Hi All tube lovers
I had an inquiry from someone who wanted to hear what a tube amp sounds like. I didn't have a demo unit in the house, so I offered to put something together for the listen.
I had a chassis with a mains transformer and I stole two output transformers from a protoype I built for another project. The primary impedance was 7k:8ohm with a 12% cathode feedback loop.
Checking the power supply I noted that I could get 250VDC B+ if I use a choke input filter. Superior regulation is essential when trying to make a pentode sound good. Eventually I had to insert a 2.2uF capacitor between the rectifier and the choke to reduce choke rattle.
I had some 6F6G tubes that are popular in old radios. I though I might as well use them, and if they do not sound good, I could always use 6V6G in stead. They like 250V and the choke input filter would deliver just that. With the 2.2uF fitted to get the choke quiet, the B+ went up to 285VDC, still in spec for ther 6F6G.
I wired the 12AU7 in SRPP mode, and it all souded great, but not what I wanted. I tried a 20 Henry choke in the driver supply, but no audible improvement. Then I moved the driver output from the top triode cathode to the bottom triode anode (turning the SRPP into a current sourced triode). Suddenly the bass and tops sounded right.
This is what it turned out to be:
I had an inquiry from someone who wanted to hear what a tube amp sounds like. I didn't have a demo unit in the house, so I offered to put something together for the listen.
I had a chassis with a mains transformer and I stole two output transformers from a protoype I built for another project. The primary impedance was 7k:8ohm with a 12% cathode feedback loop.
Checking the power supply I noted that I could get 250VDC B+ if I use a choke input filter. Superior regulation is essential when trying to make a pentode sound good. Eventually I had to insert a 2.2uF capacitor between the rectifier and the choke to reduce choke rattle.
I had some 6F6G tubes that are popular in old radios. I though I might as well use them, and if they do not sound good, I could always use 6V6G in stead. They like 250V and the choke input filter would deliver just that. With the 2.2uF fitted to get the choke quiet, the B+ went up to 285VDC, still in spec for ther 6F6G.
I wired the 12AU7 in SRPP mode, and it all souded great, but not what I wanted. I tried a 20 Henry choke in the driver supply, but no audible improvement. Then I moved the driver output from the top triode cathode to the bottom triode anode (turning the SRPP into a current sourced triode). Suddenly the bass and tops sounded right.
This is what it turned out to be:
I think he was looking for a solid state integrated amp/turntable combo. So now I have a cool single ended amp to listen to.
