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Ampeg B-18N - 1966 vintage. (tone question)

Discussion in 'Amps and Cabs [BG]' started by CosmicRay, Apr 10, 2015.


  1. CosmicRay

    CosmicRay Supporting Member

    Hello out there...
    I just acquired a 1966 Ampeg B-18N.
    It's in extremely good condition. I rehearsed with it last night, but I was somewhat disappointed with the tone. It didn't have the low, bottom end that I thought it would/should have. I actually rolled off all the treble and turned the bass all the way up, but it just didn't have the low freq response. Especially with an 18" speaker....(I think it's the original Cleveland)
    Anyone familiar with this amp have/had same issues?
     
  2. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    The amp needs to be checked out. Clean the jacks and tube sockets, check the power supply caps, and power amp bias.

    The simplest first thing to try is to change the 6SL7 preamp tubes. There should be more than enough lows. Check to see if both channels have the same issue.

    If you think that it is the speaker, try another cab. Or another amp into the cab. This can help break down the problem and identify where the issue is.
     
    nashvillebill, SirMjac28 and 99Z3 like this.
  3. CosmicRay

    CosmicRay Supporting Member

    I was going to try alternate speaker/alternate cab, but the design of the amp will not allow that.
    It has a sort of pin connector to the speaker, and the cable is not removable from the back of the amp. I may try changing the tubes, but I really did not want to invest more $ into this thing.
    But really, it has no bottom at all.
     
  4. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    There are adapter cables that you can buy to convert from the 4 pin connector to 1/4". See fliptops.net.

    If you want to build one, the wiring for the cable is shown here Tips & Tricks (including modifications) - TalkBass Wiki

    But since you don't want to go to any extra expense, the easiest solution is to disconnect the cable from the head to the cabinet, then clip a speaker cable directly to the speaker with aligator clips and a short wires. This will allow you to test the speaker with another amp. If you go through the connector, you need to connect to the two outside pins, pin-1 and pin-4.

    To get the amp to work with another cab, you need a connector that shorts pin-2 to pin-3 (the middle two pins), then connect pin-1 and pin-4 to the speaker. See the cable schematics in the wiki above.

    Does channel 1 and channel 2 both lack low end? To test the preamps, all you need is one good 6SL 7 tube. Try it in the first position, then test channel 1. Then plug the good tube into the second position, try channel 2. These first tubes conver the preamps and tone control circuits.

    Normally this amp has lots of low end. Something is clearly wrong. What you are hearing is not normal for this amp.
     
    SirMjac28 likes this.
  5. CosmicRay

    CosmicRay Supporting Member

    Yes both channels lack deep low end. Which did not seem right to me.
    I appreciate your advice and I will test it out as suggested.
    Thanks!
     
  6. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    If both channels sound the same, them maybe the preamp is fine. On the back of the amp is a pre out called ext amp. Use an instrument cable to connect from there into a power amp. If you don't want have a power amp, you can go into the input of another amp. Just be very careful with the volume levels, start low on both amp.

    If this works and there are good lows, then it would be the b18's power amp or speaker.

    There are so many simple possibilities though. Maybe the contacts on the tubes need cleaning. The power supply electrolytic caps might need replacing. A tech would need to check out the amp.
     
  7. sloppy_phil

    sloppy_phil

    Aug 21, 2011
    Toronto, ON, Canada
    Not actually named Phil
    Those amps are capable of big, big lows, and (at least mine) has a fairly extended upper range as well. Which was surprising to me.

    Even though they may look alright, there can be problems under the hood you won't notice. Had mine for 3 years before a cold solder joint on the rectifier tube socket suddenly appeared. I thought I had blown the tube or fried the socket, but it was just an old problem that finally became obvious years down the line.

    Beans knows his stuff; you are doing well by heeding the advice!
     
    SirMjac28 likes this.
  8. CosmicRay

    CosmicRay Supporting Member

    Yep, as soon as I get back to my rehearsal space I'll run it through another amp as was suggested. I'm just somewhat confused as to
    So if I run it through the amp I have at my rehearsal space, a GK 800 MB Fusion, roll off all the tone from the GK and
     
  9. CosmicRay

    CosmicRay Supporting Member

    Yep, after I try all the suggestions, I may have to take it into get checked. I hope this isn't a money pit I just opened.....
    excuse the unfinished reply that's in the above post. Hit the wrong button....
     
  10. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    The gk800mb does not have a power amp input. You can try plugging the b18 preamp out into the fx return on the gk. Be careful with the gain on the b18. See how it sounds.

    If that doesn't work, try plugging rhe b18 pre out into the input of the gk. in doint this you are chaining two pres together. That is why you have to watch the volume levels on both amps.

    On the b18, flat is at noon so start there. Set the tone controls on the gk flat as well.
    If the volumes are too high, you will see clipping amd distortion.
     
  11. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    I should add, whenever the b18 amp is on it needs to be connected to the speaker cab. When you take the pre out from the b18, soumd will continue to come out of the speaker. This is normal and you should not unplug the speaker cab.
     
  12. sloppy_phil

    sloppy_phil

    Aug 21, 2011
    Toronto, ON, Canada
    Not actually named Phil
    Hmmm, my understanding was that the 4-pin speaker cables on those amps were designed to prevent any damage to the amp if it's not plugged into the cab, and running a signal. Some sort of built in idiot-proofing, I thought.
     
  13. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    It's not going to come out of standby unless it's plugged in.
     
  14. lowphatbass

    lowphatbass **** Supporting Member

    Feb 25, 2005
    west coast
    When speakers get that fatigued you can usually hear it. Either way I would find the best tech you can to go through the amp before you use it regularly...and save all the old parts.
     
  15. TRichardsbass

    TRichardsbass Banned Commercial User

    Jun 3, 2009
    Between Muscle Shoals and Nashville
    Bassgearu, Music Industry Consulting and Sales. Tech 21, NBE Corp, Sonosphere.
    Take the one hour drive to Central Jersey Music Service in Edison, NJ. Go see Dennis Kager, one of Jess Oliver's employees and students, and one of the legendary Ampeg designers. Dennis should be able to tell you what is going on without you taking the thing apart. And, as a bonus, you will meet an Ampeg and bass legend.
     
  16. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    True. If you short the two middle pins on the amp's connector, you bypass the safety protection. It allows you to do some testing. Of course shorting pins can be dangerous if a wire slips. It can also be disabled under the chassis. The best way to do this is to build a cable adapter so that everything is safe. It could be that the speaker is the issue and needs a re-cone. It could be that the amp has an issue. Performing these tests will help narrow down what the problem is.

    A tech can do all this and any old amp should be checked out by one.
     
    Last edited: Apr 11, 2015
  17. CosmicRay

    CosmicRay Supporting Member

    Thanks for your advice, I just may do that. I contacted Ampeg directly and was told to bring it to a service tech in NYC. But I'm not taking the amp to NYC by car nor by subway.
    NJ may be best option.
     
  18. CosmicRay

    CosmicRay Supporting Member

    That's what I'll do. Thanks!
     
  19. SirMjac28

    SirMjac28 Patiently Waiting For The Next British Invasion

    Aug 25, 2010
    The Great Midwest
    That would be very cool and when I was looking at buying one of these amps I always added $500 to the price no matter how great the seller said it was.
     
    bachlover and beans-on-toast like this.
  20. TRichardsbass

    TRichardsbass Banned Commercial User

    Jun 3, 2009
    Between Muscle Shoals and Nashville
    Bassgearu, Music Industry Consulting and Sales. Tech 21, NBE Corp, Sonosphere.
    Ray dont use current Ampeg guys. Totally different company now. Not a dis on them but Dennis is just as close and one of amplifications true legends.
     

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