HD’s UniValve was the amp of2001 for us and it has continued togather worldwide acclaim for

style, innovation and, above all, tone.THD is one of the original American‘boutique’ companies. While the brandis better known in the UK now than a year or so ago, in the States theirreputation is huge and Andy Marshall’s(THD’s designer and CEO) passion forgood design and killer sounds hasresulted in many accolades frommusicians and industry giants. Theaward-winning UniValve is destined togo down in amp history as one of theworld’s ultimate studio amplifiers. Youcan easily use it live, of course, butwith a maximum output of around 17watts, clean headroom is sometimes ata premium. Which brings us neatly tothe UniValve’s big brother. The BiValve30 debuted at this year’s Winter NAMMand is reviewed here exclusively forthe first time in the UK.

Like the UniValve, the BiValve is a single-ended pure Class A design.

However, it has two output valveswhich are wired in parallel andcombined through a special outputtransformer to deliver up to around 30watts. You can use almost any outputvalve you like without touching anykind of bias adjustment, and get this: in the BiValve you can use them in anycombination as well. Combined withthe capability to take almost anypreamp valve, this makes the BiValveeven more of an amp-tweakers dreamthan its predecessor. Because there’ssuch a wide range of tone available you

can customise the amp exactly to suityour style.

The BiValve sits in the same compactpressed steel chassis as the UniValveand, except for the extra valve andcontrol plate, it looks almost identical.The UniValve’s acid-etched controlplate was inspired by Glasgow artistCharles Rennie Mackintosh; this timeround THD have gone for a marinetheme, with an intricate diamond scaledesign. The control markings arescreen printed, which makes themeasier to see, but in our opiniondetracts a little from the artistry of thebackground pattern.

Underneath the perforated steel lidthere’s a larger pair of transformers tohandle the increased output, andinside there are two ultra-thick PCBs:one for the power supply and one forthe audio. The four valve bases arebolted to the chassis and secured bylocking nuts, with hi-fi style internalbaffle plates to cut down on radiatedhum. The standard of construction is

THD BIVALVE 30 HEAD £1,199

GUITAR AMPS

The UniValve’s big brother makes its UK debut. The world’s only dual single ended guitar amp has a bigreputation to live up to: does it cut the mustard? by Nick Guppy

THD BiValve 30 Head £1,199

THD BIVALVE 30 TEST RESULTSBuild qualityFeaturesSoundValue for money

WE LIKED Limitless tonal range, good looksand useful features, with volume to spare forlive useWE DISLIKED The case isn’t best suited tolive gigging but, this aside, it’s hard to fault

T

�����

CHOICE

GIT233.thd_reprint 5/12/02 6:02 am Page 84

absolutely top class. THD are based inSeattle, which is also home town toBoeing, and most of the BiValve’s heavyfabrication work is contracted out tolocal specialist companies who servicethe aircraft industry. So now you know.

The front panel looks deceptivelysimple. Working from the left, there’s a pair of input jacks labelled ‘more’ and‘less’, followed by a treble cut switchthen rotary controls for volume, treble,bass and what THD call ‘Attitude’. It’snot a fancy name for a presencecontrol – there’s no negative feedbackloop – instead Attitude works on thedriver valve to change its response, anddoes more or less what the namesuggests: either smoothing things outor making them more aggressive.

In the centre, part of a clever noisereduction circuit, is a light bulb thatglows as the amp distorts. Dependingon your point of view it either looksvery hip or very distracting, hence asmall switch underneath to turn it off.Next to this is the level control for theHotplate – a built-in output attenuatorthat lets you run the BiValve into totalmeltdown without annoying theneighbours; there’s also a defeat switchfor this function, which adds a littleextra volume for live work.

The last three rocker switches are

for mains, standby and powerselection. The hi/lo power switch is likehaving a built-in Variac; switching tolow voltage adds a squashy dynamicfeel and reduces clean headroom, andit’s essential for valves like the 6V6which can’t handle high plate voltages.

The BiValve’s back panel is alsosimilar to its smaller cousin. There’s a pair of speaker outlets with animpedance changer, and the excellenttransformer-isolated line out – using a 6mm stereo jack socket – is nowbalanced. Fuse protection is morecomprehensive, and the BiValve alsobenefits from a pair of warning LEDs tolet you know if a power valve is faulty.

SOUNDS: When it comes todescribing the BiValve’s sounds, it’sdifficult to know where to start, orwhen to stop, for that matter. You canuse almost any power and preampvalve combination under the sun, and as a result the tonal range isvirtually unlimited.

While we liked the dual 6L6arrangement the amp is supplied with,switching from these Russian valves toa pair of the new Groove Tubes 6L6GEs(made in America to the old GeneralElectric spec) really brought things tolife. The cleaner tones have a rich,sonorous and detailed mid-range thatwill flatter any guitar, with a bell-liketreble that almost sounds like a choruseffect. Low-end response through aported cab containing a pair ofCelestion Vintage 30 speakers is fullwithout becoming too tubby.

Using the volume control inconjunction with the two inputs youcan cover the whole gain spectrum,from squeaky clean to absolute brain-frying power-amp distortion withalmost infinite sustain, and all the timethe BiValve stays totally musical. Evenat full-tilt you can still pick out eachstring within a chord, and the tonecontrols seem to have just the rightrange, whatever valves are in use.

The Hotplate feature lets you playany distortion tone at any volume level.You can even disconnect the speakersfor recording, as the amp has a built-indummy load. We lost count of thedifferent valve combinations we triedbut a few really stood out. A 6V6 withan EL34 yielded one of the absolutebest British blues/rock sounds we’veever heard. The smaller valve works tobalance out the EL34’s hollow mid-range and aggressive distortion with a unique high-end response –somewhere between the best vintageMarshall and tweed Fenders, with ahint of AC30 thrown in.

As you’d expect, the BiValve is muchlouder than the UniValve. There’s morethan enough headroom for live use,and notes seem to jump out of theloudspeakers a lot quicker. It’s adifferent effect to the UniValve’s three-dimensional warmth, but but it isequally rewarding.

VerdictThe BiValve delivers totally on theUniValve’s promise of more to come,and the result is one of the best playingexperiences any guitarist could hopefor. Tough construction, ultra-hipstyling and a unique collection offeatures add up to an amp you’llprobably never tire of playing through.The best things in life are rarely cheap,and the BiValve is definitely an amp forthe well-heeled purist – nofootswitches to change channelsmeans you have to use it the old-fashioned way, driving things from theguitar. But you can have so much fundefining your sound and then playing itthat even the most die-hard tap-dancercould be converted by this amp.

Talk about having your cake andeating it – here’s one of the few ampsthat lets you do both. Try one soon andsee if you agree.

THD BIVALVE 30 HEADPRICE: £1,199ORIGIN: USATYPE: All-valve dualsingle-ended amp head OUTPUT: Nominal 30watts RMSVALVES: Choice of twoEL34, 6L6, 5881, KT88,6550, 5881, 6V6 andmore in any combination.Choice of two ECC81/2/3preamp and more, also inany combinationDIMENSIONS: 190 (h) x 390 (w) x 230 mm (d)WEIGHT (kg/lb):15/33CABINET: Powder coatedsteelCHANNELS: OneCONTROLS: Volume,bass, treble, treble cutswitch, ‘attitude’, hotplatelevel, Hotplate in/out, hi/lovoltage, noise reductionin/out, line out level andinstrument/line switchADDITIONALFEATURES: Multiplevalve choice with no re-biasing, hotplate powerattenuator, noisereduction circuit,transformer isolatedbalanced vari-level line outOPTIONS: Chrome CageRANGE OPTIONS:UniValve 15-watt head(£899). A range of headand combo cabinets moresuited to live use iscoming soon – THD’sother hot products includethe ‘Yellowjacket’ EL84class A adaptors for most50/100-watt circuits, andvarious standaloneHotplate attenuators foralmost all impedancetypesTHD Electronics, Ltd.206.781.5500www.thdelectronics.com

THD BiValve 30RATING

Not just great sounding,but good looking too

Andy Marshall’s signatureis a guarantee of quality

The BiValve delivers totally on the UniValve’s promise, one ofthe best playing experiences any guitarist could hope for

GIT233.thd_reprint 5/12/02 6:02 am Page 85