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…
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]