Last time I touched vacuum tubes was around 1967 when I was repairing radios and TV. I remember this old radio HIFI that was stripped from a console back in the early 60s There was a 12 inch speaker and a smaller speaker I think mid range and a small sealed back cone tweeter. There was a huge power transformer on the chases and a bunch of tubes. I do not remember what the output tubes were but I do remember them being in a push pull configuration. The sound was amazing and through out the years that followed I was never able to match the sound quality with all of the solid state amps I have built or heard. Recently with the hype on the vacuum tube single ended amp hoopla I started getting the bug and turned to the Internet for research.
The transistor brought a new theory in the amplifier and speaker industries. The current fad in solid state amps was to through a lot of current at a speaker in a small sealed cabinet. I will not debate with anyone about lots or little bit of power and how they sound.
As an attempt I wanted to build a tube power amp to see if I could find that good sound I heard when I was young. The following document contains the tube amp I chose as my first tube amp. Please note that I have never liked single ended power supplies for audio amps so it was not used.
While this document describes a plan to build an electronic device which has about 360 volts DC under the chases caution must be followed. I will not be held responsible for any injuries incurred from some one following this document.
MSH MODEL-1 POWERAMP (Michael S. Holden) make no representations about the suitability of this information for any purpose. It is provided "as is"
MSH MODEL-1 POWER AMP (Michael S. Holden) disclaims all warranties with regard to this information, including all implied warranties of merchantability and fitness, in no event shall MSH MODEL-1 POWERAMP (Michael S. Holden) be liable or any special, indirect or consequential damages or any damages whatsoever resulting from loss of use, data or profits, whether in an action of contract, negligence or other tortuous action, arising out of or in connection with the use or performance of this information.
This information may include technical inaccuracies or typographical errors.
MSH MODEL-1 POWERAMP (Michael S. Holden) may make improvements and/or changes in the information at any time.
Step 1: Circuit Design History
The origin of the power amplifier design came from the schematic below, which came from the 1959 RCA RECEIVING TUBE MANUAL Tech Series RC-19
Step 2: Power Supply Schematic
Step 3: Power Amp Schematic
Step 4: Parts List
Step 5: Drilling Template
Step 6: Top Side Component Layout
Step 7: Bottom Side Component Layout
Step 8: Chassis Wood Sides & Paint
The chassis top is a piece of 20 gauge aluminum COVER PLATE, ALUMINUM, 12" x 8", HAMMOND P-H1434-22 To control corrosion the aluminum chassis top is painted with white dry powder paint and is backed at 400 D. F. This method of painting provides a stronger surface which is more scratch resistant than normal paint.
To give the project little flair all three transformers were dissembled and red power paint was placed on the outer skins.
This dry powder paint process is quick and more durable than normal spray paint. I researched it on the web and gave it a try. I will use it again.
Step 9: Chassis Wiring
Solder lugs were placed at different locations on the wire side of the chassis. A drill was used to start the tube sockets holes and finished of with a step drill. The hole sizes are listed on the layout sheet in the Chassis Construction chapter.
Rubber grummets �e uses any time a wire pass through the top side to the bottom side of aluminum top.
Step 10: Testing & Evaluating
Step 11: Lower End Frequency Response
Step 12: Tooles Used
Step 13: In Conclusion
Below is the mono HIFI preamplifier I built to go with the Model-1 Power Amp.