Welcome to SE Amp CAD, the new Windows program that helps you design, understand and modify single-ended amplifier output stages. Prior to the arrival of this program, designing a single-ended amplifier required breaking out old tube manuals, textbooks, ruler, calculator, and lots of scratch paper. Now with SE Amp CAD, you can point and click to a new output stage configuration in minutes. SE Amp CAD is a virtual workbench for single-ended output stage design. 

True Curves(tm) is the name of the new mathematical model used in SE Amp CAD. True Curves knows how a 300B or an 845 really bends: how the plate current varies with changes in grid to cathode voltage versus changes in plate voltages. With the True Curves tube model in SE Amp CAD you can quickly and easily model, evaluate, and understand a tube single-ended output stage. SE Amp CAD holds 30 tube models and over 100 output transformer profiles and displays all the output data results, the output circuit schematic, the tube's plate curves (grid voltage, plate voltage, plate current, rp, mu, Gm), the input signal and the resulting output signal--all interactively.


INSTALLING THE SE Amp CAD PROGRAM

To install SE Amp CAD, select the File menu and choose Run from the Program Manager  or from the Start button in Win 95/98. Type A:\install (if necessary, replace A:  with the letter that represents your floppy drive) in the Command Line and press  ENTER. Follow the instructions given in the installation program.

To start SE Amp CAD, double click the SE Amp CAD icon, which was created for you by  the installation program. 

Note: A right mouse button click will bring up a speed menu, which offers many of  choices as the main menu bar and is quicker to use.
 

PROGRAM NOTES 

True Curves: 
What we like best about a triode vacuum tube is its amazing linearity, the   consistent incremental change in plate current relative to incremental changes in  the grid-to-cathode voltage. But not even the 300B or 845 is perfectly linear: as  voltage increases and/or current decreases, nonlinearity increases. To compound  problems, this movement into nonlinearity is in itself very nonlinear.    Fingerprinting this nonlinearity has proven elusive. Here the irony of the situation  is made plain:  what we need to know about a triode in order to make the best use of   its linearity is knowing where it is nonlinear. Tolstoy might have said "All linear  devices are linear in the same way; but each nonlinear device is nonlinear in its  own way." Remember it is this unique bending that makes a 300B and a    triode-connected KT88 sound different.

Most old electronic textbooks give formulas based on Child's Law; these formulas  are, unfortunately, next to worthless. Here is the problem with any of the textbook  variations of the Child's Three-Halves Law formulas:  each assumes that all the  plate current vs. plate voltage lines are identical in shape and differ only in  x-axis spacing, which would be defined by the mu (amplification factor) of the   triode. But any cursory examination of the plate lines of a triode reveals that the  mu is not constant, for example, that it decreases at cutoff. Consequently, the  Three-Halves power formula must be superseded by a less optimistic mathematical  model.

Enter True Curves(tm). GlassWare is proud to introduce a new model we call True  Curves(tm).  Based on a formula derived by John Broskie, it allows the modeling of  triode plate curves to an unprecedented level of accuracy.  An example is provided  below of how close True Curves comes to matching an actual tube tracer plot of a  triode-connected 6550 (a tube not nearly as linear as the famed 300B).

Virtual Oscilloscope:
SE Amp CAD not only displays the results numerically, it also displays the resulting  wave forms. Its virtual oscilloscope quickly shows if the output stage is   functioning close to its design objectives. The deviation from linearity (i.e.   distortion) that the output stage undergoes with increasing input signal is   displayed on the fly:  as the active circuit variables are altered, the scope trace  reflects the change in wave form. 

Live Curves:
The tube curves that SE Amp CAD displays are entirely mathematically derived, which  means that you can specify the both the maximum current and voltage of the graph  along with the number of grid lines and the voltage step increments. Push button  switches toggle the display of the load line, and the IV dynamics of the output  stage. SE Amp CAD knows what both the plate voltage and current along with the grid  voltage is at any point on the graph.

Schematics:
SE Amp CAD allows the user to see the changes in the schematic immediately, as   circuit component selection is made. Furthermore, the needed component values and  the resulting changes in operational voltages are also updated on the fly. The   choices made in the circuit schematic define the circuit that SE Amp CAD evaluates.  In addition, this schematic will be printed in the "Circuit" report. 

Although SE Amp CAD deals only with the actual output stage of a SE amplifier, the  number of different circuits that can be defined is large. For example, indirectly  heated cathode or directly heated? If directly heated, center-tapped or not   center-tapped? AC or DC through the cathode? If DC, a raw DC power supply or a   regulated power supply? 

The component values needed for the cathode resistor and power supply are calculated  by SE Amp CAD instantly and displayed on the schematic. If the user wishes, the  component values can be hidden, as can the circuit voltages, in order to make the  schematic less cluttered when viewed.    

Results:
SE Amp CAD divides the results of its calculations into several groups: those that  pertain to the output transformer; those that pertain to the output tube; those that  pertain to the maximum ratings output tube; those that pertain to the    current-voltage relationships that the output stage will experience because of the  specified input voltage swings; those that pertain to the output stage (output tube,  cathode resistor and bypass capacitor); and those that pertain to the load being  driven by the amplifier. As circuit variables are changed, SE Amp CAD updates the  display of the results, making it easy for the amplifier designer to inch his/her to  the desired outcome. After a change in value of a circuit variable, those results  that are determined in part by that variable are displayed in a fuchsia color, until  the "Calculate" button has been pressed, which will restore the font color to aqua.  If an error condition, such as excessive plate dissipation, the result's font color  turns to red and returns to aqua when the problem has been corrected.

Options:
This menu allows the user to change the appearance and functioning of the program.

Circuit variables:
Circuit variables, such as tube type, B+ voltage, cathode resistor values, and grid  voltage values are entered in field boxes at the left or changed by clicking the  increment controls at the field box's left. The results are then displayed at the  program's right. 

The increment buttons serve to increase or decrease the value in the corresponding  edit field boxes by 1 or10 or 100 or 1,000 units, depending on the variable being  adjusted. For example, the smallest increment for the grid voltage is 1 volt, but  for the primary impedance the smallest increment is 10 ohms.

When entering large values directly, such as, 105,000 the easier entry method is to  type "105" and then "k."  Similarly, if entering 1,100,000, the quick way is to  enter "1.1" followed by "m." 

Output results can be displayed in either RMS or peak values. On older (i.e. slower)  computers, the voltage/current resolution can be decreased to speed result   processing. 


COMMON PROBLEMS AND SOLUTIONS

Problem: 
The program seems to run too slowly.

Solution:
As with any program running under Windows, the operating speed of SE Amp CAD is  dependent on the speed of the hardware that it is running on. Hardware   configurations that affect performance are: the amount of memory and the   speed of the video card, the processor type, the amount of real memory. While the  minimum system configuration required to run the SE Amp CAD program is a 486 33 MHz  computer with 8 MB of RAM, and a video card capable of running 256 colors, the   recommended system configuration is a Pentium 166 MHz computer with 16 MB of RAM,  and a video card with at least 256 colors. Some speed can be gained by checking the  "Coarse" selection from the "Options" menu selection under "resolution."
        
Problem:   
When I try to run the SE Amp CAD program, I get a "Not enough memory" message.

Solution:   
SE Amp CAD is relatively small in size, however there are many graphical   controls and much information which makes greater demands on your computer.   Therefore, try closing as many other programs as you can to give SE Amp CAD more  breathing room. Furthermore, maybe your virtual memory setting is too small; try  increasing it to at least 16 megs. For instructions on setting virtual memory,   lease consult your Windows documentation.

Problem:   
When I print a report from SE Amp CAD the printer never prints.

Solution:   
The solution might be to turn off the printer's spooling buffer. Oddly enough this  fix is often required when strange printing behavior arises. To use the printer  without spooling, you should specify a new printer in the Windows control   panel program "Printers." The printer newly defined will be the same as the   previous definition of the printer, except that the "spool data" feature is turned  off. This will slow the printing from the printer somewhat, but it might help the  quality of the printing. 

Problem:    
Closing SE Amp CAD wipes the entries clean and I have to reenter my data choices to  continue working on my project.

Solution:   
SE Amp CAD can store your design work so that it may recalled and your work can  continue were you left off. 

PROGRAM:     SE Amp CAD
VERSION:       1.00
LANGUAGE:  English
SYSTEM:        Windows 3.1/95/98 or Windows NT 4.0
RELEASE:      08/98
AUTHOR:       John E. R. Broskie
CATEGORY:  Single-ended amplifier output stage computer aided design program
Copyright:       (c) 1998 by GlassWare
