Fender 1976 Dual Showman Reverb Guitar Amplifier


Last Update 04-15-2012

Guitar amplifiers are evil.  Just when I thought my Selmer Twin Thirty and Vox Valvetronix were enough for the studio, I discover they are not.  My styles had been expanding, and I felt that my Fender Rhodes could benefit from a proper guitar amp (back in the 1970s before proper keyboard amps existed, keyboard players had to play through guitar amps).  The silverface Fender Twin Reverb was a very popular amplifier for guitar players, and it was the amplifier of choice for Rhodes piano players.  So I sought yet another vintage amplifier, and also possible $$$ for the restoration efforts that go along with it.

During the rapid expansion of the CBS/silverface era, many inexperienced assemblers were put to work assembling tube guitar amplifiers.  Many a guitar repair shop found that the majority of silverface Fender amps - estimated at 80% - were wired incorrectly when they left the factory.  Final inspection at the factory only verified that the amp made sound at all - quality control was nonexistent.  I would agree with this as I did audition a 1969 silverface Twin Reverb at another store, and it had horrible icepick treble sound, not at all tubey or fenderish.  I knew that buying one without auditioning it in person was extremely risky so the 'net auctions and classifieds were not an option. 

But the silverface Twin Reverbs, once a bargain on the vintage market, were starting to climb in value.  They were also a pretty heavy package for a combo.  Since I am an advocate of separate heads and cabinets (I like to swap cabinets with different speakers to experiment with sound varieties) I wondered if Fender ever made a head version of the Twin Reverb.  Turns out they did - they used the same chassis, same circuit, tubes, transformers - everything - in five different silverface amplifier models - Twin Reverb, Vibrosonic Reverb, Quad Reverb, Super Six Reverb, and Dual Showman Reverb.  They all simply used different speaker configurations for different sound, with the exception of the latter which was a non-combo head.  The DSR were sold head only or with a large 2x15 cabinet (an optional additional 2x15 cabinet was available for spoiled rich brats).  If you thought the 2x12 Twin Reverb was heavy, try the goliath Super Six Reverb with six 10s!

The idea of sharing the same chassis across different models was not new at Fender as several amps from the 1950s also shared that convention.

Also CBS used some really crappy sounding speakers in the silverface amps (with the exception of the JBL D1x0F), which can be replaced with better sounding speakers if you have the $$$.  But by springing for a head version that was not a concern as I already had a variety of cabinets with different speakers.

A search uncovered FOUR circuit revisions throughout the silverface era (1968 to 1982) but a study of the schematics did indeed confirm that all five models shared the exact same chassis and circuits.  The early ones are the most desireable as they were the same circuit as the blackface Twin Reverbs.  Then assembly of tube guitar amps got extremely lax - inexperienced assemblers got sloppy with lead dress which resulted in uncontrollable oscillations.  In a classic case of fixing the symptom instead of curing the disease, CBS added components at the power tubes that suppressed the oscillations, taking any form of that "Fender sound" with it.  This was the blackest era of CBS/Fender amp history, as retailers complained loudly of these bad sounding amps.  The changes only lasted for six months and it took so long for the retailers to sell off the jaded amps that it dawned the vintage era - players quickly learned that the older "blackface" amps sounded much better and they rose in value.  The CBS silverface was forever tainted and Fender was getting a bad reputation.  The circuit was revised in 1972 to introduce the master volume, then some time later the master volume acquired a pull switch that engaged a distortion sound.  Around 1974 the "hum balance" trimpot was designed so that Fender could install twin unmatched 6L6 power tubes and save $$$ on hand matching.  But the "hum balance" did not do its intended purpose.  The last version (and least desireable) silverface Twin Reverb boosted the power from 100 watts (four 6L6 power tubes) to 135 watts (six 6L6 power tubes!) and added a preamp output for recording.  So the ideal amp was the first ones of the silverface era, without master volume without hum balance trimpot and without the dreaded CBS "fix".

So the hunt was on for the ideal amp.  I was slowing down my gear purchases in the interest of building a house so I wasn't actively scanning the 'net auctions or classifieds for them.  One day I was out of town to my favorite electronic supply place and remembered that there was a new vintage music store across the river.  The store had closed for the day but a peek in the window arose suspicion that there was a DSR in there.  Then a week later I stopped in and it was indeed a DSR.  It was a master volume head with the dreaded "hum balance" trimpot (I preferred the earlier models which preceded these features) but this specimen are extremely clean like new.  When I auditioned it there was zero hum, zero buzz, no audio artifacts at all.  Just that beautiful Fender clean tone, and the spring reverb was heavenly.  The only problems were a couple of scratchy pots on the panel.  But the price was very reasonable.  So I not only landed a clean unit but was lucky enough to land one of the 20% that were wired correctly at all.

These master volume amps with pull switch distortion are not the most desireable Fender amps.  The master volume robs tone from the power tubes and in the 1970s CBS/Fender was so disconnected from the current tastes that they added a distortion switch (pull out the master volume knob) which doesn't sound at all like overdriving preamp tubes.  The effect is subtle - it sounds like a slight midrange boost with mild breakup.  Rather useless.  The Twin Reverb circuit doesn't really start to overdrive until it is almost wide open near 100 watts and at rather unbearable volume.  They were known to sound good with distortion pedals and the like, but better at clean sounds.  Thus they were widely neglected when the heavy metal era arose in the early 1980s followed by the grunge and modern rock of the 1990s and 2000.

Like the opportunist I am, that was fine with me as I cared little for those genres.  But styles do have a way of revolving, and Twin Reverbs were back in demand starting in the mid-2000s.  Twin Reverbs were climbing in value, while I noticed the other models with the same chassis were much lower in value.  So by purchasing this Dual Showman Reverb I got the sound of the Twin Reverb at the fraction of the price.  While I could hear a difference with the master volume at low settings, if left at maximum it is nearly identical to the non-master volume amps and does sound better.  And that "hum balance" trimpot?  I hear no artifacts that degrade the sound.  I'm an advocate of the "if it ain't broke then don't fix it" credo.  I don't see a need to address it until the power tubes are ready to be replaced, at which point I will have an expert amp tech convert it to a proper bias trimpot.

I was able to date this amp by two traits: the serial number on the back (there is info online with serial number correlated with year of manufacture) and the post-1975 logo on the front which was missing the "tail" underneath.

The Dual Showman Reverb use an RCA 7025 tube on the preamp front end (a 12AX7 graded for lower noise and highly sought after) with a 12AT7 phase inverter pushing a quartet of 6L6 power tubes.  It is a non-stereo dual channel (non switchable) system with both channels featuring volume/treble/middle/bass controls and one channel featuring reverb and tremolo (mistakedly labeled "vibrato" on the panel).  The amplifier can generate 100 watts and is very loud and clean, but pleasantly colored for that then-famous Fender "clean sound".  In another example of how CBS was so out of touch with the current tastes, they still strived to produce an amp that delivered squeaky clean sound while the Marshalls and Mesa Boogies were pointing the way of the future.  But one thing was in CBS's favor - they stocked the amps with decent tubes made by RCA, which isn't true with today's Fenders leaving the factory with cheap inferior sounding chinese tubes.  Luckily my DSR had seen so little use that it still had the original RCA tubes in it.

I tested four cabinets with the DSR, each with my strat, tele, and les paul to experiment with tone variety.  My 2x15 Bassman closed back cabinet for the DSR - with the original Oxford and an unknown speaker - sound deep and full especially with the reverb.  My Peavey 2x15 bass cabinet loaded with EVs was an absolute dud, played four chords and I unplugged it fast.  Proof that not all 2x15 cabinets sound good with guitar.  The Marshall 4x12 loaded with two Celestion 65 watt and two 70 watt speakers sound good all around.  My Vox 2x12 closed back cabinet loaded with Celestion alnico 12 watt "Blue" speakers sounded great, crisper than the Marshall.  In an attempt to restore authenticity I ordered a pair of Jensen 50w 15" speakers - while they sounded good with Rhodes piano I preferred the original speakers for guitar.  I don't identify a favorite - they all have their distinctive sound.

Moving onto the Rhodes - the Bassman cabinet loaded with 2x15 Jensens and Vox cabinet sounded the best.  While the DSR definitely gets that "classic" Rhodes sound, I still prefer the sound of the Selmer on the Rhodes.  I had hoped that the DSR would serve as a high power system for the Rhodes, but like the Selmer it does start breaking up past a certain threshold (it wasn't the speakers breaking up, it was the amp).  The Selmer had better tone color, and the presence of the tube rectifier gave the Rhodes a punch that the DSR did not have.  In the future I plan to build a new speaker panel for the bottom cabinet of the Rhodes to accomodate the Jensen 15s, since that cabinet is already empty.  A simple speaker jack panel and it will be ready to go.

Another interesting experiment for later is to try my speaker emulators - the Red Box and the Groove Tubes.

The DSR is an excellent bargain for anybody looking for that Twin Reverb sound - all you need is a cabinet with decent speakers.  The amp chassis is designed for 4 ohm loads, but 8 or 16 ohm loads can safely be used with it (albiet at decreased volume).  As with any vintage amp, be prepared to spend more $$$ on a check-up by an expert amp tech as you may find leaking capacitors (long past their expected life), worn tubes, loose tube socket connectors, bad output transformers.  This can get expensive in a hurry.

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