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1. Cathode Resistors: Larger values = less gain, Smaller values = more gain.

2. Cathode Bypass Caps: Larger values (22uf to 330uf) = More gain and bass. To tame oscillation or motor boating, try smaller (1uf, 0.1uf, 500pf) = less gain and bass.

3. Resistors between gain stages: Resistors in series with the audio path increase gain as the value gets lower. Resistors going to ground in the audio path increase gain as the values increase.

4. Put a 500pf cap across the resistor connecting the gain stages. This is a "bright cap" and is what makes the bright channel on many Marshalls and Fenders. If it’s too bright, loose it, change to a higher value, or put a resistor in series with it (try 47k-100k.)

5. The Tone Stack: The first cap (e.g. 470pf) controls treble and bass. Go down (250pf or lower) for less mids (more highs and lows) Likewise, the other 2 caps (0.022uf) can be changed. Try .1 for the bass and 0.047 for the mid. Or things in between (0.033) The resistor between them (33k) can be changed up or down for a different mid response. Also try a 50k pot (instead of the usual 25k) for the mids for more range of tone; when you turn this down the mids GO AWAY. Much different than a stock Marshall.

6. Master Volume: Comes after the treble control and feeds the phase inverter and the power section. Try a 100k-220k resistor in series, right after the MV pot. It will make the lows roll off less at low volumes, giving you a fatter tone.

7. "Smoothie" caps: There's times when the amp is bright, harsh, or "buzzy"-sounding and you'd just like to smooth it out or kill the "buzziness". There are a couple places you can add a "smoothie" cap to kill unwanted highs. One place is across the plates of the phase inverter. Marshall uses a 47pf cap here to prevent oscillation, try 120-200pf to smooth out buzziness. VOX uses a cap here with a pot for the "cut" control. Another spot is between the plate and grid of the first gain stage, try 10-20pf. Sovtek Midget 50 uses 18pf here.

8. Caps: What's best? Orange Drops, Mallorys, or the expensive "paper-in-oil" kind? What's the difference?
Basically there are 2 kinds of caps you'll use for coupling/tone caps: Polypropylene (Orange Drop 715P, Xicon, etc.) and Polyester (Mallory 150, Cornell-Dublier, etc.)
Polypropylene tends to be brighter, can be harsh-sounding. Great for Fender-type amps.
Polyester tends to be darker/smoother-sounding. Mallory 150s were used in vintage Marshalls and I like 'em a lot
The differences are fairly subtle. Paper-in-oil caps are just expensive. They don't make much/any difference in guitar amps. Save your money. For small (picofarad-size) caps most agree that Silver Mica caps are the way to go over ceramic disc caps; smoother, less harsh, although there are places where a ceramic cap can work just fine (tremolos, power sections.)

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

An addition to #8...

For a more complex sound, try using 2 different types of caps in parallel with each having half the total value. Many Trainwreck amps would use a 250pF Mica and a 250pF ceramic to equal 500pF.

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--s2
www.s2amps.com
www.category5amps.com

re: #6 - you can use this to roll off highs. A resistor in this range in front of a triode stage gives a lowpass filter due to the Miller capacitance of the triode's grid. If your homebrew design is too dark sounding - make sure you didn't put too much resistance in series with the grid. "Bright caps" compensate for Miller capacitance.

Others I have found useful:

- reducing the cap values between phase splitter and power tube grids can help with "flubby bass" - cuts off the low frequencies
- a "conjunctive filter" across the output transformer primary - a series RC filter with values chosen to shunt output power at high frequencies. This can really help if the amp has a nasty high end. Use at least 1kv rated cap and appropriately rated power resistor.
- low frequency oscillation or motor boating is sometimes due to worn out or too small power supply caps in the preamp. Power stage is coupling back to the preamp thru the power supply.

Rich