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Thread: Hammond L-100

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    Hammond L-100

    Hey y'all. Here's a "conversion" of a Hammond L-100 amplifier that I bought on eBay. I haven't done anything really major to it except for adding controls and a reverb tank. It sounds good. It's loud, but probably not as loud as it should be.

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    I'd appreciate any suggestions or advice on stuff that could be adjusted. In particular, I'm not quite sure what's up with the stage just after the reverb tank.

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    What ohm speaker are you using and is the NFB resistor of the correct size for the speaker you are using? The stage after the reverb section should be your phase inverter.

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    Hammond amp are a conservitive design and are not designed to add any colour of their own. The tubes are just coasting along and not driven hard. see B+ voltage. Power Supply sag, power tube saturation, and preamp tube distortion are harder to get. They make a very good Jazz tube amp but they are no Mini-Marshall, Vox or Fender. Beware of claims of sellers on ebay.

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    Quote Originally Posted by Cool_Ray View Post
    Hammond amp are a conservitive design and are not designed to add any colour of their own. The tubes are just coasting along and not driven hard. see B+ voltage. Power Supply sag, power tube saturation, and preamp tube distortion are harder to get. They make a very good Jazz tube amp but they are no Mini-Marshall, Vox or Fender. Beware of claims of sellers on ebay.
    Thanks for pointing me to the power supply. I'm reworking it to give 300V to the preamp. (BTW, I didn't buy this because of any eBay seller's claims.)

    I'm puzzled by the choke and 50µf cap on the plate of the 12BH7 reverb driver. Can anyone shed any light on this design? What would happen if were changed to a simple resistor and coupling cap?

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    I'm pretty much declaring victory on this project, electronics-wise anyway. Retooling the power supply rail and a few other tweaks won me a bunch more gain. It's a monster now! Kinda Vox AC15ish, and the reverb is pretty sweet. (BTW, it has all the original Hammond-branded tubes.)



    I'll post pictures when I get the cabinet made.

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    Senior Member ThermionicScott's Avatar
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    Pretty cool. I have a working Hammond L-103, and it sounds great, especially the reverb. Like you're playing in a big church or something.

    - Scott

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    this is the coupling cap to the reverb coilsspring system , it's cheaper to use a big cap then a transformer and it also cuts out the very low frequencies not going to the reverb set .. take care it has some very high DC tension of around + 300 Volts , that's why it sits in a black carton protection !

    any more problems with the l100 amps ?? mine delivers around 40 watts when modified with 2 x 6L6 all the parts in Hammond amps are very conservatively used you can get easaly the double power out of the suply tranies !

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    if you would swop the coil with a resistor you would destroy the whole setup , the coil is there to avoid very low bass frequencies to get to the reverb , they would spoil your sweet reverb sound by rumbling noisess ! remember for high frequencies a coil is a very larg impedance , for lows is it's a shortcircuit.

    all the best from belgium's Classic Hammond Tonewheel Restoration Service (regstd)

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    Noodle of Reality Steve Conner's Avatar
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    Likewise, the choke in the reverb driver plate circuit gives more output than a resistor would.

    You can think of it as a reverb drive transformer with no secondary.

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    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    head box pix

    Thought I'd top off this thread with a couple of pictures of the amp with cabinet.

    If I had it to do over, I'd make the box an inch shorter and an inch less deep. (it's 10 1/2 by 10 1/2 by 18 1/2.) I was probably overly concerned with keeping the reverb tank away from the power transformer. Oh well, I think it's okay though. Now I just need to fashion some kind of back panel for it.
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    Last edited by otto pärt; 01-25-2010 at 12:22 AM.

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    Quote Originally Posted by otto pärt View Post
    <snip>I'm not quite sure what's up with the stage just after the reverb tank.
    Presuming you are talking about that 68k feeding the cathode, it looks to me like it is a way of having a lower unbypassed cathode resistance while still being able to bias the tube with cathode bias. The result is that the stage gain is higher than it would be with an unbypassed 1.5k (say). It raises the Thevenin source voltage for the cathode resistor from 0V to something higher so that a lower Rk can be used to achieve a given cathode current.

    That's my take on it anyway.

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    Quote Originally Posted by RudeBoy View Post
    Presuming you are talking about that 68k feeding the cathode, it looks to me like it is a way of having a lower unbypassed cathode resistance while still being able to bias the tube with cathode bias. The result is that the stage gain is higher than it would be with an unbypassed 1.5k (say). It raises the Thevenin source voltage for the cathode resistor from 0V to something higher so that a lower Rk can be used to achieve a given cathode current.

    That's my take on it anyway.
    Thanks. That makes sense, I think. But why must the cathode resistor be small and unbypassed in that circuit?

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    just got one of these amps, looks likes its going to be fun!

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    L100 with reverb conversion

    I have an L100 I just purchased on e-bay. I'm looking at your 2nd and final schematic, but is the 3.9 ohm 1/4 resistor really in series with the 15W 250 ohm one? This doesn't make any sense--the 1/4 resistor will act as a small fuse for the 15W power resistor.

    Best regards,

    Dave Adams

    (a.k.a. swaptronics)

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    Supporting Member loudthud's Avatar
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    I just did the math. Surprise, the 3.9 ohm reaches 1/4 Watt at 0.253 Amps and at that current, the 250 ohm is 16 Watts. Be sure to use a flame-proof resistor.

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    WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
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    Hey There,
    I just got one of these amps myself and was planning on trying out otto's schematic...
    Couple quick questions...
    Has anyone found a 3.9ohm/.25w Flameproof anywhere in stock? It seems to be impossible to find...
    Also, what are people using for the multi-section capacitors? Seems like a 50/50/50/50 450V/500V is impossible to find as well...

    Thanks in Advance!

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    Member Ran Randle's Avatar
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    Quote Originally Posted by RedRabbit View Post
    Hey There,
    I just got one of these amps myself and was planning on trying out otto's schematic...
    Couple quick questions...
    Has anyone found a 3.9ohm/.25w Flameproof anywhere in stock? It seems to be impossible to find...
    Also, what are people using for the multi-section capacitors? Seems like a 50/50/50/50 450V/500V is impossible to find as well...

    Thanks in Advance!
    Found this one:25W 3.9 ohm 3R9 Aluminium clad Resistor 25 W Watt x 1 | eBay

    I used a pair of 33uf 450v caps as a replacement for the original can caps in a plexi 18watt clone conversion, it worked well. I've also reused the original can caps 2-50+50/450v with no issues. I guess it depends on how dried out they are and what condition they're in, hit or miss.

    I've found Partsexpress.com is a good source for caps and fleabay for the odd stuff.

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    Sorry to resurrect this thread. I have a couple of questions about your build if you don't mind

    I bought an old L-122 (I'm aware that the amplifiers in these organs were very similar to the L-100) and I'm 'converting' the reverb section of the amp to a stand-alone reverb unit and will later build an AC15 type of thing with the rest of the parts (might also try and 'convert' the phasing vibrato to a stand alone unit later on if its viable).

    My questions concern the reverb stages of your build.

    Firstly did you add in the cathode bypass cap on the parallel 12BH7 stage, or was it stock in your amp? I understand that it would lead to more gain. If you did add it in, how do you like the results? I'm considering adding a switchable cathode bypass cap to mine, as mine just has the 390R resistor.

    Secondly, what is the frequency response of your reverb signal like? Is it not too boomy with the 50uF cap? I've tested out my circuit already and I find that it has a little too much bass, for my tastes at least.

    Thirdly, do you know what the current requirements of the 12BH7 stages are, more or less? I've been trying to map out a power supply circuit, but when trying to do the calculations for the plate current of the 12BH7's, I hit a snag, as the plates are choke loaded. Apparently the correct load curve for this is an ellipse, and not a lot of fun to draw. I read somewhere that when doing the calculations for this type of arrangement, one should assume the plate load to be more or less equal to the resistor going to ground before the reverb pan (220k, ie 110k for each triode). Using these values in my calculations I've worked out the plate current to be approx 3mA per triode, however I believe that this is grossly inaccurate. Someone also posted on another forum that the total plate current for parallel 12BH7 stages should be around 20-30mA which I believe to be closer to the mark. Does anyone know how to do these calculations?

    Thanks,
    Jono

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    Quote Originally Posted by makepeace View Post
    Sorry to resurrect this thread. I have a couple of questions about your build if you don't mind

    I bought an old L-122 (I'm aware that the amplifiers in these organs were very similar to the L-100) and I'm 'converting' the reverb section of the amp to a stand-alone reverb unit and will later build an AC15 type of thing with the rest of the parts (might also try and 'convert' the phasing vibrato to a stand alone unit later on if its viable).

    My questions concern the reverb stages of your build.

    Firstly did you add in the cathode bypass cap on the parallel 12BH7 stage, or was it stock in your amp? I understand that it would lead to more gain. If you did add it in, how do you like the results? I'm considering adding a switchable cathode bypass cap to mine, as mine just has the 390R resistor.

    Secondly, what is the frequency response of your reverb signal like? Is it not too boomy with the 50uF cap? I've tested out my circuit already and I find that it has a little too much bass, for my tastes at least.

    Thirdly, do you know what the current requirements of the 12BH7 stages are, more or less? I've been trying to map out a power supply circuit, but when trying to do the calculations for the plate current of the 12BH7's, I hit a snag, as the plates are choke loaded. Apparently the correct load curve for this is an ellipse, and not a lot of fun to draw. I read somewhere that when doing the calculations for this type of arrangement, one should assume the plate load to be more or less equal to the resistor going to ground before the reverb pan (220k, ie 110k for each triode). Using these values in my calculations I've worked out the plate current to be approx 3mA per triode, however I believe that this is grossly inaccurate. Someone also posted on another forum that the total plate current for parallel 12BH7 stages should be around 20-30mA which I believe to be closer to the mark. Does anyone know how to do these calculations?

    Thanks,
    Jono

    i used 1/2 a 12au7 insted of the 12bh7 in my Hammond L122 reverb amp mod .. There are a couple thing on my schematic that have changed . the tube 1/2's that say 12at7 are actually 12au7. R9 1meg has been removed, R12 & R13 are 100k and i have a 380ohm bais resistor for the EL84's.
    Attached Files Attached Files

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    Last edited by baddog; 05-20-2013 at 04:08 AM.

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    Below are pictures of how I mounted the pots and the standoffs for the board where purchased at radioshack. The 2x10 cab is an old Kalamazoo Bass cabinet that i picked up a few years back. The amp fit in it perfectly and sounds great. The reverb is classic hammond .... nice








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    Member Ran Randle's Avatar
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    Lightning copy

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    organdonor amplification

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    Traynor coupled 12AX7's to Reverb springs through a .1uf capacitor, (high impedance primary 2250 ohms). I've used that method many times.
    Check out Traynor Studio Mate YGM-4 for example.

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