung-Sol]