Ask Amp Man: Dean Markley Signature Series Amps
Clapton, Lifeson, and Summers used them, but 30 years later, these innovative amps are largely forgotten.
Dear Amp Man,
I was hoping you could shed some light on a 60-watt tube head I recently acquired from a local pawnshop for $140: a Dean Markley Signature Series 60 head. It sounded great when I tried it out in the store, so I figured I'd take the gamble and bring it home with me. (The 30-day warrantee made the decision that much easier.) I've tried to research the amp's history online, but there really isn't much information. I know they were made in the '80s, and for a time both Eric Clapton and Andy Summers were endorsers, though I can't find any official documentation.
I have a few questions: First, what exactly does the voicing switch on the back do? It seems to select between a bright and a dark tone, but what exactly is going on? (I imagine it's for switching between single-coil and humbucking pickups, but that's just a shot in the dark.) Second, how do I use the speaker out jacks? There are six of them—two each rated at 4, 8, and 16 ohms. Are these stereo outs? I'm not sure how to connect this head to my cab, which only has a single 8-ohm input. Third, I hear it's not uncommon for a 30-year-old amp to need new caps. Is there anything I need to watch out for before I take it in for service? Finally, did I get a good deal? Thanks.
Thanks for your question. You don't see Dean Markley Signature Series amp too often, though a few graced my bench back in the day. According to my research, these amps were designed by a gentleman named Terry Laul, quite possibly with a small team of others, and were produced between 1983 or '84 through 1986. They were available in both 60- and 120-watt models. Initial production models have the same tan vinyl yours has, and later models came in black, though I'm not sure whether that was a design change or simply an option.
Another fun fact: Around this same time, a gentleman named BK Butler was also employed at Dean Markley, though I'm not sure he had anything to do with the design of these amps. If that name is familiar, it's because it adorns all of the real Tube Driver pedals, which were eventually popularized by Eric Johnson. And yes, Clapton, Alex Lifeson, Andy Summers, April Wine, G.E. Smith, and others used these amps.
This is a very simple single-channel amp with basic front-panel controls. This means you can dial in a great solo tone, and then use your guitar's channel selector—err, I mean volume control—when you want a rhythm tone. (Okay, I'm old school, but that's the way we used to do it.) But while the controls are typical, the circuitry has a rather unique midrange control. Most midrange controls are part of the amp's passive tone stack, along with the treble and bass controls. But here, midrange is an active circuit utilizing op amps. Its input is taken prior to the tone stack, and its output is fed back into the signal after the tone stack, allowing the desired amount of midrange to be mixed back in. Pretty unique!
Markley Signature Series amps include six speaker output jacks: two each rated at 4, 8, and 16 ohms.
According to the schematic, the voicing switch you asked about attenuates the output of this midrange circuit in its closed position, giving the amp two different “voices." I've also seen this switch described as a “deep" or “dark" switch, probably based on aural perceptions.
The speaker outputs aren't stereo, which would require two separate output stages. This amp only has one output transformer and one set of output tubes. There are three pairs of jacks: 4-ohm, 8-ohm, and 16-ohm. Each set is wired in parallel, and the impedance associated with each set denotes its total load. For example, two 8-ohm cabinets or one 4-ohm cabinet should be plugged into the 4-ohm jack(s). Likewise, you could connect two 16-ohm or one 8-ohm cab into the 8-ohm jack(s). The funny part is, the amp only needs one 16-ohm jack—in all the years I've been servicing amps, I've never come across a 32-ohm cabinet! It doesn't matter whether you use the top or bottom jack of each pair.
As far as replacing the filter caps, I believe you should make that decision based not on the amp's age, but its performance. That said, if the amp has sat unused for years, or you don't know its history and don't have the ability to power up the caps slowly using a Variac, replacing the caps might not be a bad idea. It may save you an emergency trip to the repair shop later—after the smoke clears!
These amps never really caught on, which keeps prices relatively low. This is great for the buyer, since there may have been as few as 200 or so Signature Series amps made. (There are boutique amps with far greater production numbers!) That alone is enough to make me think you got a great deal, but here's the icing on the cake: A few years ago Clapton's full rig from that era went up for charity auction. His two Signature 120 heads—along with a Bradshaw switching system and Marshall cabinets—sold for $4,880. Enjoy your find!