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- Green God : Born Again
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Green God SE 6AQ5 Amplifier Project 2/2022
The Original SE 6AQ5 PA Amplifier
The Original SE 6AQ5 PA Amplifier
The Original SE 6AQ5 PA Amplifier
The original SE 6AQ5 PA amplifier was discovered in the bowels of an old electronics surplus warehouse many years ago.
A new circuit featuring parallel 5751 driver stage capacitor coupled to 6AQ5 finals running in beam power mode with loop feedback was designed and installed.
The Green God : Born Again
The Original SE 6AQ5 PA Amplifier
The Original SE 6AQ5 PA Amplifier
The Green God was born from the desire to improve upon the SE 6AQ5 amplifier circuit in terms of both measured and subjective performance. The cosmetic appearance was also in need of improvements.
The chassis was stripped of all components and refinished with automotive primer, then several coats of Krylon Sea Glass satin spray paint.
The original OPT's were replaced by AES PT-31's, SE 5K/8 ohm.
New power supply filtering and signal circuits were designed installed and tested.
Green God Signal circuit schematic
Grid Stoppers, Zobel and Feedback Networks
There were some issues with load dependent stability when the amplifier was connected to DT667's Altec 2-way horn speakers. Those issues were solved by the addition of grid stop resistors on the 5751 driver tube and a Zobel network across the OPT secondary.
THD @ 1W = .73%, THD @ 2W = 1.45%, THD @ 3W = 2.55%
Measurement taken on RT Channel with 1KHz sine wave test signal.
Operating points were added to the Green God signal schematic.
Green God Power Supply Schematic
Power Supply Filter
High Voltage Snubber Network
High Voltage Snubber Network
Green God main power supply filter schematic.
High Voltage Snubber Network
High Voltage Snubber Network
High Voltage Snubber Network
The Swenson snubbers (330 ohm + .02uf 2KV ceramic cap) installed across HV secondary winding.
UF4007 1A silicon diodes in FW rectifier.
Green God Bandwidth Sweep
AES PT-31 SE OPT 5K/8
Green God Bandwidth sweep with Pink Noise 20Hz - 100KHz.
-1.5dB Low = 20Hz
-3dB High = 84KHz
Green God Phase vs. Frequency
AES PT-31 SE OPT 5K/8
ARTA STEPS Phase vs. Frequency 20 - 20KHz.
The amount of phase shift in the OPT can be a clue to its quality.
The AES PT-31 SE OPT 5K/8 is priced at less than $16USD.
Green God Square Waves
1KHz square waves
1KHz square waves
1KHz square waves
Before adding 680pF cap to feedback network.
1KHz square waves
1KHz square waves
1KHz square waves
After adding 680pF cap to feedback network.
10KHz square waves
10KHz square waves
10KHz square waves
Before adding 680pF cap to feedback network.
10KHz square waves
10KHz square waves
10KHz square waves
After adding 680pf cap to feedback network.