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Ebay 300B SE amp information
Ebay 300B SE amp information
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Old 14th August 2018, 08:43 AM   #11
Alan4411 is offline Alan4411  Wales
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Originally Posted by ashok View Post
What are the specs of the output transformer? Mine is a James with multiple taps.
That is determined by your choice of output valve and the mode you run it in. Here you have 300B in SE (single ended) mode. So typically is 2.5k to 3.5k primary.

Originally Posted by ashok View Post
Tube bias level in mA?
Guess you will have 70 to 80 volts on the 'cathode'. So Ohms law says 70 to 80mA 'bias' using the 1k resistor.

So as long as your James has 2.5 / 3.5k or similar tappings and is designed for Single Ended use (not push pull) and can handle 100mA DC or more, it will be fine.

Same if you use a choke in the power supply remember, what ever inductance you choose it has to be rated at least 200mA for stereo pair.

You cannot improve the diagram, but see to link on pcan's post #4 and all is clear.
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Old 15th August 2018, 09:52 AM   #12
ashok is offline ashok
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Location: 3RS
Ebay 300B SE amp information
The seller sent me a clear circuit diagram. Same as on the web site but this one is readable.
Now I have to get back to all the work I did on the 300B before I even bought the tubes a long time ago ! Since the diagram doesn't have any OPT impedance mentioned, I'll go with the 2.5K tap. I already made a power transformer but will have to check it again. I don't remember on what basis I ordered it. Shifting my home has caused a lot of 'memory' loss !

Just making it because I already have the tubes and transformers. Can compare it with my other tube amps.Will post results when it gets done.

Edit: I forgot to attach the drawing I got. Anyone else who needs it can check it out.
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File Type: pdf 300b(1).pdf (108.7 KB, 21 views)

Last edited by ashok; 15th August 2018 at 09:57 AM.
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