Hello Roly,
      I put a schottky diode in series with D2 as I thought that was more towards the end of the circuit. It is
exactly the sound I was hoping for. I can only try to explain it by saying, it took away the solid state brittle
sound and made it sound fuller and more resonate if that makes any sense. I cannot believe the difference
the 12" speaker and one diode made. Now I am going to do something very strange, I am going to call it complete and not make any further changes to it.
       Thank you for all your input and assistance. I only knew what I wanted I had no idea how to make it happen. This is one of the better forums on the internet for beginners in electronic modding. Thanks again.
                                                                 
                                                                     :dbtu:

Hello Roly,
        I am going to add the Schotty diode in series with D2. That should be a good starting point. Since I
now know that is the area that will have the most effect on the sound the speaker conveys that is where I will focus my attention. Enzo also had some interesting ideas about changes in the same area. So armed with all of the information I can now experiment without the fear of of billowing clouds of smoke. With a
soldering iron, DMM, and an assortment of hand tools, I feel there is nothing I cannot tear up.
        Thank you again. I will probably be posting some results later today. Good or bad !!!!!!
        This will probably be me later today    :grr   :grr   :grr

Quote from: Enzo on November 30, 2013, 04:39:08 AM
Try it this way, pull the amp chassis out of the cabinet, then run a couple clip leads back to the speaker from the existing speaker wires.  Now you can poke inside the amp all you want while it is running.                                                                                                                               If you wonder what type each diode might be, look in the schematic.  CR3,4,5,6 say 1N4003 by them, and that is the type they are.  They don't have a value, they have a type number.  CR1 and CR2 are used as clipping diodes and are type 1N4148, says right next to them.  CR7, CR8 in the power supply are 12v zener diodes, type 1N4742.
PLEASE don't mess with any of the diodes other than CR1 and CR2.   CR7,8 set the voltage for your ICs to run on, don;t change them.  CR3-6 are simply rectifiers in the power supply.  They need to be what they are.
CR1,2 act to clip the signal when it exceeds their junction voltage.  Junction voltage is what your meter is measuring.   How large they look is not the issue.   1N4148 is a small glass diode.   There is no "limit."  You could remove them entirely, the amp would try to be louder, but wouldn;t clip until the signal outgrew the IC they serve.   I have no idea which diodes you were measuring, but the 1N4148 should have a junction drop of roughly half to three quarters of a volt.  Germanium diodes have a junction drop about half of the silicon ones, 4148s are silicon.  If you installed germanium diodes, the amp would clip even harder.  CLip at lower levels.   You can add an extra 1N4148 in series with each existing one, that will double the clip voltage, so the signal can get twice as large before clipping.   SOme amp makers use LEDs for this.  Depending upon color, LEDs have something in the 1v ro 3v range of junction drop.  Remember, and LED is mostly used for its light, but it is nonetheless a diode.
If you stuck different pairs of diodes into CR1,2 places, you might get different amounts of clipping.   If you mix types, say a 1N4148 facing one way, but an LED facing the other, then the clipping would be uneven.  You might like that or you might not, up to your ear.

Hello Enzo,
All of your points are well taken. I will try a few things in the next few days. All within the parameters you have laid out. I guess the amp is older than the schematics posted online as I bought it I guess about 1985, the diode numbers are not on the board. The legend on the schematic calls diodes 1-4 (DS442). That may well be a substitute for 1N4148 but it does not make reference to it. I think I will try one in series to start. The graphs in Rolys post look promising and its an easy mod to start with. I will have to experiment with what I have for the time being.
Radio Shack here only sells flashlight batteries, cell phones, and coax cables. Everything else is special order. They will not be open until Monday anyway. The speaker change encouraged me to try and refine the amp, now that I know it has a little more potential than just encouraging people to junk it and buy a bigger one.
                Thank you for your input and all of the valuable information you provide for not only me but
everyone in general. Without your guidance the landfills would be overflowing with good equipment that
would probably only need a 10 cent fix.

Hello,
      OK, I have been doing research. I went back and pulled the amp apart. The diodes in the amp are as follows (D1-.617 - D2-.642.) I am thinking they are both the same value as the readings are so close.
      The diodes I have go from (.742 to .485) that is the range between 10 of them. After taking the amp apart I eliminated the larger ones as the ones in the amp seem to be 1/2watt, or at least I think. I am going to use one of the ones closest in size to the originals.
       What I would like to know now, is it your suggestion to remove one of the existing diodes and replace it with a different one ? If so I am wondering if the .742 would exceed a limit. The .742 and a .735 are the same as the ones in the amp as they are glass. The others are black material with silver markings. So would it be best to go up or down to start ?
        I have an idea that having two different value diodes will cause somewhat of a ripple in the flow
of the current and slightly distort the sound coming from the speaker. Hopefully in a good way.
        One more idea I would like get your opinion on, how about using two wires and alligator clips run to the outside of the amp to clip in different diodes without taking everything apart every time?
         Anyway Thank You in advance for any information, you may provide, and for all you have given
me to date. I can't thank you enough. 

Hello,
I have a few of the Schottky diodes from disassembling various things in the past. Could you recommend a value? That would get the project back on track, as everything will be closed until Monday at the earliest. Thank you in advance.

Hello,
      Yes I am aware of the ongoing debate about tubes vs solid state. Any one can start a 10 or 12 page argument just mentioning either one on any forum. I also am aware there will be no holy grail fix to make  either sound like the other. Maybe that is not the proper way to describe what I wanted to achieve now.
      I think what you just suggested is exactly what I was trying to ask for, and that will just make the sound slightly darker if that makes any sense. Sound is hard to talk about as I am sure you know. One of least descriptive and the and most talked about things are speakers and guitar pickups. All of the way the sounds are described tell you very little. To me crunch, bottom end, scooped mid range, soaring highs, is a bit much. I usually know less after I am done reading the description.
      I am going to look at the schematic and make preparations to do the mod you suggested. Thank You very much, and please know I am not a bleary eyed kid trying to turn this little practice amp into a
Marshall Double stack.

Hello,
      OK, I moved all of the inner workings into a larger cabinet. I cleaned all the pots and it is at the very
least a 100% improvement. It is really louder and a much more open sound as a result of I guess less of
the sound being confined to the small speaker cabinet and, the larger speaker.
       Now I would like to know if there is a way to (for the want of a better term) thicken up the sound?
Are there any caps or resistors that could be changed to give it more of a tube sound. I think it would be
called sag. I know I cannot make a silk purse out of a sows ear, but it is all I have to work with at this time.
      As always any help would be greatly appreciated!!!

Hello,
      Thank you for your reply Roly. It is difficult for me to grasp all of this, but small bits of information like you,and Enzo have just added in this post have brought quiet a few things to my attention. I know
you are aware of the fact that you can look at some things many, many times and not see things until they are pointed out to you. After time it comes to a point you can just look at the overall picture and
get an idea of what is going on. I am a very long way from that. But I guess it is a matter of time.
       Anyway Thanks again !!!!!!

Hello,
      Thank you Enzo, I am looking at the Fender Squier 15 I posted about in my first post. I started just
looking at the schematic and thought to myself, it's not really that complicated if I could understand a
little more about the values and such. I am not deluding myself into thinking I can become a tech over night. However I can now tell the pre amp, amp, and power source apart, before it was just a big jumble.
       So I will just keep lurking and as I do I think I will pick up things here and there. I think as I tackle
small projects things will start coming together for me. Thanks again!!!

Hello,
      You guys recently walked me through a problem I thought was overwhelming. It wasn't as bad as it
seemed. I tackled it successfully. Now after being exposed to the schematics I have a question about a
few of the ways the values are marked.
       Caps marked such as C8 10/50. What does each number mean? I think it may have something to
with the fact that the circuit has AC and DC voltage running through it. Also on the pots some have a
marking like 100KL, what does the L mean?
        Thank you in advance for any information provided.

Hello,
      I would like to thank everyone who responded to this post. I took all of your advice and used one of the organ speakers. I already had one mounted in a cabinet, so I removed all of the inner workings from the small Squier amp and installed it into the larger cabinet. I cannot believe the difference.
      I still have a minor problem with scratchy pots but I am sure some electrical cleaner will help. I am
going to make the same change to a small RMS 200 practice amp I have.
      Thank You one and all for the help pointing me in the right direction, and preventing me from doing
more harm than good.
                                                             :dbtu:

Hello,
      Thanks I will try that. I was going to build a cabinet because I have a few 12"speakers I rescued
from organs.
       I also have a 8" speaker I took from a surround sound unit, the bass part . Would that function as as amplifier speaker. The paper cone seems quiet thick. 

Hello,
       This is my first post. I live way up in Oregon so and there not much in the way of repair shops or the like in this area. I am interested in learning how to do simple repairs and improvements on my own amps and equipment.                                                                                                             I own a small squier 15 amp and would like to know if this amp worthless or are there ways to improve the sound? I have some 12" 8 OHM speakers, but I am wondering if it even has enough power to drive one of them. I would also like to know if I may be able to change any of the resistors or capacitors to open
it up so it sounds larger?
        I would appreciate any help anyone could provide. Thank You in advance!!!!