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my 300B SET project

It's been a long time since I posted on this thread. My continuing 300B projects sometimes get set aside for long periods of time. The second set of monoblocks I built are called the "Pearls" because of the pearl white / red fire paint job I put on them. I had the pearls set up with a 12BH7A as the primary tube and a 7193 as the secondary. After much tube rolling including a load of 12AU7s I concluded that these amps were not as good as the chrome amps and set them aside. About a week ago I decided to rewire them for a single 6SN7 GTB. I ordered a matched set of Tung Sol units and fired them up. This was probably the best sound I had heard from them and it was with new tubes. About 2 hours into the tests the tubes settled in, it was a remarkable difference and the brake in happened over about 30 seconds. I listened to a lot of vinyl to compare them to the chrome amps, they sound fabulous! But then I pulled out the Sinatra, Frank didn't have the live in the room presence that he did through the chrome amps so I guess the search continues. These amps have Mundorf Supreme coupling caps to the 300B and the Chrome amps have Mundorf silver foil and oil. I'm not sure if I'll find what I'm looking for by changing caps but it seems like the next logical step. 300B tubes are Sophia Royal princess and they are superb.
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It's almost 5 years to the date that I purchased the Royal Princess 300B tubes for my amplifiers. Last week I had one fatally short out. My option was to go back to the Sophia 300B-N tubes I also have. The 300B-N tubes don't do nearly as well on vinyl although they sound decent on CDs. I'm looking for input on some of the other high end tubes. I ordered a set of Genelax golden lion 300Bs to have a set of workhorse tubes but I don't expect they will sound anything like the Royal Princess tubes. I'm also looking at the KR300B and the Takatsuki TA-300B. 300B SET lovers please post your thoughts!
 
Since I built these amps I had timers installed to let the filaments warm before turning on the B+ to the tubes. They were a simple timer with a relay. I just completed a set of K&K Audio soft start units that ramp slowly up the B+. I felt this would be better on the tubes. I tested the first amp tonight and it works perfectly. Now on to amp #2!
 
Dave C said:
Since I built these amps I had timers installed to let the filaments warm before turning on the B+ to the tubes. They were a simple timer with a relay. I just completed a set of K&K Audio soft start units that ramp slowly up the B+. I felt this would be better on the tubes. I tested the first amp tonight and it works perfectly. Now on to amp #2!
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Cool. I bookmarked the soft start kits. My 300B uses a 5AR4, but the soft starts would be great with my mono blocks that use a SS rectifier.
 
I wish you'd guys post some schematics and maybe a sketch of the mods to the 7193 tube circuits. I am running a couple of plate chokes on mine.
 
WntrMute2 said:
I wish you'd guys post some schematics and maybe a sketch of the mods to the 7193 tube circuits. I am running a couple of plate chokes on mine.
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I treated the 2 7193 tubes as a single 6SN7 when I started. I played with voltage until I liked the sound. Not much more than that. The worst part is that they are somewhat microphonic. They sure sound nice though.
 
What about using trimmers to set the voltage? The 300B I built using Tube Labs board has its pots for the 300B's and pots to adjust the voltage for the drivers.
It made it easy to dial in the voltage for them.
 
After enjoying these amps about 2 years since the last post I did a tube update I'll share. My go to tube has been the Sophia Royal Princess 300B. Time moves on and I decided I'd order a set of new Western Electric 300B tubes. Compared to my 9 year old Princess tubes the WE tubes are more open and clean sounding. They also need an extra notch of volume on my transformer volume controls to get the same db measurement in the room. I've got about 14 hours on the WE tubes and I really like them, the openness and sound over the entire frequency range is phenomenal. They have slightly less bass than the Princes tubes but are smoother sounding.
 

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