Prologue 1626/5842 Tube Amplifier

This project refers to Jim de Kort's 1626 project called Prologue. A parts list is available. I use standard 6V regulators for the preamp tubes' heaters, and an LM350 variable voltage regulator as current source for the power stage tubes. Jim de Kort does have some very useful tips on regulating power for filaments on his site.

In case the original site goes down, I've decided to provide the schematics below and not just point to Jim's site. In the past I've whitnessed a few sites disappear which contained a lot of useful and interesting information for DIYers. I was planning to build an RIAA phono preamp along a nice design by Remco Stoutjesdijk (formerly ultranalog.com) featuring Nuvistor type miniature tubes. He took down the site for personal reasons before I could get into the details. Poof, gone. So just to be sure: here are some basic schematics.

Signal path

High voltage power supply

6V Preamp filament DC power supply (voltage source)

12V Power amp filament DC power supply (voltage source)

Generic filament DC power supply (current source)

Calculate R to provide the current you need.

Update [2013-10-20]

I stumbled upon an interesting site where someone had connected a “Magic Eye” tube to his guitar amp. I thought it might look cool to have two of these indicating the audio level of the left and right channels of my 1626 Prologue amp. I modified the circuit shown on the site above to suit my needs and so that I could use components that I had lying around. I tapped the anodes of the 1626 output tubes and got a nice voltage swing. I changed the capacitor Chold to 0.15uF so the magic eye is quite responsive but still has a nice rise/hold speed. I'll add some photos tomorrow.

Here is the basic schematic, which was originally posted by Michael on the 18watt site in case the original site goes down:

Update [2010-12-05]

Finished the amp today. Sounds nice and full, just like it did before I disassembled it and put it away to move it into its new housing. Now the chassis is even safe to touch without wires floating around, carrying 600V. We don't want to fry the cats or the dog, do we? Another good thing is, this beast weighs in at about 24 kilos, so noone's going to steal it. It delivers a whopping 1W (yes, one) into 8 ohms. Talk about efficiency ;)

1626 1626 1626 1626

Sadly there wasn't enough place left to fit a #80 mercury vapor rectifier tube in somewhere. The prototype featured both a an octal and a 4-pin socket so I could choose between either a #80, #83 which are both 4-bin based or 5Y3G or 5Y5GT octal based rectifiers. The #80 mercury vapor is glowing blue which looked kind of cool. I did like that.

Update [2010-12-03]

Transformers are mounted, holes for tube sockets drilled, sockets mounted and the speaker connects at the back of the chassis, too. The mains switch at the back switches the filament power supply so the heaters are able to warm up before you apply the high voltage to the plates. That's what the switch on the front does, if the mains are on. Here are a few photos I took without the glass mounted.

1626 1626 1626 1626

Update [2009-03-22]

1626housing.jpgRight now I don't have much time to spend on refining the amp or building a nice housing for it, but I have started to take the Prologue 1626/5842 Tube Amp prototype apart. I've drilled a few holes into the new housing and have mounted the inputs, volume pot and some of the iron.

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