
Found a cleaner print;


Sadly the thread on
tdpri.com doesn't have much to offer, only a long rambling debate about transistors, distortion, and negative feedback.
SWTPC - Southwest Technical Products Corp. (a.k.a. "sweat pack") had a good reputation in the day, did a lot of very early personal microcomputer stuff, S-100 buss.

The
"22 watts" is IHFM or "music power", the actual rating of the amp is 18 watts RMS (which is typical of modern small gigging combos and generally more than enough).
It claims a very high bandwidth, 20Hz to 100kHz, which is fine but would need to be confined for guitar work. (or excessive hiss)
The raw input sensitivity is 1.5V for full output. A guitar will make a noise but not drive it fully.
The raw input impedance is more of a problem at only 5k. This is fine for a power amp but far too low for an unbuffered (passive) guitar.
So you are going to need a preamp of some sort to provide;
- an input impedance of 1Meg or more
- voltage gain for sensitivity
- EQ/tonestack for sound colouration
- a volume control
The very simplest thing you can do is put a FET source-follower buffer in front of it, but it really needs a preamp that is a bit more full-blooded. But later.
On closer consideration...Uh oh ... "one silicon and one germanium output transistor" (and no emitter resistors either)
That does not bode well.
Sorry, but I don't think this circuit makes a good starting point.
PS.1. How does one decide what Ic (collector current) value to use for each stage of an amp? The information I'm using says to use an Ic of 5ma for the first transistor and an Ic of 10 ma for the second transistor. Just wondering how these values were arrived at 
I go about it backwards. For 50W in 8 ohms we need about 5 amps peak. Assuming a venerable 2N3055 output transistor, it has a current gain,
Hfe, of as low as 20 at this current. This means that it will require;
5/20 = 0.25A into the base.
Now the driver has to deliver 250mA peak, and assuming an equally venerable BD139 as the driver it has a minimum
Hfe of 40, so it will in turn require;
250/40 = 6.25mA of drive at its base.
And so it goes.
For preamp and small signal stages one can assume a current of about 1mA which is about where most small signal transistor parameters give their best, gain, noise, but this is a massive generalisation and the
datasheet always rules.
2. In the schematic above I was able to come up with values for the collector and emitter resistors for the first transistor and for the resistor from base to ground..... but then I noticed there is no direct DC current path from the base to the positive rail. How do I calculate the value of that resistance?
The base current for the first transistor is derived from the output "half-rail" (emitters of Q4 and Q5).
At power-on Q3 and Q5 start to conduct until the half-rail rises to where Q1 brings the rise under control.
This bias is also therefore a DC (and AC) negative feedback path from the output. The pot R5 is used to adjust the half-rail so it idles at half the voltage of the supply (and the AC gain ends up being whatever it is at that setting - a runcible arrangement IMO).