Category: Guitar Equipment

The Field-Coil Guitar Amplifier

Post author By admin
Post date 10/13/2010
11 Comments on The Field-Coil Guitar Amplifier

The year is 1946. You are a man of the world. Bold and sophisticated. A true musical connoisseur.

In your stately home you use music to relax and to entertain. Your Magnavox Regency 155 combination Radio/Phonograph, with state-of-the-art dual 12″ speakers, serves you well for many decades. After many long and fruitful years, the day will come that you will pass into the next life; and then I will build a guitar amp from your Enormous Radio.

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When I did in fact purchase this gigantic ‘Instrument,’ as the manual called it, it was far too large to fit in my car. So with some basic hand-tools I dissected my $25 dollar purchase in the faded parlor where it had sat for a lifetime. I removed the radio chassis (mostly junk save for some 6J5 tubes), the later-added GE RIAA phono pre (sold on eBay), the 25 watt amplifier chassis (salvaged the tubes, output and phase-inverter transformers), and two 12″ Magnavox field-coil speakers.

Luckily, my purchase came complete with all the manuals, service guides, and original warranty card. Using the schematic I was able to see how the ‘field-coil’ speakers function in this type of amplifier.

In my previous post on field coil speakers, I went into some detail about this technology and its relationship to more modern speakers. Now the time had come to actually build a working audio device using this antique technology.

I have completed the piece, and in this article I will describe some of the challenges faced, techniques used, and offer some audio examples of the end result. This is a somewhat long article, so if you just want to hear the audio, skip to the end…

FOLLOW THE LINK BELOW TO READ ON….

Guitar Equipment

Exclusive Bonus Content!

A purchase can sometimes have an unexpected collateral component.

Let’s say you know a lady who is a fan of Charlie’s Angels. Especially Kate Jackson’s ‘Sabrina’ character. On the program, Sabrina drove the much-maligned Ford PINTO automobile. You are at a local library used-book sale and you pick up a copy of the Ford repair manual for this car.

It turns out that the book has an undisclosed bonus-feature which may/may-not enhance the driving experience.

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One of the more interesting aspects of buying cheap old guitars is the odd bits and bobs that are in the guitar cases along with the instrument.

This point was brought into sharp focus this weekend when I realized that I had purchased a 1950’s Harmony tenor guitar largely due to the antique capo that was on the guitar’s neck.

A ‘Sid Kleiner’-branded Kay guitar from yesterday’s flea market contained some old bank drafts, songbooks, and obscure picks.

I wonder if I have gone off the ‘deep-end.’ But then I remember… one Will Hoover actually had a book published on some of this folky flotsam. A book which I bought. Shit.

Occasionally, a guitar case will contain the original sales pamphlet and/or retail-hang-tags that accompanied the instrument at the time of purchase. These can sometimes prove to be valuable, selling for between $10 and $5000 (if you happen to find a 1950s Les Paul guitar).

Nonetheless, my favorite random case-finds are antique string packages. As graphic-design pieces, they reveal a lot about how the guitar manufacturers positioned their instruments and their consumers. Here is a quick survey of some old packages that I have come across in the past few years.

FOLLOW THE LINK BELOW FOR MORE….

Guitar Equipment Publications

das 70s rock

Post author By admin
Post date 10/09/2010
No Comments on das 70s rock

I love German rock music of the 70s. Popul Vuh’s soundtracks for Herzog films.

Tangerine Dream and Klaus Schulze. Neu. Amon Duul II. And, of course, the immortal CAN.

There is a uniquely hypnotic, repetitive, druggy vibe to so much of this music.

It’s incredible just how different 70’s German rock music was compared to that from the UK, Italy, Sweden, and France. Much music gets described as ‘Psychedelic,’ but very little of it actually has the potential for ‘mind-alteration’ in the way that this music does.

It’s not hard to see how these sounds effortlessly transformed into ‘Techno’ in the 80s, a counter-path to American RnB’s simultaneous development into hip hop.

Appreciation of vintage German audio equipment is intense, but it is generally limited to microphones and pro-audio equipment. This is where the German reputation for precision really seems to sell the products. Now that I think about it, of the 9 microphones that I stuck on the drum kit yesterday, 6 were German. 2 Neumanns for the room, an old Sennheiser 409 above the snare drum, and some 70’s Sennheiser 441s on the rack toms and under the snare.

441s are really fantastic microphones. I wish I had even more of them.

Beyond Neumann and Sennheiser, German brand Telefunken is a favorite of audio engineers. No one hears too much about old German guitars and amplifiers though. I recently picked up this Ovation ‘Tornado.’

Ovation is an American brand (CT, actually…), but this, their earliest electric guitar, was actually composed of a German-made body with a US-made neck attached in the states. It’s a nice guitar. German makers also supplied components to US guitar-maker Carvin in the 60s and 70’s

I came across a pile of 70’s German rock-instrument magazines and catalogs not too long ago. Here’s a quick tour of some of the more interesting things I found…

The Schaller Corp’s popular aftermarket guitar tuning pegs represent perhaps the greatest US market penetration that a German guitar company would have in the 70’s. I feel like 30% of 1970’s Gibson guitars have been ‘improved’ with Schaller tuners. Looks like Schaller also made effect devices.

FOLLOW THE LINK FOR MORE….

Guitar Equipment History Technical

Fkkng magnets. How do they work?

Post author By admin
Post date 10/07/2010
4 Comments on Fkkng magnets. How do they work?

I had often heard of primitive ‘field-coil’ speakers, but it was not until i was confronted with a pair of them that I actually had to come to grips with this ancient technology.

Consider how a basic modern speaker driver works. See this excellent animation for a quick example.

There is a (usually) paper cone with some wire wrapped around a center post. The wire coil sits roughly inside a ring of magnetic material (either ceramic or metallic).

An electrical-signal is sent into the wire coil, and this causes it move relative to the fixed magnet.

OK so we all know what a paper cone is. And we all know what a coil of wire is. But what about this magnet? Where did it come from?

Well, it turns out that modern speakers use what are called ‘permanent magnets.’ As-in, the magnet has a permanent charge. The material which composes the magnet is always magnetic, regardless of any other influence. Hold a key up to the back of any raw speaker driver and you will see that yes this is in fact a magnet. And a pretty powerful one.

Permament magnets possesing enough magnetic power to function in a speaker driver are not naturally occurring materials, though. They had to be invented. And they were, largely as part of American WW2 engineering efforts. These new, powerful permanent magnets were engineerd from an alloy of aluminum, nickel, and cobalt, hence their name: Alnico magnets. In the 1950s, newer ‘ceramic’ permanent magnets were engineered, and these became the norm owing to their even greater efficiency and lower cost (cobalt is expensive as a raw material).

But what about all the speakers and guitar amps designed BEFORE the invention of this wonderful Alnico substance? These devices (and it’s rare to find one that is still in good working condition) use similar looking speakers, but with a very different type of magnet. They use Electromagnets. Meaning: they use magnets which are made of a material which only become magnetic when a large DC current is passing through it.

Exactly where the audio device creates this large DC current, and exactly what effect this arrangement has on the total system, are interesting issues to explore. This piece is a still a work-in progress.

I hope to have it completed soon, and I will post some audio examples of this antique technology at work.

Custom Fabrication Guitar Equipment Technical

some recent pieces

Last week was busy in the shop.

This is a 2-watt per-channel stereo power amp built for our friends K&D. It is tiny (only 10 inches wide). The form of the amplifier was driven by the styling of these beautiful black-lucite vintage speakers which complete the set.

The speakers were made by Speak-Easy Intercom of Kansas City, likely in the early 50’s. They are handmade from individual pieces of black lucite. I found them with the original base-station for the intercom, all in flawless condition. I replaced the drivers in the speaker cabinets. This tiny tube-audio system is intended as a casual background-music-listening setup for the home or office.

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A couple more ‘Recycled’ Tweed Champ Clones were born last week as well.

I have decided on the name ‘Cassius’ for these and all future small single-ended 5watt guitar amps. ‘Cassius’ being the name of the most famous Champ of the 20th century.

Like the previous Recycled Champs, these are freshly-built guitar amplifiers, built with largely new components, into antique cabinets. In this case, factory/school PA speaker boxes.

I built these with identical circuits, very true to the circa 1955 5E1 schematic. They use a 6V6 output tube with a 12AX7 preamp tube. They have choke transformers and a feedback circuit. The output transformer is mounted directly on the 8″ Alnico speaker in order to conserve space. I used a 6X5 rectifier tube rather than a 5Y3 so that i could use a slightly smaller-sized power transformer. The 6X5 is an excellent tube which was used in a great amount of pro-audio equipment in the 50s. These amps also will also accept 12AY7 preamp tubes for a different breakup.

These amps are very small and lightweight. They sound fantastic. Extremely dynamic. The range of sound that you can generate using the volume knob on the guitar is outstanding. The small Alnico speaker magnet make these amps less efficient than some other 5 watt amps, which makes these ideal for apartment dwellers (or anyone who lives with other people!).

Up next: this week I will be building a similar ‘recycled’ guitar amp, but scaled up: a 12-watt “Tweed Deluxe-type” amplifier with a 12″ field coil speaker.

Guitar Equipment Publications Synthesizers

I just wanna get up here and cook, man.

Post author By admin
Post date 09/30/2010
1 Comment on I just wanna get up here and cook, man.

Downbeat is one of the oldest music magazines in the world. They have been publishing since 1934. This is incredible. Downbeat primarily covers jazz music. Much of jazz was (and is) performed on acoustic instruments, or electric instruments where ‘fidelity’ and ‘natural-ness’ of tone is the desired effect. If you have been following this website you will probably guess that this is not of great interest to me. The late 60’s/early 70’s were an inclusive, experimental time for instrumental music though – consider Miles’ Bitches Brew period, Melvin Jackson, and even our friend Steve Douglas – and equipment manufacturers were beginning to create devices that our scale-ripping friends could use up on the bandstand. For evidence, let’s turn to some Psych-era issues of Downbeat and see what was on offer…

Selmer was not the only firm to offer an ‘electric saxophone’ kit. I have owned a few that VOX marketed as well. Basically these devices offer combinations of various primitive sound effects, from distortion, filtering and reverb, up to actual monophonic pitch-tracking. Some of the effects that you can get with these things are pretty radical (literally). Check out the earlier Steve Douglas post for an example.

Along the same lines, here’s a slightly later offering from Maestro, the effects division of Gibson Musical Instruments.

In an earlier post, I briefly covered the Gibson GA100, a late-50s guitar amplifier which was intended for use with classical guitar and acoustic bass. Baldwin marketed a similar product in the late 60’s. Willie Nelson has used one of these for decades with his lil buddy Trigger.

And while we’re on the subject, how about an amplifier that REALLY sells to the jazz guys?

I have used one of these (with the similarly humongous 2×12″ extension cab) and they are pretty funny…

Alright so if you’ve made it this far, I am guessing that you are prepared to follow the link below and see more of this fun stuff.

SEE MORE CIRCA 1968 DOWNBEAT ADs FOR OFFBEAT EQUIPMENT…

Guitar Equipment Icons Manufacturers

ICON: Guild Instruments

Even if you have never played a guitar in your entire life, you are probably familiar with the Gibson and Fender guitar brands.

These companies have existed for decades (a century for Gibson) and they are, at this point, American icons. The brands themselves, divorced from the actual products that they represent, get licensed for use adorning other products.

(web source)

Other great American manufacturers are even willing to co-brand with these companies.

(web source)

Gibson and Fender guitars are of good quality, and their ‘classic’ models are functionally/sonically very different instruments, so it makes sense that they have existed for so long in opposition as healthy competitors.
There are, of course, other classic American guitar brands. Martin guitars. Gretsch Guitars. And Guild Guitars. Martin has been around for over 150 years, and they are primarily very demure acoustic instruments.

Gretsch is a newer (80 years?) brand, and instead are known for garish electrics of varied quality but undeniable curb-appeal.

And then there is Guild. Guild never really had a strong identity. They kinda walked the line between acoustic guitars for ‘serious’ folkies and electric guitars for players looking for ‘something different.’ But I have always found them to be the best value in a used (vintage) guitar. The acoustics are a great balance of the chime of a Martin acoustic and the growl of a Gibson acoustic. I love my old Guild acoustic.

It’s much better then my Martins, and i can’t afford a good vintage Gibson, so… Guild is where it’s at for me. And the electrics combine Gibson build quality with the offbeat charm of the cheaper American vintage brands like Harmony and Valco. If you feel drawn to Harmony and Silvertone vintage electric guitars, but you need something that will actual stay in tune and play well… get a Guild.

GUITAR was (is?) a British guitar mag. I picked up a pile of back issues while on tour in England years ago. Here are some great examples of Guild’s 70’s lineup, taken from advertising in GUITAR. (other manufacturers on display in the same issues are Peavey, Ibanez, and Barcus-Berry).

-please follow the link for gallery of vintage British Guild Ads, as well as the conclusion of this piece…-

Custom Fabrication Guitar Equipment History Icons Technical

Recycled Champs

one of the most famous electric instrument amplifiers of all time is the tweed-covered Champ amplifier made by Fender in the 1950’s thru early 1960s. Here’s a image of one from 1959 that i pulled off the web:

Fender made true vacuum-tube champs until the late 1970s, but the tweed-covered Champ (and it’s close cousin the tweed-covered Princeton) differ from their later namesakes in a lot of ways. In the case of the final Tweed Champs, the lack of bass and treble controls means that there is roughly 20db more gain available vs the later Black Tolex-covered Champ. This does not necessarily make for a louder amp. This does, however, make for an amp that can get super distorted and generally Sound Like Awesome.

Tweed Champs cost a fortune to buy. Eric Clapton apparently used one for the Derek And The Dominos record. This fact became widely known, and they have been very expensive ever since. Fender now even makes a ‘re-issue’ (never a good idea) that sells for close to $1000.

champSchem

The schematic is posted above for anyone interested in checking it out. They are very very simple. Anyhow, since these things do sound so great and they are so simple to build, it’s a lot of fun to build them into Any Old Thing that catches your eye. Here’s a quick survey of some Champs and Princetons that i’ve built into found enclosures. You’ll see recycled Intercom units, school PA system speakers, and 16mm film projector speakers. The circuits in these are all new, built with new or lightly used parts; but the cabinets (that part you actually SEE and touch) are straight up ancient. I generally take plenty of liberties with the circuit, changing parts, adding features (reverb, add’l gain control, EQ, etc), even building them using different (but similar) tubes, and i’ve yet to be disappointed.