Kay Vanguard 704 with Vibrato

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by alex on December 23, 2011

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“A Briefcase Full of Blues” – The World’s First All Solid-State Guitar Amp



Quick Info

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

1965 Kay Transistorized Amps

1965 Kay Transistorized Amps

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 Controls

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.
  • One channel.
  • Three inputs.
  • Vibrato speed and depth controls; foot switch.
  • Volume and tone controls.

Specifications – Kay 704

Model Number 704A
Serial Number 9366
Manufacture Date 1965
Type 8″ Combo Amp
Output (Peak or RMS) 5 Watts, Peak
Pre-Amp Transistors 2N2613, 2N408 and 2N591 Ge PNP BJT, RCA USA
Vibrato Transistors 2 ea. 2N408 Ge PNP BJT, RCA USA
Power Transistors 2 ea. 2N545 Ge PNP BJT, Motorola USA
Speaker Configuration 1 x 8″ Rear Loaded
Speaker Oxford 8ES-9 Alnico Magnet
Speaker Code 465-510 (10th month of 1965)
Baffle Board 1/4″ Plywood
Impedance 8 Ohm
On-Board Effects Solid-State Vibrato
Footswitch Yes
Controls Volume & Tone
Inputs 3 Instrument Inputs
Channels 1
Cabinet Construction 3/8″ Plywood
Cabinet Covering/Color Fabric
Dimensions (WxHxD) 14″x17″x6″
Weight 8 lbs.
Power 120V AC

Schematic Diagram and Parts List for the Kay 704A

Original factory schematic diagram as photographed from inside the 704 chassis.

Kay 704A Schematic Diagram

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.

Kay 704A Parts List

Additional Resources

Links to additional information.

Photos: See more photos hereKay 704 Vanguard Vibrato

{ 15 comments… read them below or add one }

weldon January 1, 2014 at 12:04 am

i had a 704 kay amp and kent guitar in the 60s they were new—–i had to pawn them to move away–i found a kent guitar and now looking for the amp-can you help thanks weldon bent


alex January 1, 2014 at 9:13 am

Thanks for stopping by the website. 704 amps are hard to come by these days. Not many survived the 1960’s. Ebay is probably your best bet, as I see a few show up there each year. Craigslist another option. Good luck!


big gee February 1, 2015 at 1:56 pm

I have one of these 704 Kay in great condition for sale make an offer


Tom J April 7, 2015 at 4:28 pm

I have a Heater II reverb amp type 58 with the tag that says “Manufactured by beautiful girls in Milton, Wis.
under controlled atmosphere conditions”.
Can you help me get a schematic ?


alex July 26, 2015 at 9:58 pm

Hi Tom.
That reverb unit was made by OC Electronics and was used in many amplifiers sold by Sears, Wards, etc. in the late 60’s early 70’s. I don’t know if a schematic is available, but you might try Schematic Heaven.


Brandon Nathaniel March 13, 2016 at 6:06 pm

Anyone have the Kay 800 specs?


alex March 13, 2016 at 9:26 pm

Hi Brandon!

I am not familiar with the Kay 800. Was that the solid-state big brother amp to the 704? I am familiar with the Kay 803 model, but it was a tube amp.

Sorry I wasn’t be much help!


Brandon Nathaniel March 15, 2016 at 2:58 pm

Hi Alex! I just purchased the 800 off a guy on and it is indeed solid state. I found a picture of a prior sale of the same amp on eBay and on the picture were the specs for the 800! It has an 8″ speaker @8ohms, I believe it’s 3 watts and the one I bought sounds fantastic. Just ordered an 8″ Celestion speaker replacement due to arrive this weekend. This model sadly does not have the vibrato. Let me know if there’s any other details I can share. I’m doing a full body restore (fabric and all) over the next few weeks.

-Brandon Nathaniel


alex March 17, 2016 at 7:48 am

That’s sounds great! Please send photos when you have a chance.



Robert August 5, 2016 at 8:38 pm

I have just picked up a good 704 that appears to be all original. The cabinet is in need of a good restoration. Does anyone know of a good restoration shop?


alex August 5, 2016 at 8:47 pm

There are a few shops in my area (Portland, Oregon) but I have not used them for a vintage restoration. Maybe a Google search for shops in your area??? But I’m concerned that the cost of restoration would exceed the value of the amp.

Good luck!


Robert July 12, 2017 at 7:01 pm

just a follow up to my original post. I am planning on recapping my amp and replacing the rectifier diodes with a new full wave rectifier package. Does anyone know where I can find a repair manual or any other document that provides output voltage and amps on the main power transformer?


alex July 12, 2017 at 10:45 pm

There might be a repair manual out there somewhere, but finding one is next to impossible. But the circuit design is so simple and classic that any good solid state amp technician would have no problem working on it. I go the Audio Synaps in SE Portland, he’s very good.

Some words of advice (for what its worth):
1. Replacing worn and defective parts with exact replacements will maintain the value and classic sound of the amp.
2. Replacing the germanium rectifier diodes with something completely different will hurt the value of the amp.

Remember, these amps appeared at the dawning of solid-state technology and are considered the first all solid-state guitar amps ever offered commercially.

Good luck!


tom January 25, 2018 at 10:25 am

A 704 just got donated to a local charity shop, and I volunteered to clean it and see if it had any value. A steady hum occurs which does not change with advancing the volume control (nor any other). Should I try to get it serviced, sell it as is, or put it in the dumpster where it was headed?


alex January 25, 2018 at 1:38 pm

Hi Tom,

The 704 is very rare these days, not many survived. It’s hardly worth anything in the condition you describe, but someone with the right touch and knowledge could get it going again. The cost of service may exceed the actual value of the amp, unless you know someone that will give you a great deal. If so, get it repaired! If not, then slap $30 on it and sell it as is.

Good luck, and please let me know if you get it repaired. I would love to hear how it turned out!


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