What's that tube doing there?
 

Would someone please explain to this newbie how/why that tube (5U4G?) is mounted ON the power transformer? Is this common?

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Yeah, I've seen that in older radios...generally from the '30s-early '40s. Don't know why they did it that way...

Running the leads above to the socket is no more difficult than below to the chassis, so the "how" is just to do it. I think some CBS-Columbia TV sets had transformer-mounted rectifiers too. Philco did that trick in a lot of their radios going way back to the thirties.

It cuts down on the necessary "real estate" needed on the rest of the chassis. Area the tube would otherwise occupy. Also gets the heat the 5U4 generates up and away from other circuits. Also the transformer manufacturer sells it as a unit piece, and it's a few less things the TV manufacturer has to assemble.

How the internal hookup is done: The high voltage secondary is center-tapped, and that tap goes to ground, under the chassis. The other two ends of that secondary connect to the tube plates. Both sections of the secondary are (some large integer number) and a half turns around the transformer core. And there's a 5V secondary to run the 5U4 filament, which is also centertapped. Have the filament secondary ends connect to the 5U4 filament, and have the filament secondary center-tap come out the bottom of the transformer. The center tap is (some small integer number of turns) and a half turn away from either end of the tube filament. Then that feeds the filter caps. Phase it right and the filament winding adds a few more volts to the high voltage secondary to produce B+.

I wonder if that was a "Motorola thing"? I worked on a 60's B&W console that had a 5u4 mounted on the transformer. I was surprised to even see a 5u4 in a mid 60's set...

A lot of the Philco 1930's radios used a 5Y4 mounted on top of the power transformer. There were some TV sets that had sockets for 2 5U4's on the transformer and they angled out away from each other about 30 degrees.

I have seen this on some Hoffman TVs and Philco radios. It is not that uncommon.

Magnavox for one.

Bob H.

I think the old Hoffman TV we had when I was a kid had that. I remember seeing it occasionally when I was a kid experimenting on TVs. (Our house was the neighborhood TV dump back in the 60s and early 70s)

Add Admiral to the list.

Didn't RCA do it as well with one of their colour TV chassis, CTC-5 or 7 I think.

I also remember the practice was used in some Australian designs as well, The early PYE W101 & W201's mounted the 2 6N3 rectifiers on the power TX & I think there was a couple of others as well.

I've got a 21" Zenith with 2 5U4's on top of the power transformer, it's also got push-pull audio outputs, quite a set.

Sylvania had a set with TWO 5U4s in the transformer case, mounted at a 15-degree "V" angle to eachother... WEIRD!

Charles

It was the CTC-7... Only some suffix letters though. Others had seleniums. (or is that selenii in plural :D )

Charles

Actually, the CTC-7A Had two 5U4's mounted on top of the box the transformer was in. The other series of that chassis run had them on the chassis in front of the transformer.

I believe it was the CTC 10 that went to silicons.

CTC 4 had seleniums, and CTC 5 had 5U4's on the chassis.
I have also seen a 5U4 on the transrormer of one Bendix tv, and a 5Y4, I believe it was, on the transformer of an RCA radio.

Bill Cahill :scratch2: