Randall RD45H

Discussion in 'Reviews' started by Tetanus, Nov 7, 2016.

  1. vonno

    vonno New Member

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    I bought a 3 years old used RD45, maybe a tube replacement could be a good choice.
    Do you have any info from web or constructor about bias adjustment, if it is required? Did you do on your amp?
    Anyway the sound is still good, a little dark (I know it is characteristic of this amp). Do you think with 5881 have less low frequencies?
    Thanks!!!
     
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  2. Robstafarian

    Robstafarian The Good and Wise Call Me “Rufus”

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    5881 tubes have much the same low end as 6L6 tubes; the primary difference between them is that 5881 tubes compress earlier than 6L6 tubes.
     
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  3. Tetanus

    Tetanus Well-Known Member

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    I've done the biasing myself.
    There are 4 screws at the bottom of the amp, undo these and you can remove the chassis from the wooden case.
    Carefully though. Mine was so tight that it took me quite a force to remove it.

    Then i used a Bias probe. (This is the main reason i had to remove the chassis as the power tubes won't fit with the additional probes in)
    The Bias trim pots are on the top of the chassis, front if the power tubes.

    Regarding to the tone of 5881 vs 6L6:
    I found the 5881s sounds better for me. But there are not that big of a difference. It easily can be due to the different brand/manufacturer.
    I hear a bit tighter response, a touch more mids. And with the 5881s l can turn the volume up just a notch, which might not seems a big difference BUT it absolutely makes it easier for me to run the amp on quieter settings. (Valve amp, loves a cranked volume or run at least on 9-10 o'clock)

    What preamp tubes are you using in your rd45 ???
    I would like to experiment with these...



    Sent from my iPhone using Tapatalk
     
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  4. Tetanus

    Tetanus Well-Known Member

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    you can see the Bias adjuster trim pots on this photo:
    [​IMG]
     
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  5. Robstafarian

    Robstafarian The Good and Wise Call Me “Rufus”

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    I cannot see a photo.
     
  6. Tetanus

    Tetanus Well-Known Member

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    I've just linked the one from my original post... don't know why it isn't visible. I can see it on my side...
     
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  7. Tetanus

    Tetanus Well-Known Member

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    ohh and one more thing:
    be not afraid to turn the Mids and the Presence controls up a lot!

    as I hear it on this amp:
    more Mids are helping you cut through the mix of course but it seems the Mid on this amp raising some almost bass frequencies (acts like a lower-mid freq. control). Therefore I turn the Mids up (almost max) and dial back the bass to around 11 o'clock.
    Presence is for mid and high frequency feedback in the power-amp section. Therefore it can help you a lot to get a tight, mid heavy tone.
     
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  8. Tetanus

    Tetanus Well-Known Member

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    i saved the photo and marked the Bias trim pots. Hope it works this time:
    IMG_5584 bias trims.jpg
     
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  9. Robstafarian

    Robstafarian The Good and Wise Call Me “Rufus”

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    That works quite well!
     
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