Blackface Deluxe Reverb extension speaker question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by 6789, Mar 20, 2006.


  1. 6789

    6789 Member

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    The Blackface Deluxe Reverb has an 8 ohm speaker output.

    If I connect a speaker to the extension speaker jack and keep the internal speaker connected, will both jacks output 8 ohms?
     
  2. Dave C

    Dave C Gold Supporting Member

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    Both jacks are wired in parallel , the BFDR output transformer is 8 ohms. Two 8 ohm speakers in parallel are 4 ohms . Fender OT's can handle up to a 100% mismatch such as this without having any problems . It'll work fine.
    Dave C
     
  3. John Phillips

    John Phillips Member

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    With any other Fender amp I would agree with Dave, but the Deluxe/DR is the exception... due to the odd (factory) choice of OT ratios, the amp is already significantly low-mismatched even when running an 8-ohm load - the true matching load impedance is about 12 or 13 ohms from what I remember.

    I would not run 4 ohms from it, especially if you're going to really push the amp - the tubes won't like it at all.

    I'd maybe consider running the internal 8-ohm speaker and an external 16-ohm cabinet at the same time (though even that is outside the safe mismatch range, just), but I would avoid using two 8-ohm speakers.

    I'm sure many people have done so over the years and not blown anything though...
     
  4. Shea

    Shea Member

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    So, I suppose a Deluxe Reverb might sound better if one were to replace the 8-ohm combo speaker with a 16 ohm one.

    Shea
     
  5. John Phillips

    John Phillips Member

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    Yes.

    The best-sounding DR I've ever heard was a '69 SF fitted with a 16-ohm 65W McKenzie. At the time I couldn't understand why it was so much better-sounding and LOUDER than any other DR I've ever heard, since I assumed the "mismatch" would reduce the power. Later I found out about the mismatched stock ratio and it all made sense. Also why fitting a DR with 6L6s and still using the stock 8-ohm speaker works so well...

    That characteristic flubby/pushed-too-hard-mush sound of a DR is actually very characteristic of a low mismatch, if you know what to listen for... not actually of 6V6s, even though the DR is usually thought of as the 'classic' 6V6 amp.
     
  6. 6789

    6789 Member

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    Does this apply to the new Deluxe reverb Reissues too?
     
  7. blkjazz

    blkjazz Supporting Member

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    Bump.

    I'm curious about this too.
     
  8. JJman

    JJman Member

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    What is the impedance ratio of the transformer in them?
     
  9. 6789

    6789 Member

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    John left the Gear Page building a long time ago.
     
  10. Ronsonic

    Ronsonic Member

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    The turns ratio squared.

    Sorry. Not really meaning to be a smart ass.

    Next time I've got one on the bench I'll look into this.
     
  11. bluetweed

    bluetweed Supporting Member

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    Most of the new transformer companys replacements are true 8 ohms, so no worries there.
     
  12. GearPagent

    GearPagent Member

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    I have a 77 partially bf'd DR (retains the larger and saggier rectifier). Tried the 16 ohm thing with a k120. Sounds pretty amazing. Was having a hard time finding the right speaker for this amp. I agree with it sounding flubby and weirdly mismatched with the 8ohms. Haven't gigged it like this yet but I had it up pretty loud. Didn't seem to notice too much volume loss.
    Now I will probably try some other speaker styles in 16ohm when the speaker bug starts to itch again. Am curious if the 77 was still using the "16 ohm" tranny. Described above.
     
    Last edited: Dec 18, 2013
  13. pdf64

    pdf64 Member

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    I think that Deluxe Reverbs have always been specified for an 8 ohm load.
    The output transformer primary impedance being 6k6 ohms compared to 8k ohms of the Tweed Deluxe.
    John's point may have been that a 6k6 ohm load was a bit too low for 6V6 at VB+>400V; it enabled a high output power but at the expense of excessive stress on the tubes and obtaining the best tone from them. Doubling the speaker load impedance to 16 ohms would double the primary impedance to 13k ohms, which posters above seem to think gave better results.

    My view is that 13k ohms seems rather high; when heavily overdriven, the 6V6 screen grids may take a beating and at speaker resonance, at which the impedance may rise to ten times the nominal value, inductive flyback emf may become excessive, especially on a non-interleaved winding arrangement, such as the DR OT.
    Pete
     
  14. GearPagent

    GearPagent Member

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    I am well over my head in this discussion, but I like the sound I'm getting at 16ohm. Seems like I should expect shorter tube life?

    Also, I think the JBLs are closer to 6.x on the 8ohms and 13.x on the 16's. Is that gonna make a difference? Or are those numbers funky too? ie multimeter read resistance vs audio signal?
     
  15. pdf64

    pdf64 Member

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    Possibly so, especially if used heavily overdriven.
    Cranked into a mismatch will stress things that much more.

    Yes, those readings are for dc resistance, the ac impedance value of the speaker will be higher.
    Pete
     
  16. zzmoore

    zzmoore Member

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    John Phillips...a Prince of a guy. ;)
     
  17. drbob1

    drbob1 Silver Supporting Member

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    John was REALLY helpful, has he been gone that long?

    Anyway, I've heard some discussion of JBL history, AFAIK the original D120/D120F speakers were actually about 12 ohms and were the same speaker whether labeled as 8 or 16 ohm. IN which case they'd be PERFECT for a Deluxe with the original OT?
     
  18. pdf64

    pdf64 Member

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    Oh no, I feel another internet myth being spread.
    It seems bizarre that a major reputable manufacturer would knowingly mislabel such a key aspect of their products.
    Is this discussion based on anything substantial?
    Speakers are made with various nominal impedances and it's possible the odd one or even a batch were mislabelled in error but that's somewhat different to the above assertion.
    Pete
     
  19. GearPagent

    GearPagent Member

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    Ok well now I'm a little spooked... Especially after reading the hilarious and insult-laden and potty-mouthed google groups on the same subject (lord valve???). Totally thinking of going back to 8ohm v30. How many people have actually fried amps with a 16ohm load? I'm thinking of taking a survey on the main amps and cabs thread to see how much damage these rouge impedances have wrought over the years.
     
  20. pdf64

    pdf64 Member

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    Your saggy rectifier (5U4?) will act to lower the VB+ when under heavily overdriven conditions, so that may help to mitigate the issue.
    It would also be beneficial for the screen grid resistors to be flame retardant metal oxide type, 1 watt rating; consider increasing their value to 1k, although that may affect the amp's tone.
    A 220 ohm 5 watt metal oxide resistor across the output transformer secondary winding will help to protect against open circuits and limit the maximum impedance at resonance.
    Combining the above measures may help to mitigate failures and minimise additional stress on the tubes resulting from the mismatch.
    Pete
     

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