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Thread: JBL 6230 service manual?

  1. #1
    Senior Member Russellc's Avatar
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    JBL 6230 service manual?

    Hello,
    I have the above amp and owners manual, which includes a schematic but no mention of what the bias should be set to, or I am so stupid I missed it. Is there a seperate "service manual" that I can aquire?

    I only saw the bias adjustments on the schematic, is there a way to adjust DC ofset short of replacing input devices?

    Has anyone experimented with tweaking this amp for "home" use, like increasing supply capacitance, replacing rectifiers with freds or schotky devices, or other such audio nervosa?

    It is an enjoyable amp as is, but when I put my P-P 6550 amp back in the chain, it is so much more transparent it is ridiculous! Do I just need to enjoy it for what it is and shutup?

    Thanks in advance,

    Russellc

  2. #2
    Dang. Amateur speakerdave's Avatar
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    In my experience the 62xx series of amps are good, listenable amps, but I do not look to them for the most high definition reproduction. I've heard the 6230, 6260 and 6290. I have not tweeked my amps, all used, so it is always possible they could use some attention. However, the biggest one, the 6290, to me sounds the most musical used full range (but it has fans).

    I made a comparison similar to yours at one point with a 6260, an Audio Research VT60 and a McIntosh MC2200. The 6260 had the tightest bass reproduction, the VT60 was cleanest and most enjoyable to listen to overall, but the MC2200 was the best compromise if I wanted to have an amp that would support an occasional loud session, which the VT60 would not do. In fact I used the VT60 most of the time.

    I will be using a pair of 6260's to power the bass in a biamped dual woofer design. It is just the amp for that application because they can be switched to dual mono, using one input, so each of the four woofers will have its own channel, so I do think they are useful amps. That having been said, I do plan on converting eventually to four channels of Citation II. Anyone who thinks tube amps cannot make bass needs to hear that amp. Solid state bass power is 'tight," yes, but to me it is too dry much of the time. I should add, though, that woofer type and enclosure type and tuning are factors in this. But I prefer the Citation II to 62xx for the transition into the vocal range, which my woofers will be covering. And of course you need to be able to operate within the power limitations of (sane) tube amps. I figure 240 watts on woofers with no crossover insertion loss will be plenty in my listening room and neighborhood.

    The 6260 and 6290 have fallen out of favor as SR amps because they are old, and they are heavy, but that weight is in a power supply so substantial, that the power rating for lower impedance rises proportionally. You can't say that about very many amps, so I think they are a bargain for good, basic amplification with good headroom. The 6290, besides being musical, has true grunt and will produce 600 watts per channel into 4 ohms, or 1200 strapped into 8. For me, they offer a low-dollar option for experimenting with bi- and tri-amping. They can also offer satisfying reproduction for many over the long term. I too think it would be great if some knowledgable person would look into using them as a platform for modding up a refined home audio power amp.

    David

  3. #3
    Senior Member Russellc's Avatar
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    Thanks for the response, I hope someone has the answer about whether a seperate "service" manual exists, or how the bias is set on the amp.

    Dont misunderstand, I love this amp for what it is and intend on aquiring a 6260 as well. Jbl/urei stuff is VERY well designed and the amp appears bullit proof as well as way easy to work on. The compromises made in this amp were likely for a very good reason, and I certainly am not qualified to second guess them, and I dont want to substitute reliability for some "tweak" of the week. Just wondering if anyone had tinkered with one for these purposes is all.

    Like a lot of amps, it does get more transparent as it stays on longer, and for the money invested is definately a winner. Anyone wanting to play with bi amping could do a LOT worse for a LOT more money. Last night I was listening to it while watching TV, with A7s as the "home theatre" system...very impressive...this small amp really has an iron grip on the altecs.

    My tube 6550 amp produces wonderful bass, but its seperate power supply is larger than most entire power amps, with hugh 1400 mfd 450 volt caps!

    I cant wait to find the matching 6260. The 6290 isnt off my list, but mostly overkill for my purposes and there is that fan, but it is dual mono all the way through, unlike the 6230, which doesnt appear to even use dual rectifiers.

    Russellc

  4. #4
    RE: Member when? subwoof's Avatar
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    end the madness...!!

    There is no magical *tweak* that will make the amp more "transparent" and changing the diodes to "shottkeys" or adding PS caps won't make it more (insert irreverent marketing word here)...

    Like Steve martin said about a fine wine, " flaccid yet absurd "

    So much of the "high end" audio world is bent on making a 1% improvement in your listening experience for a modest 500% improvement in your financial outlay....

    The noise floor in your listening experience could be improved by that same 500% by simply adding weather stripping around the window to keep the outside noises outside.

    Anyways, there is no separate service manual for any of the 62XX series and the bias info is already there.

    For ANY ( read: professional ) class AB amplifier that uses standard bipolar outputs the bias is measured across the base to emitter junction of any one of the output devices. Set the bias pots for a reading of .350V and you will be just fine.

    The higher the bias, the less distortion in MOST cases BUT it's also the reason amplifiers get damaged. When the bias is too high, the entire chassis gets hot and there is less room for thermal buildup before something bad happens. If the bias is too low you have more distortion due to the crossover notch BUT that is still magnitudes lower than almost all other "inaccuracies" combined...

    Spend your money wisely..power is good.

    And that 6290 fan can be made quieter than a kitten fart.

    sub

  5. #5
    Senior Member Russellc's Avatar
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    Thanks subwoof,
    Thats what I figured, searches finding no one doing this here, likely no one is doing it anywhere for the reasons you stated.

    Thanks for the bias info, and the heads up on the 6290 fan noise/lack of noise. By the way, I received the caps today and will install tonight.

    Russellc

  6. #6
    RE: Member when? subwoof's Avatar
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    polarity

    *do* note the polarity for all 5 of them...otherwise it's a test of your saftey glasses. It's a lot easier to snip + destroy the old caps and remove the leads one at a time ( you will NOT save them ).

    Caps are cheap. circuit boards are not.

    When I *recycle* these amplifiers into commercial apps, I set the bias at .250

    For home use I use .350

    For future service call income, I set at .450 like the manual suggests.

    Above .500 we have ignition / liftoff


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