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Old 13th June 2009, 06:34 AM   #11
rknize is offline rknize  United States
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I've slowly been making progress on the chassis for this amp. I've re-breadboarded the amp to check out the final arrangement and see how the switchable B+ and heater voltage works. Oh man, I've missed this amp. With 45s in there...it has some kind of magic... Was listening to some old Erich Kunzel stuff...it was a hoot.

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Old 19th June 2009, 06:08 AM   #12
rknize is offline rknize  United States
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Here we are sporting the 5-pin sockets with a pair of VT-225s strapped as triodes. They sound quite nice. More grunt, like a 300B...not sure if they are as detailed as a 45 though. Need to spend some time with them. I'm running them at 50mA, which seemed reasonable. Any suggestions on bias current?

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One of the tricks of this amp build will be modular sockets on the output tubes. The Tubelab SE can drive all sorts of things. The UBT-2s don't have UL taps, so I'll just stick with triodes and triode-strapped pentodes. I plan to make 2 or more different octal sets for driving EL34s and friends as well as sweep tubes. The 4 and 5 pin are these "johnson" style sockets, but the octals will probably just be the normal ones on little adapter plates.

This one's for you, George!

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Old 23rd June 2009, 06:39 AM   #13
rknize is offline rknize  United States
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Quote:
Originally posted by rknize
...a pair of VT-225s strapped as triodes. They sound quite nice. More grunt, like a 300B...not sure if they are as detailed as a 45 though. Need to spend some time with them.
Nope...45s FTW. I was, or rather wasn't, noticing some things in some live recordings. Similar to the 300Bs, the VT-225s sound what I would call "veiled" compared to the 45s that are just so clean sounding. It wasn't until I was listening to some old, live Simon and Garfunkel recordings that I was finally convinced. They are not the best recordings but they just sounded so flat...I thought maybe I was playing the wrong album. It motivated me to go back to the 4-pin sockets. Sure enough...the 45s brought it back.

I'm starting to wonder if it maybe has more to do with the higher operating voltages when running 300Bs and VT-225s. Perhaps some interaction between the coupling cap and the gate capacitance of the MOSFET?
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