1625 Push-Pull Amplifier driven by 6N9S-6N8S(Concertina phase inverter)
OverviewAfter 3 years on my DIY Audio journey, I finally made my own Output Transformers. Looking back wasn't that easy. I'm not intrinsically a patient man to take-on the complexities of winding an Output Transformer. I have to grow my hair literally and extend my patience a little bit. Girls called the process "Tiis Ganda" hahahah
The design was pretty much similar to the OddWatt but instead of using 6l6gc, I have used 1625 which is very similar to 6L6 but uses 12.6V on the heater.
Winding the Output Transformers
These OPTs were design to run at 40W @ 20Hz with an Impedance of 8K. But this amp is only running approximately at 25 watts per channel. This OPT uses an interleaved design of 5 primary winding sections and 3 secondary winding sections. Sounds complicated? Yes, for first timers like me it is but maybe I'll get used to it as time goes by and more practice.
Draft paper for inter-layer insulation. Without those, wires will fall in between the previous layer.
At this point, 1st primary winding sections were done. Side-by-side comparison for each section to ensure consistency between both OPTS.
Double NOMEX insulation plus Kapton tapes at the side.
1st secondary winding section were done. This is the 16 ohm tap.
2nd primary winding section continuous.
Done.. One layer of Draft Paper and then Nomex tape
Bifilar winding on the 4Ohm secondary winding section.
Done with the 4Ohm secondary section
Another primary winding section
Done with the primary section
After 12 days of OPT winding or 6 weekends windings are finally done
and time to put those eyelets.
Impedance testing with a Variac
Varnish Dipping and Sun baking
Winding the Power TransformersAfter winding those OPT, it makes Power Transformer a walk in the park
Starting off with the primary winding
Secondary Windings
HV tap done
Meanwhile, Transformer covers are painted with Hammer tone paint
Heater windings done
Ready for Testing
Enclosure works
Enclosure done and painted.. Installed the faceplate
Wirewound pots for balancing the cathode current
70% done
All done... I have to wait another weekend before doing the actual test.
Actual TestingAfter I turned ON this amp, I didn't have much problems and most voltage measurements are as Expected. After one hour of playing at full volume, my Power Transformer temperature rises from 30 degrees to 47 degrees Celsius. Although a temperature rise of 17 degrees Celsius is okay I have tried removing the CCS using TL783 and changed it to Cathode Resistor with a bypass capacitor (blue one on the picture above). After listening to it, I have decided to keep the Cathode Resistor.
Sound ReviewIt's been a long write-up so I'll make this short. The sound sits between being punchy and luscious. Just exactly the right tightness but not punchy. It has the clarity and warmness of 6L6 tubes. Tested several records on this amp from Louis Armstrong, Earth Wind and Fire to the heavy metal ACDC, Megadeth and Pantera.
AcknowledgementsBig Thanks to Tony Tecson for our never ending design reviews and discussions at elab.
Many Thanks to Edrel Sison for bringing-in the best quality materials for our builds.
Gerry Sta. Maria for these lovely 1625 bottles.
And to my lovely Wife for her never ending support for my DIY endeavors.
