Why did Leo go with 3.2 ohm speakers?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mojo2001, Feb 10, 2008.


  1. mojo2001

    mojo2001 Member

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    Always wondered about this...

    Wouldn't it have made more sense to use 8 or 16 ohm speakers for better power transfer from tubes, especially in a low-power amp like a Champ?

    Was this a provision to drive paralleled speakers in an external cabinet?

    Was there a 5 cent saving in secondary wire in the output trans?

    My experience with low-powered tube audio amps is that such devices seem a lot happier driving loads above 8 ohms.

    If you look at early theater speakers, many of them were 24 or 32 ohms to parallel up in dual woofer cabs, yielding a nice high 12-16 ohm load.

    What do you think?

    Joe
     
  2. jh45gun

    jh45gun Member

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    Fender was not the only one My Silvertone 1472 is a 3.2 ohm load as is my Zenith Chassis that I used for my 5e3 build so evidently back in the 50's a 4 ohm load was popular. I know in the case of my Zenith it was because it was running two 8 ohm speakers in parrallel and the tweeters did not register as they had the crossovers effecting the impedance reading. For my Silvertone though it was a 3.2 ohm rateing on the schematic which we know is 4 ohms.
     
  3. SatelliteAmps

    SatelliteAmps Member

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    The short answer is that Leo didn't. The Champ is usually the one that gets this question due to the schematic, and most people using a DMM to measure the resistance of the speaker, rather than actually measuring the impedance. If you measure resistance of a 4 ohm speaker you get a reading of 3.2 ohms. Impedance is a different measurement. Same with the Silvertones.
     
  4. Swarty

    Swarty Member

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    Leo probably got a sweet deal on either speakers and/or the OT. This was his bottom of the line student amp and I'd bet cost was the biggest factor.
     
  5. phsyconoodler

    phsyconoodler Member

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    It probably had more to do with the output transformers he bought.Again,there are no 3.2 ohm speakers.That is just the DC resistance on your meter,not the actual impedance.And the only place he used them was on champs anyway.
     
  6. mbratch

    mbratch Member

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    Leo thought 3.2 was a "lucky number".

    (Sorry, just had to throw another speculation into the mix :))
     
  7. mojo2001

    mojo2001 Member

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    Of course the AC impedance is higher than the DCR of the voice coil--and only 4 ohms Z at a few frequencies...but the difference between 3.2 and 4 ohms is moot in the context of my question.

    Certainly the 4 ohm setup DOES MAKE SOUND so it is not a totally insane choice, but if you look at 50s audio design, output transformers were more likely to have 8 and 16 ohm taps than 4 and 8 ohm.

    There were some 4 ohm speaker drivers back in the day but these were relatively uncommon.

    I suppose the "sweet deal" on some surplus parts is as good a theory as any.

    I'm probably looking for an engineering rationale that just isn't there.
     
  8. KissTone

    KissTone Supporting Member

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    Some things to keep in mind...
    • Early Fender amp designs were modified from manuals supplied by tube makers;
    • Early Fender amps might have parts sourced from multiple vendors;
    • Amp designs were constantly evolving;
    • Designing an amp around a "sweet deal" on a single component is not only unlikely, it's not practical;
    • The 'legend' of Leo's frugality has been exaggerated to mythic proportion---he tried to build a product that was serviceable, sounded good and was profitable. It was a business, so see my previous points.

    Now, did I know Leo? No. But neither did you.;)
     
  9. jh45gun

    jh45gun Member

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    Other amps back then did not strictly go by the schematic either as some Fenders. The Silvertone amps made by Danelectro and I would suppose the Danelectro brand themselves swapped parts around from what I have heard same as what Fender did.
     
  10. Swarty

    Swarty Member

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    I doubt much engineering went into these.... they were for kids to play their Duo-Sonics and lap steels through and probably considered a joke by intermediate and advanced players. Playing dirty was taboo at the time, and there is very little clean volume available even with a low output pickup. So I will maintain that price point was the biggest consideration in the design of these amps.
     
  11. donnyjaguar

    donnyjaguar Member

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    I'll ask Leo during our next seance.
     
  12. ajbergren

    ajbergren Member

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    I don't have the reference handy, but the original Fender amp designs actually did come essentially out of the RCA (I think) tube manual. No disrespect intended by anyone, but it is the truth. Sure the designs evolved, but tube amps started pretty basic!
     
  13. MisterAgreeable

    MisterAgreeable Member

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    The RCA tube manuals don't have complete amplifier designs. They have circuit prototypes for various amplifier stages - phase inverters, push-pull power sections, etc - but no values filled in for components. Leo did not significantly reinvent tube amplifier technology, but that's not so surprising.

    I think part of the problem is that rock journalists don't understand circuit design. If you look at Richie Fliegler's book he makes note that one of Leo's designs was identical to an RCA circuit, but if memory serves it was for a very rudimentary component - a phase inverter, I think. He shows the two diagrams side by side. The RCA design was just a sketch, but people see that and think that Leo just lifted the design straight from the manual.

    (I think Fliegler went on to become a Fender vice president after he wrote that book. Ironic.)

    It's would be like saying the people who made your lawnmower had used a design found in an engineering textbook if that book had a drawing of a rudimentary internal combustion engine. They certainly didn't invent internal combustion but still a ton of engineering went into the effort.
     
  14. jh45gun

    jh45gun Member

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    William I have seen that reference so often I suspect it is true or it is the biggest lie ever but look at it this way those early tweed amps were SIMPLE circuits. My 5e3 started out life as a Zenith Mono amp out of a Zenith Phonograph FLoor model. With the exception of one tube the rest are the same I had to change a 6j5 preamp tube to a 12ax7 otherwise the rest of the tubes were the same for the amp and the phonograph. The Circuit of the PHono had a one tube preamp section same with the 5e3 though the tubes were different and the 12ax7 has more gain as it is two sections The PI section was close as the 12ax7 did half preamp half PI and the power section was push pull with 6v6's while these amps are both the same vintage who copied who? Zenith and RCA and others were making amp circuits for their radio's and Phonographs long before Fender started making amps and those circuits are very simular sure there are differences like the inputs and other subtle differences but I doubt Leo would be offended by the charge he copied circuits. Here is a brief BIO where it says he started fixing radios so where do you think he got those ideas for amp circuits?
    Clarence Leo Fender came into the world on August 10, 1909, at the family ranch in California. His parents ran a succesful orange grove, located between the cities of Anaheim and Fullerton. Leo became interested in electronics around age 13, most likely from his uncle, who had built a radio from parts.

    Leo began dismantling and repairing radios himself as a hobby, never afraid to tinker with electronics to see what the result would be. In 1928, Leo enrolled in junior college as an accounting major. Leo was sharpening the business acumen that would serve him well throughout his career.
    Two events in the early 1930's would change Leo's life. One was when, in the early 1930's, he was approached by a bandleader to construct a PA system for use at dances. The second, around the same time, was when Leo met Esther Klosky. Esther became Mrs. Leo Fender in 1934.
    Trying the safe route first, Leo hired on with the State of California as an accountant. In 1938, he took a chance and opened the Fender Radio Service in downtown Fullerton. Soon, musicians began coming to Leo in search of improved guitars and amplifiers. Fender began K & F Manufacturing with fellow inventor Doc Kauffman (who designed guitars for Rickenbacker) in a shed behind the radio shop where, in 1945, he unveiled his first electric guitar.
    In 1946, Leo opened the Fender Electric Instrument Company in Fullerton. It was there that he created the legendary Telecaster and Stratocaster — arguably, the most popular and successful guitar designs in history.
    Fender moved the small factory to 500 S. Raymond Ave. in Fullerton, and, in 1965, sold it to CBS Musical Instruments.
    Although, by his own admission, he "could not play a note," Fender went on to be inducted into both the Rock and Roll and Country Music halls of fame — recognition of the tremendous impact he had on contemporary society through his musical inventions. After the non-competition clause expired in the CBS sale agreement, Leo began designing guitars and basses for Music Man. The Sting Ray and Sabre are two Fender designs. In the 1980s, Leo opened the G&L business on Fender Avenue (named for him) in Fullerton. He continued to work there every day until his death on March 21, 1991, from complications from Parkinson's Disease.
    The company began as Fender's Radio Service in late 1938 in Fullerton, California, USA. As a qualified electronics technician, Leo Fender had been asked to repair not only radios, but phonograph players, home audio amplifiers, public address systems and musical instrument amplifiers. (At the time, most of these were just variations on a few simple vacuum-tube circuits.) All designs were based on research developed and released to the public domain by Western Electric in the '30s, and used vacuum tubes for amplification. The business also sidelined in carrying records for sale and the rental of self-designed-and-built PA systems. Leo became intrigued by design flaws in current musical instrument amplifiers, and he began custom-building a few amplifiers based on his own designs or modifications to designs.
     
  15. HighwayStar

    HighwayStar Member

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    Back to the 3.2 (or 4 Ohm) vs. 8 or 16 question, one thing to consider is you will get twice the power from a 4 Ohm load as you will from an 8 Ohm load, providing you are driving it with the same RMS Voltage.
     
  16. jh45gun

    jh45gun Member

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    William Fender was familular with Rickenbacker they were partners for a while and yes there were guitar amps way before Fender started making them they date back to the 30's. Still Fender got his ideas from circuits he was familular with and that was Radio and Phono circuits it just makes sense. IF you want to get into the "borrowing discussion" BobCrooks who started Standel who made amps often accused Fender and Gibson two of his biggest competitors of stealing his designs. One of the first SS amps he made he made small circuit boards( modules) enclosed in resin that plugged into a main board. He did this so no one could steal his new circuits. It was a flop as then no local tech could work on the boards and when Bob got some bad modules made it spelled disaster for the company and soon after Standel went Bankrupt. According to this site there were many first that Standel came up with and Fender later copied.

    http://www.standelamps.com/about_us/story/story_p05.html
     
  17. HighwayStar

    HighwayStar Member

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    His guitars were all copies too. They all has six strings, frets on a neck and a magnet with wire wrapped around it to pick up the sound.
     
  18. jh45gun

    jh45gun Member

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    Hey I am not knocking Fender he was a pioneer in the business and made some great stuff. How ever I do think he copied good ideas and put a stamp of his own on them and nothing wrong with that.
     
  19. cameron

    cameron Member

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    It's not so much that he was copying the designs, as that he was basing his designs on the prototypes provided by RCA. RCA was designing the tubes and along with those designs was providing examples of how they might be used. Fender wasn't alone in basing his designs on how the tubes were intended to be used. The other amp designers were basing their circuits on the same basic guidelines. That's why amps from all manufacturers prior to the mid-50s or so tend all to be cathode biased (unless single-ended). Only once RCA gave its stamp of approval to the fixed bias design to eke more power out of a pair of tubes did people start adopting it.
     
  20. ajbergren

    ajbergren Member

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    Okay, the reference is the Soul of Tone by Tom Wheeler. On Page 24 it states, "He started with familiar tube manuals, widely available components and standard circuits patented by Western Electric scientists at Bell Labs and licensed to Fender by AT&T/Western Electric."

    It also has a quote from Richard McDonald "Those early circuits were widely available, but no one had built the kind of amps Leo Fender wanted to build..."

    It goes on to say how he re-imagined the circuits to do things that were especially important for guitar. Thus, I think there is a blend here. Yes, he BEGAN with circuits that existed, and yes he DEVELOPED them to new heights.

    I wasn't trying to stir the pot this much, but I think Leo was always trying to get more clean power out of his designs, and part of the "Magic" of those early circuits lies in the way they distort. This is really why guitarists are still using Tube Amps today. No doubt Leo was visionary and did things that were way ahead of his time. However, much of the mystic over the old tube amps is the way in which they distort, which was a negative thing in those days. Thus, Leo probably did not foresee the importance of tube amp distortion when he was making those designs.

    As always, YMMV, but this is my interpretation.
     

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