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Thread: 5E3 - Why does it distort above 360 plate volts?

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    5E3 - Why does it distort above 360 plate volts?

    Hi I just acquired a bet up 5E3 clone. After some fixing up I notice how the plate voltage is low compared to a SF Princeton Reverb. Giving it less headroom, like further in the opposite direction from a Twin.
    It has 330v and from what I read anything above 360v would make the amp distort at any volume. Is this simply because of the lack of NFB? If yes, then NFB was probably space age electronics when it was discovered.. even though distortion is interesting for us on guitar.

    ********* Oh!! wrong forum, can't find the Delete button?

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    Lifetime Member Enzo's Avatar
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    The use of negative feedback actually goes back several centuries, predating electronics. In vacuum tube circuits, it was already a thing by the 1920s. The RDH has a whole chapter on it. The Radiotron Designers Handbook was written in 1934.

    There is nothing new about our guitar amps.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Enzo View Post
    There is nothing new about our guitar amps.
    With the possible exception of HOW they are used. As in, intentionally driving them into clipping for distortion. Well, new as of the mid 60's I guess. But it certainly became progressively more aggressive through today.

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    "Never bet your life on somebody else doing their job." SoulFetish's good friend

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

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    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

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    actually more plate voltage should give more headroom,if biased correctly.
    This amp distorts easily not only for the missing NFB,but also for the volume pots behaviour,they are wired in such a way that basically at 3 you already have a signal capable of overdriving the power stage and that leads also to further distortion in the concertina splitter.
    Many times people put a 12ax7 in V1,where it was supposed to be a 12ay7,that means more gain.

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    Senior Member Pedro Vecino's Avatar
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    My idea is that 360v is the ideal voltage for that amp. Raising the voltage serves only to make overdrive transition more abrupt. For me there is no interest since that is the strong point in that amplifier.
    If using a 5Y3 the voltage is 330V, probably changing it to a 5V4 should rise appreciably. However it would be convenient to test other aspects of the amp. Clones cause me panic just by naming them

    As for the volume potentiometers, the curve of the Alpha do not work very well. As curiosity, I discovered some potentiometers a few days ago that are a dream in that amplifier. These are the new ones that Mesa uses in the Mark V. I had a pair of those amplifiers to which I installed a pushpull in the gain of channels 2 and 3 to access the classic EQ of the Mark IV in a selectable way (in certain modes they sound with the mid-shift of the Mark IV in fixed form, always activated) and I stayed with four of them. They are of the style (plastic and metal) of the Rectifiers / Nomad and others but with 24mm. Absolute control over the volume in 5E3. It would be ideal to know if someone knows their origin and if there is possible access to them.
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    Quote Originally Posted by Iplayloud View Post
    ... from what I read anything above 360v would make the amp distort at any volume.
    Where did you read this statement? It seems wrong to me. Generally, higher voltage will give you more headroom i.e. less distortion for a given volume.

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    Bent Member Chuck H's Avatar
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    Last edited by Chuck H; 08-03-2018 at 01:14 AM.
    "Never bet your life on somebody else doing their job." SoulFetish's good friend

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

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    Quote Originally Posted by Chuck H View Post
    Thx Chuck. One can only speculate on the reason, if it is indeed true. Higher V -> more gain -> oscillation-> distortion??? More testing is required.

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    Bent Member Chuck H's Avatar
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    KingCameron seems to be referring to the effects of changing any single aspect of the 5e3 design without respect for how it affects other operating parameters. In this case raising plate voltage without adjustment to the cathode bias resistor on a 5e3, which already runs damn close to class A stock. I expect the tubes might even be over dissipating at idle.?. I mentioned this in the other thread with the same title.

    In other words... KingCameron is saying that you can't increase plate voltage for the 5e3, period, without the knowledge that you need to balance the voltage with current to maintain the 6v6's safe operating parameters. He also seems to have some experience with a few builds for this model. How you can build more than one of any tube amp and NOT recognize that relationship confuses me. He is giving incomplete and incorrect information and advice using the voice of experience. Iplayloud shouldn't drink the internet KoolAid.

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    "Never bet your life on somebody else doing their job." SoulFetish's good friend

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

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    Quote Originally Posted by Chuck H View Post
    KingCameron seems to be referring to the effects of changing any single aspect of the 5e3 design without respect for how it affects other operating parameters. In this case raising plate voltage without adjustment to the cathode bias resistor on a 5e3, which already runs damn close to class A stock. I expect the tubes might even be over dissipating at idle.?. I mentioned this in the other thread with the same title.

    In other words... KingCameron is saying that you can't increase plate voltage for the 5e3, period, without the knowledge that you need to balance the voltage with current to maintain the 6v6's safe operating parameters. He also seems to have some experience with a few builds for this model. How you can build more than one of any tube amp and NOT recognize that relationship confuses me. He is giving incomplete and incorrect information and advice using the voice of experience. Iplayloud shouldn't drink the internet KoolAid.
    too many gurus today speak about gain,that alone doesn't mean distortion,they don't even know how many types of distortion can occur and what happens if,they just paint by numbers substituting mustards and carbon comps and listen with their gpolden years
    sorry for the rant.

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