Click here to see more pictures of my amplifier!
Click here to see how you could build your very own version of this amplifier!
Click here to read about my upcoming projects!
This is a page about the vacuum tube amplifier I spent most of January and early February building. This is the very first vacuum tube amplifier I've ever built. Based on a design featured in the January 1995 issue of Popular Electronics, this seemingly simple design uses two 60FX5 vacuum tubes wired in a push-pull configuration. It is powered by line voltage alone (no special high-voltage power transformers, just two 120V to 12.6V 3 amp transformers wired back-to-back for isolation purposes), which is converted to DC using a silicon rectifier, and then filtered using a NOS (no leakage) multisection 100 microfarad electrolytic capacitor rated at 350 volts (an old Cornell-Dubilier, I plan to replace it in the future with a new-manufature LLC multisection cap). From there, 120VDC goes to the 60 volt filaments of the tubes (wired in series), while a 330 ohm 5 watt power resistor (actually a 300 ohm 5 watt resistor and a 30 ohm 10 watt resistor wired in series) lowers the voltage to 92VDC for the plates/screens of the tubes. The amplifier uses four resistors (one 20 ohm 5 watt potentiometer for hum-balance control; two 47 ohm 1/2-watt fixed resistors , and a 220 ohm 1 watt fixed resistor) to lower voltages further. The original design called for the amp to be built on a large baseboard, and the power supply to be separate and wired to the amplifier using Fahnestock clips. I built my amplifier on a traditional aluminum chassis (12" x 6" x 2") with the power supply on the same chassis (a good distance away from the tubes), and added a power switch and an indicator light. I built it, and it worked on the second try (I had to resolder some connections and bend the socket pins away from each other). I think it sounds teriffic for a first project. For a journal I wrote while building this amp, click here.
Tube: (2) NOS Sylvania 60FX5 pentodes, $2.20 each
Output Transformer: Hammond 1608 8,000 ohm 10 watt transformer, $36.82
Input Transformer: AES 157 Nickel-Core Interstage Transformer, $15.95
Power Transformer: (2) Radio Shack 120 volt to 12.6 volt CT 3 amp transformers, $9.99 each
Rectifier: 4 amp 400 PIV silicon full-wave rectifier
Capacitor: N.O.S. Cornell-Dubilier four-section 60-100 microfarad capacitor (CDE#DD0474.2A) three sections rated 350 volts, fourth section rated 50 volts
Hum-Balance Potentiometer: Radio Shack (?) 20 ohm 5 watt potentiometer (schematic calls for 25 ohm 2 watt)
Fixed Resistors: (2) 47 ohm, 1/2-watt; (1) 220 ohm, 1-watt; (1)330 ohm, 5-watt (used 300 ohm 5 watt and 30 ohm 10 watt in series)
TOTAL COST: $90.87
Here's a schematic of my amplifier:
Words Used To Describe Tube Audio
My Favorite Tube Web Sites
Antique Electronic Supply
Tube Data Search Engine
Tube Amplifier Newsgroup: rec.audio.tubes