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Thursday, December 7, 2017

845 Mono Amplifiers - Part 2


In part 1 about these single ended mono blocks with the 845 tube, I showed some first photos mainly of the chassis materials. In this part I will show the assembly steps.

The interstage transformer, decoupling choke of the driver stage and most important capacitor in the driver stage are mounted directly under the top plate.

This enables short signal path wiring.

The high power resistors are mounted on a separate aluminium rail close to where they are needed.  Here a detail of the mounting technique:

The output transformer, decoupling choke of the output stage B+ and final choke of the LCL filament supply are on the next level right below the top plate:

The most important capacitor of the output stage, in this case a NOS paper in oil type, is close to the output transformer to have a short signal loop. On the next level below there are the main capacitor banks for smoothing of the high voltage:

The cutout is there to leave room for another choke which will be mounted on the next tier below.

Another set of capacitors and the choke mentioned above:

Again a cutout, this time for the main power transformer which will be on the bottom tier.

The power transformers (separate for filament and high voltage) and the first LC section of the filament supply:

The filament transformer is not mounted yet, it will reside in the upper left corner. Next we see a photo of the finished amp without chassis which shows how all these modules are stacked together:

As you can see almost no space inside is left unused. Right side view:

I wanted to keep the height of the amp to my standard chassis size of 40cm (without tubes and feet), 30*30cm floorspace. So each layer had to be carefully planned to fit everything in. Left side view:

Testing of the amp is complete and assembly of the second mono block is underway. Stay tuned for an update with the finished units.

Best regards