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Hi!I wonder how it sounds connecting the speaker to pins 1 and 5 of output transformer....I'd probably bypass the output attenuator. Choke for power supply filtering is very effective ...I recommend putting it first, in place of the 125 ohm resistor. and leave R31 as is. Maybe need a low value resistor in front of or just after the choke...like 10 ohms...just have to try and give it a listen.You can still use PACO power supply to investigate....for instance, power center tap of output transformer from PACO to see what if any hum is picked up in circuit from tube V4 or the +310 rail. Who knows but maybe the balance pot on output tube cathodes is totally cancelling the power supply ripply passing through output transformer primary....if so you can use a smaller choke and put it in place of R31.DC filaments help get rid of/reduce hum sometimes as can a filament supply center tap. The HP201C is using a pseudo center tap for filaments. Some tubes have a failure mode in which they pickup more hum from ac filament than they did when they were new....I'm not sure what broke but I run into it frequently enough that I always check by subbing in a new tube (I'm referring to V4).Do you have a variac? I always use a variac to bring up voltage slowly after I've made changes in the power supply. I use a smallish fuse in the variac....3 amps for testing line level stuff and 5 or 6 amps for power amps. I use fast blo for best protection since I'm bringing up the variac voltage slowly...so don't need slo blo fuse.Lastly...the recording you posted sounds good...be careful not to lose that sound. I make recordings at various points of a mod making sure to keep levels the same for easy comparison later. I just record with my focusrite scarlett 2i2 cuz it's good enough....and I can afford to replace it if I blow it up which I have done. I keep a Hum Eliminator in front of the Scarlett except when I really need to have a the "instrument" impedance (a mere 47kohm) but even then I have a film capacitor in front of that...I think it's 10.0uf 600v....physically big but worth the protection. I have at times made recordig of the B+ rails. I have 100kohms on the output side of that capacitor and make the connection to the B+ rail before connecting to the Scarlett to protect it from the high voltage pulse that will come though the capacitor upon connection to the B+ rail. Note on the Hum Eliminator: good frequency response out to 50khz but low frequencies saturate is easily. Have to keep levels to -10db if I'm looking at frequency below 50 hz. I plan to buy a better transformer for this front end application. Non-saturation up to 15db should be findable.
Hi!
I wonder how it sounds connecting the speaker to pins 1 and 5 of output transformer....I'd probably bypass the output attenuator. Choke for power supply filtering is very effective ...I recommend putting it first, in place of the 125 ohm resistor. and leave R31 as is. Maybe need a low value resistor in front of or just after the choke...like 10 ohms...just have to try and give it a listen.
You can still use PACO power supply to investigate....for instance, power center tap of output transformer from PACO to see what if any hum is picked up in circuit from tube V4 or the +310 rail. Who knows but maybe the balance pot on output tube cathodes is totally cancelling the power supply ripply passing through output transformer primary....if so you can use a smaller choke and put it in place of R31.
DC filaments help get rid of/reduce hum sometimes as can a filament supply center tap. The HP201C is using a pseudo center tap for filaments. Some tubes have a failure mode in which they pickup more hum from ac filament than they did when they were new....I'm not sure what broke but I run into it frequently enough that I always check by subbing in a new tube (I'm referring to V4).
Do you have a variac? I always use a variac to bring up voltage slowly after I've made changes in the power supply. I use a smallish fuse in the variac....3 amps for testing line level stuff and 5 or 6 amps for power amps. I use fast blo for best protection since I'm bringing up the variac voltage slowly...so don't need slo blo fuse.
Lastly...the recording you posted sounds good...be careful not to lose that sound. I make recordings at various points of a mod making sure to keep levels the same for easy comparison later. I just record with my focusrite scarlett 2i2 cuz it's good enough....and I can afford to replace it if I blow it up which I have done. I keep a Hum Eliminator in front of the Scarlett except when I really need to have a the "instrument" impedance (a mere 47kohm) but even then I have a film capacitor in front of that...I think it's 10.0uf 600v....physically big but worth the protection. I have at times made recordig of the B+ rails. I have 100kohms on the output side of that capacitor and make the connection to the B+ rail before connecting to the Scarlett to protect it from the high voltage pulse that will come though the capacitor upon connection to the B+ rail. Note on the Hum Eliminator: good frequency response out to 50khz but low frequencies saturate is easily. Have to keep levels to -10db if I'm looking at frequency below 50 hz. I plan to buy a better transformer for this front end application. Non-saturation up to 15db should be findable.
