The road to nirvana

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My journey into Photography, Horology, and Audiophilia

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A type 10/50/300B Amplifier

When I sold my DL103, I was fortunate to hear the system of the buyer. He has a DIY vintage Altec speakers and a tube amp with 10Y as the power tube. This became my inspiration to make my own speakers using Altec drivers and a 10Y amp of my own.

I sourced two pairs of the thoriated tungsten version of the 10Y/VT-25. My prototype used a chassis salvaged from a previous project.  I wanted minimal hum from the power tubes so I used DC for the filaments. They were glorious!

But just hours listening to my new amp, one of the 10Y died :-( I asked the source why it happened (there was no tube tester available during the purchase) and he told me it could be the filament heating as the 10Y are picky about it. I was depressed and the project never materialized to completion.

Then comes the 50. A friend of mine who hoarded lots of type 50 tubes asked me to pick a pair from a big box and they turned out to be both globe Cunningham UX-350 and matched (talk about luck huh?) This project pulled the plug on the Gordon Rankin 807 amp as I will be using the Hammonds for this. I had some custom grid chokes made too, as the 50 is limited to 10K for the grid leak. I used the same chassis for the GR 807 to prototype this project.

Here's the first iteration type 50 amp with AC for the filaments.

With the success of the prototype and knowing that the 50 also has 7.5V filament requirements, I decided to come back to the 10Y tube. I made adjustments (switchable) to the cathode resistor for proper 10Y operation and it's another success! I now have a 10Y/50 amp that is switchable :-) Here's the picture of the same amp using the 10Y tube-

I haven't heard my 300B tubes for a while now and curious about using the 5842 to drive a 300B, I asked my winder to make a pair of 0-2.5-0-5V filament transformer. I wired it in a way that I can switch between 5V (300B) and 7.5V (10Y/50) filament operation. I selected the same value cathode resistor I'm using on the 50 to bias the 300B. It was a success again, which gave birth to what I call a Tri-Amp :-)

An opportunity came much later and I was able to get a decent powder coated chassis for this project. I rewired everything to this new chassis and it looks beautiful in black. Here's the most recent iteration of this project.

With Cunningham CX-350 globe tubes.

With Hytron VT-25 coke bottle tubes.

With generic China 300B coke bottle tubes.

Here is the current schematic.