It looks like AES shipped everything I asked for - I'm in trouble now... What will be interesting is putting together a project to properly utilize a pair of One Electron UBT-3s. I have a lot more single ended than P-P transformers at present - that might change next time I make an Edcor order.
I have a pair of UBT-3's on my shelf. They have been here since the development of the Tubelab SE. They were mounted in my Lexan amp for a while, until I heard, and subsequently bought some Electra - Print OPT's. The UBT-3's have been used for a lot of experiments so I know what works and what doesn't.
The UBT-3's sound very good in their intended application, and I have tried them in The Tubelab SE design with 300B's, 2A3's, and triode wired 307A's. They also work well "ratioed up" (8 ohm load on the 4 ohm tap) with the 45 tube. They have also been used in this design with several triode wired sweep tubes, like the 6AV5.
They have been used in a Simple SE with all of the usual tubes and several not so usual types. The typical 3K load and 350 to 375 B+ volts works good. I prefer the 6K ohm load with 450 volts B+ with these transformers and the Transcendars from Ebay.
The UBT-3's are not without flaws. The Primary DCR is 285 ohms. This means that about 10% of your output power will be burnt up as heat in the DCR of the primary. These transformers had the second lowest efficiency of all the SE OPT's that I have tested. The high DCR severely limits the ability to use these OPT's "ratioed down". Operating them as 1500 ohm OPT's rasies the power loss to at least 20% and one 750 ohm experiment ended with me getting 4 watts out of a 15 watt amp (yes, I was violating the 110 mA max rating).
The UBT's have spent their entire life here in this room, except for a few trips to various listening tests. For most of that time they have been confined to a solitary life in their original boxes. Oddly, they have developed a light surface rust on the laminations. They are the only transformer that has done this.
So do I, and I have been building P-P amps lately.
I think it can be up to twice that amount if you consider the secondary DCR, too. However the real loss also depends on the tube you use. The practical insertion loss in also a function of the Zout of the device.
Cheers,
45
Ok, what did I get? Well, I got a UBT-3 as companion to the one I already have. This will be set aside to await a worthy project. I also got some 6BN4As and 12AQ5s for a preamp project I'm calling "The Evil Sandman". If you guessed there was some silicon involved, you'd be right. Details will follow when I actually start to build the thing. Anyway, It'll be my first tube preamp.
A nice acquisition were 10 6LR8 vertical deflection tubes for a buck and change apiece. These were all Sears branded tubes (actualy Sylvania), with the tip-off on top, for that irresistible squatty retro look. These will definitely find their way into some amps - maybe a single-ended partial feedback amp I've been contemplating.
A nice acquisition were 10 6LR8 vertical deflection tubes for a buck and change apiece. These were all Sears branded tubes (actualy Sylvania), with the tip-off on top, for that irresistible squatty retro look. These will definitely find their way into some amps - maybe a single-ended partial feedback amp I've been contemplating.
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