[Synchrodyne]

Originally Posted by Pieter H

One of the remarkable facts is that again an AFC-enabled tuner is offered, in this case the AT6361/02 UHF tuner. The same happened consistently in VHF. This must have been a feature driven/requested by external customers, because, apart form one high end set using VHF AFC, I've not found any Philips TV's using AFC. It was simply too costly, requiring a substantial amount of additional circuitry including 2 (half) valves.
Is someone aware of any consistent use of AFC in other TV brands, preferably using Philips tuners?

I don’t have anything that directly connects AFC with Philips tuners, but here are some more general observations that might help to create a broad background picture.

AFC was used in some early American TV sets of the split-sound type. In those cases, the AFC bias was taken from the sound channel discriminator and used to control a reactance valve. The same bias could be and sometimes was used to control a centre-zero type tuning indicator such as the 6AL7GT magic eye.

With the advent and subsequent widespread use of intercarrier sound, AFC (and tuning indicators) disappeared from American practice in the early 1950s.

But it returned for the 1958 season, reintroduced by Westinghouse, by which time it was known as AFT (automatic fine tuning). This (rather complex) Westinghouse system was the subject of an article entitled “Automatic Fine Tuning is Here” in Radio-Electronics (RE) for 1958 February, page 56ff, and it was also described in an IRE paper (1). A key point was that the reactance element was a crystal diode, making it a relatively easy addition to the standard forms of two-valve VHF tuners.

Evidently by 1957-58 it had been realized that finding the correct tuning point for intercarrier receivers was not an easy operation for typical consumers, and that something better was needed. About a year or so before that Canadian Radio Manufacturing Corporation had devised a tuning indicator circuit, used in some Canadian Philips TV receivers, that used a conventional peak-reading magic eye. This was described in RE 1957 June, page 57ff. An interesting point was the care needed to derive a reasonably symmetrical peak around the vision carrier from an IF channel where the same carrier had been subjected to the Nyquist slope. I think that the same considerations would have applied to AFC when derived from the vision carrier. In fact. It had come up previously, in 1952, in GE’s effort to eliminate some of the intrinsic ills of intercarrier sound. It used an IF sidechain with a peaked and narrow bandwidth vision carrier, thus minimizing Nyquist phase modulation of it. The circuit was briefly described in RE 1952 January, pages 31 and 32. With the benefit of hindsight, one may see that the peaked vision carrier could also have been used to feed an AFC system and a peak-reading tuning indicator.

I don’t know to what extent AFT was adopted by American industry in the decade following 1958, but judging by several magazine articles, both AFT and tuning indicators were foci of attention again in the 1967-70 period, suggesting that AFT had not become “routine” before then. But its significance by the second half of the 1960s was indicated that a TV AFT IC, the CA3034, was c.1966 just the second release item in RCA’s planned range of TV ICs, the first having been the CA3014 intercarrier sound unit.

Turning to Europe, other than the UK, Wireless World (WW) for 1959 September, pages 403 & 404, had a brief item on German TV receivers in which it noted that AFC was universal in sets that covered Band III (surely that was all of them, and AFC was also used for Band I) but that only one setmaker, Graetz, had was using AFC for Band IV, as well. I have attached the pertinent WW page, which includes an outline of the Graetz circuit:



If indeed AFC (at VHF) was “universal” in German practice, then one would suppose that some German setmakers were using Philips tuner variants equipped for AFC. And it would also be reasonable to suppose that if universal for VHF, AFC also became universal for UHF once the details were worked out. So, the German market requirements may well have been the driver for Philips’ introduction of AFC-capable VHF and UHF tuners.

Practical Television for 1962 December, page 123ff, carried an article on intercarrier sound, based upon then-current European practice, which included the comment that “…the great majority of good CCIR receivers have gone over to automatic frequency control of the main tuner.” The block schematic shown early in the article included an AFC loop with a PCF80 AFC IF stage, 2 x OA79 discriminator, PCF80 DC amplifier and AFC diodes in the tuners, CA159 for VHF and BA102 for UHF. I have attached the pertinent page from the article:



In respect of the UK, WW 1959 April, page 159 reported that GEC had developed an AFC circuit using a silicon diode as the reactance element and controlled by bias derived from a discriminator in the sound channel. Whether it was ever used in a production receiver I don’t know.

WW 1959 October, page 441, provided details of the system used by Murphy to provide AFC, for FM only, on its combined TV-FM receivers. This used a point-contact germanium diode, controlled by bias from the FM discriminator by a triode DC amplifier. Given that FM and (AM) TV sound shared the same 6.31 MHz 2nd IF (Murphy had adopted conversion for the TV-FM sound channel about a year earlier), it is perhaps a little surprising that AFC was not also used for TV sound. I don’t know what make of VHF tuner Murphy used, but perhaps not Philips, as I am not sure that Philips/Mullard ever offered a Band I/II/III VHF tuner for the combined TV-FM case.

Then WW 1960 October, page 490, provided an outline of the AFC system used on the Dynatron TV50 TV-FM receiver chassis. This applied to both FM and TV sound. In the FM case, AFC bias from the 10.7 MHz discriminator was used. In the TV sound case, the 38.15 IF channel MHz included a double-diode that served as both a discriminator and AM demodulator. A junction diode was used as the reactance element. As the VHF tuner for the TV50 was shown as having Mazda valves, I suspect that it was not a Philips unit.

Thereafter I have seen nothing on British TV receiver AFC until the advent of colour, when it was used by some setmakers for UHF.

On the AFC vs. AFT terminology, I suspect that AFT was preferred for the “second wave” of TV applications for two reasons. One was that “AFC” in a TV context had become indelibly associated with flywheel line timebase systems, so that a different name was needed for what might be called the “tuning assistance” system. Deutsch, in his 1951 book (2), had a separate chapter on “Automatic Frequency Control”. The first part referred to the line timebase application, the second part to local oscillator control, so one might say that the line timebase case took priority.

And the other reason was that “automatic fine tuning”, dispensing with manual fine tuning, was the intended purpose of those second wave systems. Earlier AFC systems may have had as their primary purpose the holding on tune of a receiver that was initially set to the correct tuning point manually. On the other hand, American practice continued with AFC for systems frequently applied to FM receivers. In Europe, the association of “AFC” with line timebases had not been established, so that there was supposedly little or no confusion when AFC was used in connection with receiver tuning.

I was fooled once though, when looking at the schematic for the Sonly TUM-100, a System M outboard tuner (receiver)-modulator combination for use with the late 1960s CV-series of video tape recorders. On the one hand there was a circuit board identified as “AFC”, but on the other hand neither the VHF not UHF tuners (shown simply as blocks in the schematic) had any apparent inputs for AFC bias. Upon closer inspection it turned out that the AFC board contained a miniature flywheel line timebase system whose function was to generate properly timed gating pulses for the gated AGC system!


Cheers,


All of the above-referenced magazine articles are available at the excellent AmericanRadioHistory.com
site, at: http://www.americanradiohistory.com/, as follows:

Radio-Electronics: http://www.americanradiohistory.com/...aster_Page.htm

Wireless World: http://www.americanradiohistory.com/...d_Magazine.htm

Practical Television: http://www.americanradiohistory.com/...n_Magazine.htm



(1) The subject IRE paper was: Automatic Fine Tuning in Television Receivers; K. E Farr & L. J. Sienkiewicz, Westinghouse Electric; IRE Transactions on Broadcast and Television Receivers; 1958, BTR-4 Issue 2, pp.63-73.

(2) Sid Deutsch; Theory and Design of Television Receivers; McGraw-Hill, 1951.