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Old 12th Nov 2017, 11:54 pm   #21
FERNSEH
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Default Re: Vintage Television Technology.

The circuit diagram of the RCA KRK124 VHF tuner as fitted in the KCS136M chassis. Note that the 6CW4 Nuvistor valve was still in use in 1965.
Certain models employing this chassis featured a three function ultrasonic remote control system. The usual channel stepper plus volume up and volume down. The remote control is the mechanical "pinger" type. An interesting feature of this remote control system is the "Standby" and "Off" functions which are coupled up to the motorised volume control.

Introduced in 1960 the HMV model 1920 was a de-luxe 23" 405 line mono TV receiver. This up market model employed a single button remote control system which operated a motor driven turret tuner. A position was chosen on the tuner selector drum to provide the function "Standby". To prevent the receiver going into standby when searching for the required TV channel a thermistor was introduced into the relay switch circuit to give sufficient time for the Standby function to be implemented. The remote control handset was a mechanical device.

DFWB.
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Old 13th Nov 2017, 12:41 am   #22
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Default Re: Vintage Television Technology.

The RCA advertisement shown in the immediately preceding post also mentioned its VHF TV valves. 1951 had been a significant year for VHF TV valve developments, in that it saw the introduction of both the double triode cascode RF amplifier and the triode-pentode VHF oscillator mixer.

This RCA advertisement, covering the 6BQ7 double-triode and 6X8 triode-pentode is illustrative:

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I suspect that they were parallel developments, with an earlier start for the 6BQ7, as RCA had been working on an improved VHF TV RF amplifier since c.1948. But they ended up being somewhat co-dependent. The pentode mixer became desirable with the introduction of the “40 MHz” IF, which being just below the lowest low-band channels, led to regeneration problems with triode mixers on those channels. The pentode avoided the need for neutralization. On the other hand, the pentode mixer, being relatively noisy, was not such a good idea on the high-band channels, where a triode would be generally satisfactory and quieter. So, if it [the pentode] was to be used, it needed to be preceded by a high-gain, low-noise RF stage, for which purpose the cascode was an excellent fit. Given that the industry already had double triodes (6J6 and 12AT7) for oscillator-mixer service, then clearly a single envelope triode-pentode was desirable, as reversion to a three-valve VHF tuner would have been unwelcome. RCA emphasized that the 6X8 was equivalent to half a 6J6 plus a 6AG5. Both of those were WWII VHF valves that saw extensive use in early American TV receivers. It was not until c.1950 that successors to the 6AG5 arrived in the form of the 6CB5 (mild improvement) and 6CB6 (bigger step change).

GE also had a contender for the cascode amplifier, namely the 6BK7:

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It did not offer a companion triode-pentode, though. Perhaps it’s view was that the double-triode would continue to serve in the oscillator-mixer role. In 1947 it had introduced the 12AT7 for frequency changer use in both TV and FM receivers. This valve had lower microphony than the 6J6, so was a better choice for split-sound TV receivers and FM receivers. Even after the triode-pentode arrived, there was some ongoing use of double-triode frequency changers in VHF tuners. That is illustrated by the later development of 600 mA series-string variants, namely the 5J6 and 6AT7.

Tung-Sol had a triode-pentode oscillator-mixer, the 6U8, but not its own cascode valve:

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The 6U8 had separate cathodes for the triode and pentode sections, but with the pentode suppressor grid internally connected to the pentode cathode. The RCA 6X8 had a combined cathode, but a separate pinout for the pentode suppressor grid. RCA appeared to have strong views on the benefits of that at the time, and for example its 6CB6 VHF pentode had a separate suppressor pinout whereas the 6AG5 (and 6CB5) had the internal connection. The 6U8 was, I think, more influential on following practice, and it’s interesting to note that the RCA 1954 advertisement attached to the preceding post included the 6U8 as well as the 6X8. The 6U8 became the ECF82 in Europe, from which was developed the PCF82, registered as the 9U8. Later, the 9U8A (with controlled heater warm-up time) was added to the American series when 300 mA series-string valves were introduced.

About the 6U8 Tung-Sol also said:

“The construction and characteristics of the 6U8 provide designers with extremely desirable flexibility in combining circuit functions. The pentode section of the tube may be used as an I. F. amplifier, video amplifier, sound limiter or synchronizing separator. The triode performs satisfactorily as a horizontal or vertical oscillator, or sync clipper.

“Wherever there is need for a triode and a pentacle in a receiver, they can be combined in the 6U8.”


Thus, the 6U8 was also the first multipurpose TV triode-pentode. In American practice, this led to a whole plethora of multipurpose triode-pentodes, distinct from the frequency changer group. Early amongst these, in 1954, were the 6AN8 (RCA) and 6AU8 (GE). RCA also developed the 6AM8 TV diode-pentode. On the other hand, the 6AU8 triode was said to be suitable for operating in diode-strapped mode. In Europe the preference seemed to have been to use the frequency changer triode-pentodes for multiple purposes. Philips had introduced the PCF80 (along with the PCC84 cascode double triode) in 1953, and Mullard had described its frequency changer application in “Valves, Tubes & Circuits” (VT&C) #15 and 16 of 1954 March and April. It followed with VT&C #26 and 27 of 1955 February and March, whose topic was effectively “101 positions for the PCF80”. I suspect that the much larger American TV receiver market allowed a greater range of valve types than could be managed in Europe without diseconomies, and also colour TV receivers benefitted from multi-unit valves if the envelope count was to be kept reasonable.

RCA had not presented its 6X8 as a multipurpose valve. But it did say:

“The RCA-6X8 is especially suitable as an oscillator-mixer in AM/FM receivers.”


That it could be used as an FM frequency changer is not unexpected. But the AM application was at first surprising, considering that post-WWII American AM practice was almost completely based upon the pentagrid frequency changer, mostly the 6BE6. It had eschewed the triode-hexode/heptode type post-WWII, even though those had been used pre-WWII.

But that AM application might be explained by the fact that early American practice in respect of AM/FM receivers was that the same front end could be used for both AM and FM, and for example Zenith certainly built such circuitry. The 6BA6 remote cutoff pentode and 6BE6 heptode were both specified for FM use. The 6SBY7 (octal) heptode was developed by RCA for better FM performance than provided by the 6BE6, and a noval-based version, the 6BA7, followed c.1948. The 6BJ6 remote-cutoff pentode was a bit better at VHF than the 6BA6. But Zenith had adopted the 12AT7 as frequency changer for both FM-only and AM/FM receivers soon after it became available. No doubt it was much better for FM, and presumably acceptable for AM given that it was preceded by an RF amplifier. Perhaps RCA, seeing this and also that its 6BA7 was not likely to have longer-term success, saw an opportunity for its 6X8. This would certainly have been a better AM frequency changer than the 12AT7. In other literature, RCA also noted that for FM, the 6X8 pentode could be operated triode-strapped, with the inference that it would then match a 12AT7 in that role. RCA also offered a 150-mA series-string version, the 19X8, for AC-DC radio receiver use, possibly the only “TV” triode-pentode for which that was done. Consistent with this theme, when RCA embraced the 6U8, it also slated it for AM/FM use, although I don’t think that was done by other makers.


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Old 13th Nov 2017, 10:57 pm   #23
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Default Re: Vintage Television Technology.

Quote:
Originally Posted by Synchrodyne View Post
Thus, the 6U8 was also the first multipurpose TV triode-pentode.
That was not quite right. The Philips ECL80 preceded it, and was a multipurpose TV valve even though it did not cover frequency changer or IF amplifier applications. The ECL80 dates from 1949 or 1950. The earliest reference that I have is for the Mullard version in Wireless World (WW) 1950 May, p.195. It was mentioned along with the EF80 as a being a new TV valve, but then the EF80 had had previous mention in WW 1949 November, p.440.

Also, the 6X8 and 6U8 frequency-changer triode-pentodes might have been preceded by the Mazda 10C2, with a 100-mA heater and on the Rimlock base. However, I havenÂ’t found any information as to when this valve was released. WW 1949 November noted that Mazda had a new range of 100 mA heater TV valves. (There also were some with 200 mA heaters). The 10C2 was not mentioned, but then the full range was not listed, so it could have been amongst them. Possibly it was intended for use as a frequency changer for Band I-only superhet receivers, as an alternative to say a self-oscillating 10F1 pentode. Thus, it may not have been designed with Band III capability in mind.

Quote:
Originally Posted by Synchrodyne View Post
RCA also developed the 6AM8 TV diode-pentode.
Sylvania might have been first with the 6AM8. It was described as being a combination of a 6CB6 with half of a 6AL5. RCA contributed the similar 6AS8 TV diode-pentode.


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Old 14th Nov 2017, 11:22 pm   #24
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Default Re: Vintage Television Technology.

Fortunately, the development of TV tuners over the period at interest (from the later 1940s and into the 1970s) has been fairly well covered in the literature. The following articles, which I found mostly by now-and-again casual searching, are all from magazines and journals available at the very excellent http://www.americanradiohistory.com/ site.

>>>>>>>>>>>>

RC 194711 p.32ff FM and Television Design Part I – Tubes and Circuits Used in High- Frequency R.F. Amplifiers

RC 194712 p.32ff FM and Television Design Part II – Special Circuits and Tuning Equipment Used for Very High Frequencies

RCA-R 194803 p,136ff Radio-Frequency Performance of Some Receiving Tubes in Television Circuits

TT 194901 p.36ff A Front End for Television Receivers (GE Two-Tube with 12AT7)

FM-TV 195003 p.09ff Continuous Tuning for TV Sets (Dumont)

TVE 195005 p.19 The Printed Circuit TV Tuner

PTV 195012 p.295ff Tuner Unit for Television (RCA Turret)

RCA-R 195103 p.03ff Use of New Low-Noise Twin triode in Television Tuners (6BQ7)

FM-TV 195105 p.12ff Zenith VHF-UHF Tuner

TT 195105 p.54ff Two-Tube Television Tuner Design Part 1 (Magnavox)

TT 195106 p.54ff Two-Tube Television Tuner Design Part 2 (Magnavox)

TT 195108 p.30 TV Receiver Manufacturers Ready with UHF Conversion Devices

E 195212 p.118ff Stable Oscillator for UHF TV Receivers (RCA 6AF4)

E 195212 p.134ff One-Channel Converter for UHF Television (RCA)

RE 195301 p.57ff UHF Circuitry

E 195305 p.222 Tubes for UHF Application

RE 195308 p.38ff Cascode Type Front Ends Part 1

RE 195309 p.58ff Cascode Type Front Ends Part 2

RCA-R 195309 p.318ff A VHF-UHF Television Turret Tuner

RCA-R 195312 p.461ff A Capacitive-Tuned Ultra-High-Frequency Television Tuner

R&TVN 195504 p.42ff New TV Turret Tuner (Standard Coil New Design)

TT 195504 p.80ff Designing TV Tuners for Color Receivers

WW 195508 p.397ff The Cascode – And Its Advantages for Band III Reception

RE 195601 p.48ff New “Rainbow” Tuner (Standard Coil)

RE 195607 p.30ff The Neutrode- New VHF-UHF Tuner (Standard Coil)

PTV 195803 p.361 Multi-Channel Tuner Installation

R&TVN 195805 p.65ff New TV Front End Designs

PTV 195807 p.598 13-Channel Turret Tuner (ABMP version of the Fireball)

RE 195808 p.43ff New Circuits in TV Tuners

EW 195912 p.106 Tuner for Transistor TV (General Instruments)

RE 196001 p.42ff TV Tuner with a Guided Grid (Standard Coil)

RCA-E 196008,09 p.28ff A Nuvistor Low-Noise VHF Tuner

WW 196010 p.474ff Permeability Tuners for Television (Bush)

RE 196102 p.72 TV Tuner Uses Nuvistor Triode

E 19660321 p.109ff For a Good Mixer, Ass One FET (TI; proposal to use a jfet mixer in UHF tuners)

PFR 196812 p.14ff A Look at RCA’s Solid-State Color Part 1 (RCA KRK-142 Tuner)

ES 197012 p.38ff The All-Electronic Tuner

EI 197009 p.72ff TV Tuning Goes Electronic

>>>>>>>>>>>>

The magazines and journals are:

E Electronics
EI Electronics Illustrated
ES Electronic Servicing (formerly PF Reporter)
EW Electronics World
FM-TV FM-TV Radio Communication
PFR PF Reporter
PTV Practical Television
R&TVN Radio & TV News
RCA-E RCA Engineer
RCA-R RCA Review
RC Radio Craft
RE Radio-Electronics
TT Tele-Tech
TVE Television Engineering
WW Wireless World

>>>>>>>>>>>>


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Old 16th Nov 2017, 1:23 am   #25
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Default Re: Vintage Television Technology.

Some of the BBC Research Department Reports (RDRs) covered aspects of valved UHF TV tuners.

RDRs are available on-line at: http://downloads.bbc.co.uk/rd/pubs/r...eport-list.pdf.


RDR 1958-13 described tests on an RCA-Victor UHF tuner the regular North American type, with a bandpass input, diode mixer and 6AF4A oscillator.

One of the conclusions was:

“The performance in respect of noise factor and sensitivity is surprisingly uniform over the band. The value of noise factor (15 to 17.5 dB) is quite good for a mass-produced tuner with such a wide frequency range.”


RDR 1958-17 described tests on an NSF combination of a Type 110 VHF turret tuner and a Type 107 UHF adaptor.

The UHF adaptor followed American precepts with a bandpass input, crystal mixer and EC93 oscillator. The EC93 was also known as the 6BS4, but I suspect that the latter was from the RETMA registration of what was a European development, as it the 6BS4 was not mentioned in American articles on UHF tuners and valves that I have seen.

One of the concluding comments was:

“The noise factors measured on the v.h.f. channels are exceptionally good for a standard commercial tuner. On the other hand, the noise factor measured at 650 Mc/s is rather poor, and is at least 3 dB worse than that quoted by the manufacturers.”

The VHF tuner used a PCC88 sharp cutoff frame-grid RF amplifier and a PCF80 oscillator-mixer.

Anyway, from the nature of the NSF combination, one may see that at least one major German manufacture did some early work with the American style of UHF tuner.


RDR 1959-08 covered tests on a couple of UHF amplifying valves, namely the GEC A2521 and the Mullard TDO3-5. The Brimar 6AM4 was mentioned but not tested.

Here an introductory comment was pertinent:

“In superheterodyne receivers the mixer stage is an important source of noise. At lower frequencies the selectivity of a receiver and the signal-to-noise ratio of its output can be improved easily by preceding the mixer stage by a stage of r.f. amplification. At u.h.f. amplification is difficult owing to transit-time effects, and the noise introduced by an amplifier stage becomes comparable with that introduced by the mixer stage. Careful design of the valve and its associated components is therefore necessary to obtain any advantage over the present commonly-used arrangement of a crystal mixer as the first stage.”


Perhaps that was why, in the German case, it was necessary to develop the EC88/PC88 with better performance than the EC86/PC86 for UHF RF amplifier service in order to get the noise factor low enough to justify the two-valve approach to UHF tuners.


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Old 1st Dec 2017, 12:54 am   #26
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Default Re: Vintage Television Technology.

Some comments on the UHF tuner noise issue were provided in Fink (1).

Of conventional UHF triodes, it was said that they did not compete with a crystal mixer if the first IF stage were designed for low-noise.

Comparatively expensive disk-seal and pencil triodes competed with the crystal mixer, and some very costly types outperformed it.

A noise figure of 10 dB was claimed for well-adjusted UHF tuners employing crystal mixers. I suspect that this was a best case, with typical numbers running somewhat higher at the top end of the UHF band.

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A graph showing the comparative noise figured for the various UHF triodes was also presented:

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It’s a pity that we don’t have similar curves for the PC86 and PC88.


Against that, an early (1953) UHF tuner by Tarzian and used by Sylvania was something of an outlier:

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It had no RF amplifier, but used a 6AN6 as a grounded grid mixer, fed by a 6AF4 oscillator.


Cheers,



(1) Donald G. Fink, Editor-in-Chief; Television Engineering Handbook; McGraw-Hill, 1957; LCC 55-11564.
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Old 1st Dec 2017, 10:26 am   #27
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Default Re: Vintage Television Technology.

The ECL80 one of the first Mullard/Philips B9A 'World Series' was employed as a frequency changer in the first Pye superhet series FV1 35/38.5 IF. This was a high gain receiver in it's time. [1951] John.
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Old 2nd Dec 2017, 3:39 am   #28
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Interesting! I guess that one should always expect some setmakers to use valves outside of the application ranges recommended by the valve makers. I don’t think frequency changer was amongst the ECL80 applications covered in Philips Book IIIC. I guess that that Pye receiver was Band I only; the ECL80 at Band III frequencies would be something of a stretch.

The early use by Pye of a “high” IF is notable. Evidently back in 1949 a BREMA Special Committee had made the case that an IF in the 34 to 38 MHz range was desirable, but it was then too early to make a general recommendation (Wireless World 1952 April, p.145). The said committee was revived in 1952, and in late 1954 BREMA recommended the 34.65/38.15 MHz numbers (WW 1954 December pp.582,583)

Anyway, the ECL80 would seem to lay claim to having been the first triode-pentode frequency changer used in a production TV receiver. My best guess in the American case is that the 6U8 and 6X8 would have been first used in some 1952 season models, perhaps announced late in 1951.


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Old 2nd Dec 2017, 4:59 pm   #29
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Default Re: Vintage Television Technology.

Circuit of PYE FV1 series front end. John.
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Old 2nd Dec 2017, 9:52 pm   #30
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Thanks for that. One may impute the possible thought processes that led to that circuit and the use of the ECL80. With a high IF, just under channel B1, a pentode mixer was desirable, given that triodes would regenerate in that situation and would require neutralization. But the IF and channel B1 adjacency also outruled a self-oscillating mixer, which pointed to having a separate oscillator valve if a pentode mixer were chosen. The extra valve was no doubt not too welcome. Then someone had the idea of looking at the then-new ECL80, and found that it would do the job. Problem solved! (And the future anticipated, both in terms of the oscillator-mixer valve type and the use of a high IF.)

In that Pye receiver, was channel selection a customer control, or was it a preset? My guess is more likely the latter.

Rather oddly timed was Cyldon’s introduction of a 5-channel Band I-only TV tuner unit in 1953, namely its TV5. This had an EF80 RF amplifier and an ECC81 oscillator-mixer and was intended to provide one or other of the “low” IFs in use at the time. It seemed to be rather late in the day for such a unit, as by then the setmakers were probably thinking in terms of 13-channel Band I and Band III tuners for their future models. Cyldon introduced its TV12 12-channel VHF tuner, the TV12, initially for export, very soon after the TV5. I am not aware that the TV5 was ever used by a setmaker.

Here are the earliest references to the Cyldon TV5 that I have seen:

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The TV12 was mentioned in the initial TV5 advertisement.

In this TV12 advertisement, the TV5 had a brief mention:

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And by early 1954, the TV5 seems to have been reduced to remainder or “fire sale” status:

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In the TV12 case, the IF output was said to be in the 40 to 47 MHz range.

At the time, only two TV IFs had been standardized as best I can determine, although some that were to become future standards were already in use. (In saying that, I don’t know when the early Russian standard of 27.75 MHz sound, 34.25 MHz vision was established.) In the USA, the RETMA “high” IF channel, originally proposed in 1948, was 41 to 47 MHz, with sound at 41.25 MHz and vision at 45.75 MHz. In Italy, the 40 to 47 MHz channel, with sound at 40.25 MHz and vision at 45.75 MHz had been established by Government decree in 1952 April. It looks as if Cyldon had been guided narrowly by what had been standardized rather than more broadly what was in use.


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Old 30th Dec 2017, 1:14 am   #31
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Default Re: Vintage Television Technology.

Returning to American UHF TV tuners, the 1964 model year does seem to have marked the beginning of the transition from valves to transistors. All TV receivers manufactured after 1964 April were required to have UHF tuners. Electronics World (EW) ran an article about UHF tuners in its 1964 June issue, page 28ff, available at: http://www.americanradiohistory.com/...aster_Page.htm.

Given as typical example circuits were both valve and a transistor models from Standard Kollsman:

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The Standard Kollsman UT transistor UHF TV tuner had been announced earlier in 1964:

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Although the oscillator valve in the valve model was not identified in the EW article, it was probably the then-new 2/3/6ZD4. Standard Kollsman was using the 6ZD4 in its UHF converters as advertised earlier in 1964:

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RCA had announced the 2/3/6ZD4 during 1963. So even with transistors on the horizon, RCA still thought it worth developing an improved UHF oscillator valve to supersede the erstwhile 6AF4A.

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Old 30th Dec 2017, 1:16 am   #32
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Default Re: Vintage Television Technology.

Winegard also used the 6ZD4 oscillator valve in its UHF converters of the time, claiming reduced drift and microphonics, and longer life.

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Some of the Winegard models had a Nuvistor IF amplifier. And some had a transistor RF amplifier, either remote-mounted or within the converter itself (although I’d guess not in the UHF tuner “box”.) This used a 2N2966 PNP transistor, as described in a Radio-Electronics 1964 July article.

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Thus, a fully-equipped Winegard UHF converter of 1964 had an interesting mix of technologies, transistor, crystal diode, conventional valve and Nuvistor.


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Old 30th Dec 2017, 2:03 am   #33
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Default Re: Vintage Television Technology.

The EW and RE are are mine of information, I perhaps spend a bit too much time reading them.
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Old 30th Dec 2017, 11:37 am   #34
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Default Re: Vintage Television Technology.

Hi All,
The ECL80 that was used in the V4 series of sets as mixer/oscillator employed the then popular I.F. of Vision 16.00 MHz. Sound 19.5MHz, not the later Brema frequencies of about twice the frequency.
Victor
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Old 30th Dec 2017, 4:54 pm   #35
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Default Re: Vintage Television Technology.

The Pye V4 service manual shows: V1 RF amplifier [EF80] V2 vision and sound mixer [EF80] 16/19 mc/s IF.

Early versions of the dual band model VT4 were 16/19mc/s but to add confusion, later versions were to BREMA spec 34/38mc/s. All two band models employed the PCC84 and PCF80 in the highly successful incremental tuner. John.

I'm fairly certain that only the FV series employed the ECL80 as mixer/oscillator.
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Old 30th Dec 2017, 6:25 pm   #36
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Default Re: Vintage Television Technology.

The Pye FV1 and the later 16" and 14" console cabinet versions FV2C and FV4C employed the ECL80 as the mixer-oscillator. FV series had near BREMA IFs of 34.5Mc/s vision and 38Mc/s sound.
1953 models Sobell T143, T144 and T145 also employed the ECL80 as the mixer-oscillator.
IFs 16.5 and 19Mcs.

DFWB.
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Old 30th Dec 2017, 6:39 pm   #37
G6Tanuki
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Default Re: Vintage Television Technology.

It seems very odd to me to use an ECL80 - the pentode part's something I would more associate with an audio output stage!

I guess it was all they had in 1950.

( The ECF80 and ECF82/6U8 came on the scene a couple of years later )
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Old 30th Dec 2017, 11:30 pm   #38
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Default Re: Vintage Television Technology.

Some thoughts as to why the ECL80 was used as a TV frequency-changer were recorded in post #30 upthread.

As well, the ECL80 was designed to be a multipurpose valve, and as well as AF and field output applications, the pentode section was intended for use in functions where an “EF” rather than an “EL” type might normally be employed, such as sync separator and half of a line timebase multivibrator.

Some output pentodes turned out to have quite good RF properties. The EL85 was the noval-based successor to the EL42 “small” radio output valve (from the initial Philips Rimlock series) rebottled, rebased, and given a separate suppressor grid pinout. It was then specified for RF use up to 100 MHz, as well as for AF output purposes. The empirical evidence is that the ECL80 pentode was similarly capable in RF terms.

In post #22, addressing inter alia the 6U8 and 6X8 American triode-pentode TV frequency changer valves of 1951, I noted that RCA also described the 6X8 as being suitable for AM and FM radio frequency changer applications. I have since confirmed that RCA did use the 6X8 (and its 19X8 150 mA series-string counterpart) for this purpose in some of its FM-AM radio receivers of the period. In these, the 6X8 pentode was used as such as a mixer on AM, but triode-strapped on FM. Previously, RCA had used the 6J6/19J6 for this purpose.

The 6J6, developed by RCA during WWII for military VHF applications, had been the de facto standard frequency changer valve in early post-WWII American TV practice, and was also sometimes used for RF amplifiers. In 1947, GE released the 12AT7 for TV and FM front end applications. Apparently, this was preferred over the 6J6 for split-sound TV receivers because of its lower microphony. One would infer that likewise it was a better choice for FM receivers, but perhaps RCA preferred to use its own 6J6 rather than the GE-origin 12AT7, at least until the 6X8 was available. Zenith adopted the 12AT7 as frequency changer on both bands for its FM-AM receivers. GE did a bit differently; it used the 12AT7 as an FM frequency changer, but for AM, one half was used as an oscillator feeding the 1st FM IF pentode (often a 6AU6/12AU6) which doubled as an AM mixer.

Notwithstanding the general change to the cascode-plus-triode pentode combination for VHF TV tuners for use with the 40 MHz “high” IF, some of the tuner makers continued to offer the option of pentode RF amplifiers (such as the 6AG5) and/or double-triode frequency changers through the 1950s. For the latter, the 6J6 seems to have been the valve of choice, with the 5J6 being introduced c.1954-55 for 600 mA series-string applications. With its 450-mA heater, the 6J6 may have afforded a more robust oscillator section than the 300 mA 12AT7, so was preferred on that basis, at least where microphony was not an issue. (Both the 6U8 and 6X8 had 450 mA heaters.) The 12AT7 was of course designed with a “split” heater to allow one valve type to fit both 6.3-volt parallel and 150 mA series-string heater systems. It also fitted 300 mA series-strings and 12.6-volt parallel systems.

VHF tuners with pentode RF amplifiers and/or double-triode frequency changers were probably aimed at the lower cost receivers, where performance expectations were lower. The reminder occasioned by the continued existence of the simple pentode RF amplifier alongside the cascode may have added impetus to the search for something nearly as good as the cascode and nearly as simple as the pentode, hence the neutrode and tetrode.


Cheers,
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Old 31st Dec 2017, 4:18 pm   #39
FERNSEH
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Default Re: Vintage Television Technology.

From the 1958 Mullard Maintenance Manual, page 109.
The ECL80 triode-pentode:

Combined triode and output pentode primarily designed for use in television receivers with the triode as a frame blocking oscillator and the pentode as a frame output valve. Other applications include the use of the triode as a line blocking oscillator, AF voltage amplifier or in multivibrator circuits and the operation of the pentode as an audio output valve or a synchronising pulse separator.

No mention of the application of the valve as a mixer-oscillator in television receivers. Another TV receiver that employed the ECL80 as the Band 1 frequency changer was the Peto-Scott TV1422, although later versions of this 1953 set employed the PCF80.
In the Philips 1446U series TV receivers an ECL80 was employed in the second stage of the 8.5Mc/s sound IF amplifier. Triode section employed as the AF amplifier. PL82 output.

DFWB.
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Old 2nd Jan 2018, 4:33 pm   #40
G6Tanuki
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Default Re: Vintage Television Technology.

Thanks: this thread's been really interesting, both from the historical timeline and the perspective of the different broadcasting/regulatory environments applying between the US and the UK (and Western Europe) over the years.

No doubt there was another factor rather involved in the choice of valves by TV manufacturers: the commercial tie-up between TV makers and valve-manufacturers who were part of the same organisation [Philips and Mullard for example, or K-B and Brimar]. TV designers would no doubt have been 'strongly encouraged' to specify only valves made by another branch of the organisation, rather than using those made by competitors, even if their competitors had potentially-better valves in their product line-up.

Smaller 'independent' manufacturers not linked to the big valve-makers would no doubt have had greater freedom in sourcing their parts [and so if something bad had emerged - like the appalling reliability/short life of some Mazda CRTs in the post-WWII-period they could choose a different supplier for their next design].
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