Acoustic 136 head..Anybody know what Ohms it runs?

Discussion in 'Amps and Cabs [BG]' started by Trentonswartz, Jul 29, 2009.

  1. I just bought an old '70s Acoustic 136 head for $100. I have an old Ampeg v4 cab loaded with Eminence 250w bass speakers at 8 ohms. I have a feeling this head is either 4 or 2 ohms, but it doesn't say it anywhere on the head and I can't find a schematic. I can rewire my cab to run at 2 I'm hoping that's the actual impedance.

    The amp sounds loud and fine on the high stuff, but can't hold a bottom end to save its life. Its very distorted, even at low levels when I hit the low E string. Is this just a result of incorrect impedance, or does it just need a good re-capping? I intend on re-capping it anyway because there's a pretty noisy hum. Thoughts?
  2. lfh


    Dec 18, 2003
    Stockholm, Sweden
    The 136 was a bass combo, so someone must have pulled the amp section and put it in a case. The corresponding head was the 140 (electronics identical to the combo sibling AFAIK), rated 125 W RMS @ 4 Ohm. I've heard of 140:s surviving 2 Ohm loads, but that wasn't supported officially back in the day. At 8 Ohm you run into clipping pretty quickly.
  3. I noticed that about the difference between the 136 and the 140, and this head looks identical to the 140, but has the 136 name plate...don't know how or why, but it is.

    Anyway, I tested the head using a 4 ohm cab just to see if the clipping was a result of that, and what I got was a louder signal that still clips (just as I suspected). The mismatched impedance just gave me a lower wattage from the head, but only resulted in a volume decrease. The clipping still happened exactly how it was into the 8 ohm cab, which makes me believe there's something else wrong with the head. Do the capacitors affect clipping like that? Since it's pretty noisy, would changing the capacitors fix the hum and the distorted bass? There literally is hardly any bottom end coming out of this amp, and I'm always hearing people rave about these amps being huge and never distorting.
  4. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    It's very possible that new caps would indeed fix those problems. But unless you know what you're doing (and honestly, if you're asking, you probably don't), take it to a tech, lest the caps kill you. I had a 136 combo for years and it absolutely was loud and clean.
    Bill Whitehurst and Count Bassie like this.
  5. MusicManLN3


    Feb 21, 2010
    From what I've seen there are two 136 combos. A vertical one resembling Acoustic's other models, and a horizontal one with a different look. Found the latter at Guitar Center the other day and was wondering if it's a smart buy. $329 used and looked like it was in great condition.
  6. MarTONEbass

    MarTONEbass Supporting Member

    Jun 19, 2009
    Norton, MA
  7. giantjerk


    Jan 18, 2003
    Allen, TX
    I literally just got back from (trying) to play through this head and cab. All the pots were extremely scratchy and I could not get it to play a clean signal through any of the four inputs at any volume. Even with the volume pots all the way down it would only pass intermittent signal and produced really LOUD crackly noises. Disappointed, I really wanted to pull the trigger on this one.
  8. orange joe

    orange joe I am serious and don't call me Shirley

    Sep 7, 2012
    Albany NY
    I was scoping that one out as well.Sorry to hear that its in such bad condition.
  9. Gaolee

    Gaolee Official leathers tester and crash dummy

    I have a 126, which is the slightly later version of the 136. I like it well enough, but there's no way I would pay $200 for it now. There are better amps out there.
  10. DavidC96


    Nov 30, 2006
    I have an Acoustic 136 that my Dad bought me in May, 1971. Acoustic had just released this model. A rep from Acoustic was there asking me how I was going to use the amp. I told the rep the amp was going to get put on a school bus a lot. The label on the cabinet said 8 Ohms. The owners manual indicated the amp ran at 150 watts at 4 Ohms. I figure it runs at 100 watts. The cabinet is a 1x15” cab that is “horn loaded” with a vent to the side - Not downward. This gave the cabinet a “stereo wide” sound that got bigger and louder the farther away you were from the cab. The amp has a mid-range sound that isn’t “boomy”. If I wanted “boomy bass” that I could feel, I would flip the cab on it’s side with the vent downward. This would double the volume and boost the lows. The hassle with that was flipping the cab moved the on/off switch right next to the ground. The combo weighs 80 lbs. That didn’t feel like much when I was 15, It feels like a lot more now that I’m 61. It was my “70’s amp”. Even though I fixed the amp in 2010 (the motherboard cracked thru the center, “killing the amp”), I mainly use the cabinet with different amp heads because of the “stereo wide” sound I get. Right now, I use a MarkBass Nano-Mark head that puts out 200 watts into 8 Ohms with this cabinet. The nanoMark puts out massive “boomy” bass tone, so I don’t have to flip the cabinet. :)

  11. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    Wow, never saw a 136 that looked like that before! Mine was the more vertical one (not mine...I sold it in the 90's):

    TomB and Gaolee like this.
  12. Gaolee

    Gaolee Official leathers tester and crash dummy

    My 126 looks exactly like Jimmy's 136 did. It works just fine still. As long as the PCB doesn't break, the amp may live forever.
    JimmyM likes this.
  13. BassmanPaul

    BassmanPaul Inactive

    I really get a chuckle when we gab away about something started by someone who has not visited the site since September 2009. He joined stayed nine months and was gone like a wisp in the wind! <sigh> Who says I ain’t a bit poetic like? :D
    JimmyM likes this.
  14. Bryan Owen

    Bryan Owen

    Dec 16, 2016
    I just landed here doing a search for the same problem. (Anybody still around?) :)

    Someone recently gifted me an Acoustic 136 combo. It was super quiet and scratchy sounding and I'm sadistic enough to tinker with the thing, so ...

    Trentonswartz -- did you ever come to any conclusion as to what was causing your problem? I'm having it too.

    As mentioned above, the service manual says it's rated at 125W @ 4 ohms. I just measured the existing speaker (not sure if it's original) at 4.3 ohms.
  15. Bryan Owen

    Bryan Owen

    Dec 16, 2016
    Also, as to the wide vs. tall Acoustic 136 configurations... as best I can tell, the first year (1971) had the wide side-ported configuration, and 1972 forward had the tall (bottom-ported) configuration. They probably got tired of flipping the thing on its side. ;-)
  16. TomB

    TomB Supporting Member

    Aug 24, 2007
    I built a head case for a 136 and used it for club gigs for years. It was a little shy in the lows (into a 4-ohm 402 cab) but a 10-band MXR EQ pedal solved that nicely.
    Last edited: Jan 6, 2022