I'm in the market for a new project and recently came across some iron that may make it possible for a reasonable amount of money, but I've got some questions. If you folks would be willing to help out I'd sure appreciate it!
First off, I'm looking to make a dual mono PP 300B-anybody point me in a direction for schematics? Yes I've searched and googled but didn't come up with much. I'm hoping to use something like a 6SN7 if possible since I've got some extra octal ceramic sockets gathering dust.
Second, rectifiers: Any reason I couldn't use 5AR4s? I've got more than a few lying around and I've found some good iron with 800vct HV and 5v 3amp windings. With the 1.9 draw of a 5AR4 and the 1.2 of a 300B I think I'd be OK at 3.1 amps?
Third, output iron: I've found some 50 watt 5k Z PP outputs. Would these work for PP 300Bs?
Any help would be most appreciated-I'm jonesing to start a new project and if the iron I've found will work, I may even be able to afford it!
Thanks,
mr mojo
First off, I'm looking to make a dual mono PP 300B-anybody point me in a direction for schematics? Yes I've searched and googled but didn't come up with much. I'm hoping to use something like a 6SN7 if possible since I've got some extra octal ceramic sockets gathering dust.
Second, rectifiers: Any reason I couldn't use 5AR4s? I've got more than a few lying around and I've found some good iron with 800vct HV and 5v 3amp windings. With the 1.9 draw of a 5AR4 and the 1.2 of a 300B I think I'd be OK at 3.1 amps?
Third, output iron: I've found some 50 watt 5k Z PP outputs. Would these work for PP 300Bs?
Any help would be most appreciated-I'm jonesing to start a new project and if the iron I've found will work, I may even be able to afford it!
Thanks,
mr mojo
I am sure you understand the 300B needs a seperate filament supply. Go to http://www.tubebuilder.com//schematic1.html & look at the PP300B schematic
amperex,
I appreciate the help! So I need a separate filament supply for the 300Bs because of the center-tap? Or is it a hum issue?
Will a 5k PP output xfrmr work? The schematic shows 5k and I'm guessing it's PP output, not SE?
Also, where would I find the power supply for that PP 300B at tubebuilder? Would I have to design the power supply myself?
Best,
mr mojo
I appreciate the help! So I need a separate filament supply for the 300Bs because of the center-tap? Or is it a hum issue?
Will a 5k PP output xfrmr work? The schematic shows 5k and I'm guessing it's PP output, not SE?
Also, where would I find the power supply for that PP 300B at tubebuilder? Would I have to design the power supply myself?
Best,
mr mojo
The design requires a cathode resistor that floats the 300B cathodes up at +77 volts to provide cathode bias. The filament requires no center tap, seperate winding & a 200-ohm hum balance pot across the two filament wires with the selectable 'wiper' to ground.
The 5AR4, of course, requires a seperate 5.0 volt winding. Hammond makes low cost 5.0 volt filament transformers.
(edit)- Forgot, the 5K transformers are fine business for your application. A 2K to 5K resistor can drop the B+ from the 300Bs to the other tubes. Use a 10uF polyproplyene cap after that resistor to ground. Sollen 600 volt as great.
The 5AR4, of course, requires a seperate 5.0 volt winding. Hammond makes low cost 5.0 volt filament transformers.
(edit)- Forgot, the 5K transformers are fine business for your application. A 2K to 5K resistor can drop the B+ from the 300Bs to the other tubes. Use a 10uF polyproplyene cap after that resistor to ground. Sollen 600 volt as great.
There was a very nice p-p 300B project in Audio Anthology Volume 1. It was originally published about 50-55 years ago, but there's no reason not to update it a bit around the edges and use it.
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