are used in the vibrato circuit. The Tube Amp Book by
Aspen Pittman (published by Groove Tubes LLC, 2002) is
a good source of schematics for tube amps, but it has only
three Epiphone schematics, none of them use 6V6 output
tubes. There are 450 amp schematics in the book, you
probably could find one with a vibrato circuit which is
similar to the Epiphone. The book can be purchased from
several electronic music sources, including Antique
Electronics Supply ( www.tubesandmore.com). They
also have several other books on tube guitar amps; A
Desktop Reverence of Hip Vintage Guitar Amps by
Gerald Weber also contains schematics.
[#2054 -February 2005]
I need to purchase a good, reliable, and low-cost
schematic capture/board layout program.
functionality and mode of operation. A plus is that the
website contains a tutorial on the use of the software.
Moreover, the book Build Your Own Printed Circuit
Board by Al Williams (McGraw Hill; ISBN: 007142783X)
contains a very detailed step-by-step procedure for this
The software, tutorial and manual can be downloaded
The complete version can also be purchased from the
previous websites at what I consider to be a very
reasonable and competitive price.
#2 How does free sound?
Go to ExpressPCB or PCB123's site and download
San Diego, CA
#1 I have used Eagle™ by CadSoft very successfully
( www.cadsoft.de/). The demo version is free and fully
functional, although it’s restricted to two layers and
Eurocard size. This can give the user a good feel about its
[#2052 -February 2005]
I recently purchased a 48 VDC to 12 VDC switching
power supply from a surplus place. What are the
general rules of thumb for getting this thing to work?
I know switchers need a load, but on which output?
It has + 3 V, + 5 V, - 12 V, and + 12 V outputs. I am only
interested in the + 12 10 A output. This supply has a
couple of sensing circuits; what do they usually tie to?
NUTS & VOLTS
Circle #42 on the Reader Service Card.
The input power required will be that used by the
load(s) connected to the output line(s) plus losses (heat)
within the power supply. Make sure your power source ( 48
volts DC in your case) is suitable (can deliver required
Not all switching power supplies require a minimum
load, although some do. If the power supply seems
unstable or output is not in specification, add a fixed
resistor (or suitable light bulb) to each output. Use Ohm’s
Law V=IR to figure, say, 200 mA load on each output.
Increase current only if needed and do decrease if possible.
The sensing circuits must tie to their respective output
voltage lines. They are used for what is called "remote
voltage sensing." For many applications where the load is
physically close to the power supply, the + and - sense lines
are tied right back to the power supply terminal’s + and -
output lines of their respective voltage. If the voltage drop
between the power supply and load is noticeable and
causes a problem (possible with 10 amps at 12 volts), the
sensing lines are connected at the load (not power supply
terminals) + and - and the voltage drop across the load
lines will be compensated, i.e., reduced to zero.
Erik von Seggern