Deluxe Reverb with 6L6s ?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by GenoBluzGtr, Feb 22, 2009.

  1. GenoBluzGtr

    GenoBluzGtr Silver Supporting Member

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    A friend has DRRI that he uses 6L6s in. No mods, no other 'adjustments' other than biasing... He's been using it this way for over a year with no problems...

    Now I am intrigued, but more cautious than him... would this be an issue? Could there be transformer or circuit damage waiting to happen? Should I try it?

    Thanks!
     
  2. wyatt

    wyatt Member

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    Well, let's look at it this way.

    You're running...
    6x12A*7 tubes for a total of 1.8A current draw (.3A ea.)
    2x6V6GT for .9A current draw (.45A ea.)
    Total = 2.7A

    He's running...
    6x12A*7 tubes for a total of 1.8A current draw (.3A ea.)
    2x6L6GC for 1.8A current draw (.9A ea.)
    Total = 3.6A

    Now, a vintage BFDR power transformers can supply 3A of current draw on the filament windings. I can't find specs for the modern 641316 part, but everything I read implies it is also 3A. Which means he's asking his PT to supply 20% more current than it can on that coil, which is taxing. It's not good for the PT to do it, plenty of people do, so it's a YMMV situation, as long as you accept the risk that it may need repair one day. I would never do it with a vintage BFDR; but with a DRRI, there isn't anything in the amp i can't pull out and replace if needed.

    But you can replace the rectifier with a SS one, like a WeberVST Copper Cap, this doesn't free up the 2A of current available on the 5V tap to go elsewhere, but does take a little stress off of the PT.

    Other things to consider, you will now have a 4000K primary impedance on the OT, which means the secondary impedance is now 4 ohms.
     
  3. GenoBluzGtr

    GenoBluzGtr Silver Supporting Member

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    So I would be better off just running the JJ 6V6s if I wanted a little more headroom?
     
  4. wyatt

    wyatt Member

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    Yeah. 6L6's in a DR has a similar problem as Tweed Deluxes, the output transformer limits the output anyway, you just get a more "6L6" sound. To really get a useful increas ein headroom, you need to come close to doubling output, a more efficient speaker works wonders.
     
  5. rockon1

    rockon1 Member

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    Yep.and a speaker that is 3db more efficient is like doubling the power of the amp! Bob
     
  6. GenoBluzGtr

    GenoBluzGtr Silver Supporting Member

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    Just curious... if the current flow is a potential problem, would using a higher resistance Rectifier Tube mitigate that? Higher resistance=lower plate voltage, which means less current flow... right? or am I missing the point?

    I do realize that lower plate voltage means lower headroom, but If you could use a 5U4 or 5Y3, you could really knock the plate voltages down to minimize current draw, right?
     
  7. phsyconoodler

    phsyconoodler Member

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    It's the filament current that is the issue,not the B+ voltage.The filament voltage is 6.3v AC for all the tubes except the rectifier,which uses a different tap at 5V AC.All those windings are different,and using a diode rectifier will only free up the 5v winding,not the 6.3v one.
     
  8. wyatt

    wyatt Member

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    +1.

    A guitar amp is pretty economically laid out. A modern, high-end, tube hi-fi amplifier would dedicate separate transformers for the high B+ voltage and each of the filaments, but in the olden days of radio and guitar amps, it was easier to package two or three transformers into one (and still is). Each has it's own job, but they all share the heat generated when one is overworking.

    They ideal situation is to swap out the power transformer with one that can supply plenty of current for whatever tube you want to use. Allen, Mercury and just about everyone else makes one. As long as the ratio for the B+ voltages are the same, you would never tell the difference, it's just that one would be more robust and versatile than the original. For instance, the current Allen replacement (5V 3A, 6.3V 5A) can supply enough current for 6V6's, 6L6's, KT66's and even EL34's and your choice of rectifiers.
     
  9. wyatt

    wyatt Member

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    Ah, see, here is a sure way to blow the transformer. The stock BFDR transformer only supplies 2A on the 5V filament transformer...a 5U4 takes 3A. So, now one would be taxing both the 5V filament transformer and (if running 6L6's) the 6.3V filament transformer as well.

    No, lowering B+ voltages is often necessary if you want to plug a 6V6 into a 6L6 amp; but going the other way, the big issue (as noted) is the filament current.
     
  10. GenoBluzGtr

    GenoBluzGtr Silver Supporting Member

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    That's why I come here... thanks guys. I appreciate the info and thanks for making it clear!

    I guess I'll stick with my Vibroverb for my 6L6 tones.. and keep that smoky DRRI for what it does best, huh?
     
  11. shakerAU

    shakerAU Member

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    How does it sound compared to a regular DRRI??

    I found this article a while ago that might be of some interest....

    http://acruhl.freeshell.org/mga/main/deluxemod.html
     
  12. wyatt

    wyatt Member

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    There are a few things wrong with the article. First off, just plugging 6L6's into a Deluxe Reverb does not make it a bigger Fender amp, the smaller output transformer just doesn't transfer the output well to speakers.

    Also, I've read all of the same advice, in almost the exact same wording, but there was always a caveat that it should only be performed on Silverface DR's, which have a larger power transformer and *can* handle 6L6's.
     
  13. phsyconoodler

    phsyconoodler Member

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    6L6's do make the tone a little cleaner and rounder sounding.I would stick with 6V6's myself and optimize what you have with speakers/tubes/tuning.
     
  14. GenoBluzGtr

    GenoBluzGtr Silver Supporting Member

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    It sounds different, but not much. The clean is "cleaner" and a bit more punchy... the tone has a grittier/harder edge to it, but is still cleaner... if you can understand that. More apparent bottom end, and it seems to have more volume, but not a huge amount more (a DRRI is quite loud for a 22 watt amp!!).

    I think I actually prefer the 6V6 tone as I like my cleans more smokey and lush... but I do really dig the gutsy feel I get from my Vibroverb and my Tweed Bassman when I really get a chance to kick it into high gear...

    Maybe Egnater should build a Rebel that will allow blending of 6L6s and 6V6s, huh??
     
  15. wyatt

    wyatt Member

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    Honestly, if you weren't comparing side-by-0side, you wouldn't notice it as much. Once your ears adapt to something new, the amp will sound completely different again anyway.

    It does tighten up the low end and 6L6's have their famous scooped mids (the midrange "kink").
     

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