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Thread: Fender Blues Deluxe Reissue Questions (microphonic preamp tubes)

  1. #1
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    Fender Blues Deluxe Reissue Questions (microphonic preamp tubes)

    Hey thanks for reading,

    Recently had the power tubes replaced in my fender BDRI. Now that I have it back home from the tech, I have two preamp tubes going microphonic on me (the two tubes with the foam spacer, on the far right on the amp.) Microphonic is a stretch, it's bad.

    Question 1: (slightly off-topic) Can a loose ground in my strat actually cause an issue in my power tubes? I only had the power tube issue after getting my strat back from a tech and noticing a seriously loose ground connection when tilting it. Not looking to place blame honestly, it's just been lingering on the mind. Though admittedly I'm pretty sick and tired of the services I have nearby.


    Question 2: When replacing preamp tubes, is it ideal to rebias a fender amp like with power tubes?

    Question 3: In any event, is there a recommendation for a replacement of the preamp tubes (stock are 12ax7), I've seen others toss 12at7's I think.

    Thanks again

  2. #2
    Forum Member Don's Avatar
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    Re: Fender Blues Deluxe Reissue Questions (microphonic preamp tubes)

    1. No. A bad ground in the guitar will not affect the power tubes.

    2. No. Bias adjustment is not required with preamp tubes. Their bias is preset and requires no adjustment.

    3. Some other preamp tubes can be used. The 12AY7 was used in the first position on some tweed amps. It has a gain factor of 40 (compared to 100 in a 12AX7). The 5751 preamp tube is popular as well (it has a gain factor of 70). A 12AU7 has a gain factor of 20. These tubes can be used to tame the lead channel in some amps. I don't usually use 12AT7 in circuits that didn't originally call for them.
    The following are broad generalizations, but JJ pramp tubes can warm up a bright amp. Russian preamp tubes can add a little "sparkle" and Chinese preamp tubes can be good in high gain amps. I use the Sovtek 12AX7LPS as a phase inverter tube in most amps that call for a 12AX7 PI.

    Let us know if new preamp tubes take care of your microphonic issues. It's usually tubes, but if not, there are other items that can cause microphonics. Input jacks and tube sockets, for instance.

  3. #3
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    Re: Fender Blues Deluxe Reissue Questions (microphonic preamp tubes)

    Thank you very much don, it's appreciated!

    I'll be sure to check back if anything.

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