Fender 300 Bass Slimline

Discussion in 'Amps and Cabs [BG]' started by mouthmw, Jan 29, 2015.

  1. mouthmw


    Jul 19, 2009
    Does anyone have any experience with those amps?
    These are made 1980-1982, and are if I'm not mistaken 300W solid state amps, rack system.
    I might borrow one from a local guy to test it out on a gig (through a GK NEO 412) in a few weeks.
    Until then, it's REALLY hard to find any info on those. I guess they weren't very popular.

    My guitarist does amp/electronics repair and he had this one serviced, he's really impressed with the quality though and likes the tone a lot. I still haven't tried it though. Thoughts?

    They don't go for much used either:

  2. mouthmw


    Jul 19, 2009
    Bumpety bump?
    Linnin likes this.
  3. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    They didn't sell that well, I've seen very few here in the USA (in Croatia it must be super rare!) and never played through one. It was an expensive amp at the time.
  4. mouthmw


    Jul 19, 2009
    Yea, not very popular. I have seen one in classifieds near here though, and they don't go for much used (was 300 Euros + it came with a 210 or 212 cab).
    Oh well, I might test one on a gig, see what it does.
  5. Linnin


    Jul 19, 2012
    Linningrad, Earth
    I'll bet it sounds great! If you have good ears and know what you're doing EQ wise, it appears to have a lot of tonal flexibility available.
    mouthmw likes this.
  6. I have got one on my repair bench right now to restore it. Our band's bass player and friend had one and he is the first owner.
    It seems to be fenders first solid state amp and they were quite expensive in the 80's according to him.

    Sadly, this has been the second time for him he has shot his JBL 2204 bass speakers due to power transistor burn out causing DC on the speakers.

    I emailed Fender customer support for the schematics and owners manual and got them one day later in my mailbox.
    The power amp schematic is much alike the Harman-Kardon Citation circuit and uses the same RCA power transistors (unobtanium)

    So far the following issues were listed:
    3 of the 12 power transistors short circuited. complete shortcut between all pins. (RCA 1BQ5 1BQ9)
    the two driver TO66 2N3584 and 2N6211 PNP/NPN driver pair dead.
    RCA29B bias transistor also dead.

    The power transistors are mounted on a aluminum cooling block using special TO3 sockets.
    These sockets are mounted on PCB mounted turret shaped sockets.
    IMHO these PCB turret sockets are very fiddly and prone to develop bad electrical contact. So I desoldered and junked them all and soldered the sockets directly to the PCB.
    Power transistors replaced with a set of 12 fresh MJ15024 and a MJE15032/33 PNP/NPN pair for the drivers.

    Also the 2 large power caps valued 22.000 uF @ 80Volt measured 5000 uF with my B&K ESR Cap meter ESR was about .120 ohm.
    So they will be replaced if the repairs proved to be successfull.

    I'll also add some DC protection circuitry to prevent future catastrophes :p

    The last time he used it with that 2x15" JBL dead coffin speaker cabinet, it sounded deep and loud (jazz bass on the input)
  7. PaperbackRyder

    PaperbackRyder Gold Supporting Member

    Apr 21, 2007
    Maynard, MA
    I had one of these way back. Had a matching 2x15 (sealed) cab as well. Liked the cab ok, but the head was a real pain in the ass. Twice had the same issues noted above; failed power transistors. As my only rig, I couldn't deal with it. My band started to make some money so I sold it to a guy who has hated me ever since. I got me a 70's SVT with two 8x10 cabs for like $700. Sweet. Wish I could do that again!
    If Marcel's fix makes it reliable, then good on him.
  8. I think these are the suspicious parts making bad contact with some of the power transistors.

    The PCB fits on it using the TO3 sockets as a big connector. But they do not make good enough contact IMHO

    Here an overview of the PCB and the cooling block
    and an inside view of the whole shebang
  9. mouthmw


    Jul 19, 2009
    It sounded great! I just might pull the trigger on it. I'm not an amp/electronics expert, but I showed this thread to my guitarist who is extremely savvy in this area, being his hobby and an extra income. Anyways, he didn't notice any problems with the power transistors and he doesn't agree with all of your techniques MarcelB (using ESR Cap meter on those value caps is what I remember him strongly disagreeing with). Oh well. The amp had incredible power because of the huge transformer, very direct, very focused but warm and clear tone. Awesome pair with my GK NEO 412.
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