More DC restoration questions

[Zenith26kc20]

Was looking thru the RCA tube manual and saw the 6BJ7 listed as a triple diode used in color TV as a dc restorer. I found it very curious as I cant find a set using this tube at all.
Anyone have any idea what set used it? If so, maybe it can be used in later sets without dc restoration

[old_tv_nut]

A triple diode would be used for DC restoration in a set that has R,G,B drive to the CRT. Not useful for the luminance channel of a set that drives the cathodes (luma) and grids (chroma) separately, I think. (Except maybe if there was a design requiring DC restoration on the three chroma signals)

[old_tv_nut]

By the way, ALL sets, even those that do not have luma DC restoration, must have DC coupling or restoration in the chroma. Otherwise, the gray scale tracking drifts depending on scene color content. RCA put DC restoration in their X-Z demod matrix circuit, although books don't explain it. The blanking pulse on the R-Y, G-Y, B-Y matrix amplifier sections causes them to draw grid current [edit - in the amplifer triode, not the CRT], which makes the grid/cathode into a DC restorer diode.

[wa2ise]

Originally Posted by Zenith26kc20

Was looking thru the RCA tube manual and saw the 6BJ7 listed as a triple diode used in color TV as a dc restorer.

The GE data sheet says that each section is like a section of a 6AL5. You might be able to use this 3 diode tube as a ratio detector for the FM sound demodulator, and the 3rd diode to detect the video. But most TV makers used quadrature detectors for the FM sound, and silicon or geranium diodes for video detectors, when this tube came out.

[Pete Deksnis]

The CT-100 and 21-CT-55 are two of the very few sets that used this tube for DC restoration.
Oops! the 6BC7 is the triple diode RCA used in the CTC2.

[dtuomi]

I wonder if this tube might have been used in early composite or RGB monitors used in television stations. It would seem like these kind of video displays could make better use of it than the average television set.

David

[old_tv_nut]

The RCA TM-21B monitor in the 1960 Televison Terminal Equipment catalog, 3rd edition, says "The output amplifiers also contain d-c restorers in the form of feedback-stabilized gated clamps."

The tube complement (61 including the kinescope):
4 - 6AL5
6 - 6BQ7A
1 - OA2
4 - 6AU8
1 - 6W6
1 - 5651
2 - 6BK4
1 - 6AN8
2 - 6CD6-GA
1 - 3B2
8 - 6AW8
1 - 6X4
4 - 6080
6 - 12AX7
2 - 6AU4-GTA
1 - 6CG7
1 - 1X2B
1 - 6BC7
8 - 12AT7
5 - 6197
1 - 21CYP22

(The catalog does not include schematics.)

[Zenith26kc20]

four 6080's
That's a lot of regulation! My tektronix 533 only has two!