EL84 Tube Amp Revisited

…and the next tube amp build on the horizon of completion.
I have been playing this amp quite a bit lately, and I keep checking the parts against my schematic. Today I noticed that the chassis wasn’t grounded, and the heaters were referenced to the output tube’s cathode voltage. I figured I would make a few changes.

I referenced the heaters to ground using two 180 ohm resistors. I also connected the ridiculous looking star ground to the chassis to keep someone from accidental death. I’d rather pop a fuse than pop a human being should something come loose in there.

This amp has a little hum to it, and I’ll check that out in Duncan’s power supply design program. Single ended amps need some stiff HT supplies to keep the 120Hz hum from moving the speaker. It won’t be anytime soon that I mess with that though.

I would like to point out that I dated the turret board “April 23, 2010.” I have learned some since then. One thing for sure is this: that thing is a wiring mess.


This is my latest project amp that hasn’t quite made its debut on Tech-Tut.com. I call this “Upcycle” because it is made from quite a few pieces of trash. A chassis and toroid power transformer from a Backline 250 bass amp, some capacitors from a desktop PC power supply, tube sockets and transformers from the original 6DG6GT tube amp that I recently redesigned, feet and handle from some amp that was scrapped, and pots left over from some other experiments. Some of the caps were also from the old build. Many parts came from my inventory (which isn’t much), and I purchased a few items new to fill in the gaps.

I believe that I have only spent about $120 on this amp. The speaker was $60; I bought a 12″ Jensen speaker. I wish I could afford a Weber.

I’m getting better at this. Once I get some paint of the cabinet and get my logo embroidered on the black burlap, I’ll put a design blog post explaining how I built this thing.
This is the dry fit of the chassis of “Upcycle” in the cabinet. This amp has a few more steps to go before it is complete.


This is the revised 6DG6GT amp. It is a single tube output. You can see my logo on the speaker cabinet. This amp has a Weber Blue Pup 8″ speaker.

About robbie

I am an electronics enthusiest and a ham radio operator (W1RCP). I like to play with electronics. It's fun and educational. I looked forward to working in the engineering field in the future. I have a BS in Electronics Engineering Technology from DeVry University. I also have an Associate's degree in Marketing Management from Moultrie Tech, and a diploma in Electronics from MTC.