829b Push-Pull AmplifierOverviewThe thing about DIY is that you can do it in your spare time. Yes, it took me about 7 months to finish this amplifier. But it was all worth it. I had doubts on my design, thinking it will not work the way I want it but it turned out to be awesome.
On top of the laws (Ohms, thermodynamics, etc.) that we have to follow, designing an amplifier has subjectivity as well. And the designer has to balance things or be biased on some aspects of it. I guess an analogy to this is a man looking for a woman. At some point he has to determine if he wants to have a high performance woman at a high cost or a woman with moderate performance at a moderate cost. Performance and cost are most likely to go together but in worst cases it could be a low performance at a high cost. John, what are you talking about? Amplifiers are our mistresses... Well that's what I was suspecting hahahha
But anyway, this amp was loosely based on Seiichiro Suzuki 829b Push-Pull amplifier. However, instead of using a cathodyne phase inverter, I took the route of using LTP. Many amps like Audioromy FU29 have already used Cathodyne Phase Inverter. The main advantage of LTP over Cathodyne is that LTP is very linear. The 829b needs to be driven by low impedance output and this LTP using 12AU7 is a good candidate.
Playing safe with the input driver design, I have used a 12AT7 SRPP like you usually see on HIFI amps. Amplifiers using SRPP were called "distortion less audio amplifier" way back in the 50's.
The Output Stage uses the exquisite 829b a double tetrode tubes used in VHF radios in its hay day. I have been collecting a few of these tubes since about two years ago. And prices including the Russian GU-29 soared up on ebay after Cayin and Finale Audio made their amps using these tubes.
...And here's how I did it.
Power Transformer WindingEnclosure layout, Drilling and Paint JobPoint-to-Point - Look mom, no PCBGut ShotCathode Bypass CapacitorsHV, Bias and Heater SupplyBack PanelSide-by-side with my 6V6 Push-Pull amplifierIn Action12AU7 Glowing829B GlowingSound ReviewWifey's ReviewListened to mostly Crossover JazzThis design is one of those that allows one to listen to all instruments/frequencies in a song. In fact, it was the first time I noticed a husky voice from a song I've been hearing forever from radio stations (okay, it would be a little too unfair to compare far too distant sound qualities, but...) But even if you are hearing these instruments and voices all at the same time, they do not compete with each other for your attention. What each does is do their part, and complement each other, like how a good sound engineer should arrange a song.
My Review This amplifier sounds like a MOSFET in a tube.
Clear, Punchy and Lively. I have listened mostly to 90's music to test this amp and turned out awesome. I could say this is not a Luscious kind of amplifier.
AcknowledgementsAs always, this amp could not be made without all the advises from
Tony Tecson. I am and the rest of the DIY community is thankful of having you around.
Edrel Sison for bringing the best goddies we could have for our builds.
Gerry Sta. Maria for the driver tubes.
Enrico Resurreccion for the wood works.
People at Elab and fb group "POWER AMPLIFIER & ELECTRONICS CIRCUIT TECHNICIAN FORUM" for continuous technical discussions