Lord Valve Revieweth the Electro-harmonix Hot Tubes

I just got one of the new Electro-Harmonix "Hot Tubes" distortion/overdrive pedals, and of course the first thing I did was take it apart and lick all the pieces. It looks pretty good inside, aside from the fact that it was a bitch to take apart and an even worse bitch to put back together. It uses two tubes, described in the "manual" (half a page) as "12AX7EH," but the ones installed were Sovtek 12AX7WB. (Not my favorite by any means.)

THE OUTSIDE

It's a pretty cool-looking gizmo, 7-1/2" X 4-3/4" X 1-3/4", made from two C-shaped pieces of brushed aluminum which fit together to form the box. The tubes stick right up out of the top of the pedal through a couple of holes, around 2" from the stomp switch. In order to keep them from getting smashed, the tubes live under a little gazebo (this word is really the best name for it) made from a half-cylindrical piece of pretty stout aluminum with a bunch of holes drilled in it; it sits on two hexagonal standoffs, and goes all the way across the pedal.

While it looks pretty cool, I don't like the fact that the tubes stick up through holes in the top of the pedal. Plenty of dirt from the player's shoes is going to find its way inside the pedal, and I'm the dude who's gonna hafta clean all that crud outta there when the pedal finally croaks. Can't have everything, I suppose.


THE TONE

It has five controls: Master, Gain, Drive, Bass, and Treble. The tone controls are the peaking type, with a fairly sharp Q, and a sweepable band center point. As far as I could tell, the Bass control has a range of around 2-1/2 octaves, starting at around 60 Hz. I used a pink noise generator and my ears to eyeball this, so I don't know how accurate it is. (Probably dead solid perfect, but then... I *am* Lord Valve. Somebody stop me...)

The Treble control (also sweepable) has a less pronounced effect than the Bass knob. Both of these controls were *extremely* interactive, and a tiny adjustment of either would often produce a huge difference in the tone. The instructions mention that for some settings of these controls, oscillation will occur. No shit. These filters are *hot*; whenever I encountered oscillation, a tiny tweak of either tone control was usually enough to get rid of it without radically altering the effect I was trying to achieve. Since there is a lot of boost occurring in this pedal, there is a noticeable amount of tube noise ("blow") present. It uses DC heaters (more on this below), so there isn't much 60 Hz hum happening in the pedal itself; of course, "guitar" is probably the Swahili word for "hum," so you'll get plenty of that when you plug yours in, especially if it has single-coil pickups. Guitar hum is inevitable when using the amounts of gain the Hot Tubes can provide, especially with the more extreme settings...and this thing is *extreme*, no doubt about it. 120Hz hum, however, is present in larger amounts than I would have thought. There's a workaround for that one, though...the "Gain" control appears to use a stage which is out of phase with respect to the "Master" control, so if you tune it right, you can null most of the 120Hz off the output. I may experiment with using some larger caps in the HV supply later on.

I found the "Drive" control to be much more useful than the "Gain" control; extreme settings of the "Gain" control just sounded buzzy to me. Of course, I'm a *terrible* guitar player (and I don't use distortion on my Hammond, since I'm a jazzer) so I'm going to have to wait until my fearless assistant Scooter Barnes is finished getting laid or high or bailed out or whatever it is he's been doing instead of showing up for work for the last three days to hear what this gizmo can really do.

One thing I can tell you, though, is that the Hot Tubes pedal has one serious *shitload* of sustain, more than damn near anything I've ever heard before. It's *smooth* sustain, too...not the kind that jumps from level to level as the string decays. Nice. Good crunch, too. I can't wait to hear a real geetah-picker through one.

THE GUTS

It comes packed in one of those nifty-looking finger-jointed plywood boxes, with a slide- off top. The box is way bigger than the stuff inside, so I have a suspicion that the box was spec'd at some earlier phase of the design process, when they thought the pedal was going to wind up being a lot larger than it is now. No matter, plenty of bubble wrap was used to keep things from slamming around in the box.

The Hot Tubes runs on a 12VAC 1000mA wallwart, two-prong type, which has a piece of 20-gauge zipcord hanging off of it with a strange-looking (and probably completely unobtainable) two-pin connector on the end. This connector has one large rectangular pin and one smaller round one, sticking right out of the plastic with no shell around them. I know for a *fact* that a lot of these warts are going to croak from being shorted out when someone kicks the wire out of the pedal and those exposed pins hit metal. It's a 1-amp wart, so it's gonna spark real purty when this happens. And it *will* happen, guaranteed. If I was going to take this pedal on the road, I'd chop that bogus connector off the end of the wart's output wire and replace it with a standard low-voltage power connector, the coax type found on most effects pedals, the kind that can't be shorted accidentally if it pops out. Since it's an AC wart, polarity doesn't matter.

Inside the unit are some very good quality parts. They used a clever trick to obtain the HV for the tubes; instead of using a diode ladder (like many of the "tube" pedals which run on 12-volt wallwarts) they used a little encapsulated toroidal power tranny; this is a PCB-mounted device with two 115V primaries and two 9V secondaries. The slick trick they pulled with it was to wire the secondaries in parallel and put the primaries in series, and then operate the tranny BACKWARDS by putting the 12VAC from the wallwart into the paralleled 9V secondaries and obtaining a 238VAC output from the seriesed primaries. The 238VAC is then input to an inline fullwave bridge, which gives around 280VDC at the input to the filter section. The 12VAC from the wallwart is also fed directly into another bridge, to provide raw DC for a 7812 regulator which is used for the filament supply. Interestingly, the regulator has a small bi-pin lamp soldered from its output terminal to ground, right between the two tubes. I could determine no reason for this lamp to be there, other than to make it look like the tubes were lighting up a lot brighter than they normally would. Egad. Anyway, the plate voltages on the four triode sections are 125, 160, 117, and 132 VDC, with three 220K plate resistors and one at 150K. The tubes are in PC-mounted ceramic sockets.

Most of the resistors are carbon film type, with a few metal-films here and there. All the signal- path caps appear to be 400V Mylar or Poly types. The PC is standard green fiberglass. The pots feel really good; I couldn't tell who made 'em, as there was no logo or lettering of any kind on them anywhere. Imported, to be sure. Two were duals, the other three were singles. They are all mounted to the the chassis, with flying leads going down to the board. (This is part of why the pedal is so hard to take apart and put back together... once you have the PC out of the chassis, you have 5 pots waving in the breeze on the ends of a whole mess of wires.) They elected to drill some small holes next to each pot to take advantage of the antirotation studs, which most manufacturers clip off; a nice touch. Lockwashers, too. The knobs are push-on type, which fit *really* tightly on the split/knurled pot shafts. There are two LEDs on the pedal; one for power-on indication and another (marked "status") to indicate whether the effect is engaged or not.

This pedal is TRUE BYPASS (yay!), accomplished by means of a 12VDC DPDT relay operated from the 12V filament supply. As far as I could tell, the operation of the relay was noiseless. I confirmed true bypass by taking a direct reading from tip-to-tip on the input and output jacks with an ohmmeter. BTW, the jacks aren't labeled, so you have to guess. I guessed wrong, and thought the damn thing wasn't working at first. Boo. Here's the *best* part, though...NO SAND IN THE SIGNAL PATH. I mean nil point zippity-shit, nada! The whole thing is 100% tube from input to output; the only sand in it is used for rectification and regulation. Probably why the thing sounds so damn good.

HEADS-UP

There's a typo in the instructions. They tell you to make sure that you get a 100mA 12VAC wallwart if you need a replacement; this should be specified as a 1000mA (or 1 amp) device. If you hook a 100mA wallwart up to the Hot Tubes, it'll melt in a few minutes. The one it comes with is a 1000mA type.

THE BOTTOM LINE

If I were a geetah-pickah, I'd probably buy this. I'm going to carry it in my store, that's for sure. The overall build quality is very good, it looks great, it sounds *killer*. (If it sounds good with *me* playing, imagine what *you* could do with one... ;-) This one's a winner. It'll probably be selling in the under-$200 range soon.

Lord Valve

VISIT LORD VALVE'S WEBSITE: http://www.nebsnow.com/LordValve
Specializing in top quality HAND SELECTED NOS and
current-production vacuum tubes for guitar and
bass amps. Good prices, fast service.
QSC amps, RNC compressors, lots of other good stuff!

NBS Electronics, 230 South Broadway, Denver, CO 80209-1510
Phone orders/tech support after 1:30 PM Denver time at 303-778-1156

I'm not an asshole, but I *play* one on the Internet. - Lord Valve

Return to Analog Man Electro-harmonix page.