Hi everyone, I'm a newbie here @ DIY so please bear with me.
My question is this: I have recently built the 16LS kit from S-5 Electronics and I would like to switch the bridge rectifier chip for the B+ with a rectifier tube (5u4GB maybe?). Has anyone done this or does anyone have a good schematic to do this? Could I use a separate trans. for the 5U4's heater?
Why would you want to do that?
It's something I definitely wouldn't recommend. The forward voltage of Si diodes is typically 0.7V. Have a look at the 5U4GB spec sheet and the plate characteristic. The forward voltage is a good deal higher, and can approach 100V or more. You'd lose a helluvalot of voltage by replacing the Si diodes.
For one project, I used a 5U4GB precisely because the PTX I had overvolted badly with Si diodes: 458Vdc (unloaded) as opposed to the design nominal DC rail of 350Vdc. This vintage, NIB PTX (a Stancor: 650Vct/150mA; 5.0V/3A; 6.3Vct/5A) was obviously designed to use this type in a 350V power supply. The current rating was right, but I needed to lose 100V, which was the forward voltage picked off the plate characteristic.
I did find, after many different search term combinations, find a reference to this type of connection. It stated to use a CR filter for each of the 2 cathodes, then tie the far end of the two resistors together to combine the two rectifier outputs. The resistors acts to balance the load between the two rectifiers. As an educated guess for this circuit, a 10uF cap followed by a 50R resistor may work. The same reference also stated that paralleling the transformer secondaries, as long as they are matched, and using just 2 diodes also works.
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