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Thread: Tube mic - capacitor off mic element increase

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    Tube mic - capacitor off mic element increase

    Last night, I took out the 1000pF ceramic cap and swapped in a .0033uF [edit] orange drop which fit fine. Cathode cap is upgrade to hi-grade semiac? type. Can't recall the exact name again but it still electrolytic. Was this ok?
    I might swap in a 1.2 V rechargeable AAA battery yet as I love this sound.
    I forgot to write down the plate voltage but it is likely 50V too high as I'm using an Apex 460 power supply. But the tube seems fine still...a 6ZH1P.
    The transformer sure seems big/robust.
    Question:
    If I were to add a pre-transformer-Send— via drilling a small hole in the mic's-case rear and add a "mini" jack maybe like 1/8"—would this net a purer sound option? So basically a Send right from the tube.
    I have an extra wire, I think, along the long Muti-wire cable but I was fearing cross-talk.
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    Last edited by Guitarist; 03-30-2020 at 01:12 AM.

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    Are these 6ZH1P tubes very high quality? Is there a better substitution (even though I am pretty happy here?
    I see the 5654 now, so that might be good one to phase in later.

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    Last edited by Guitarist; 03-30-2020 at 12:26 AM.

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    Quote Originally Posted by Guitarist View Post
    Last night, I took out the 1000pF ceramic cap and swapped in a .033uF orange drop which fit fine.
    Your schematic shows .0033uF, big difference to .033uF. Which did you use?

    I would think the transformer is built in to the design, so I doubt it would sound better bypassing it. Could actually sound poorer.

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    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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    Oops, yes just .0033. A that impedance I'm not sure if that will extend the lows some or, as you imply, just saturate that transformer.

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    I was referring to 'bypassing' the transformer by using a pre-transformer send.
    As far as increasing that cap value, it sounds like you got a low end boost which you like. I don't know about saturation, but you might have issues with 'pop' depending on the user and proximity.

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    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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    Aha, right I didn't yet consider pop.
    Well, I don't have the extra parts for that Send right now anyways so, that can wait.
    These Oktave mics sure sound sweet!

    thanks for your insights!

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    The cut-off frequency with a 1nF coupling cap and 1G input resistance is 0.16Hz. Do you need lower?
    The cathode network of 3.6k and 22F means a corner frequency of 2Hz, same question.

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    Ahhh, well that might suffice. I don't want the studio to vanish hitting a 0Hz wave!
    That answer as I was wondering— what those values might be—thanks so much.
    OT aside, .1 to 400KHz is pretty good!

    Should I leave the pentode schematic alone? The screen grid, G2, is simply tied to the plate. There is some free, untapped gain here but I read that pentodes prefer lower voltages and this power supply is way high, like 200V.
    At the plate resistor is now 200k, perhaps a 100k from B+ and a .1uF to ground to revert to pentode mode?
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    Last edited by Guitarist; 03-30-2020 at 02:40 AM.

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