The road to nirvana

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My journey into Photography, Horology, and Audiophilia

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AK-450, A type 45 Amplifier

I've read a lot of good things about the Western Electric 417A miniature 9-pin triode, but the price is too steep for me. When I was offered to buy a couple of 5842- a cheaper equivalent, I bought two pairs. One pair is Amperex gold-pins and the other pair is Raytheon. It is at this stage that I asked for help in designing a 45 amplifier based on the 5842. The Audio Asylum thread can be found here. The friendly folks at Tube/DIY Asylum were very helpful, but special mention should go to Thorsten of Thunderstone Audio who really spent time explaining the stuff to this newbie, me!

For this project, I decided to put some money on it and invested on a pair of Tamura F-475 and choke. The power transformer is custom wound by a local winder. Since my wood working skills are basically non-existent, I decided to have a wood base made by a wood worker from Laguna.

The first thing I did is to figure out a good layout based on the top plate that was cut from 4mm aluminum using a jigsaw.

Looks good for me! so I decided to see how it will fit the wood base with some parts mounted to the top plate.

Not bad eh. It took me about two days to finish this amplifier. And when done, it looks like this:

My current version is a cap coupled circuit with lots of iron. I experimented on using choke loading on the 5842 driver, using a 100H @ 20mA plate choke. On the 45 grid, I removed the grid leak resistor and changed it to a grid choke with 5,000H @ 3mA rating.

Here is the current schematic.