Hammond L100 AO-43 amp project help?

For those building and repairing amps on their own. Learna and share ideas.

Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Sun Feb 01, 2015 5:50 pm

PeterS wrote:Cool.

Have you seen the Duncan Tone Stack calculator? It's interesting and educational to play with...

http://www.duncanamps.com/tsc/


I downloaded and installed it and wow, what a sweet tool. The tone circuits I added were lifted from an article I found about another fellow who converted a Hammond amp chassis so I was hoping they would be a great starting point...which they are. I am very pleased with the range of the controls. However that said, I will now be able to alter resistor and cap values and "see" the results instead of actually having the solder & unsolder components...sweet! It appears the circuit that I plagiarized and added to my unit is the circuit shown on the "James" tab with just a couple of value differences.

My son was home for the weekend from college and played the sh*t out of it last night and it sounded terrific. I did notice that now when I turn up the reverb above about 75% there is a low level hiss. Does anything come to mind there?

Thanks for all the help!
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Re: Hammond L100 AO-43 amp project help?

Postby PeterS on Sun Feb 01, 2015 6:06 pm

Does anything come to mind there?


The signal from the reverb tank is small, so there's a lot of gain in the recovery amp. Try changing the tube. If it's a frying bacon type hiss it could be the plate resistor in the recovery amp.
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Sun Feb 01, 2015 9:01 pm

PeterS wrote:
Does anything come to mind there?


The signal from the reverb tank is small, so there's a lot of gain in the recovery amp. Try changing the tube. If it's a frying bacon type hiss it could be the plate resistor in the recovery amp.


Looking back at the schematic, it would seem that V7 (12bh7) is the reverb recovery amp and then the plate resistor to check would be R311 then right (a 1K 1/2 watt going to the choke)? Or should I be checking R317 related to V6 (12AX7 pin 1)?

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Thanks
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Re: Hammond L100 AO-43 amp project help?

Postby PeterS on Mon Feb 02, 2015 1:10 pm

R317 is the one. You could also experiment with upping C304. Also try changing V6, the 12ax7.
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Mon Feb 02, 2015 9:25 pm

PeterS wrote:R317 is the one. You could also experiment with upping C304. Also try changing V6, the 12ax7.


R317 read a little high at 125K instead of the 100K spec so I replaced it with a new 100K 1/2 watt. I also swapped in various pairs of 12ax7s into V6 & V8 but there is no difference. Tried JJ's, TAD, Penta Labs, Sovteks and Mullards so it appears that neither the tubes nor the resistor alone are the cause. Maybe it is just going to be this way as you said it is a very weak signal and this is a low power amp so I have it up on the volume pretty high as well (about 7 or 8).

I haven't yet swapped in different values for the C304 1200pf cap but will and perhaps that will help. I can live with it as it is sinces the reverb comes on well at 1.5-3 on the a scale of 1-10 and doesn't begin to fry bacon until about 7 :-)

Ummm...I'm making myself hungry as everything is better with bacon :laff:
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Tue Feb 03, 2015 2:51 am

Housekustoms wrote:
PeterS wrote:R317 is the one. You could also experiment with upping C304. Also try changing V6, the 12ax7.


I haven't yet swapped in different values for the C304 1200pf cap but will and perhaps that will help.


Shoot, I put in a .06uf and it was noisier yet. Don't have anything smaller evidently so I can't try going the other way quite yet. Thought I had at least one 12AT7 to try too hoping that might quiet it down with the reverb turned up and yet not kill my overall gain/volume too much but I don't have even one. 12AU7's I have but they stoled all my volume.

Have to try again once I get the some more variety of parts :dumass: :dumass: :dumass:
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Wed Feb 11, 2015 2:52 am

Hi again,

I still haven't solved the reverb hiss (frying bacon) but I have made further changes and holy crap you should hear this Hammond scream now. I made some more changes and freed the thing up and it is really is becoming quite a guitar amp now. Easily twice the volume as before and clear as a bell. Seems more like 40watts although I don't claim to be a good judge of that. I added a reverb presence/brightness control and a mild overdrive control so I now have these controls.

Volume
Gain
Bass
Treble
Reverb Level
Reverb Presence/brightness (I plan on added a 6-way rotary with increasing capacitance to further add choices in this one)
Overdrive (and it goes from 0 to dirty)

Wow I am quite impressed with it. I invented virtually nothing here so I don’t personally take the credit. But things suggested by forum members PeterS, wiring suggestions and advice by Unit_1, tone controls that I plagiarized from the Lil' Tiger amp by G. Forrest Cook and mods from Kon Zissis in Australia on the Hammond Organ Forum including the overdrive and general modifications to free the Hammond circuitry to be more of a guitar amp have really made a complete facelift of this original circuitry.

It is a whole different animal now. I am still messing with subtle changes but will post a revised schematic once I am done messing with it and ready to commit it to a nice cabinet. Played through the original 12" alnico pair of speakers from Hammond that lived their life coupled to this same chassis (one bass and one treble) it really has a wonderful tone. Smooth as can be but it barks when you want it to. The Zener diode overdrive creates a distortion reminiscence of early Cream albeit at reduced volume. Haven't found a way to reduce the "reduction" in volume that occurs since so much signal is clipped by the Zeners when it is cranked up.

Overall however I can say without hesitation I am more than pleased with the results of this experiment. Many thanks to all the contributors both active in this forum as well as those who've silently contributed thanks to Google :-) I did this as a hedge against senility as I have fewer weekends ahead of me than behind me and it has been very satisfying so thanks again to PeterS and Unit_1 without whose help I could not have made it this far. I'll post a schematic once I have one in hand and eventually pictures of it in its cabinet...Mullard EM87 magic eye tube included :-)

Thanks!

:not_worthy: :not_worthy: :not_worthy:
Last edited by housekustoms on Tue Aug 04, 2015 6:15 am, edited 2 times in total.
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Re: Hammond L100 AO-43 amp project help?

Postby Unit_1 on Wed Feb 11, 2015 4:36 pm

:highfive:

another successful multi-member project!!!!! :cheers:
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Re: Hammond L100 AO-43 amp project help?

Postby PeterS on Wed Feb 11, 2015 11:43 pm

Yes, good stuff. Wish I'd known about the MAGIC EYE tube back when I was building amps...
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Fri Feb 13, 2015 3:30 am

Got the EM87 circuit wired and working after a couple of snafus. Still have to build a bracket to hold the socket and tube so I have some flexibility in where I end up placing it once the whole deal is put in a cabinet. Figured I should start out with it being independent from the chassis since it isn't likely that it will be able to be seen with the chassis placed as I intend to do (much like a 5e3 for instance).

Here is a brief video of it in operation. Seems to work rather well. Looks even better in person as the video tends to saturate the image a bit.

NOTE: This was just my simple test...please excuse the demo as arthritis prevents me from having the flexibility my fingers once had...and I was never particularly talented in the first place...I make 'em but no longer play them. I was lucky to get this much on video :-) I'll have my son exercise the unit when he is home this weekend and will post something that will be worth listening to.



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Re: Hammond L100 AO-43 amp project help?

Postby Clanger on Fri Feb 13, 2015 6:54 pm

Well done house kustoms,

I think this is a very inspiring thread;

- Shows the forum at its best;
- Advice humbly sought , advice freely given
- Resulting in a totally one off amp, much more interesting than any clone project.
- Interesting features like the selection of tone section design and the magic eye.

Kudos to all involved!
"Please feel free to copy this information and use it to make friends and influence people at your favourite social gathering" - Doyle
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Fri Feb 13, 2015 8:15 pm

I couldn't agree more nor could I have ever done this without such great forum participation and Google! :not_worthy:

Here is the bracket I made to mount the Magic Eye tube so that once I mount the chassis & reverb into a cabinet it can be adjusted to show through a slit window I'll build into the front of the cabinet.

Image Click for full size image

Image Click for full size image

I'll draw up the schematic noting the changes to the original and get that posted soon too.

Thanks again!
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Re: Hammond L100 AO-43 amp project help?

Postby Unit_1 on Sun Feb 15, 2015 12:07 am

Hey Steve,

I got the really clean ao-43 from the bay today. *really clean*

I got this nifty set of pliers designed especially for removing/replacing power cords, double action so you barely have to squeeze and POP out they come. The edges are curved so it fits right into the slot with perfection. Love it!!!

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I'm going to probably use this one as the first Matchless Lightning clone 'cus this one still stinks of fresh spray paint

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And of course, greenie caps for a green board!

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Last edited by Unit_1 on Mon Feb 16, 2015 4:22 am, edited 1 time in total.
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Re: Hammond L100 AO-43 amp project help?

Postby PeterS on Sun Feb 15, 2015 12:50 am

I have a pair of those awesome Heyco strain relief pliers too. I wonder if mine's a different size - the handles are red.
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Sun Feb 15, 2015 12:55 am

I will find and get a pair pronto. I find few things as frustrating as trying to put those fittings either in or out and get sufficient compression to be tight on the cord and not visually booger up the cord or the fitting at the same time!!

And wow, that chassis and tranny look like new :-)

Thanks!!
Last edited by housekustoms on Tue Aug 04, 2015 6:17 am, edited 1 time in total.
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