Bill Vencil - Univalve

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THD Univalve

THD Electronics produces some of the better amplifiers available in today's overcrowded market. I've been a Univalve user for quite some time, and have never ceased to marvel at its tone and sensitivity. 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

Over the years that I owned this little beast, I've participated in discussions on the wonderful Univalve.net user forum. As a "public service", 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; elusive, on the expensive side. Great cleans, but turns into a growling monster when pushed. Marshall-like tonality with the right preamp tubes.

Mazda 6V6GT - France, not quite as elusive as the Visseaux, more affordable. 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.

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, elusive, but not too expensive. 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 Tonebone too!

Tung-Sol 6K6GT - haven't seen too many of these, but they are cheap. And they sound pretty daggone great. Less wood than the Visseaux, a little more sparkle. And they overdrive more too.

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.

6AK6

A 1.1 watt tube that works with an adapter from the now defunct amp company, Smicz. 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:

Cifte, GE, JAN Phillips, Motorola, RCA, Tung-Sol