Old Bassman + new Hartke speaker = impedance question

Discussion in 'Amps and Cabs [BG]' started by The Mule, Mar 21, 2004.

  1. Hello y'all! This is my first post on Talkbass. I was recommended this forum because of the expertise that should be available around here. I sure hope someone could :help: me with this question I'm having:

    I just purchased a 1968 silverface Fender Bassman top at a vintage guitar fair. I have tested it by connecting it to the speaker of my Hartke Kickback 12 combo amp. Everything went fine, no problem at all & it sounded great (both with bass and guitar).

    But now I wonder if the difference in wattage/impedance between the Bassman (50 watt/4 ohms) and the Hartke's speaker (120 watt/8 ohms) can and/or will damage the Bassman if I keep using it this way. Is it absolutely necessary to use the Bassman ONLY with a speakercab with a 4 ohms impedance? I realise this might be a very stupid question, but I really don't have a clue...

    AMJBASS Supporting Member

    Jan 8, 2002
    Ontario, Canada
    The Hartke kickback uses a 4 ohm 12".

    AMJBASS Supporting Member

    Jan 8, 2002
    Ontario, Canada
    Sorry. I was under the impression that the amp was 120 watts at 4 ohms. My mistake.
  4. That's OK, thanks for your reply anyway :)
  5. tomg


    Mar 15, 2004
    Mule, the:

    The Bassman should have a 4 ohm load, for best results. For the long story, consider a couple of things:

    1) There is a general opinion "out there" that mismatching a Fender tube amp by one "step" in either direction (2 ohm or 8 ohm, in this case) is something the output transformer is robust enough to handle, and therefore ok.


    2) Whereas a s.s. amp will generate maximum power at the lowest recommended impedance, but function fine with a higher load impedance (albeit with a lower power output), tube amps are intended to be operated with the indicated impedance, period.


    3) The extension speaker jack on your Bassman is wired in parallel with the regular speaker output, and is only active when both are in use. Otherwise, the ext. jack is shorted to ground. As there is no switch to accomodate other impedances, and as Fenders cab options for the Bassman were limited to 4 ohm models, I can only guess that they would have expected you to use two 4 ohm models together, if employing a second cab... for a total load of 2 ohms.


    4) I have on more than one occasion blown tubes and burned screen resistors in my Fender Bassman 100 (also 4 ohms, playing a bass) into an 8 ohm cabinet at moderate levels, for what turned out to be short rehearsal periods. This amp functions without a problem during regular use with a 4 ohm cabinet.


    5) I have used my Fender Bassman (50 watt, 4 ohm, playing guitar) with an 8 ohm cab on occasion to no ill effect.

    Both of the aforementioned amps are/were in good working order, as I probably spend too much time tending to their every need. An argument could be made that this over-attentive parenting is setting them up for failure in the "real world", but that's a discussion for another thread, and possibly another forum. In any case, there is more tech info available on mismatching upward (4 --> 8 ohm), and the problems to expect, such as transformer flyback energy, etc. In my case, there was notably less volume, and the amp seemed to be running hotter. Oversaturating the OT? I dunno.

    So, all that to say, use a 4 ohm cab. Or don't. But don't be suprised if you have a problem with the wrong speaker load. Then again, don't be suprised if you don't. How's that for a clear answer?

  6. Well, the only thing that's clear to me, is that there might be no clear answer to my question. But to be on the safe side I should try to find a 4 ohm speakercab? More reactions would still be appreciated off course! :help:
  7. Everything TomG said is true, but I do not agree with it. :D Nah, just kidding, I pretty much agree with it.

    I'd run the Bassman with 8 or 4 ohms with no worries. It'll probably be fine forever.

    Chris (electrical engineer, if you're wondering about my credentials)
  8. Thankz Chris & Tom, I'm going to give it a try for a while, but I'll try to find a 4 ohm speakercabinet because I'd hate to damage the Bassman in the long run. Funny how something I thought to be a silly question turns out to be this difficult to answer! :meh:
  9. Well, I've made up my mind and was seriously looking around for a 4 ohm speakercabinet. I really liked my Hartke Kickback 12 combo (solid state) and I've got the Bassman to cover the tube-sounds. So a few days ago I've decided to trade the Kickback for a Hartke HA 1400 top and 2100 Pro speakercabinet.

    The 2100 Pro is 200 watt max @ 4 ohms, the HA 1400 is 140 watt @ 4 ohm and the Bassman is 50 watt @ 4 ohm. That can only be a nice and practical combination, one great speakercab and having to change only the speakercable from SS Hartke top to Bassman top. I'm only an at home player anyway. I've already got the 2100 Pro and it works great with the Bassman (only some noise coming from that darn old thing, but I already expected that, it's from 1968 and that's older than I am!). The Hartke top will be coming next week to fullfill my longing for an ultra-clean amp to use with my Alembic bass.

    Anyway, my problem is solved. Thanx! ;)
  10. Rockbobmel

    Rockbobmel Supporting Member

    I ran a SF Bassman (50 watt) into an 8 ohm cab for a while and it worked fine. I also run a Bassman 135 into an 8 ohm cab, and pushed it hard, and there was no ill effect. HOWEVER, it is my understanding from what I have heard that, Fenders are at their best at 4 ohm loads, meaning better output, sound, and speaker cone control.