EL84 Push-Pull

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EL84 UL Push-Pull Stereo Power Amplifier with Hashimoto Transformers

This amplifier was originally featured on the October 2003 Issue of the "High-Fidelity Audio: Radio Technology" by Mr. Tadaatsu Atarashi.  Mr. Atarashi designed this amplifier based on the EL84 schematic diagram published by Rogers in England.   Mr. Atarashi chose this design because of the uniqueness of the positive feed back that the original blueprint adopted.  This positive feedback is applied back to the input stage cathode from the phase splitter's cathode.  The reason why Mr. Atarashi was interested in the positive feedback was, from his past experiences, Mr. Atarashi suspected positive feed backs would yield somewhat brighter sound than not having any positive feed backs.

For this project, Mr. Atarashi used Hashimoto PT-180 power transformer, C-15-200CH and C-30-40 choke coils, and HW-25-8 output transformers.  The speaker system Mr. Atarashi used for his listening test was a pair of Western Electric, WE-735C monitor speakers.  EL84 power tubes were from Electro Harmonistic.  Because of the size of the EL84, Mr. Hashimoto was not expecting to hear the powerful, but shining sound from his vintage speakers.    



EL84 Class AB1 Push-Pull UL Connection Data Sheet (43% Screen tap)


Plate Voltage: Va 300 Volts
Screen Voltage: Vg2 300 Volts
Cathode Current (0 Signal): Ik(0)  80 mA
Cathode Current (Max Signal): Ik(max signal) 90 mA
R.M.S. Input Voltage (grid to grid): Vin(g-g) r.m.s. 16 Volts
Plate to Plate Load: Ra-a 8,000 Ohms
Power Output: Pout 11 Watts
Total Distortion: Dtot 0.7%

Schematic and Actual Characteristics

bulletSchematic & Harmonic Distortion


bulletInput/Output & Frequency Response


bulletEL84 Data Sheet from Mullard
bulletEL84 Data Sheet from Philips

          Data Sheets are from Frank Philips


















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Last changed: 02/01/15

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Last updated: 02/01/15.