Showdown:  Stereo Amps!
 by Greg Gagliano

Copyright 1997, 20th Century Guitar Magazine

The heyday of stereo instrument amplifiers is long over, but they still hold a certain interest with players and collectors alike.  The most notable stereo amps were made by Magnatone, Gibson, and Ampeg, though others, such as Guild, got into the act too (see “Forgotten Guilds” TCG, October 1996).  These amps were marketed for “instruments” with the primary aim towards guitarists and accordionists.

This month’s showdown is between Gibson, Ampeg, and Magnatone.  I chose two representative models from each company.  From Gibson, a 1960 GA-83S Stereo-Vib and a 1961 GA-79RVT; from Ampeg, a 1964 Echo Twin and a 1964 Super Echo Twin; and from Magnatone, a 1960 Custom 280 and a mid-1960s Custom M-14.  Sheesh, it looks like this could be a long and technical article!  Relax... it might be a little lengthy, but it’s not too technical and there are lots of pictures, so read on.

The Gibson GA-83S was a short lived model introduced around 1959.  About the size of a Fender Twin, it has the classic tweed look of late 1950s Gibson amplifiers.  The only effect that the amp features is tremolo, but this is to be expected since the design predates the age of combo amps with on-board reverb (1961).  The Gibson catalog claims true vibrato (pitch modulation) for this amp, but after listening to the true vibrato Magnatone amps, the Gibson sounds like it has tremolo (volume modulation) very similar to that used on brown Tolex Fenders (i.e. terrific).

It has a single Jensen P12R mounted to the front baffleboard and a pair of Jensen P8Ts mounted to each side baffle.  Yes, that’s right... this amp has a pair of 8 inch speakers mounted on each side of the amp!  The side mounted speakers are not just there for CGF (Cool Guy Factor).  They play an important role in the unique sound of this amp which we’ll get to in a moment.

First, let’s go over the tube compliment.  Every true stereo amp has two separate power amps.  As such, they have more tubes,  an additional output transformer, and sometimes an extra power supply compared to a standard mono amp.  The GA-83S uses a single power supply rectified by a 5AR4, a pair of cathode biased 6BQ5/EL-84 power tubes for each amp, and preamp sections fueled by four 12AX7s, three 6CG7s, and a single 12AU7.  These tubes are readily available and not too expensive.  The amp is good for about 17 watts per side (stereo) or 35 watts mono.

The controls are smartly laid out.  There are two stereo input jacks and two mono inputs jacks.  There are three stacked pots each with concentric knobs for volume, treble and bass.  The outer knob controls one channel while the inner knob controls the other.  This makes it quick and easy to find the correct knob for adjusting.  A tremolo frequency control and a tremolo depth control are also present, as well as a stereo/mono selector switch.  A footswitch jack for activating the tremolo effect is located under the chassis.  Sadly, this amp was missing its footswitch so a grounding plug had to be fabricated in order to activate the tremolo.

In mono mode, the amp is plenty loud and sounds fabulous for blues and rock.  The 6BQ5s go into a creamy smooth overdrive about a quarter of the way up the volume dial.  Clean tone is limited, but boy what a great sound it has.  In stereo mode, the amp suddenly becomes “three dimensional” sounding.  It’s no different than if you are listening to an FM station that is not precisely tuned in (mono signal) and then suddenly you get it tuned in perfectly and the stereo signal makes the sound “jump out” at you.  Believe me, it’s difficult to play a mono amp after playing a great sounding stereo amp.

The side mounted speakers add to the “presence” factor of the amp.  They also have a magic effect on the tremolo signal.  In mono mode, the tremolo is typical of that found on any late 1950s guitar amp, which is to say, quite nice.  However, in stereo mode the tremolo pans between the left and right set of speakers.  The resulting sound is unbelievably cool since it sounds like a Leslie rotating speaker!!  Wow!  You don’t miss having reverb with this amp at all.  The bluesy overdrive and the pseudo-Leslie effect are all that you could want or need.

The GA-79RVT, with its bandstand cabinet, is generally acknowledged by players as one of the finest amps made by the Gibson Company.  Introduced in 1961, this amp brought on-board reverb to Gibson’s amp line.  As such, it was somewhat of an upgrade from the GA-83S.

Like its older brother, the GA-79RVT uses a pair of cathode biased 6BQ5/EL-84 power tubes for each amplifier to drive a pair of Jensen P10Q speakers.  There is a single power supply with solid state (diode) rectification for both amp sections.  The preamp section consists of three 6EU7s, a 7199, and a 12AU7A.   These tubes are available, though NOS 7199s and 6EU7s are pricey.

The speakers are splayed in a 45 degree angle to accentuate the stereo separation. In fact, the Gibson catalog claims “180 degrees of stereo separation.”  While the stereo effect is accentuated, there is a “dead zone” right in front of the amp which doesn’t disappear until you’re at least 15 feet (4.6 meters) away from the amp.

The control panel contains a volume, treble and bass for each channel, reverb intensity, tremolo intensity and tremolo depth.  Like the GA-83S, the GA-79RVT treble and bass controls, as well as the tremolo controls, are the “stacked knob” concentric pot type.  However, these are not nearly as easy to use as on the GA-83S.  There are guitar and accordion inputs for each channel, and a single stereo input jack.

The reverb and tremolo effects are only available on Channel 1 in stereo mode.  The tremolo effect is quite nice, better than a blackface Fender tremolo, but not as good as, say, the tremolo on a brown Fender Concert.  The reverb is deep and splashy like a Fender, but with a longer decay rate.  Adjusting the reverb depth control above a setting of “7” results in a very muddy signal, but you really don’t need to go that high to get surf reverb.

The amp has good, tight bass response and the same creamy overdrive as the GA-83S, but with slightly better headroom.  In mono mode, the amp has even more headroom and better bass response which is well suited for jazz.  Stereo mode is more conducive to electric blues.  At 15 watts per side (stereo) or 30 watts mono, the GA-79RVT can be used for gigs in smaller venues.

Ampeg’s stereo amplifiers were made from 1962 to 1964, and were primarily marketed to jazz guitarists and accordionists.  The first of these was the Echo Twin (models ET-1 and ET-1-B).  The ET-1 and ET-1-B differ only in terms of rectification and power tubes.  The ET-1, produced from 1962 to 1963, used a pair of 5Y3 rectifiers and two pairs of 6V6GT power tubes.  The ET-1-B, made from 1963 to 1964, employed solid state rectification and 7591A power tubes.  Both versions used four 6SL7 preamp tubes and put out 30 watts mono and 15 watts per side (stereo).

These tubes are readily available and affordable, except for the 7591As.  Svetlana keeps pushing back the date for production of their 7591A so, until then, new old stock tubes at $50 a pop are the only alternative.  Thankfully, the Ampeg’s cathode biased design and relatively low operating voltages (compared to 40 watt blackface Fenders) are very forgiving which means long life for power tubes.  Also, these amps can be fully restored now that St. Louis Music is using the same blue check tolex, diecast logos, and tan/silver grill cloth as was used in the old days.

There is a volume, tone, tremolo depth and tremolo intensity control for each channel and a single input for each channel.  A toggle switch activates the reverb and reverb depth is controlled by increasing the volume on Channel 1.

The control arrangement is less flexible for reverb depth, but the speaker driven type reverb is rich and full-bodied.  The dual tremolo sections make for a really wild amp, especially when tremolo speed for each amp is set out of phase.  The tremolo setting possibilities seem endless, especially if you are using a stereo output guitar or an accordion with stereo pickups.  You can run the neck pickup clean with reverb and the bridge pickup with tremolo.  I get dizzy just thinking about it!

The Super Echo Twin (models ET-2 and ET-2-B) was the deluxe version of Ampeg’s stereo amp and was offered concurrently with the Echo Twin.  At nearly $380 in 1963, the Super Echo Twin cost about $40 more than the less fancy Echo Twin.

The schematics show that the Super Echo Twin is essentially two Reverberocket amps connected together.  The ET-2 and ET-2-B are nearly identical except for rectification and power tubes.  The ET-2 version produced from 1962 to 1963 used a pair of 5Y3 rectifiers and two pairs of cathode biased 6V6GT power tubes.  The ET-2-B was made from 1963 to 1964 and employed solid state rectification and cathode biased 7591A power tubes.  Both versions used four 6SL7 preamp tubes.

In mono mode, the Super Echo Twin pumps out 30 watts of warm, clean power.  In stereo, the player has command of two 15 watt channels.  Each channel drives a separate Jensen C12Q speaker.  Each amp has a separate power supply, fuse and rectifier.  The additional power transformer certainly made the Super Echo Twin more costly to manufacture, but if one amp dies during the gig, you can continue playing on one cylinder firing in mono mode.

The controls consist of tone and volume for each channel, tremolo depth and speed, reverb depth, and a channel selector switch.  There are two inputs (guitar and accordion) for each channel as well as a stereo input jack.  A footswitch for activating the reverb and tremolo is hardwired into the amp.  I really like Ampeg’s idea to hardwire in the footswitch.  This way it doesn’t get lost like those of so many (too many) Fender amps.

Overdrive doesn’t occur until the volume knob is nearly maxed out.  However, high headroom was exactly what Ampeg intended for this amp and many of their other amplifiers.  Ampeg founder Everett Hull was a jazz nut and felt that the amplifier’s sound should stay clean.  Overdrive and rock-n-roll were dirty words to Mr. Hull.  That doesn’t mean that this amp isn’t good for blues or rock.  On the contrary, since the amp stays on the edge of overdriving, it has excellent touch control.  It’s sweetly singing sustain makes it one of the nicest sounding amps with a Stratocaster that I have ever heard.

Where the Gibson GA-83S’s stereo tremolo and the Magnatone Custom 280’s true vibrato are the hallmarks of those amps, speaker driven reverb is the hallmark of the Super Echo Twin.  See “Outboard Reverb, Part II” in the January 1997 issue of 20th Century Guitar for an explanation of speaker driven reverb.  If you think the Ampeg Reverberocket has the best reverb of any combo amp, think again.

The Super Echo Twin takes reverb richness one step further.  The slight time delay that accompanies the deep-as-the-ocean speaker driven reverb accentuates the stereo separation since the dry signal is run through one channel while the reverb signal is sent to the second channel.  Reverb and tremolo is only available in mono mode on both channels and only on Channel 2 in stereo mode.  The stereo tremolo effect sounds better than any mono tremolo I’ve heard, though not as cool as the Magnatone vibrato.

The Super Echo Twin is remarkably versatile and sounds equally good with a guitar equipped with single coil or humbucking pickups.  Its sonic potential stretches from blues to jazz making the ET-2 one of the finest guitar amps ever to come out of Ampeg’s Linden factory.  If there is one drawback to this amp, it is the tone control.  While the amp sounds great, it would have been even more flexible if it had separate bass and treble controls.  The single tone control is probably the only gripe (besides the 7591A dilemma) that most Ampeggians have with the early to mid 1960s Ampeg guitar amps.

The brown bomber Magnatone Custom 280 in this month's bake-off was top-of-the-line in 1960.  It was made in Torrance, California by Magna Electronics, Inc. just before Estey acquired the company.  Made between 1957 and 1960, this is also known as the “Buddy Holly” model since it was used by Buddy Holly.  As with the Gibson GA-83S, the Custom 280 design predates the use of on-board reverb.  However, it does feature true vibrato, rather than tremolo which makes it unique.

Like the other amps under review, it also sports dual power sections, with a pair of fixed bias 6CZ5s on each side. This is a plus for the cash-challenged amp collector, as these seem to be reasonably plentiful (new old stock) and won't cost an arm and a leg to replace when it's time.  The rest of the tube compliment consists of 3 x 12AX7, 3 x 6CG7, 1 x 12BH7A, and a 5U4GB rectifier.  That’s a lotta tubes, but true vibrato does that to a stereo amplifier.  Other features include two Oxford 12L5N alnico speakers as well as two 3 inch tweeters in a Twin-sized cabinet.

The control panel is separated into four major sections:  Channel 1 has two inputs, loudness, treble, bass and a mellow-normal slide switch.  Channel 2 has two inputs and is identical except that it has a normal-bright slide switch.  Oddly, there is no stereo input jack!

The Stereo Vibrato section has intensity, speed, a jack for the footswitch, a two-way "remote" knob that switches between instrument and footswitch (this is a mystery), and a second two-way knob to switch between stereo and normal.  The Speaker Control section has a two-way knob for internal (speakers) on or off, and two jacks for remote speakers 1 and 2.

The first thing you might notice on plugging in is that, with roughly 25 watts per side, it's one of the few Maggies actually loud enough to gig with!  Plenty of frequency shaping tools, too... normal/mellow switch on channel one, normal/bright switch on channel two, with bass and treble controls on each side for your tweaking pleasure.  The second thing you may notice is that no matter how long you spend twisting the dials and flipping the switches, this amp just doesn't have the built-in tonal depth and authority of the Ampegs or Gibsons.  Go ahead, knock yourself out.  You'll only end up with calluses and will still come up short.

Overall, it's a bit tight and dry sounding, with that typical Magnatone lower mid-range roll-off that gives a crisp bottom end for all your Duane Eddy moments.  The amp hardly overdrives at all, at least in terms of what most readers will think of as "overdrive."  After about three-quarters of the way up on the volume knob, the amp’s tone starts to thicken and soften, but stops way short of sounding gnarly or rude.  Rather, the tone just gets richer and more complex.

But what about the famous all-singing, all-dancing true pitch changing stereo vibrato, you say?  I was lucky enough to have access to two 1x12" extension cabinets similar in type to what must have been optionally available to the original purchaser, so on they went.  What I originally thought was a pot to balance the external speakers turned out to be an internal speaker on/off switch, but a balance was found by moving the amp back about two feet behind the extra cabs in a reverse "bowling pin" set-up.

Pass the Dramamine!  Now this is worth the price of admission.  Being a Maggie neophyte, I kind of expected a harsh panning effect, but it's actually more like a much smoother tube-driven stereo chorus unit.  At less dramatic settings, it's the sound you hear backing about a million doo-wop tunes.  By mid-point you're doing the Pretenders twenty years early, and if you keep turning those big cream stovetop knobs you'll find yourself playing underwater in Electric Ladyland.  It's hard to believe that this stuff was available in the late '50s.  This is an amp I can truly give my highest rating to, which is "You hardly even miss the reverb."

The Estey made Custom M-14 is a “suitcase” amp, i.e. - it has a plastic cab that looks like a Samsonite suitcase.  Actually, these were fabricated from television cabinets, but they still look like suitcases to me.  Like the Custom 280, the M-14 has true vibrato, but no reverb.

The tube compliment consists of 4 x 7189A power tubes (fixed bias), 4 x 12AU7, 2 x 12AX7, and 1 x 12DW7 in the preamp.  The amp uses a single power supply with solid state rectification. The speakers are two 8 inch units plus two 3 inch “tweeter” speakers.  Since I did not open disassemble the amp, I don’t know what make or model speakers were installed.  However, Jensens were used in most of the “suitcase” Maggies that I’ve encountered so that would be a safe bet.

The controls consist of Volume, a Mellow/Normal/Bright selector, Vibrato Speed, Vibrato Intensity, Stereo/Mono switch, 2 inputs per channel, and a Treble and Bass control for each channel.  The amp is good for about 18 watts per side stereo and close to 40 watts mono.

This is a high headroom amp like the Ampegs.  It doesn’t begin to overdrive until the volume knob is nearly dimed.  The stereo separation is not as distinct as on the other amps in this comparison.  Like the other amps, however, the M-14 is louder in mono mode than it is in stereo mode.  The tone is clean and warm, and the vibrato’s chorus-like effect certainly makes up for the lack of reverb.  The vibrato, however, is only available on Channel 1.

Now we get to the part of the article where I give you my opinion about which of these amps is “best.”  Well, I’m happy to report that they are all really fine amps.  However, I do have my favorites.  The Gibson GA-83S is just too cool to look at, too cool for blues tone, and too cool with its Leslie effect that I’ve got to have one someday.  However, despite it’s high CGF (how many amps do you know with five speakers?), it really is tonally limited to one, albeit great, sound.  Better yet is the Gibson GA-79RVT because it has reverb and a little more headroom to add to its versatility.

To be honest, I don’t care for the Magnatones overall tonality, but that is really irrelevant.  What matters is what you like.  The Maggie’s stereo vibrato is so much fun that everyone should have one in their amp stable.  The Ampeg Echo Twin’s twin tremolo circuits are too cool for school, but the ET-1 is not nearly as flexible or diverse an amp as the Super Echo Twin.  So, that leaves the Ampeg Super Echo Twin as my pick of these six stereo amps.  It has plenty of power for gigging, tons of headroom, the best on-board reverb ever, and a really sweet and versatile tonal range.

How much do these things cost?  These amps were all produced in relatively low numbers since they were very expensive to manufacture and had limited appeal even back in their day.  As such, they aren’t too easy to find.   The GA-83S pictured here is the only one I’ve ever seen and it wasn’t for sale, so it’s impossible to give a price range for it.  The GA-79RVT is highly regarded by players and collectors and since it is a Gibson.... it’s expensive.  These typically fetch $1000 and up if they are clean and original.  The Maestro and Bell versions bring a little less.  The Magnatones have a cult following.  The Magna Electronics stereo amps, especially the Custom 280, are the most expensive and range in price from $500 to $800 for clean, original examples.  The Tonemaster and Titano versions bring a little less.  The Estey made Maggies are typically found for less than $600.  The Ampegs, up until recently, have been overlooked and priced low.  However, prices have been steadily climbing and clean Echo Twins and Super Echo Twins fetch $450 to $650.  Note that less than perfect examples of all of these amps can be found for considerably less dollarage.

The GA-83S is courtesy of Matt Kesler and Jim Strahm at Midwestern Musical Co., thanks to Alex “The Amp Detective” Volpe for sharing his Maggie Custom 280 and Ampeg Echo Twin, thanks to Gregg Hopkins at Vintage Amp Restoration for the test drive on the GA-79RVT, and thanks to Gary Lollar for providing the Custom M-14 for this article.

About the author:  Greg Gagliano, part-time bassist and full-time biology guy, often wonders when stereo tube amps and accordions will make a comeback.

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