MLA2500 with 8874s

I found this amp at the Cleveland hamfest in 1980. It had been (ab)used by a CBer and needed much work. It also needed new tubes. I didn't have 8875s and wasn't gonna spend $400 for a new set. Fortunatly I had a set of 8874 pulls from a friend. So I set out to give the 'ol girl new strap.



I started by rebuilding the power supply. That finished I stripped the original tube sockets and associated wiring.
After cleaning the tube sockets and finding a new bias zener I turned my attention to mounting the tubes to allow more air than the original muffin fan provided.

I fabricated a new tube box and mounted the original sockets on it. I then rewired the socket according to the original schematic.

The filament and cathode connections are brought into the side of the box using feedthru caps.



The muffin fan is replaced with a blower capable of supplying the needed air for a pair of 8874. The new mounting plate and new tube box are mounted to the amp with 4-40 hardware.

These pixs show the original 8874s I placed in service in 1980. Recently, a shorted B+ cap took out the original transformer(datecoded Apr.1977).

Curious, I checked the fuse to see why it hadn't blown. To my chagrin I found a 30 amp no blow in the fuseholder. I never checked it after purchasing the chassis 24 years ago.

Such is the life of a Buddly !!!