Hi folks,
Following my first 300B monoblocks built in 2021, I'd like to share my latest 300B monoblocks built in 2023.
Features Highlights:
-5.5W effective output from each channel
-Each block contains an 100VA Power transformer, an 10H choke and an 35W output transformer
-All of the B+ and filament voltages are regulated by LM317
-Soft start for filament voltages (to prevent inrush current from damaging the filaments)
-starts from 1.9V to 5V and 6.3V in 10 seconds
-Delayed soft start for B+ (to pre-heat the filaments before supplying B+ for prolonged tube life)
-starts from 20V to 376V in 30seconds after 30seconds delay upon power ON
-Timer function achieved by 555 IC
-Solid state relay for B+ for prolonged life
-Zero-crossing detection (achieved by the solid state relay)
-Plenty of RC snubber networks used to reduce damping and noise
Following my first 300B monoblocks built in 2021, I'd like to share my latest 300B monoblocks built in 2023.
Features Highlights:
-5.5W effective output from each channel
-Each block contains an 100VA Power transformer, an 10H choke and an 35W output transformer
-All of the B+ and filament voltages are regulated by LM317
-Soft start for filament voltages (to prevent inrush current from damaging the filaments)
-starts from 1.9V to 5V and 6.3V in 10 seconds
-Delayed soft start for B+ (to pre-heat the filaments before supplying B+ for prolonged tube life)
-starts from 20V to 376V in 30seconds after 30seconds delay upon power ON
-Timer function achieved by 555 IC
-Solid state relay for B+ for prolonged life
-Zero-crossing detection (achieved by the solid state relay)
-Plenty of RC snubber networks used to reduce damping and noise
Thanks. It's a bit complicated as a tube monoblock. Basically 3 LPS and an 2-stage amplification:
No, that's the output from the output transformer - COM, 8ohm and 15ohm
Sorry, I don't have a square wave test picture.
Ah - it's a 6SN7. It's marked on the PCB. Several ways of using a 6SN7, and according to Stephe the 3 stage circuit is the worst (Sun Audio etc). Could be paralleled, could be SRPP.
In Hong Kong , we have a skilled tube technical . So you can share some experiences with others. What is the reason for the output power of 5 watts?
One of the reasons to design the output to 5.5W is to prolong the life of precious 300B. The other reason is that the operating point. I chose the operating point which has a balance between 2nd order harmonics and power output, according to a data sheet (I don't recall which data sheet, probably from WE?)