I often get complaints that my electronics are too big and consist of too many chassis. So I came up with this integrated amplifier. It is not only a full function amplifier with volume control and 3 line inputs, it also has a phono section on board with built in MC step up transformer.
This requires a lot of tubes. 10 Signal tubes in total. the phono stage is implemented with 6SF5 and 6J5 triodes. The circuit is exactly the same as in the Octal Phono Preamplifier. The 6GL7 serves in the linestage which shares the same circuit with the Octal Line Preamplifier. Basically the preamp section is the same as in the Octal Preamplifier MK3. To make the amplifier complete a stereo version of the low cost 6CB5A amplifier was added.
The PSU got it's separate chassis to keep the chassis size and to avoid interference with the phono section. To fill up the PSU chassis it got a full wave bridge rectifier with 4 6AX4 TV dampers and a choke input filter. Two LC section provide the smoothing of the B+. Inside the chassis is a filament transformer which is part of a DC heater supply for the preamp section. The power amp section is AC heated.
Some photos of the assembly steps. The top plate with capacitors and output transformers mounted:
The output transformer had to be mounted sideways so that they fit under the 100mm transformer covers.
The preamp tube sockets are mounted on rubber dampers:
Heater wiring and some of the coupling caps:
Adding solder strips:
Adding all the remaining parts:
Prewiring the back plate:
Ready to be mounted into the wooden frame:
Just two controls, input select and volume:
The backside is quite crowded:
Starting from the right: Phono MC inputs, Ground post and ground lift switch underneath. Next two switches for selecting the step up ratio of the build in MC transformer. Followed by 3 line inputs. The 5th pair of RCA jacks is a line out. The signal after the line stage section is routed to these so an additional amp can be connected or the component can be used as a preamp. The speaker jacks on the bottom and the power supply connector on the left.
The entire amplification chain for an analogue system in just two boxes. Five Amplification stages. All Octal tubes. No more complaints about size please ;-)