Results 1 to 5 of 5

Thread: late 70's UL super reverb speaker impedance

  1. #1
    Join Date
    Apr 2008
    Thumbs Up/Down
    Received: 0/0
    Given: 0/0

    late 70's UL super reverb speaker impedance

    Does anyone have this amp? I'd like to know the individual speaker impedance for this amp, schematic says 16 Ohms:

    But I have four 8 Ohm speakers (they look stock, blue fender label, CTS I guess) in my amp, paralleled total load measured is 2.3 Ohms.
    The back of the amp says 4 Ohm minimum load. My best guess is that the previous owner replaced the speakers with incorrect impedance. Or Fender screwed up...

    0 Not allowed! Not allowed!

  2. #2
    Join Date
    Feb 2015
    Thumbs Up/Down
    Received: 1/0
    Given: 0/0
    So it looks like it should be a 4 ohm load the amp is expecting so the speakers should be 16 ohms each.
    Do the speakers have an ohm spec on them? Do they say 8 ohms or are you assuming?

    I would start by un-soldering all 4 speakers and measuring them individually at the speaker with no wiring attached. They all measure about the same.
    If they were 8 ohms, the reading should be less then 2 ohms (like 1.x).
    2.3 does seem on the low side; what type of meter are you using? is it set to the lowest setting for ohms?

    0 Not allowed! Not allowed!

  3. #3
    Supporting Member Jazz P Bass's Avatar
    Join Date
    Dec 2008
    Wernersville, PA
    Thumbs Up/Down
    Received: 181/2
    Given: 84/0
    Yeah, the schematic shows (4) 16 ohms in parallel for a total of 4 ohms.

    I wouldn't put the blame on Fender.

    Aside: the output transformers used back then are pretty tolerant of slight mismatches.
    2.3 compared to 4?


    0 Not allowed! Not allowed!

  4. #4
    Supporting Member
    Join Date
    May 2006
    Staffordshire UK
    Thumbs Up/Down
    Received: 143/0
    Given: 211/1
    Well, the speaker resistance should be a bit lower than the nominal impedance; but then most meters will read high on such low resistances. So best to do as per post #2.
    The VHT on these amps is rather high, so if it's going to be pushed hard, to give the tubes a fighting chance it may be a good idea to ensure that the intended load is connected.

    0 Not allowed! Not allowed!

  5. #5
    Old Timer
    Join Date
    May 2006
    Chill-Ville, VA
    Thumbs Up/Down
    Received: 264/4
    Given: 556/11
    I think the extra .3 or so ohms can probably be accounted for with meter lead resistance, along with that mile of speaker wire back there. I'm with Jazz on this one, especially if that OT is original. Because even if they WERE all 16 running in parallel, add an extension cab, bang, 2 ohms.

    My Bassman has run for many years with the wrong load, and not quietly, either. And the only tube death came when the bias caps dried out & failed.


    0 Not allowed! Not allowed!
    "... If an older Boogie and classic Marshall had a (clearly illegitimate) child and you baked it in an oven set to clown shit crazy." - Chuck H. -
    "When receiving a shock I emit a strange loud high pitched girlish squeak." - Alex R -
    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Reverb mods for '70's Super Reverb
    By Steve A. in forum Mods & Tweaks
    Replies: 6
    Last Post: 01-10-2018, 02:13 AM
  2. Replies: 4
    Last Post: 09-04-2014, 01:21 AM
  3. Replies: 6
    Last Post: 10-31-2010, 09:28 PM
  4. 70's Super Reverb problems
    By andymef in forum Music Electronics
    Replies: 1
    Last Post: 12-31-2008, 04:36 PM
  5. Reverb mods for '70's Super Reverb
    By Steve A. in forum Guitar Amps
    Replies: 3
    Last Post: 07-20-2006, 06:56 AM


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts