Psst... Ready to join TalkBass and start posting, make new friends, sell your gear, and more?  Register your free account in 30 seconds.

Aguilar DB359 - internal trim pot?

Discussion in 'Amps and Cabs [BG]' started by todd 4ta, May 8, 2004.


  1. todd 4ta

    todd 4ta

    Apr 3, 2003
    Indiana
    I was swapping out the preamp tubes on my DB359, and noticed a small trim pot right between the two 12AX7 tubes.

    Does anyone know what this trim pot does, and how it should be adjusted? I can call Aguilar on Monday, but I have a hard time waiting......

    Thanks
     
  2. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    could be a bias adjustment trim for the power tubes.
     
  3. todd 4ta

    todd 4ta

    Apr 3, 2003
    Indiana
    Is that in addition to the two tiny bias adjustment trim pots on the back of the amp? Is this just a guess?
     
  4. I saw that too! Let me know what you find out ! :)
    I'm runnin' an RCA 5751 in v1,a sovtek 12ax7LPS in v2 and a Phillips 5814 in v3 and 4x6550we sovteks... :D ..it's great !

    JJ
     
  5. toniwonkanobi

    toniwonkanobi Supporting Member

    May 23, 2008
    Northern California
    Endorsing: 1964 EARS, LLC.
    anyone ever figure this out?
     
  6. toniwonkanobi

    toniwonkanobi Supporting Member

    May 23, 2008
    Northern California
    Endorsing: 1964 EARS, LLC.
    Update: I called Marco @ Aguilar Amplification and he gave me the skinny. Basically, there are three trim pots that are not considered user-servicable (i.e., you'll have to take it to your tech and have him/her mess with these). The good thing about these three little pots is that unless you change the type of preamp tubes used, you shouldn't have to mess with these little buggers. The bad news is that if you've already messed with them, or want to mess with them because you just like messing with stuff, you'll need an oscilloscope to accurately calibrate all three trim pots.

    Trim pot 1: with the amp facing you, this trim pot is in between V1 and V2. It controls the gain calibration

    Trim pot 2: this is the AC voltage balance or something...in between V2 and V3

    Trim pot 3: this is the only one that the average joe could try and mess with...it controls the level difference between the pre and post EQ DI levels (which should be close to equal anyways, unless you just want the post EQ level to be really hot or something...compared to the pre EQ).

    Hope this helps the other three DB 359 TBers out there lol ..
     
  7. Highpost

    Highpost

    Feb 14, 2011
    ny. nyc
    Thx.
     
  8. DJJazzV

    DJJazzV Gambling is illegal at Bushwood, sir... Supporting Member

    May 17, 2007
    New Jersey
    Yes, it does help. Thank you. I was getting ready to change the preamp tubes until I read your post.

    I did just have a fun time setting the bias on the power tubes though. The manual states to set the bias at .060. I checked them, and both bias settings were about .098! I guess that's hot. I fixed that right away. Both to .060 now. Simple.

    Does anyone have favorite power and preamp tubes that they installed in the Aguilar DB 359? Mine still has the originals, so maybe they should be changed. Maybe not, but it's always fun!
    Was there a standard brand & exact type for the 3 preamp tubes that were originally installed in this amp? I'd like to know if mine had been changed at some point, if so, perhaps the internal calibration may be off now?

     
  9. toniwonkanobi

    toniwonkanobi Supporting Member

    May 23, 2008
    Northern California
    Endorsing: 1964 EARS, LLC.
    np! :)
    here is some correspondence Dave B. and I shared when I was asking the same questions:

    [about preamp tubes cont'd]

    "Hi Anthony,

    We did use those JAN's in the very early days. We wanted to make sure that
    we didn't introduce any unnecessary distortion in the DB 680. We were
    getting GE tubes which were also very low noise. They are a little weak
    though, and you may be better off with a regular 12AX7, it's a matter of
    taste. Just avoid anything marked "high gain". "

    [preamp tube brands]

    "Hi Anthony,

    The last place we were getting tubes from was New Sensor (Sovtek). It's
    important that they are not miss-sized since they have to fit in a finite
    space in the chassis. You should check that they are not too long and get
    two matched pairs. You can use any 12Ax7 tubes; but I would avoid anything
    labeled as "high gain". Also, we used Chinese 12 AU7's, which at the time
    were better than the Russian ones.

    Hope this is helpful.

    Best Regards,


    Dave Boonshoft
    President
    Aguilar Amplification LLC
    599 Broadway, 7th fl.
    NY, NY 10025

    ph. 1(212) 431-9109, ext.11
    fax 1(212) 431-8201
    dboonshoft@aguilaramp.com"

    [power tubes]

    ... are re-branded Svetlana 6550Cs. Just get two matched pairs.

    Oh and as far as the power tube config goes...

    I am a circuit 'tard so I had to ask Dave about this... i wanted to know which tubes were the pairs. So if looking at the amp from the back, going from left to right, the pairs are 1 & 4 and 2 & 3. So if you need to replace one, replace at least both in that pair.

    Also note that the Svetlana 6550C's are a little longer than their Aguilar re-branded ones were back in the day, and thus, stick out a tad more ..so be careful.

    Hope this all helps!

    Edit: the first correspondence above mentions JAN tubes. Talking about NOS 5751's
     
  10. DJJazzV

    DJJazzV Gambling is illegal at Bushwood, sir... Supporting Member

    May 17, 2007
    New Jersey
    That is fantastic information! Thank you very much.
    Since the amp is plenty loud, and they bias fine perhaps I should leave the power tubes alone for now.

    I have the following 3 preamp tubes, and I'm guessing original. The amp is almost mint.
    Slot 1 (with the metal casing): Sovtek 12AX7WA
    Slot 2 (next to the metal casing tube): GE JAN 5751
    Slot 3: No idea. Not a mark on it. ??? I guess it's that Chinese 12AU7 mentioned.

    Maybe it's best to leave all of them alone. :)

    Thank you again.

     
  11. toniwonkanobi

    toniwonkanobi Supporting Member

    May 23, 2008
    Northern California
    Endorsing: 1964 EARS, LLC.
    Yeah man np! Honestly, I was always a fan of turning tube amps back to stock with the "stock" offerings (not to be confused with "NOS," since may amps never shipped with NOS tubes). I did that to my Eden VT300, Sadowsky SA200, Aguilar DB 750, and the Aguilar DB 359 I had for a while. Tube-rolling was never my thing, as I think it changes the character of the amp, which would take away from (IMO) what the original designers had in mind. Take the DB 750. Lots of bass audiophile guys would say swap a Telefunken into V1. I disagree -- why change the wooly nature of that amp? What is there to like about the 750 if not for that wooly tone, you know? If you want clean, get a Markbass haha.

    No but really, i understand why they do tube-rolling, as most stock tubes are crappy chinese or russian tubes that don't really sound all that special. I just don't practice that myself...

    Good luck buddy!

    BTW: you'd know if the power tubes were bad. I would go ahead and buy a new set in case one tube starts to go, you'll at least not have to wait a week+ in shipping transit times.
     
  12. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    just as a comment to this unless the amp has a bias pot for every two tubes there in no such thing as a "pair" in an amp with more than two tubes. In your example 1 & 3 would be as much a pair as 2 & 4.
     
  13. toniwonkanobi

    toniwonkanobi Supporting Member

    May 23, 2008
    Northern California
    Endorsing: 1964 EARS, LLC.
    Paul, I *believe* that is the case with the DB 359. At least, there were two dials one could turn. Does that seem right Paul?
     
  14. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    If there are two bias pots then it's logical to feed a tube on each side of the OPT primary from each pot. That way you do have "pairs". Similarly the SVT with its two pots can be considered in triples.
     
  15. toniwonkanobi

    toniwonkanobi Supporting Member

    May 23, 2008
    Northern California
    Endorsing: 1964 EARS, LLC.
    I figured as much. Thanks for the input Paul!
     
  16. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    A trimpot is not necessarily evidence that something should be adjusted. ;)

    When I worked at Sennheiser years ago an end user sent in a wireless mic for service. It appeared to turn on but put out no RF signal. I called him to find out what the symptoms were and how it had failed. The guy couldn't figure out why it didn't work--all he did was open up the handheld unit (the transmitter) and saw a bunch of screws that weren't tightened all the way down (the tuning slugs in the RF coils and transformers), so he took care of that. And the darn thing stopped working after that!!

    That was a time-consuming repair.
     
  17. DJJazzV

    DJJazzV Gambling is illegal at Bushwood, sir... Supporting Member

    May 17, 2007
    New Jersey
    I'll stick with that first tip. As long as I don't change the type of tubes, they should be alright. I'm not messing with the trip pots.
    Great story! Weren't the screws plastic? That should have been the first tip that they weren't really just screws.
     
  18. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    The "screws" that he said weren't tight and needed fixing were threaded ferrite slugs inside the little RF transformers and coils. Ferrite is essentially iron powder mixed with a binder and molded into shape. The Sennheiser transmitters back then used direct FM on a lower-frequency oscillator, then a series of several class C frequency multipliers to arrive at the carrier frequency. Each multiplier used an RF transformer as part of its tank circuit and to couple the signal to the next stage.

    The ferrite slugs were brittle and couldn't take much torque. If a little piece happened to chip off around the slot, it wasn't too bad, as the thing could still be tuned--it just wasn't as easy to turn the slug with the little non-ferrous screwdriver. But a couple cranked-down slugs in this guy's unit were cracked badly and had to be replaced. And cracked tuning slugs aren't easy to remove.

    Sometimes after tuning and aligning a wireless mic system I would put a small piece of beeswax on top of each tuning slug and touch it with the soldering iron so it melted and covered the top of the slug. This would help secure the slug and keep vibrations from causing to to turn. A secondary benefit was that it would also conceal the slot from people with an adventurous screwdriver. It could've saved this particular end user's company at least a hundred bucks, I think.
     
  19. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    +100000 Amen to that!!!!
     
  20. Highpost

    Highpost

    Feb 14, 2011
    ny. nyc
    I am interested in tube rolling. I still have the original stock tubes. Mr . D B was surprised when I brought my db 359 in once to fix a pico filter . He said my 359 was in excellent condition. I think these units usually came in banged up. I wish I knew how many of these units Aguilar built. I will wait till these tubes act up and then change them. I remember they carried the replacement sets on their website once.

    A little off topic , I recall reading something about how the 12 au tube was eventually removed from the preamp section to reduce noise.? Or that 12 au tubes are noisier than other tubes. ?

    I hope one of you guys can make a suggestion after you have tried a few different tubes. I did once ask Mr. Avenius when do i have to change the tube on my db900? And he answer. "Probably never". I didn't dig deeper. I would like to try different tubes in my db 900 first and start from there. If I find something sweeter for my db900 I'll put that tube in the db 359.