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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Ebay 300B SE amp information

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ashok ... did you scroll down the ebay listing?
There is lots of blank space, but keep going and everything you need to know is there about half way down the page. I guess if you need more - best advice is take great care.

Just 3 examples from the listing.
 

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What are the specs of the output transformer? Mine is a James with multiple taps. Tube bias level in mA? Of course load has to be there while testing. I'd use a power resistor ! Don't think this is going to be too easy ! I can't read anything on the circuit diagram. What did you guys open the file with ? The standard programs on my PC give blocky unreadable text. Thanks everybody.
 
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.

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.
 
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 !:D

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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Hi
I also bought one of these. I traced the pcb as best I could as I am definitely no expert as I couldn't reconcile the one provided by the ebay seller. If I can attach it here I will. I looked around and made some transforms and choke choices based on my little knowledge. On the webpage it indicated transformer of 320-0-320 is required.
 
Ebay 6sn7/300b schematic

Apologies for any errors in the circuit. I left out an led included on the heater circuit. I am hoping to breathe life into it soon but would like someone with more experience to check my wiring etc before I switch it on for safety.
 

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My build of this amp is complete and I must say I am enjoying the sound immensely. I don't know if it's hyperbole on my part but I long to get home from work and put the music on now. Though I have a low level of hum which annoys me and haven't been able to resolve this doesn't take away from the sweet sound. I had been listening to my class d theatre amp which is quite good especially the bass frequencies I know now it messes with the naturalness in some way. I took it to a guitar amp tech to check my amateur work before I turned it on he said the biasing could be improved if I wanted. I might do this when I have more experience and find out what he meant by that :(. But in the meantime enjoy.
 
Though I have a low level of hum which annoys me and haven't been able to resolve this doesn't take away from the sweet sound.

AC filaments? Balancing pots? It is hard, at least for me, to totally eliminate hum with a true triode with 5 or more watts using 103db speakers but with DC filaments and balancing pots I reduced it to an acceptable level. I do believe my build would be quite with 90db speakers. It takes some effort though. I used Arta to set my balancing pots which helped a lot.
 
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