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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 1st November 2017, 03:44 PM   #1
jslateiv is offline jslateiv  United States
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Default New TSE 300b Build

Hello all, I've been lurking awhile, reading through these threads a lot (and the TL website),... and have decided to build out a TSE 300b. That said I have a pretty good understanding of the circuit, thermal requirement for the semi's, etc,...

I have decided on a Hammond 274BX (750CT) and some 1Electron UBT-2, and a choke for r4.. Knowing that the PT is running high and the considerations that have to be made for increased Cap V (C4,6), and resistor power ratings.. I want to make sure that my B- will stay in line,.. I have been playing around w/PSUDII trying to get a handle on exactly what/how the higher PT V will effect the B- and what I may need to do (if anything) to keep the loaded B- in line (~300v)

So my 1st main question is what is the current draw on the B- leg? Looking at the schematic I am thinking that the r11,13,12 (r channel) will pull ~3.5ma to ground. Not sure how much to add in for the FET,.. all of this x2 has me thinking ~12ma total on the B- supply,... Obviously the load you use in PSUD has a dramatic effect on the B- V and is needed so I can make sure that my Resistor watt ratings and values are good,..

Thanks for the help! Really looking forward to sharing the experience online. Pics and all!
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Old 1st November 2017, 04:12 PM   #2
tomchr is offline tomchr  Canada
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George/Tubelab and I make similar recommendations regarding the operating point of the 300B. In part because I read his website, tried his suggested operating point, and really liked it.

There are a number of operating points commonly used with the 300B. Many sit around 360 V, 60 mA and provide a few watt with relatively high distortion. Others, such as George and I, suggest 400 V, 85 mA as that gives you higher power at lower distortion. So you're aiming for a B+ in the range of 360-400 V.
In PSUD II, I would simulate the amp as a 200 mA current source load for a stereo amp. This would imply that the driver tube is running a bit hot, but hey... 200 mA is a nice round number and it's close enough for government work.

You're going in the right direction. Keep at it!

Tom
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Old 1st November 2017, 04:31 PM   #3
jslateiv is offline jslateiv  United States
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Thanks for the reply Tom. Yes I am aiming higher. Looking for a plate voltage around ~380v,.. and ~80ma.. PSUD modeling puts my B+ ~406V and some of that will drop across the OT's, The UBT-2's are 430ohm, so at 80ma they should drop 34v, correct, right?

Still, it's the B- I'm worried about,.. modeling at 5ma gives me 460v at c7,.. 15ma gives me 346v at c7,.. big difference and some adjust could be needed if that ma figure is truly lower,.. just not sure what it truly is for proper modeling. Thanks again for the feedback,. -Johnny
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