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Friday, March 14, 2014

Pure 45 Bliss, Part 1


This months posts will be mostly about the 45 triode. I already presented a pair of 45 mono amplifiers earlier and the tube itself got intensive coverage as Tube of the Month. This post is about the 'Pure 45 Bliss' amplifier. This is an amp which uses a 45 to drive a 45. No alternative tubes can be plugged in, no switching. Pure 45 magic.

Part 1 will show the assembly of this pair of monos. As the previously built amps this is a 4 chassis affair. The power supplies have been done in the same design, but the signal section looks a bit different.

This amps use silver transformers throughout! A Lundahl LL7903Ag silver input transformer which provides some extra gain to compensate for the low mu of the 45 as driver. The first 45 is transformer coupled to the output tube through a LL2746Ag and the output transformer is a LL1682Ag. Here a photo of the top plate with the interstage and output transformers mounted along with the oil caps:

The other side showing the improved solder terminals of these transformers:

Unfortunately these beautiful blobs of silver need to be hidden under transformer covers due to the exposed terminals.

All the signal wiring is done with teflon insulated solid core silver wire:

The top platte carries pretty much all the parts and wire through which the signal travels, except the input transformer which is placed inside the chassis.

A close up of the wiring to one of the transformers:

Besides the input transformer, B+ and filament chokes go inside the chassis. Both tubes are DC heated for zero hum operation:

The connection between input jack and input transformer is also done with a twisted pair of the silver wire which runs in the white sleeve from front to back. The there side of the chassis:

Connecting the top plate to the chassis:

Wires between the two parts are mostly filament and power supply wires. The only signal wire between the two is from the input transformer to the driver tube grid and the ground connection to the input transformer.

The power supply is done in a similar fashion as previously shown PSUs. The top plate carries the high voltage transformer, B+ smoothing caps and the rectifier bridge. Here a photo of the prewired PSU plate:

B+ and filament chokes are placed inside the chassis along with the separate filament transformers for driver and output tube:

Stay tuned for part 2 with photos of the finished amps and some sound description of this all silver 45 / 45 amp.

Best regards


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