Is a PT secondary center tap a must?

[sepulchre]

Hello,

I have a Classictone 40-18015 power transformer. Its secondary has 300v at 200mA between the red leads, but has no center tap.
Can I do without it? Or should be derived with resistors to ground as in many heater wire instances?

I'm only noticing this now that I have it in my hands or I might have chosen a different PT.

[pdf64]

A full wave bridge rectifier should be used https://www.electronics-tutorials.ws/diode/diode_6.html
It is not feasible to use resistors to simulate a CT, as the CT is required to deliver current.
It works with a heater windings as in that case, the 'simulated' CT is not required to deliver current.

[SoulFetish]

The short answer is that for a normal high +voltage DC supply commonly used in amplifiers, using a non-centertap sedondary is completely fine and in some respects more efficient and simpler. In vintage tube amps CTs were used because it was a practical design technique using vacuum tube rectifiers (which were the only type of rectifiers until the advent of semiconductors). Part of the reason you the are still commonly used in amps is because old habits die hard. But, center tapped secondary supplies offer advantages in many cases, and are almost always used in linear designs which use a bipolar supply (+/- voltages).
Merlin has some great pages on his site which explain some different types of secondary supplies and rectifier circuits are used. These are a quick, to the point overview which should clear things up for you:
http://valvewizard.co.uk/psu.html
http://valvewizard.co.uk/bridge.html

[R.G.]

As an historical note, the full wave center tapped (FWCT) power transformer circuit was developed so that only two diodes would be needed for power rectification, not four diodes as in a Full Wave Bridge (FWB) circuit. The change to the transformer was less costly than two addition rectifier tubes back when only a tube rectifier was available.

An FWB circuit done with tubes requires at least three rectifier tubes; you can do the positive side rectifier with a dual plate/single cathode tube, but there are no single-plate, dual cathode tubes that are practical to build. This is a consequence of the fact that all tubes use electrons to work, not positrons or protons. All tubes are "N-channel"; there are no "P-channel" tubes.

[TUBEDUDE]

Yes, there are no "P channel tubes". Tubes don't have channels but i get what is meant.

Just to be clear though, solid state devices don't output currents of positrons or protons. Just electrons. The internal operations are described with hole theory and the movement of doping materials added to the silicon. But carriers aside, they all emit electrons.

[R.G.]

Yes, there are no "P channel tubes". Tubes don't have channels but i get what is meant.

Yeah. Tubes don't gots channels, dey gots corridors.

Just to be clear though, solid state devices don't output currents of positrons or protons. Just electrons. The internal operations are described with hole theory and the movement of doping materials added to the silicon. But carriers aside, they all emit electrons.

Yes. Outside particle acceerators, the only charge movers are electrons and ... er, holes.

Strictly speaking, no semiconductor device excepting Field Emission Triodes - which are confusingly similarly acronym-ized with Field Effect Transistors, but are quite different - no semiconductor device emits anything in the same sense that a cathode emits electrons. They all do charge carrier flow by shuffling excess electrons to other atoms, or shuffling the lack of an electron to other atoms. One of those "OK, I don't want to do this for a living" moments was when in a semiconductor physics class they took pains to point out that you can have current in a semiconductor by majority carrier or both majority AND minority carrier, that "majority" could be either an electron or a hole, and in a major/minor carrier setup like bipolars, you have both. And that both flows were different. Different not least by the fact that if you do experiments which reveal the mass of a charge carrier, the mass of an electron moving as an N-type carrier is ...different... from the mass of an electron moving the opposite direction as a hole or P-type carrier.

OK, all done with semiconductor physics there.

[TUBEDUDE]

Wow, if the masses are different hole flow is actually hole flow. I had always assumed it was just looking at the "apparent" flow of holes as a shadow of the electrons moving ftom shell to shell.
Thanks R.G. !

[R.G.]

That's the thing that really got people's attention. Got mine!

[sepulchre]

So, while you guys were answering my question without me knowing (I get no notification even though I checked the box to), I figured out that I needed a full bridge rectifier. It works great!

Thanks. The thread has some interesting stuff about particles and things. So, good stuff and things!

[pompeiisneaks]

So, while you guys were answering my question without me knowing (I get no notification even though I checked the box to), I figured out that I needed a full bridge rectifier. It works great!

Thanks. The thread has some interesting stuff about particles and things. So, good stuff and things!

Yeah sorry email has stopped working on the forum some time ago, and I've yet to get Allynmey to help me set it up again. He owns the forum itself, as well as the domain, so only he can do the needful there. He's told me he's not too worried about it. Therefore just make sure you check in here regularly

~Phil

[sepulchre]

Hey, keeps us coming back, eh? Frequent checks of this place could never be a bad thing.