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Thread: Fender Amp

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    Default Fender Amp

    For those who remember when electronics glowed a pleasant orange colour and generated enough heat to keep a house warm in winter, please consider the circuit below.
    A lovely fender guitar amp with classic topology.
    Quick quiz: what is the function of the highlighted block and how does it work?
    No doubt, many will immediately recognise the circuit function, but those for whom semiconductors are the only electronics they know, it may get the grey matter stimulated?

    "The saddest aspect of life right now is that science gathers knowledge faster than society gathers wisdom." - Issac Asimov



Look Here ->
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    I'm old enough to know the answer (I used to repair them =), but will leave it for the younger guessers =)
    Last edited by wotnot; 21-08-21 at 02:37 PM.

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    Nothing to be seen.
    If Postimg that is malware blocked on my side and it is not a false positive.
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    preamp

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    Quote Originally Posted by hoe View Post
    preamp
    No. The two 7025 twin triodes are the preamps.
    "The saddest aspect of life right now is that science gathers knowledge faster than society gathers wisdom." - Issac Asimov

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    Maybe distortion/reverb ?

    I have no electronics training.....

    usages.kangaroos.sound
    Last edited by hoe; 21-08-21 at 04:30 PM.

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    Here you go fester ;


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    Quote Originally Posted by hoe View Post
    Maybe distortion/reverb ?

    I have no electronics training.....

    usages.kangaroos.sound
    Not reverb (no reverb tank), but getting warmer.
    "The saddest aspect of life right now is that science gathers knowledge faster than society gathers wisdom." - Issac Asimov

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    Quote Originally Posted by wotnot View Post
    Here you go fester ;

    THanks Wotnot.

    Probably the most controversial thing about Fender, their Vibrato !
    When in fact it is a tremolo. It is a low frequency oscillator(LFO) that modulates the amplitude, NOT pitch, which they do with a tiny neon lamp and a photo resistor.

    To add confusion they called their whammy bar on the Strat a tremolo.


    Hoe, the classic Fenders are not suitable for distortion, even if you drive them with a foot pedal booster amp, the distortion sounds awful.
    However their practice amp, The Champ, was indeed used for distortion as it only had a few watts and you could drive the power output valve to oblivion but then with a microphone in front of the speaker into the PA or recording pad.

    This explains why I got quite a few Champs for repair with broken output transformers but the owners all wanted them fixed.
    A classic Fender Twin Reverb shines with clean sounds. Can't even remember having to repair one, just replaced working valves with Groove Tubes or other minor modifications.
    Last edited by Uncle Fester; 21-08-21 at 06:20 PM.
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    Quote Originally Posted by Uncle Fester View Post
    THanks Wotnot.

    Probably the most controversial thing about Fender, their Vibrato !
    When in fact it is a tremolo. It is a low frequency oscillator(LFO) that modulates the amplitude, NOT pitch, which they do with a tiny neon lamp and a photo resistor.

    To add confusion they called their whammy bar on the Strat a tremolo.


    Hoe, the classic Fenders are not suitable for distortion, even if you drive them with a foot pedal booster amp, the distortion sounds awful.
    However their practice amp, The Champ, was indeed used for distortion as it only had a few watts and you could drive the power output valve to oblivion but then with a microphone in front of the speaker into the PA or recording pad.

    This explains why I got quite a few Champs for repair with broken output transformers but the owners all wanted them fixed.
    A classic Fender Twin Reverb shines with clean sounds. Can't even remember having to repair one, just replaced working valves with Groove Tubes or other minor modifications.
    Well done Fester, you are correct about Fender and their nomenclature: Vibrato is not Tremelo.

    My favourite piece of reasonably modern tremelo was Johnny Marr's legendary intro to The Smiths' "How Soon is Now"

    "The saddest aspect of life right now is that science gathers knowledge faster than society gathers wisdom." - Issac Asimov

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    Not only the intro, that tremolo goes through the whole track like a metronome with a groove, quite unusual.
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    I know nothing about vacuum tubes but, given the "pedal" switch it had to be something to modify the signal. When Fester described the circuitry, I can easily see it now.
    I'm out of my mind, but feel free to leave a message...

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    I built solid state counterparts for that circuit but I cut my teeth on the glow in the dark stuff so I would be cheating to reveal what this is and how it works.
    The country boys just love the sound from this as well as switching the phase on the dual pickup Fender strats.

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    Quote Originally Posted by Hunchback Tech View Post
    The country boys just love the sound from this as well as switching the phase on the dual pickup Fender strats.
    ...err, the Strat has three pickups, I think you mean the Telecaster, which the country boys and gals love for their twang.

    While you can get useful hollow 'out of phase' sounds with the Strat(wiring the middle pickup reverse gives you two), that famous twangy sound is also emphasised by the bridge design of the Tele.
    Last edited by Uncle Fester; 17-11-21 at 11:30 AM.
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    Quote Originally Posted by Uncle Fester View Post
    THanks Wotnot.

    Probably the most controversial thing about Fender, their Vibrato !
    When in fact it is a tremolo. It is a low frequency oscillator(LFO) that modulates the amplitude, NOT pitch, which they do with a tiny neon lamp and a photo resistor.

    To add confusion they called their whammy bar on the Strat a tremolo.


    Hoe, the classic Fenders are not suitable for distortion, even if you drive them with a foot pedal booster amp, the distortion sounds awful.
    However their practice amp, The Champ, was indeed used for distortion as it only had a few watts and you could drive the power output valve to oblivion but then with a microphone in front of the speaker into the PA or recording pad.

    This explains why I got quite a few Champs for repair with broken output transformers but the owners all wanted them fixed.
    A classic Fender Twin Reverb shines with clean sounds. Can't even remember having to repair one, just replaced working valves with Groove Tubes or other minor modifications.
    My mate owns a Fender twin. So what are groove tubes and how are they better ?

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    Quote Originally Posted by loopyloo View Post
    My mate owns a Fender twin. So what are groove tubes and how are they better ?
    Groove tubes have a very tight tolerance in the specs and are sold matched for the power stage although I use now Electro-Harmonix who do that too.
    Unmatched power valves can lead to unwanted distortion and premature failure when they are not performing symmetrical in push pull stages.

    In the pre-amp stage their triodes have higher gain, sound brighter and are less microphonic than generic brands.

    They cost more (back in the 80's and 90's when I installed them a lot), today all the classic tubes are expensive except some Russian ones.
    Last edited by Uncle Fester; 17-11-21 at 12:19 PM.
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    Quote Originally Posted by Uncle Fester View Post
    ...err, the Strat has three pickups, I think you mean the Telecaster, which the country boys and gals love for their twang.

    While you can get useful hollow 'out of phase' sounds with the Strat(wiring the middle pickup reverse gives you two), that famous twangy sound is also emphasised by the bridge design of the Tele.
    Maybe it was the Teles, but the first and third or the center on the strats had a mod to switch phases.
    Leo got it right when he designed the guitar and more than just the bridge.
    Tubes had their own unique distortion it took years for solid state to duplicate. Today, they use ADSP and it is close.
    I keep hearing about all this power from amps, and my old twin at 50 watts you could hear in the next county.
    Something about that transformer coupling.

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    Quote Originally Posted by Hunchback Tech View Post
    Maybe it was the Teles, but the first and third or the center on the strats had a mod to switch phases.
    Leo got it right when he designed the guitar and more than just the bridge.
    Tubes had their own unique distortion it took years for solid state to duplicate. Today, they use ADSP and it is close.
    I keep hearing about all this power from amps, and my old twin at 50 watts you could hear in the next county.
    Something about that transformer coupling.
    Don't get me started with digital signal processing.
    I have all the amp modelling software on my iPAD and heaps of VST amps for my DAW and when comes to something with a binary input like an organ (talking Hammond B3/C3 emulation here) they do good stuff but when capturing and dealing with the dynamics of a guitar they all fail.

    Nothing beats the real thermionic valve.

    The reason why a valve amp appears louder than it's transistor counter part is that rather then the sharp clipping you get with transistor(even worse with digital amps), they overdrive the output by adding harmonic whole multiples of the input (mainly from the fundamental frequency). This is like adding registers of an organ, that makes a dull sine wave appear much more powerful and dominant.
    There really isn't much more power involved, the amp is just 'tricking' our ears.
    This works best with bass but can get messy with complex chords where all these harmonics might not 'harmonise' with each other anymore and then it will sound ugly distorted.

    Of course the speakers in your old Twin had a massive sensitivity(efficiency) hence able to entertain the next county.

    Transformer coupling is always a big headache when designing amps. There are limitations(non linearity) that don't contribute to a better sound but may have an influence on the sound. Generally they should be designed that all distortion is created in the valves and not from saturation of the transformer.
    I never really looked much into this and if the tiny output transformer that more frequently fails in heavily overdriven Champ amps gets saturated and overheats from that.
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