# Rectifier question

OK, here’s the deal:

I’ve been arguing with a guy who tells me that there is no difference between a 4 diode full wave bridge rectifier or a 2 diode center tapped transformer setup.

I say there is a difference - in the full wave setup, both secondaries are charging the cap at each 1/2 cycle while the 2 diode setup only one secondary at a time is used. What do you all say? (see attached pic - assume both transformers and both caps are identical).

Center tap - half the transformer is working each half wave. Half the transformer voltage.

0.7 volt drop.

4 diode full wave . transformer voltage. 1.4V drop.

Otherwise full wave rectification.

What kf says is almost true. They are both full-wave rectification, and will both give approx the same output voltage [save a diode drop]. The main difference is, in the bridge ckt, the 2 windings are wired in parallel, so you'll actually be able to get 2X the current out, as the other ckt.

Alternately, with the bridge ckt, you could wire the 2 windings in series, rather than parallel, and then you have the same current out as the other ckt, but at 2X the voltage.

Any transformer with wasted windings will be operating at less than optimal efficiency (it will get a bit hotter with
the 2-diode setup than the bridge-rectifier all else being equal).

oric_dan: What kf says is almost true. They are both full-wave rectification, and will both give approx the same output voltage [save a diode drop]. The main difference is, in the bridge ckt, the 2 windings are wired in parallel, so you'll actually be able to get 2X the current out, as the other ckt.

Alternately, with the bridge ckt, you could wire the 2 windings in series, rather than parallel, and then you have the same current out as the other ckt, but at 2X the voltage.

Good answer....otherwise what would be the point ever using a full wave bridge? Back in the stone age we used 4 mercury vapor rectifiers in a bridge because in a half wave configuration, you just couldn't get enough power out to run the transmitting tube. It was cool to watch the MV's pulse on voice peaks.

Yeah, those are some really cool tubes. Nice colors. Ever seen a magic-eye tube?

Learning: Good answer....otherwise what would be the point ever using a full wave bridge? Back in the stone age we used 4 mercury vapor rectifiers in a bridge because in a half wave configuration, you just couldn't get enough power out to run the transmitting tube. It was cool to watch the MV's pulse on voice peaks.

I had an old AN-ART-13 transmitter that I built a power supply for. It needed 1500 volts DC for the transmitter plates, 400 VDC for everything else and 28 VDC for the tube heaters and motors that tuned it.

The 1500 volt power supply had a pair of 866B tubes in it. The power supply had time delay relays in it to:

First: Turn on the rectifier heaters and the 28 VDC supply Next: Turn on the 400 VDC supply Finally: Turn on the 1500 volt plate power

At full load those 866B tubes glowed a bright purple and the plates just barely started to show red heat.

BTW, the transmitter had an 813 final, a pair of 811 triodes in push-pull for AM modulation (Heising modulation) and various smaller tubes for everything else.

One day my back yard dipole got hit by lightning and that was the end of the transmitter! :( (luckily I wasn't using it when it got hit).

Yep, I homebrewed my 4) 813’s in grounded grid amp. 4) 866b’s sitting on 2KV with about 20 ufd. of oil filled capacitors. All that to a 100’ tower with a 4 element Gem Quad. HELLO RADIO! But mother nature came through and the side winds of a tornado that went through a neighboring town, GOODBYE TOWER! What a mess. Fortunately, it blew it out into my cornfield. I sold the amp at Dayton the following spring. Downgraded to a single 4-1000A that I homebrewed. Now people talk with a keyboard and not a KEY, _ _ … …_ _

W9, WA2, oh boy, OT's! [73]

You know our Ham radio motto don't you? If your antenna didn't fall down last winter then it's too damn small.

Lefty WA6TKD

retrolefty: You know our Ham radio motto don't you? If your antenna didn't fall down last winter then it's too damn small.

Lefty WA6TKD

My little inverted V dipole was big enough to attract a lightning strike and fry my beloved ART-13! :(

Learning: Yep, I homebrewed my 4) 813's in grounded grid amp.

FOUR 813's??? Wow that's impressive.

Since we're being off-topic here... years ago a friend of mine and I built a linear amplifier with a 3-1000-Z triode in grounded grid.

My buddy was adjusting the bias pot in the rear with the transmitter keyed and loaded up to full power. He reached over the top of the amp with his right arm and about a 2 inch long wicked blue with yellow fringes arc jumped from the plate connector to his arm.

It made a loud hissing sound and crawled up his arm like a "Jacob's ladder". In the probably 1/4 second reaction time it took him to yank his arm away and yell, that arc grew to 3 inches long and slashed a 6 inch long charred (no blood) gash in his arm.

The smoke and smell of burning skin was horrible.

That wound seeped and oozed for a good month. It would scab, then break open, then scab again, then break open.

At first it only looked like a thin black line, but it turned out to be completely destroyed tissue 1/2 inch wide and a good 3/8 inch deep.

Ouch!

Learning: Now people talk with a keyboard and not a KEY, _ _ ... ..._ _

Those are the "No code" licensees who I would dare say do not qualify to be called "Amateur Radio Operators".

I've got an Advanced class license. They don't even have those anymore! Show you how old I am! :)

Yep had to make a trip, and sit in front of an official beady eyed FCC Examiner. I nailed myself working on a Radar cavity in the service and luckily only arc'ed a couple of spots about a 1/4 inch apart on one finger. But they do make you a believer. That was 48 years ago, I told my kids that it a small snake bite scar, haha.