Twin Reverb Conversion
Can a healthy back and good sound coexist?
The Twin reverb is a standard bearer in the amplifier world. To many people this was the sound and appearance that epitomized a guitar amp, especially back in the days when clean amps were at the heart of many Pop/Rock songs. I know that I've wanted a Twin for many years and finally I made a great deal on a barely used Twin. I carried it out to my vehicle and came back into the store wondering if I had made a mistake. Even a 50' trek left a strong impression in the form of some aching back muscles, and I have a healthy back! I also have every intention of keeping my back healthy and I've come to the conclusion that the 80 pounds or so that the average Twin weighs is somewhat more than prudent to carry on a regular basis.
Name Something that is White, Loud
and 80 lbs. of Pure COOL!
Back in the days of the Ventures and other Surf-Rock bands the sight of a big Fender piggyback amp covered in blonde tolex was pretty common. The king of those amps was the brownfaced Showman amp, a 100 watt amp with two channels and a lush tremolo circuit that added much more than just a pulsating change in volume. These amps actually had little in common with the Twin Reverb that first came out in 1964, they were a breed apart and very versatile. The head was over 26" wide and the cabinet was 32" wide with either a single 12" or 15" speaker mounted in a tone-ring. These cabinets had extraordinary bass response and the center cap of the JBL speaker gave it a high tech look that still is impressive many years later. I can remember looking at pictures of the Ventures standing in front of their amps and thinking that was the coolest thing I had ever seen.
That Gives Me an Idea.
The answer for my Twin problem seemed to be obvious, break it into a piggyback configuration and end up with the looks of a Showman and the features of a Twin Reverb. This is not to imply that the features of a Showman are less desirable than those of a Twin. Given my choice I'd go with the Showman but I already have the Twin and I am quite happy with the sound it produces.
At this point it's probably important to note that the Twin Reverb and the Showman did eventually merge into an amp known as the Dual Showman Reverb. This particular amp was for all intents and purposes a silverface Twin Reverb chassis mounted in a massive head cabinet and sold with a 2x15" speaker cabinet that was 45" tall by itself. Because this was the first Showman to feature built-in reverb the head cabinet was unusually tall at 13" and looked almost like a very squat combo amp. The entire setup weighed in excess of 150 lbs and was almost as impressive as a full Marshall stack. While these are excellent amps it just wasn't the look I wanted and I was certain that with enough effort on my part I could have both the appearance and the sound that I craved.
Life has taught me that nothing is as simple as it seems on the surface and I was certain that converting this amp to a piggyback would prove the point. Being cautious by nature I checked around hoping to find someone that had tried a similar project and sure enough I found out that Mel Waldorf of the Surf band Meshugga Beach Party had done something similar using a '67 Twin as a starting point.
The first thing that I learned from his input was that the 9" cabinet height of the original Showman head didn't leave much room for a reverb can. The stock 17" unit would make changing the power tubes impossible so it is necessary to use a shorter, 9" reverb can. I found that the proper Accutronics unit is available for a very reasonable price but the depth of the reverb is not as great as the 17" OEM unit in the Twin.
However, armed with the knowledge that a 9" high cabinet will accept the Twin Reverb chassis I went ahead and ordered the head cabinet from JD Newell and chose smooth blonde tolex with wheat grill-cloth. The cabinet arrived well packed and beautifully made. The Twin chassis slid into place easily and the chassis straps were in place in a matter of minutes. I reinstalled the tubes and ended up with a very attractive package.
When the 9" Accutronics reverb can arrived I installed it on the bottom of the cabinet, slightly in front of the preamp tubes. By this point it was definitely getting tight inside the cabinet. Still, it all fit somehow and nothing had to be jury-rigged. The head was now a complete and concise unit that worked well and was easy to carry with one hand.
The Accutronics can was a bit thin sounding so I've also tried a Ruby Tubes long-decay 9" reverb can which gives more depth but the long decay can be a bit bothersome in some situations. It's almost like dealing with feedback. I find that I prefer the Ruby can as long as the reverb is set below 2 - 2.5 but above that it becomes too cluttered sounding. At this point I have gone back to the Accutronics can and will probably stick with that until such time as I can swing the purchase of an external tank. A long decay can just didn't work in this amp.
Decisions, decisions.
Ordering a speaker cabinet proved to be more daunting of an endeavor. The issue came down to selecting the right speaker, the right cabinet style and having it match the output impedance of the amp. I have always loved big, beefy speakers and this was a great chance to pile on the cone area . . . but I didn't. After a lot of consideration I decided to go with a single 15" speaker (176" sq. cone area) instead of a pair of 12" speakers (226" sq. cone area) because of weight considerations. The speaker I chose was an Eminence Commonwealth, a versatile speaker that will easily stand up to the output of the Twin without flinching.
I had flirted with the concept of trying to make this a universal speaker cabinet that would handle either a guitar or a bass but as I researched this idea it became apparent that this would in all likelihood yield a speaker cabinet that sounded bad for guitar and wasn't all that well suited to bass amplification either.
At the same time as I ordered the speaker itself I also stocked up on some extra speaker cables. I make it a point to buy speaker cables of a different brand than my guitar patch cables. I want them to be as distinct as possible. If you try to plug your guitar into your amp with a speaker cable it will probably be noisy with lots of hum and buzz but if you use a guitar patch cable to connect your speaker to your amp you could end up with an expensive amplifier repair.
Putting It All Together
The original piggyback amps of the early '60s used some simple hardware to mount the head positively to the top of the speaker cabinet. Beyond that, the speaker cabinets usually had tilt-back legs which allowed the whole unit to be aimed slightly upward for better sound dispersion both to the player and to the audience. A mounted up amp like this is a formidable chunk of hardware and if you are tilting it back on carpeting it might be wish to use something to dissipate the pressure and avoid damaging the carpet. A set of small plastic cups such as are used under casters can be a good thing to have with your amp if you intend to use the tilt-back legs.
Of course none of this matters until you have installed the speaker and this is a task best undertaken slowly, carefully and with much planning. The problem is that speakers are heavy and have a delicate speaker cone. Of all the tasks involved with this process this is the only one I considered nerve wracking but I did survive the experience and so did the speaker.
Cranking it Up
Well, the proof is in the playing and once I had everything assembled and ready to go I plugged my Duo Jet in, hit the switch and gave it a listen. At first the sound was very crunchy, almost certainly a matter of speaker break-in. It still sounded good but it just had a very abrupt attack and decay.
To accelerate the break-in I plugged my Jaguar Bass VI into it and played some low tones at moderate volumes. I would not recommend letting fly with a lot of deep bass notes at high volume but with caution a standard speaker can withstand some of this treatment and it really exercises the cone.
The crunch effect has abated to a great extent at this point and the overall sound is warm but clear. The highs are abundant to the point that I had to turn the Bright switch off. Beyond that, it simply refuses to distort even when cranked to 10.
It currently holds a place of honor in my living room, sitting in unused space right in front of a bay window and it commands attention from anyone that walks into the room. The blonde cabinet and the sheer size of this thing are something to behold. The sound is even better.
