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Thread: I need help with a L-100 Hammond amp

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    Question I need help with a L-100 Hammond amp

    Hello all, I am new to this blog and amp modification and electronics in general. I have been modifying hammond amps to work as my main amps for my keyboard set up (a Nord Electro and Nord Rack 2x). The Nord sounds sooooo much better through tube amps!!!

    So my question, I recently plugged in a stock L-101 (AO-43) rev/power amp and it popped my circuit breaker. I do not know how to test a power transformer to see if it is no good and need to get this amp back up and running asap if at all possible. The only replacmen I could find was the TrekII solid state replacement (replaces the refractor tube & power tranny) but it is supper expensive. Any suggestions on replacement tranny's or how to check to see if it is the power tranny that is bad?

    Also dose anyone have schematics to modify this AO-43 to rune 2-6l6's, I'v heard that you can get around 40watts with this amp modified to run 6L6's.

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    Remove C314 (across the primary) and the rectifier (5U4). Does the breaker still trip? If not, the PT is probably ok. I strongly suspect bad filter caps (C316-319) or a bad 5U4.
    No way to run the amp with 6L6's. You'd need a new PT, new OT, different tube sockets , etc.

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    Thanks for the info, I appreciate it a bunch. I will check this Sunday and see what happens. I hope its a cap or rectifier, replacing the PT would be expensive!

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    Update: I just removed the rec tube and C314 plugged her in and the breaker did not trip. Im going to order new can caps, 5U4 and see what happens. Thanks a ton for your input and help!

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    Yep, seems you're on the right track. Keep us posted.

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    I'v heard that you can get around 40watts with this amp modified to run 6L6's.
    The power of each power amp depends from the voltage and current MT from one side and the raa OT and the power tubes on the other side.
    At each power amp when replacement power and output transformer, and electrolytic capacitors eventually adapt for new voltages, will get more power. Excitation from the power amp mostly will be sufficient
    More power = higher current through the MT and OT. Thick wire, MT and OT core area must be adapted to increased power. Existing main and output transformer less power, will hardly do the job in the modification that you plan.
    The trouble this the modifications is that the main and output transformer are more robust, or possibility of their installation to the existing chassis modest dimension.

    Hammond schematics
    http://www.captain-foldback.com/Leslie_sub/leslie_schematics.htm
    http://www.captain-foldback.com/Hammond_sub/hammond_schematics.htm

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    Last edited by vintagekiki; 07-11-2010 at 10:10 PM.

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    I was unable to find can caps that match the exact specs but did find 50/50@500v JJ, Richey GOLDS and F&T caps available. Would the 50/50@500v work. The schematics call for a 50/50@450v. Would I need to run a bunch of diodes in series to drop the 500v down to 450? It seems like I'd need a crap load of diodes since I've heard they only drop voltage by like .7?

    Thank you guys for your help.

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    Bunch of diodes (1N4007) in series аs replacement rectifier 5U4 will not drop +HV voltage from 500V to 450V. Substituting rectifier (5U4) with diodes 1N4007 get a higher + HV. Does the first electrolytic capacitor adapted to the new voltage?

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    A capacitor of higher voltage rating than the one called for will work just fine. The rating just tells you how much voltage can be safely placed across the part. In fact you're probably better off with the higher rating because the AC line voltage from the wall socket tends to be higher these days than it was when the amp was made.

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    -tb

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    I am not actually going to modify this amp. I am buying new can caps because mine are no good. I am also replacing the 5U4. Thanks for the help!

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    Good to know. I just placed an order for new can caps and 5U4 for this amp. I should have it all mid next week. I'll post an update, hopefully it will say that the amp works again and sounds great!

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    So I replaced the can caps and rec tube and the amp sounded amazing...for a while...
    I replaced R336&337 3.8 ohm resistor and 10k pot and she purred once again. I am however not getting full sound. I am in the process of ordering new caps/resistors for a thorough rebuild. It will be worth it, these amps sound great with my Nord's. If anyone play's a Nord, do it a favor... run it through a nice tube amp. I just got an AO-44 reverb amp and it is sweeeeet. Just remove the volume compression circuit and your pretty much good to go, I think I'm going to have it drive my Leslie type 25 booster amp. Should be nice.

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    Update: So what happened was the new JJ can cap's I bought were not the correct physical size and therefor were creating a wired ground loop that was somehow cutting the signal I was getting from the amp because of the way I had to mount them. I ordered a few can cap clamps and with the help of some electrical tape, I was able to remount the caps, so that the ground of each cap was bussed with the tube sockets but did not contact the chassis. Sure enough the amp is back in action, man this amp sounds sweet!

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    Hi, I am also having problems with the L100 power amp tripping the circuit breaker when turned on. I removed the 5U4 rectifier but
    none of the tubes lit up and when the tonewheel generator switch connected it just tripped the breaker. Don't know about the C314 can't see it on the chasis.
    All wiring checked out okay. The power chord has been replaced as the old one had deteriorated (its over 45 years old). I had used the white swell pedal RCA for line out through a distortion pedal when it failed. I don't suppose that might have caused it to fail?? Its DIY as there are no Hammond techs to speak of here in Oz . I'm not really tech savvy, I'd rather play 'em than fix 'em. But if there is a simple fix or trouble shoot I'd appreciate the help. It would be a pity to throw the beast out in the trash.

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