BIRTH OF A NEW AX84 HIGH OCTANE TUBE AMPLIFIER
(
click on any photo for A larger picture)


This page details the construction of an AX84 High Octane style amplifier: www.ax84.com

Features

  • Hi-Gain 12ax7 Preamp

  • 6BQ5/EL84/SV83 Power Tube in Class-A Single Ended Configuration provides a surprisingly loud 5 watts or so of output power

  • Cathode-follower driven Bass, Mid and Treble tone controls allow you to shape your sound. Alter the values of the components in the tone stack to tailor your sound.

Many thanks to Ramiro Silva for his excellent construction web page with plans, photos, the works. Ramiro is a gifted amp builder with extraordinary attention to detail.

See his amps website here:  www.silvatone.bravepages.com


CONSTRUCTION: WIRING THE CHASSIS PART I
TRANSFORMERS & HEATERS

 

February 21, 2006 (5 Hours)
Cumulative build time, 19 hours

After polishing the chassis to a brilliant shine, it was time to start final construction. This page details installation of the transformers, mounting to the turret board and tube sockets, and wiring the heaters. How did this take me 5 hours? Well, I guess twisting the wire and making sure everything was perfect takes time. Also, great music and ample breaks for snacks helps.

Step one was to install the transformers and tube sockets. I used rubber grommets for the transformer wires as they pass through the chassis. The white ceramic sockets and gold mounting rings look good on the gloss white paint.

NOTE: Although it has been removed for these photos, I always keep a thick towel under the chassis to prevent scratching the finish during construction.

Next time I'll put a shield on the inside of the chassis to protect it from overspray! Note that only three screws are installed in the power transformer. That is because I still need to run a wire to that screw from the turret board to ground the buss bar.

I've sanded off the overspray around the hole to ensure good ground contact. I also sanded around one of the output transformer mounting holes to make sure it was well grounded.

I used Hillman 1/4" x .140 x 1/4" Nylon Spacers as standoffs for the turret board. These were about 50 cents at Lowes.

These spacers don't leave much clearance between the board and the chassis. We used the dental mirror to make sure there were no problems under the board after mounting. Having the right tools certainly makes the job easier.

I purchased some twisted Teflon wire on eBay, but the twist was quite loose. To get a nice tight twist, I attached one end to an electric drill, and the other to my filing cabinet. Let the wire shorten as it tightens to get a nice, tight twist (see large photo).

NOTE: This photo illustrates three types of heater wiring for three different tube types.

Heater wiring detail for 12AX7 9-pin (noval) socket. For 6.3VDC heaters pins 4 and 5 are connected to the white wire and to each other, with pin 9 receiving the black wire.

NOTE: DO NOT WIRE THE EL84 SOCKET THIS WAY! Connect white to pin 4 and black to pin 5, and do NOT connect the pins to each other. On the octal socket connect white to pin 7 and black to pin 2.

It may be overkill, but I used hemostats as heat shields when I wired the PT leads to the diodes. Again, having the right tools sure makes things easy.

Finished Part I. The transformers, turret board, tube sockets, and heaters are all mounted and wired. Next comes adding the switches and finishing this beautiful beast.


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OCCI HARD AT WORK ON QUALITY CONTROL


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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