Introduction
I got a very old TV from a colleague, it had been stored in his parents attic for almost 30 years. It was huge and ruined from the time it was stored, so he only brought me the electronics which mainly was produced in Denmark. It did not contain PCBs, only bird nest wiring between tube sockets and plugs.
I scavenged the different parts for among other things: AC flyback transformer, tubes, sockets, plugs and resistors. All the capacitors was worthless due to age.
I decided to reconstruct a tube amplifier from the power transformer, output transformer, tubes, sockets and resistors from the TV set.
Safety
WARNING!: Working with electricity is dangerous, all information found on my site is for educational purpose and I accept no responsibility for others actions using the information found on this site.
Read this document about safety! http://www.pupman.com/safety.htm
Limitations
The output transformer is a single end transformer and as I only had one, it was going to be a mono amplifier with only one output tube.
WARNING: The power transformer is more of a autotransformer as the primary and secondary are not isolated, so grounding the secondary neutral is not possible, this can result in dangerous situations and the mains neutral is also the neutral for audio input!
Construction
I found a old schematic that had a good resemblance with the components I had from the TV set, the original schematic can be seen here.
Here is a redrawn schematic with a few changes, tone and volume control is left out since they did not work as intended and only brought a lot of noise and squeaking into the amplifier. I used a UCL82 tube instead of the ECL82, the difference is the heater voltage where I use 50V instead of 6,3V.
I first made a test setup to tinker with the amplifier, not very pretty or for that matter, safe.
The amplifier was built into a stainless steel box that was thrown out due to a damaged lid, so I used the lid as a bottom plate and installed the transformers, capacitors and circuits on this, the box comes on as the entire enclosure. Only the single tube is left outside the box along with the different jacks on the backside.
The original Telefunken UCL82 tube made in Germany.
The complete amplifier as it stands today.
Conclusion
I reached my goal that was to build a tube amplifier from the parts I had already at hand. I only spent money on some proper speaker and input connectors.
This small 2 Watt amplifier is capable of playing real loud and the many different types of the triode/pentode xCL82 tubes like PCL82, ECL82 etc. makes for good small amplifiers or for headphone amplifiers.
Demonstration
Demonstrating a audio amplifier is something that can only be done experiencing the amplifier in person, but you will have to do with this video of my amplifier playing.
Congratulations for the project.
When I was a child, I made one with 50BM8 (50 Volts) withou input transformer (very simple) and with a resistor to lower the voltage (from 11o to 50 V).
Now I wanto to to one stereo, for use with my iPod. What do you think? Can you help me with the scheme?
Thanks a Congratulations again.
Roberto
Nice one, do more tubes projects!
Hey Radu
I am actually finishing my article about a 2x 30W EL34 amplifier that I finished just recently, check back soon 🙂
Hi Mads.
I would like to build this amp from Claus Byrith. I have not much experience, but I think this project should be possible.
I have read the instructions for the layout but still doesnt understand it.
Is the diagram for one channel ? And why are there 3 tubes?
Best regards Peter Rasmussen
Hello Peter
Claus Byrith instruction are well written and covers almost every detail, you should do fine 🙂
The schematic only show one channel, but the power supply is valid to use for two channels. As it is noted in the schematic.
The three tubes have different jobs, it is from left to right the pre-amplifier, phase shifter and output tube. The ECC83 tube contains two triode sections, so the pre-amplifier and phase shifter can be implemented with only one ECC83 tube. The EL34 output tube handles the heavy load of driving the output transformer.
Kind regards
Mads
Hi nice little amp, i like the warm sound.
any idea if a EL95 would suit this schematic?
kind regards
Daniel
Hi Daniel
The EL95 is only a pentode where the UCL82 is a combined triode and pentode, so you need another triode tube to use the EL95.
The EL95 also requires a load with double the resistance of the UCL82, so you need to find a output transformer with a 10K primary for the best results.
Kind regards
Mads
Nice tube amplifier circuits. Very good project. Circuit
Hello Mads,
I suffer the same horrorific sound when implementing a volume knob. However i see a lot of schematics including such a solution. Also when it is making those sounds then in the dark you can see sparking between legs 6 and 7 from the tube. When i remove the volume controll and just put my phone directly on the grid i have no problems.
I can’t see what iam doing wrong. Schematic is the same. Only you do not use a decoupling capacitor on the preamp.
Nice job on the housing, put’s the tube in perspective.
Kind regards,
Henk
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found mine UCL82 in the forest with some other components like transformer some other tubes and output transformer. Everything was realy rusty, but everithing seems to work. Found all the other compounents in an old barn. All capacitors are new. I added a Magic eye and a tube diode from the forest. At the end I’ve got a realy nice tube amp that i gifted to a friend of mine. I kept the Volium Controll. Friend dicovered a cheep Radio thats makes this tube amp sound awesome.
This thing Rocks
Thaks you.
What a great story Emil! I am happy that this article could help you 🙂
It’s home edition of electric chair.