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Seymour Duncan Convertible 100 Watt Tube Head 2-Chan, Modular Preamp - $475 (Marietta)

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This has been my travelling companion for quite some years now. It is one of the all-time sleepers, with a wealth of features, capabilities and tone-shaping options. It is ideal for blues, blues-rock and classic rock with an exceptionally warm "clean" channel and a "lead" channel that, in my opinion at least, rivals the JTM45, JCM800 and Metaltronix (Lee Jackson) heads I owned previously.

The amp's controls exhibit a high degree of interactivity, so expect to spend more than a little time with it to find exactly the tone you've been looking for. For example, a slight increase in one of the tone controls can produce a larger-than-expected increase, which in turn affects the overall balance. It took me at least a full month to "learn" the amp.

One of the unique features of the Convertible 100 is its "ultralinear" output transformer. Without getting too far into the details, the transformer interacts with the power tubes in a way to minimize output stage saturation while providing even response at any volume. This is especially beneficial in an amp like the Convertible, where you'd want the output stage to faithfully recreate the sounds of the modules.

Another feature worth mentioning is the variable "damping" or "negative feedback" control on the back panel. This lets you control the interactivity between the amp and the speaker, resulting in tighter bass (all the way up) or more open bass (all the way down) with full variability. While there's a dedicated speaker output for the damping control, it actually works with any of the outputs. Again, there's a lot of interactivity going on between the "damping" control on the back and the "variable power" control on the front.

At this point it's helpful to discuss exactly what the "variable power" control does. It's not a master volume, and it's not a power attenuator, at least as we've come to think of that. Rather, it's a circuit that emulates full power at any output level. There's a discussion of it if you surf for "Joe Bonamassa Talks About the Seymour Duncan Convertible Amp." The explanation begins at about 4:00. (No hyperlinks allowed in FB listings.)

OK, so now on to the modules. I went through at least 10 modules to arrive at the current configuration. The first module, Classic, is shared by both channels. The "clean" channel sports a Normal and a Presence module for maximum clarity and bite. In conjunction with the excellent onboard Reverb you'll get a clean tone with more warmth than a Twin Reverb and better clarity than a Marshall. If memory serves correct, I installed a 5751 (70% of a 12AX7) in the Normal module to cut the gain down further.

The "lead" channel uses Classic and Hi-Gain Hybrid modules for a lead tone and attack that is at once reminiscent of a Marshall JCM800 yet with a bit of a bump at around 800Hz, which reminds me of Michael Schenker's tone when he was with UFO. It's surprisingly rich and complex with very compelling overtones. Not polite at all. BTW the Hi-Gain Hybrid is all but impossible to find and a quick $200 if you decide to pull it to resell. But don't. Power tubes are a quartet of Groove Tubes EL34's. Rectifier is GT as well.

The rear panel has a wealth of connectivity options including 4/8 ohm outputs, a "variable damping" (aka "negative feedback") control for tighter bass or more open leads with dedicated output, two AC convenience outlets, an effects loop with send level control, and pentode/triode switch for creamy overdrive at lower volume. There is also a "slave" output which is line-level.

Also included are a special passive volume control that allows you to sweep the Variable Power control in real time. I chose this pedal because of its ability to limit its range using the control on the side. This, in turn, allows you to sweep a particular range of the Variable Power control. In addition, there's a single button footswitch to enable channel switching.

Following is a list of all known areas of concern: The internal fan is a little noisy. It sounds as if the bearings have worn down (bit of a rumble.) Some tubes are microphonic (not sure which and won't hazard a guess.) There is noise when you power the amp up (sounds to me like filter caps.) However, if you let it warm up with the standby switch engaged it seems to abate after two minutes. No guarantees though. The amp was dropped in transit (Thanks, GC!) and the handles are bent. I'm not certain if there are a couple of scratchy controls but let's just say there are and you might be pleasantly surprised. Vinyl covering could be reglued on back along the top edge. BTW the lower (blue) input is only active if the upper one is active, which is a feature, not a defect. This is my best good faith observation and recollection, so, please, no crying if I overlooked something.

The obvious question is, at this point, if the amp's so great why am I selling it? The answer is twofold. First, here in the Atlanta area, there are very few venues left that permit bands to play at high volume. And second, accordingly, I've had to reinvent myself for the opportunities that are available here. So I'm singing and playing to tracks in restaurants. Call me crazy but somehow I don't think a 100 watt all-tube head through a pair of EVM-12L's would be appropriate.

In closing, this has been a heckuva amp for me and after extolling its many features and qualities I find myself a little reluctant to let it go. But I think it's unlikely that I'll have the opportunity to play at sufficiently high volume to justify keeping it, so better to find a good home for it. Thanks for looking!

post id: 7751485488

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