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Radiospares OT Vs. Drake OT For JTM45

Discussion in 'Building the Classics' started by C-Man, Jun 9, 2021.

  1. C-Man

    C-Man Member

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    Surprisingly there aren't that many threads out there comparing the two. What do you prefer in your JTM45 builds and why?
     
  2. neikeel

    neikeel Well-Known Member

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    Depends on spec of amp
    Are you talking originals or clones if clones whose?
    I have done lots!
     
  3. C-Man

    C-Man Member

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    Lets say both original and clones or better yet what do you prefer in each category? Since the original vintage discussion may be down to specific amplifiers lets just keep it to amplifiers you have actually built or clones.
     
  4. neikeel

    neikeel Well-Known Member

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    The RS is marginally cleaner in lower registers but breaks up nicely and does saturate when overdriven. My Drake equipped one is remarkably similar but maybe breaks up a little earlier. I have had one from 65 with Drake that had relatively little clean headroom but the 65 I have now is as sweet as a nut.
    You have to consider the chokes are different in both. The RS comes with 20H choke rated at a lowly 70mA which allows the power supply to squish earlier vs the Drake 3H 250mA one e were which holds up longer.
    Given otherwise identical amps (same Mullard pres GEC KT66 and Mullard GZ34 with B+ of 450v filtering at 32/32/16/16 they are very similar and you would be pushed to tell. Btw I have my current Drake equipped 65 labelled as a keeper and I sold the 64. But it was close.
     
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  5. C-Man

    C-Man Member

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    Do you think it is possible to get the same clean sparkle type sound out of the Drake that one might find from an RS OT?
     
  6. neikeel

    neikeel Well-Known Member

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    Yes
    You stick with stock JTM45 schem with correct voltages and use 100pF bright cap on vol 1 pot. Use 270k mixers and 560pF mixer bypass cap that helps. 27k on 16ohm NFB.
     
  7. william vogel

    william vogel Well-Known Member Gold Supporting Member

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    The full 450-455 volts on the plates of the power tubes is important to the clean headroom. Dropping off to less than 420 is not advised.
     
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  8. Chris-in-LA

    Chris-in-LA Well-Known Member

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    My Ceriatone BB wasn’t sparkly enough with the 100pf on the volume pot. I saw that the Metro build uses 500pf, so I went with that, more open sounding. You might try a few different cap values in that spot.
     
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