Hi Guys,
I have just read all the comments on this thread, and it looks like many of you are finding that this amplifier is a sleeper and can sound good if a few things can be changed. I thought I would drop a line here and tell you my reaction to all the stuff that is suggested here.
First thing (almost always) the speaker must go. it's cheap and plastic and would make a great speaker for the beach or camping. I am sure the cone could withstand water, but the sound is very unmusical for serious playing.
Second thing is that adding more parts, or trying to make a 'booster box' in the amp with the 'provided' op-amp is more technical than most owners could do confidently. Changes should be in small steps so that you know what it is that you did that made (or lost) that sound.
I will summarize my mod again for those who did not catch it in an earlier listing. I am not an Electronics Designer of Analog Audio, but I have been blowing up stuff before I was ten and did earn a Electronics Technician Certificate to fill in some of the things that I didn't know (about theory, design, etc,) and have worked in TV repair, High-End Hi-Fi ($$$) and custom installations while building, testing and tweaking amps.
I tend to over mod things and it becomes less satisfying to keep on modding things to death. Trying to make a cheap little amp sound like a Marshall stack is not going to happen. But if you want to get much better sound for the fewest bucks, you need to get the 'sand' out of the circuit. I want to be connected to the speaker, not dealing with quantum leaps inside a plastic part.
When the op amp was removed, there was very little gain to play with. You can get output tube distortion if you play it hard, with hot pickups and perhaps your favorite stomp box. I feel that some of the best distortion comes from those little boxes on the floor. 2 tubes are not going to get you a lot of gain (unlike my Epiphone VJ that could through careful parts section) so why try and make things harder for the amp, your time and money, and your general satisfaction of PLAYING, not tweaking. I do both- and I do admit I play MUCH more than I tinker. My amp sounds very good, and there isn't anything in it to make it solid-state, but I do some tricks in front of it.
My pedal layout in guitar into a homemade tube distortion box with one 12AX7 in it, then a dbx 119 compressor/expander, and then to a Picoverb for lushness. That all goes in the to the amp with the controls the way they are printed (stock look) and no other holes to drill, etc.
Get a copy of the schematic and layout and just try this if you really want all-tube sound. If you want metal, or loud headroom, you will not get it from this amp. But it is a great case, chassis and transformers just begging to make music.
Begin by cutting the trace after the input jack leaving R10,R11 for input loading. This will be just before pin 3 of op amp. Run a short length of coax from there to pin 2 of the 12AX7, and ground this wire at only one end (to prevent ground loops).
You will be cutting the volume pot out of the circuit and reroute wires as follows-keep the tone control circuit for now).
Connect the middle wiper to pin 2 of 12AX7. Cut out the R7, 220K resistor and the pot will take it's place for the load and volume control BETWEEN the two 12AX7 halves (this is so your guitar and/or you stompbox can play clean into the preamp tube or to push it more into output stage distortion)
Connect the top of the control to the junction of R15, R29,and C28: and the bottom to ground. Cut out the 100K (R15) (or R27, 10K) Resistor(s) so that the second half of the preamp tube is driving the same load. So you are basically removing R15, R27 and R7. You can increase the gain by floating a highish value resistor between the grounded end of the volume control (or a 500K or more pot) which gives you more drive voltage out of the second stage of the preamp, but I left that the way it is because it does give me the balanced sound (clean and dirty) that I want.
No parts, but a few pieces of wire, a speaker, and your time.
If you don't feel comfortable doing this, I still offer to do it anyway you want. (shipping is least expensive if you just send me your board and i will do it all for you and ship it back to you ($5.00 shipping) you put the board back in. Alternately, you can take the chassis out of the box and ship that to me, so you don't have to do anything other than unscrewing it back together, and the shipping wont me too bad.
Mark (manoteal at cox dot net)