Questions about 6x4 - 6x5 rectifiers and 2a3 tube

[kagliostro]

The cathode of the 6x4 and 6x5 is separated from the filament and the filament request is of 6.3v

Is safe to use such tubes with atransformer that has only one 6.3v winding, so the rectifier and all the other tubes are supplied by the same wires

or to have two separated 6.3v winding is a must also as to avoide possible noise ?

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Looking in the web I've seen a little oscilloscope project that uses a 6SN7 triode as rectifier, old '30 practice

so a strange idea come to my mind, if a triode can be used as a diode, may a diode like the 6x5 be used as 2a3 triode, not in place of a 2a3, only in the same way ????

I know, sometime I've strange and crazy idea

Thanks

K

[sluckey]

It's OK to use 6x4 and 6x5 on the same filament winding with other tubes.

A triode can always be strapped as a diode (tie 2 elements together). But a diode can never be used as a triode because it is missing the third element... control grid.

[kagliostro]

Hi Steve

I was thinking that as in the 6x5 the cathode is separated from the heater, the cathode can be used as a grid

but I reflected on this topic and all depends on how physically is build a cathode and a grid

Thanks for the info

Franco

[HotBluePlates]

Hi Steve

I was thinking that as in the 6x5 the cathode is separated from the heater, the cathode can be used as a grid

A control grid is a spiral of wire; the electrons pass through the gaps between adjacent wires.

A cathode is a solid metal sleeve; no space for the electrons to pass through.

In general, you don't want the issues that come with filamentary triodes (those whose filaments are also the cathode). They are more susceptible to hum (which can be neutralized, but is more difficult than with heater-cathode tubes), because the filament is always part of the signal path. Even d.c. operation of the filament presents problems, because it will impact tube bias.

[PRR]

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[kagliostro]

Hi PRR

 

That is the nicest explanation I've never seen

is an idea for a cartoon about Tube Amps ?

Very sympathetic and effective 

Thanks

K