[Ericus Rex]

Roger,

How can I learn some about tube amp design?  Are there books that start from the basics and go into different circuits and such?  I'm not wanting to get into the tube amp biz but I would like to understand what I see when looking at an amp's innards and viewing schematics.  All help is appreciated.

ER

[Roger A. Modjeski]

The Radio Amateur's Handbook published annually by ARRL was one of the first books I used. I bought the 1962 edition. Anything pre 1969 will have lots of tube circuits but after that most of it went solid state. All editions cover basic electronics. They can be had from ham radio guys and on eBay.

[Ericus Rex]

1963 40th edition is on its way!

Thanks Roger

[Roger A. Modjeski]

Let me know what you find useful.

[Ericus Rex]

I'm starting at the beginning with the basics.  Lots of fuzzy areas (for me, at least) have already been fleshed out within the first three pages - these are things I have read about but didn't really understand.  Can't yet get my head around the properties of A.C..  The figures in the book diagram it like a sine wave which doesn't make too much sense to me....  I'll read a bit more and think about it some more before I make myself look like the total idiot I am by asking you.

Thanks for the recommendation!

[Roger A. Modjeski]

Understanding electronics came easily to me because I started young and had a keen interest. Adults taking up a new skill will have a harder time. Ask anyone who has taken up a musical instrument later in life. We learn these things more easily when we are young.

The older student has some advantage if he has asked simple questions arising from the world around him. A good example is to consider the voltage, current and power of things in our everyday life. Here are some examples:

1. When you turn on a 100 watt light bulb, how much current is drawn? How much power is involved? Ask the same question for the electric burner on your stove or oven. The motor in your HVAC system? I found that the motor in my gas furnace used as much electricity as a small heater so I decided to just use an electric heater directly for my bedroom and not use the furnace at all

2. Why are vacuum cleaners rated in amps while most motors are rated in horsepower? What is different about these motors?


3. What common devices use AC directly? What common devices convert AC to DC in order to function. What common devices can use either?

4. What is the basic difference between AC and DC?

Answers:

1. amps = watts/volts ( or volts x amps = watts) so the current is .8 amps. Some people round it off to 1 amp for simplicity. The 60 watt lamp is easy, 1/2 amp. Incandescent lamps work equally well on AC and DC. For AC the RMS value is 120 volts in the typical household. The peak voltage is 160 V for a sine wave and 120 volts for a square wave. Drawing the wave and realizing that the area under the curve is what matters will help.

2. These appliances use brush motors (Edison) and will run off AC or DC. The current is farily constant not varying much with load.

A table saw or drill press uses an induction motor (Tesla) and will only work on AC. Their speed is determined by the frequency of the sine wave. In countries with 50 cycle power they run 20% slower. You can easily control the speed of a brush motor with a variac or a light dimmer. The same treatment will overheat an induction motor.

3. Any electronic device powered by AC first converts that to DC at various voltages. Transformers set the voltage. Diodes allow conduction in one direction only and capacitors store charge to smooth out the ripples. DC looks like a flat line and the electrons flow from negative to positive with no reversal.

4. AC looks like a wave in the ocean going both above and below the mean depth. An AC voltage wave alternates around 0 volts going both positive and negative. The current flow back and forth in the wire.

[BobRex]

Ericus,

Do you have a local community collect with an electrical technology curriculum?  If so, check to see if you can audit the first 2 or 3 classes (basic electronics, DC circuits, AC circuits...)  That will teach you the math and theory behind amplifier circuits and give you the opportunity to learn how to use various meters.  It will cost you an evening or 2 a week and maybe $100 per course.

[Ericus Rex]

BobRex,

Great suggestion.  I thought of doing something like that but figured it would no longer include tube info/circuits.  But I guess I would need an understanding of solid state as well since it's now included in many tube designs.  Since I'm having some trouble with the basics maybe taking the intro courses would be a good idea.

Roger,

The trouble I've been having with the AC/sine wave thing is this;  the Radio Amatuer's Handbook never states (at least not yet) that the wave changes from positive to negative and vice versa.  It merely states that the second half of the wave is going in the opposite direction of the first half.  I take it that both are true and related.  I can understand that a change in the polarity would cause the current to pass right back down the path it just came from due to being attracted back to the atom that just kicked out the electron (did that make sense?).  But, since we're taught from childhood that electricity is derived from both the + and - what is going on with the grounded side of things?  Is it positively charged during the second half of the cycle or is the whole +/- thing a misconception?  Further, is the whole wave being divided between the two (not counting ground) prongs/cables of the power chord: positive 1/2 cycle in one wire, negative in the other?  Thanks for your patience with these basic questions.