From the tail end of the vacuum tube era, a real Tone Gem in the genre of garage band tone.
Editor’s Note: This is Part One of a two part series on modifying the Silvertone 1421 guitar amp. This article is a work in progress, so please check back for additional info and updates.
The 1960’s Silvertone 1421 Combo Tube Amp (also originally sold as the Sears 10XL) is a great little vintage tube amp. It’s compact size makes it easy to carry to practice or a to small venue. It’s low 10-watt tube output (actually, closer to 5-watt) is perfect for the recording studio. It has two instrument inputs going into one channel, volume and tone controls, and a fantastic 12AX7 tube tremolo circuit, playing out to an 8-inch speaker. The sound here is definitely in the garage band category, but you can coax some great sounds out of this little guy.
The all-tube version of this amp was made from 1968 to 1972, and was later replaced with a all-transistor (solid-state) version in 1973. I picked this one up off eBay a few years ago. It’s a 1970 model and is all original, except for the brown speaker grille fabric (which is ugly!).
Below is a photo of my Silvertone 1421 after it first arrived. The vinyl covering, the controls, the faceplate were all in excellent condition for its age; no tears or scratches. The original vinyl handle was flexible and intact. The only problem this amp had was a stuck (frozen) power switch. I replaced the bad switch with a new heavy-duty toggle, and replaced the old two-prong power cord with a new grounded cord. When I powered it up for the first time it was amazingly quiet for an old tube amp.
The knobs and faceplate were in great condition. The handle was still flexible and firmly secured to the cabinet. But the original toggle switch stuck (frozen).
Front view showing the replaced grille cloth over the original baffle board and speaker.
Rear view of cabinet. You can see the new grounded power cord that I added.
The Sears product label on the rear panel showing the model number and vacuum tube layout.
A view of the chassis through the back panel vent.
Photo of the cabinet interior, showing the chassis and the original 8-inch speaker made by CTS.
A closer view of the chassis.
The 8-inch speaker with ceramic magnet made by CTS (code 137).
Another view of the chassis, showing the power transformer, the filter capacitor can, the output transformer, and the tubes. The on-baord tube complement is one 6X4 Rectifier tube, two 12AX7 tubes for preamp and tremolo circuits, and 7189 power tube.
Here is the baffle board removed from the cabinet. The board was nothing more than 1/8″ thick Masonite.
Here is the cabinet with the baffle board removed.
This great little combo tube amp was built by (who?) and sold through Sears and Roebuck in the late 1960′s and early 70′s. It was originally sold as the Silvertone Model #1421, and in later years as the SR 10XL, and lastly as the Sears 10XL. Oh, the photo of this amp looks innocent enough, but, this is one serious sounding tube screamer. And you won’t usually find them as nice as this one!
Summary: A 10-watt tube combo with tremolo and 8-inch speaker. Hand-wired. Lots of midrange growl that transitions into a creamy overdrive. Great for classic and indie rock, jazz, blues, country and rockabilly. Use as a practice amp or at small venues. Perfect for recording.
Pluses (+): Vintage British, Vox-like, valve sound in an affordable practice amp. Compact and lightweight.
Minuses ( – ): Cheaply constructed lightweight cabinet and thin vinyl covering. The original grille cloth was fragile, and most are completely deteriorated by now. Loud enough for a small venue (i.e. coffee shop) but not for anything larger.
Surprises: 1) The 7189 output tube! This is the higher plate voltage version of the EL84 tube made famous in British amps of the 60′s; and 2) The 8-inch Oxford Alnico speaker sounds great!
Value ($): Depends on the condition and market demand. I have seen them run from $100 to as high as $500.
Similar Amps: The original 1960′s Vox AC4 practice amp. Nothing else in the Silvertone line is similar.
The Complete Silvertone 1421 Review
(Stay tuned… this section under construction)
The 1421 Photo Gallery
This amp is in fantastic condition for it’s age. It even came with the factory original vinyl dust cover. It is all original, except that I replaced a broken power switch, and then replaced the old 2-prong power cord with a safer grounded cord. The tubes, chassis, speaker, cabinet and finish are all in perfect condition — sans for the cigarette-sized hole burned into the original grille cloth (not by me, it came that way!).
The Sears 10 XL was sold through Sears and Roebuck in the late 1960’s and early 70’s. The 10 XL is a single channel, 10-watt (peak) combo amp for electric guitar with a very cool built-in tube-powered tremolo effect.
This little amp first appeared in the 1969 Sears Catalog as a 10-watt tube-powered amp and, transformed into to a solid-state amp around 1972, and then discontinued in 1973. The label on the rear panel identified this model as Silvertone 257.1421100.
The photo of this little amp looks innocent enough. But don’t let the its appearance fool you! This is a serious sleeper of a tube amp, and sounds fantastic. Perfect for your next garage band. And you won’t usually find them as nice as this one!
Summary: A 10-watt tube combo with tremolo and 8-inch speaker. Hand-wired. Lots of midrange growl that transitions into a saturated overdrive. Great for classic and indie rock, jazz, blues, country and rockabilly. Use as a practice amp or at small venues. Perfect for recording.
Pluses (+): Vintage 1960’s tube sound in an affordable practice amp package. Compact and lightweight.
Minuses ( – ): Lightweight constructed cabinet and vinyl covering (it’s a Sears amp!). The original fabric grille cloth was fragile, and therefore most are completely deteriorated by now. Not really loud enough for a big venue, but still perfect for those small and intimate gigs (i.e. coffee shop).
Surprises ( ! ): 1) The 7189 output tube! This is the higher plate voltage version of the EL84 tube found in famous British valve amps of the 60’s; and 2) The 8-inch Oxford Alnico speaker sounds great!
Value ($): Depends on the condition and market demand. I have seen them run from $100 (beat up and not working) to as high as $500 (too much!).
Similar Amps: Unique, nothing else in the Silvertone line is similar. Preamp tube (12AX7) and power tube (7189 version of EL84) used in the 1960’s Vox AC4.
The Sears XL Story (as best I know it)
The Sears 10 XL was a member of the Sears XL Series of amplifiers that first appeaed in the late 1960’s and ran through the mid-1970’s. The XL Series followed the venerable Silvertone 1400 Series (1472, 1482, 1483, 1484, 1485) from the early to mid 1960’s. The XL Series ranged from the little 5 XL (3-tubes, 3-watts) to the giant 200 XL (200-watts solid-state).
Before the XL Series, the Sears Silvertone 1400 line up of amps was designed and built by the famously efficient and economical Danelectro Company of Neptune, New Jersey. Danelectro was founded by the pioneering electronics engineer and builder Nathan Daniel. Nate Daniel specialized in building quality musical instruments and gear at reasonable prices. Danelectro built and supplied all the guitar amps to Sears and Roebuck from about 1958 to 1968. In 1966 founder Nate Daniel sold his company to MCA, and unfortunately by 1969, MCA had to shut down the operation and thus the original Danelectro Company no longer existed.
From about 1968 to 1972 the smaller amps in the Sears XL Series (the 5 XL, 10 XL, 40 XL) continued to be hand-wired tube amps. But by 1973 the entire XL line – except for the little 5 XL – had transitioned to all solid-state electronics. Exactly who built these XL amps for Sears remains a uncertain. We have speculated that the 5, 10 and 40 XL’s were still built in New Jersey with left-over parts from the defunct Daneletro.
The chassis of the 10 XL is all hand-wired point-to-point electronics with a 6X4 tube rectifier, a 12AX7 preamp tube, a 12AX7 tremolo tube circuit and a single 7189 output power tube. The amp has volume and tone controls, Tremolo speed and intensity controls, two 1/4″ guitar input jacks, and one 1/4″ tremolo foot switch input jack.
The loudspeakers that came in the Sears 10 XL varied throughout production. All speakers were 8-inches in size. But the manufacturer and type of speaker varied. This particular model has an 8-inch speaker made by Oxford with an Alnico magnet, which perfectly compliments the lower output level of the 7189 power tube, and sounds great in this amp. Some other 1421 models were made with speakers from the CTS or Fisher factories, and by my account, those all had ceramic magnets instead of Alnico.
The Baffle Board and Grille Cloth
The baffle board is typical Silvertone quality: 1/8″ pressed board (Masonite). That just helps to establish this amp’s personality. The original silver, gold and green sparkle fabric that covers the baffle board is quite delicate, and in most cases rotted away over the years. Thankfully, somehow the original fabric survived on this model.
The 10 XL Photo Gallery
This 10 XL is in fantastic condition for it’s age. It even came with the factory original vinyl dust cover and tremolo foot switch. It is all original, except that I replaced a broken power switch, and then replaced the old 2-prong power cord with a safer grounded cord. The tubes, chassis, speaker, cabinet and finish are all in perfect condition — sans for the cigarette-sized hole in the original grille cloth (not by me, it came that way!).
Drop dead, new old stock guitar, amp and accessories.
A guitar time capsule discovery. While out trolling the flea marts, pawn and antique shops today, Jon and I ran into this absolutely beautiful 1967 Tesico EP-7. It came with its original matching Checkmate 12 amp, guitar strap and cables. It was entire ’67 Teisco electric guitar starter package, minus the original gig bag (but the seller might have had that hanging around, too). Even though the set was 45 years old, the guitar and amp were as new as the day they came out of the Teisco factory. Someone must have received the set back in ’67 and then locked it on a closet. The nitrocellulose finish was perfectly glossy, the chrome was gleaming, and the rosewood fingerboard and brass frets appeared to never have been played before today. We did hear some hum coming from the solid-state Checkmate 12, but that may have been caused by the super-cheap unshielded guitar cable we were using. The EP-7 sounded just “OK” through it’s little solid-state amp. But when we plugged it into a ’47 Harmony tube amp, those two single coil pickups really began to shine. We were impressed by this little guy. It was the find of the day, and maybe the year.
“A Briefcase Full of Blues” – The World’s First All Solid-State Guitar Amp
Summary: 1965 5-watt solid-state combo amp with built-in vibrato effect; 8-inch Alnico speaker; seven Germanium transistors and five Germanium diodes. Point-to-point hand soldered. Perfect little amp for practice or recording.
Pros: Vintage 60′s tone. Extremely compact and portable design. Vintage Germanium transistors and diodes. Simple chassis layout.
Cons: Cheap, lightweight construction and paper-thin fabric covering (but hey, it’s lasted this long already).
Surprises: This old school amp designed more like a tube amp than a solid-state amp. The 8-inch Oxford Alnico speaker sounds great! Awesome vintage vibrato circuit.
Value: Street prices vary by condition and demand, but the price of these continues to rise.
Similar Amps: Kay 700, 705 and 706 of similar vintage. It’s possible, but not certain, that there may be some similar Kay-built amps with a Truetone (Western Auto) label.
Introducing the Kay Vanguard Series
In 1962, the Kay Musical Instrument Company of Chicago introduced the Vanguard line of guitars and amps. That new line included the Kay Vanguard Amplifier with Vibrato, Model 704 (Model No. K-704). The Vanguard 704, along with other Vanguard amp models 700, 705 and 706, were the world’s first mass-produced all-transistor (solid-state) guitar amplifiers. While some transitional hybrid amplifier circuits had previously existed, which paired solid-state electronics with traditional vacuum tubes, Kay was the first company to offer a full line of exclusively solid-state amps to market in ’62. The Vanguard 704 was part of that line and was frequently seen offered with the Kay Vanguard solid-body electric guitar.
A marketing advertisement from 1965 says that the K-704 was built with seven transistors and five diodes.
A Compact Design
In contrast to the heavy, boxy, amplifiers of the 1950′s, the engineers at Kay set out to create a new series of amps styled for the Modern Space Age. The new Vanguard Series was designed to be compact, lightweight, sleek in appearance. Finished in a rad two-tone pattern, the tapered vertical design had a top mounted control panel, and a cabinet barely deep enough to house the speaker and chassis. The new look was unique for a guitar amp of the day and remains unique today. However, the lightweight cabinet materials made it more prone to excessive wear and tear. Therefore, not many of these amps have survived.
The Vanguard 704 features three instrument inputs into a single channel; a volume control and a tone control. The power switch is built into the tone control knob. The vibrato controls include speed, strength, and a jack for a foot switch. A sturdy brass handle is ready to go places.
Old Germanium, New technology, Old Circuit Design
What really makes the Vanguard 704 interesting today is its 1960′s Class A amplifier design and chassis layout. Since solid state technology was still relatively new at the time, the Kay engineers built the preamp, vibrato and the output circuits similar to the old tube circuits, except using Germanium transistors and diodes substituted for vacuum tubes. Because of this design the K-704 sounds akin to its tube cousins of the day. Based on traditional tube amp design of that period, the vacuum tubes were replaced in the hand-wired circuits with seven Germanium transistors and four diodes. The old Germanium transistors sound a little “looser” than the newer Silicon versions, which make them perfect for these low wattage amps. However, Germanium never could handle the heat and raw power of higher watt amps. But Germanium still has a following and is used in low voltage applications, like custom built effects pedals.
According to the pots, it’s a 1965 model. Completely original. A 5-watt wonder. It’s circuits and layout are traditional for the period, but seven germanium transistors and four diodes in place of the traditional vacuum tubes. A single front-loaded 8″ Oxford Alnico speaker. Not a whole lot of lower mid-range. But then again, no low end speaker flab either. The tone kinda reminds me of Led Zep. Mild overdrive at full volume from my Gretsch 5120 humbuckers. Growling, howling overdrive from my Silvertone 1445 with Teisco single coils.
Vibrato, CCR, and The Midnight Special
The vintage Germanium powered vibrato circuit stirs up a deep swirly tremolo that simply sounds awesome. The Kay Vanguard with Vibrato is perfect for nailing that stirring, swelling, sound that Creedence Clearwater Revival played on songs like The Midnight Special and Run Through the Jungle, and other great CCR recordings.
If you are a fan of that vintage 60′s and 70′s tremolo, then this effect alone was worth the price of this unit.
Compact, ready-to-go “suitcase” design.
Two-tone fabric over wood construction.
Five watts output.
7 Germanium transistors.
4 Germanium diodes.
8-inch Oxford “Heavy Duty” Speaker with Alnico magnet.
Vibrato speed and depth controls; foot switch.
Volume and tone controls.
Specifications – Kay 704
KAY 704 – VANGUARD with VIBRATO
8″ Combo Amp
Output (Peak or RMS)
5 Watts, Peak
2N2613, 2N408 and 2N591 Ge PNP BJT, RCA USA
2 ea. 2N408 Ge PNP BJT, RCA USA
2 ea. 2N545 Ge PNP BJT, Motorola USA
1 x 8″ Rear Loaded
Oxford 8ES-9 Alnico Magnet
465-510 (10th month of 1965)
Volume & Tone
3 Instrument Inputs
Schematic Diagram and Parts List for the Kay 704A
Original factory schematic diagram as photographed from inside the 704 chassis.
Original factory Bill of Materials (or, “parts list”) as photographed from inside the 704 chassis. Notice that transistors Q1, Q2, Q3 and Q4 are all Germanium transistors made in the USA by RCA and Motorola, as well as diode D1.
A great little clean tone amp with real vintage vibe. Why practice on a modern digital piece of (insert your favorite phrase here) when you can play a pure analog classic on the cheap!
Here’s a great little solid-state analog-powered practice amp for electric guitars. Around 5 to 10 watts of power into a vintage 10″ American speaker with Alnico magnet. These little Kalamazoo amps were produced in Kalamazoo, Michigan (of course!) in the 1970’s next to their larger Gibson siblings, and were very well built compared to other inexpensive amps of that era. All real plywood construction and baffle board; no pressed fiber board. This one gets plenty loud for practice, or small gigs. Like most solid-state amps of that era, it produces a clean tone all the way to up full volume. You will need to add a good pedal to get that tube-like distortion, like a BOSS DS-1, a Tube Screamer, or my personal analog preference a vintage DOD Overdrive.
Built in 1971.
Somewhere between 5 and 10 solid-state watts.
Two instrument inputs.
Volume, tone/on-off switch, red pilot light.
Black vinyl “tolex” covering.
Nice, vintage 10″ Alnico speaker.
No tremolo or reverb on this model.
Vintage, pure analog, solid-state guitar amplifier.
Made in Kalamazoo, Michigan – the home of Gibson at that time – where they took the art of building great guitars and amplifiers seriously.
Classic, made in USA, Alnico magnet speaker. Kalamazoo speakers always sounded great!
Not your modern mass-produced digital garbage manufactured off-shore by ???.
I have gone thoroughly through this amp and played it for hours.
All wiring, components are original and in good condition.
Everything functions as it should, and this amp is very quiet when idling.
It still has the 2-prong power cord, but works just fine.
No major cosmetic damage.
Some slight separations of the tolex vinyl at some corners, but have to be up close to notice.
Some light surface scratches on the control panel, again, can only be seen up close.
There’s just a bit of looseness in the speaker fabric.
The Kay 704 Vanguard with Vibrato was the world’s first all transistor solid-state guitar amp, introduced by Kay Musical Instruments in 1962. Based on traditional tube amp design of that period, the vacuum tubes were replaced in the hand-wired circuits with seven germanium transistors and four diodes.
I bought this from a guy on eBay. According to the date codes found on the potentiometers, it’s a 1965 model. Completely original. A 5-watt wonder. A single front-loaded 8″ Oxford Alnico speaker. Not a whole lot of lower mid-range. But then again, no low end speaker flab either. The tone of this amp makes me think of Led Zep. Mild overdrive at full volume from my Gretsch 5120humbuckers. Fantastic OD howl from my Silvertone 1445 with its Teisco single coil pickups. The solid-state vibrato circuit is simply amazing! The vibrato effect alone was worth the price.