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Old 3rd Jul 2019, 12:23 am   #21
Synchrodyne
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Default Re: EF91 to EF80

Hi Ed:

I am not aware of any on-line source for a consolidated set of the Mullard “Valves and their Applications” (VATA) series of WW advertisements.

Quite a few, but by no means all are available from the copies of WW held at the American Radio History Site, at: https://www.americanradiohistory.com...d_Magazine.htm. Many of those issues are devoid of their front and back advertising sections, but at times the VATA advertisements were within the editorial section, so have been preserved.

Here is the list of the Mullard VATA issues that I have found and have on file:

Click image for larger version

Name:	Mullard VATA Partial List.jpg
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ID:	186111

There are too many to assemble into a compressed .pdf – PDF Converter Professional won’t do it. I think it has an upper limit to how many documents can be assembled at one time, although I don’t know what it is. Perhaps it can be done in successive stages – I’ll try that soon.’

Some observations on the VATA series:

The first 17 issues, all written by M.G. Scroggie, were numbered 1 through 17.

Subsequent issues, without mention of Scroggie’s authorship, were unnumbered.

They ran through to at least the WW 1952 August issue, having started in the WW 1947 January issue.

The succeeding “Valves, Tubes & Circuits” (VTAC) series started with the WW 1953 January issue, so it is reasonable to assume that VATA had finished by the end of 1952.

As the VATA for 1952 August covered the PY81, I’d speculate that some of the 1950 and 1951 issues covered the Mullard World Series of TV valves, including the EF80. I’d also expect the EBF80 to be in there, and perhaps the EQ80 enneode/nonode. So these would be worth finding, I think.

I have one datapoint that indicates that Mullard reprinted some of the VATA series with additional information (much as it did for most/all of the VTAC series). And that is a reprint of VATA covering the hi-fi amplifier with EF37, ECC33 and EL37. (Although I can’t recall wherefrom I downloaded that.)


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Old 3rd Jul 2019, 1:45 am   #22
Synchrodyne
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Default Re: EF91 to EF80

As best I can determine, the EF92 originated as the Osram W77, which was the remote cutoff HF pentode in its initial “77” series of miniature receiving valves. The basic radio series comprised the W77, the X77 heptode and X78 triode heptode, the DH77 double-diode triode and the N78 output pentode, supplemented by the Z77 high-slope “TV” pentode and the D77 double-diode amongst others., all on the B7G base. There were 100 mA series-string counterparts in the 107/108 series.

In keeping with British/European practice of the time, the W77 had a lowish slope, in the 2 to 2.5 mA/V range. I have seen it said that this was done to allow easy substitution of the miniatures in existing circuits. The Mullard EF41 and Mazda 6F15 had comparable slopes. On the other hand, American immediate post-WWII practice favoured a higher slope, around 4 mA/V, as provided by the 6BA6. This came to general British/European practice later on, with the EF89 of c.1954-55. Although of course Brimar was offering the 6BA6 from the start of its miniature activities, and this valve was also available from other European makers as the EF93. Osram adopted it as the W727 in its “727” series of c.1953-54.

The initial British/European miniature receiving valve ranges were characterized by having a low-slope remote cutoff HF pentode and a high-slope VHF sharp cutoff pentode, but not a sharp cutoff HF pentode or a remote-cutoff VHF pentode.

The corresponding American range did include a sharp cutoff HF pentode namely the 6AU6, as well as a sharp cutoff VHF pentode, the 6AG5. The 6AU6 was quite widely used in European practice, also known as the EF94, but less so I think the 6AG5 (EF96). Interesting is that whilst Brimar could have featured the 6AG5 for the high-slope VHF role, it found it preferable to introduce its own clone of the Z77, the 8D3 (later 6AM6).

The high-slope remote cutoff VHF pentode did soon appear though in the form of the EF43, which was counterpart to the EF42, and was followed by the EF85. Initially Philips positioned the EF85 as an FM radio valve, I suspect because its preference was for using sharp cutoff valves such as the EF80 in TV IF applications, including agc’d stages. But when the frame-grid era arrived, the EF183 (remote cutoff) and EF184 (sharp cutoff) appeared to have had equal billing.

I don’t think that there was ever a remote cutoff counterpart to the EF91. Rather the EF85 was used where that type of valve was required (e.g. as in the Marconi Atalanta marine receiver).

American practice stayed with the sharp cutoff VHF pentode for a while, the 6CB6 of 1950 being a notable development of the 6AG5. The effort to sort out TV agc problems (well-documented by RCA) led to controlled sharp cutoff valves (e.g. 6CF6) as well as the semi-remote cutoff type (6BZ6), with a seemingly endless series of successors. Some US TV setmakers adopted the EF183 (6EH7) and EF184 (6EJ7) when they became available from Amperex.

It may be noted that the initial American miniature receiving range did include a low-slope remote cutoff pentode, the 6BD6, but this seems to have had little use. I can’t trace that this had a sharp cutoff counterpart. Mazda did offer a low-slope (2.2 mA/V) sharp cutoff HF pentode on the Rimlock base, the 6F11, so this was an exception to normal British practice, but it too seems to have had little use.

The EF81 was simply the noval-based version of the EF41. Similarly there were the ECH80 (noval ECH42) and EL80 (EL42). These I think would have been rare in British/European equipment, but I have a notion that they may have been used by Australian setmakers to some extent, although that needs to be confirmed. (There would have been no need to do the same with say the EBC41 and EB41, as suitable B7G types existed (6AT6 and 6AL5), and mixing of B7G and B9A bases was routine.)

As far as I know, only the EF8x and EF18x series followed the convention of using even final digits for sharp cutoff valves and odd final digits for the remote cutoff types. It did not apply to the EF9x series, which ran as follows:

EF90 apparently not allocated, but E90F was the special quality version of the 6BH6
EF91 sharp cutoff, high-slope VHF (Z77)
EF92 remote cutoff, low-slope HF (W77)
EF93 remote cutoff, intermediate slope HF (6BA6)
EF94 sharp cutoff, intermediate slope HF (6AU6)
EF95 sharp cutoff, low-noise high-slope VHF (6AK5)
EF96 sharp cutoff, high-slope VHF (6AG5)
EF97 remote cutoff 12-volt HT car radio HF
EF98 sharp cutoff 12-volt HT car radio HF (although better known as an AF driver)
EF99 apparently not allocated, but E99F was the special-quality version of the 6BJ6.

Nonetheless, with the EF97 and EF98, it does looks as if Philips did follow the odd/even convention, and these were remote/sharp cutoff counterparts.

The 6BH6 and 6BJ6 were essentially low-consumption (6.3-volt, 150 mA heaters) versions of the 6BA6 and 6AU6 respectively, in part intended to better suit mobile applications. They also had improved VHF performance, enough so to make then credible for FM receiver RF use. Their 150 mA heaters meant that they could be used and were beneficial in AC-DC FM-AM receivers.

Returning to the EF80 and EF91 story, as noted above, the EF42 was part of that, and here is some more Mullard VATA material on that:

Click image for larger version

Name:	WW 194801 p.22 Mullard VATA #12 EF42.jpg
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ID:	186114 Click image for larger version

Name:	WW 194802 p.30 Mullard VATA #14 EF42 continued.jpg
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ID:	186115

Whilst the EF91 (Z77) and EF92 (W77) were not counterparts, Marconi did use this pairing in many of its HF receivers, including its more elaborate point-to-point SSB/ISB models (e.g. HR92, HR21), which stayed in production to the mid- or later 1960s. The EF91 served as 1st RF amplifier, with no or fractional and/or much-delayed AGC, and the EF92, with full AGC, as 2nd RF amplifier. This was said to provide the best noise performance at upper HF. (I’d need to check to be sure, but I think the noise figured quoted for the CR150/6 (thought to use the EF91/EF92 combination) was noticeably better than that for the HR22, which had two 6BA6 (W727) RF stages.) I don’t know what Marconi used as first RF amplifier for its late valved HF receivers, such as the HR120, but the EF91 seems to be a fair bet. If so, this would be indicative that the EF91 remained current into the 1960s.


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Old 3rd Jul 2019, 2:57 am   #23
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Default Re: EF91 to EF80

Quote:
Originally Posted by Synchrodyne View Post
Similarly there were the ECH80 (noval ECH42) and EL80 (EL42).
That should have been EL80 (EL41).
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Old 4th Jul 2019, 12:42 am   #24
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Default Re: EF91 to EF80

Quote:
Originally Posted by Synchrodyne View Post
Hi Ed:

I am not aware of any on-line source for a consolidated set of the Mullard “Valves and their Applications” (VATA) series of WW advertisements.

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

Some observations on the VATA series:

The first 17 issues, all written by M.G. Scroggie, were numbered 1 through 17.

Subsequent issues, without mention of Scroggie’s authorship, were unnumbered.

The first 17, the Scroggie issues, are in fact available on-line at: http://www.vk6fh.com/vk6fh/valves%20...plications.htm.


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Old 4th Jul 2019, 1:11 am   #25
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Default Re: EF91 to EF80

They are also available here:

http://www.r-type.org/ephemera/ephe015.htm,

as are some of the later issues, including a discussion of the EF80 in WW 1950 September.

But downloads of these are low resolution and difficult to read.



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Old 4th Jul 2019, 9:27 am   #26
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Default Re: EF91 to EF80

I have fond memories of EF91's when maintaining Cossor oscilloscopes which contained a whole swag of them in a distributed amplifier (with a coaxial delay line in the base). Enormous scopes - the type number of which escapes me. They did perform well and the delay circuit enabled inspection of the rise time of very fast pulses.
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Old 4th Jul 2019, 8:02 pm   #27
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Default Re: EF91 to EF80

Hi Synchrodyne, thanks for the info.
As a matter of interest I had a quick look through some 1947 and 1950 Electronic Engineering mags. I had expected to find the VATA sheets there, but no joy, only the normal stuff, together with some data on more exotic stuff such as Ignitorons, photocells etc.
There were a few data sheets from Brimar and GEC but a bit disappointing for the professional version of WW

Ed
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Old 4th Jul 2019, 9:15 pm   #28
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Default Re: EF91 to EF80

The Mazda 6F12 appears to have appeared in 1947 [Murphy V114/116]. It was 1949 before the EF91 appeared in Television receivers, the first being the Ferguson 941T and the KB CV40. Am I right? I have thought about this for a while.
The Mazda 6F1 and 6F13 had .35amp heaters. What were Mazda thinking of? John.
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Old 5th Jul 2019, 8:15 pm   #29
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Default Re: EF91 to EF80

It's always interesting to look back and see how different manufacturers did things.

Many say that the EF91 was the logical followon from the EF50 - particularly in the immediately post-WWII TRF single-channel TVs, but it always puzzles me why there were no B7G/B9A versions of the EF50's "Aligned Grid" compatriot the EF54?

http://www.r-type.org/exhib/aaa1093.htm

And whwre does the EF55

http://www.r-type.org/exhib/aaa0075.htm

fit in? It had a really rather impressive gm of 12.5 !!

The "Frame-grid" EF183/184 - are they perhaps the lineal descendants of the EF55? They both have similar gm. I remember coming across these in TV IF-strips where they were so 'hot' gain-wise that they needed to be neutralised by way of specific 5%-tolerance values of screen-grid-to-top-end-of-anode-tuned-circuit capacitors.
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Old 6th Jul 2019, 1:46 am   #30
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Default Re: EF91 to EF80

The EF50, EF54 and EF55 were all mentioned in comparison with the EF42 in Mullard VATA issues #13 and #14, attached to post #22, above. It is evident that Philips/Mullard saw the EF42 as an improved successor to the EF50. The EF42 was said to be better than the EF54 at FM and TV frequencies, the latter inferred to mean Band I. But the EF54 was better at higher frequencies, up to 250 MHz. The EF55 was evidently seen as a video amplifier valve.

Something to bear in mind is that Philips originally saw the B9G base as remaining alongside the Rimlock base in order to cater for those – at the time thought to be few – valves that required 9 pinouts. So there were probably not immediate plans to do any rebasing of the EF54. The sudden and unexpected arrival of the B9A base (which evidently surprised some American makers as well) caused a rethink, as did the emerging fact that there would actually be quite a few TV and FM valves that required 9 pinouts.

Also, I think that Philips saw the B7G base as specifically suitable for battery portable miniature valve (although the Rimlock base was used for “stationary” receiver battery valves). However, probably industrial and military demand for a wide range of “AC” valves on the B7G base resulted in its much more extensive use by Philips/Mullard.

Thus the EF42 morphed into the directionally improved but in some ways constrained EF80 on the B9A base. The better performance of the EF54 at Band III frequencies was made redundant by the advent of the cascode double triode (ECC84/PCC84 in the Philips list) for VHF TV RF amplifier work, so from the domestic receiving type viewpoint at least, there was no need to reissue it on a B9A base. On the industrial/military front, it would appear that the need for a very low-noise, high-performance miniature VHF pentode was addressed by the release of the B7G-based EF95, a clone of the American 6AK5. (Mullard also offered the 6AS6, which was the dual-control derivative of the 6AK5.)

The EF55 was probably “overkill” for domestic TV receiver applications. In the initial Philips/Mullard World Series of TV valves, the dedicated video amplifier was the EL83/PL83. This appears to have been a derivative of the UL41 9-watt output pentode. I don’t know whether the EF55 had a miniature successor for industrial applications. Whether a 10 watt anode dissipation valve in a standard B9A envelope would have been desirable for industrial purposes is I think questionable. The E180F, with slope of 16.5 mA/V and 3-watt anode dissipation, might have been a step along the way to the EF183/184.

The EF91 is really something of an enigma. As G6Tanuki said, it is presented as a successor to the EF50 and also as the predecessor of the EF80. It might well have been so, but the evidence that I have been able to find does not support these notions. The best interpretation I can make is that the Osram Z77 was the original of this type, with all of the other UK valve makers then issuing clones, even though in some cases, e.g. Mullard and Mazda, they had developed their own miniature high-slope VHF pentodes. Possibly at some early stage the military and government users saw this valve as being a key type in a post-WWII B7G range, and wanted diverse supply. That Marconi was a major supplier of radio equipment and tended to use Osram valves may have been a factor.

Whilst the EF80 & co. may have been generally better TV valves than the EF91, the latter might have been better for narrow-band applications in HF receivers, etc., where it was used in new designs until quite late on. Even for FM IF work, “narrowband” valves might have been preferred, except for limiters. For example, there is some evidence of a migration from the “wideband” EF80 to the “narrowband” EF89 for the 1st and 2nd gain stages in later FM-only IF strips.


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Old 6th Jul 2019, 1:51 am   #31
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Default Re: EF91 to EF80

Quote:
Originally Posted by Heatercathodeshort View Post
The Mazda 6F1 and 6F13 had .35amp heaters. What were Mazda thinking of?
The Mazda 6F13 dates back to at least mid-1947 and was its high-slope “TV” pentode in its initial domestic miniature receiving valve series. Thus it filled the same role as did the EF42 in the Philips/Mullard domestic miniature series. At the time I don’t think that 300 mA series-string heaters had been established as a norm for British and European TV receivers. Probably that was cemented in 1949 when Philips decided to go that way and developed its “World Series” of TV valves accordingly.

Thus the EF42, with a 330 mA heater, and the 6F13, with a 350 mA heater, were developed for 6.3-volt parallel heater systems and I suspect that in each case the heater current lay where it fell as a result of designing for the desired performance. The EF42 had a 100 mA series-string heater counterpart, namely the UF42.

Given that Philips was a prime mover in respect of the 300 mA series-string heater system, it is not so surprising that it was first to offer a high-slope “TV” pentode tailored for that application, including delivering the desired performance at 170 volts on the anode. The EF80 was constrained to simultaneously suit 6.3-volt and 300 mA heater systems. I suspect that is why it had a lesser slope than the EF42.

On the other hand, Mazda appears to have been thinking that the TV series string case could be addressed with a mix of valves with 100 mA and 200 mA heaters. This precluded having valves that would simultaneously suit both 6.3-volt and series string heaters. Thus the 6F1 appeared late in 1949 as an improved 6F13, inter alia with two cathode connections, but with the same 6.3-volt, 350 mA heater, accompanied by a 100 mA version, the 10F1. Amongst the Mazda 200 mA Rimlock issues was the 20F2 VHF pentode with a slope of 10.6 mA/V.


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Old 12th Jul 2019, 12:37 am   #32
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Default Re: EF91 to EF80

The empirical evidence is that the EF80 and EF91, although in the same general class, were sufficiently different that carrying both in the Mullard range was justified. It was not really an either/or situation. There does appear to be some published data to support this.

In the Mullard VATA for the EF91, attached to post #16 above, it was said:

“In a high gain I.F. amplifier the important factors are slope and input and output capacitances. The ratio gm/(Cin +Cout) is a useful figure of merit for I.F. valves, since it is a measure of the gain and bandwidth product. The figure of merit for the EF91 is higher than for any other high-slope pentode.”

The EF91 had a nominal gm of 7.65 mA/V, Cin of 7.0 pF and Cout of 2.0 pF. That gave it a figure of merit of 7.65/(7.0 + 2.0) = 0.85.

In comparison, the EF42 had a nominal gm of 9.5 mA/V, Cin of 9.5 pF and Cout of 4.5 pF, giving a figure of merit of 0.68.

The EF80, still in the future, but only just, when that VATA was published (1949 September), had a nominal gm of 7.4 mA/V, Cin of 7.5 pF and Cout of 3.3 pF, for a figure of merit of 0.69, essentially the same as the EF42.

For applications where that figure of merit was pertinent, then the EF91 might have been a better choice than the EF80. But there must also have been applications where the EF80 bettered the EF91 when it came to the situationally most important parameters.

The Mazda 6F13 had nominal gm 9.0 mA/V, Cin 9.5 pF and Cout 4.4 pF, for a figure of merit of 0.65, so close to that of the EF42. The following 6F1 had the same gm, Cin of 9.0 pF and Cout of 4.6 pF for a figure of merit of 0.66, probably not materially different to that of the 6F1.

Valves choices were discussed in the paper on the BBC VHF AM-FM comparator receiver designed and built to BBC requirements by R.N. Fitton (Ambassador). It used both the EF42 and EF91. As a short-run, special-purpose model, it would not have been subject to the usual production constraints that pointed to standardization on one or the other. The RF section (both input and interstage) was wideband, and the EF42 was chosen as RF amplifier to obtain the lowest noise whilst still using a pentode. It was noted that the EF80 and 6F1 would have been even better, but neither was available when the receiver was designed. But the mixer was an EF91. This worked into the 1st IFT, which was relatively narrow band. The oscillator and AFC valves were also EF42s, very high slope being a requirement for both. (It was noted that the 6F1 would also have been suitable had it been available.) The 3rd IF stage was an EF91 (the 1st and 2nd, both agc’d, were EF92s). The two limiter stages were EF42s. One has the impression that had the EF80 been available, it would have been used for the RF amplifier in place of the EF42, but that the latter would have been retained for the local oscillator and AFC functions. Thus the EF80, EF42 and EF91 would have all had a place in that circuit.

I have looked through data on hand to find confirmed late applications of the EF91 in newly designed equipment. The most recent of those was in the Eddystone 880 HF receiver of 1959, where it was used under the 6AM6 moniker as the 3rd and final 500 kHz IF amplifier, the first two stages using the 6BA6 (EF93). The Eddystone 880 was also the basis for the Marconi H2301 of later 1964, retaining the EF91. I don’t think that Eddystone had previously used the EF91 very much, so one assumes that it was chosen as the best fit for the specific role rather than because it was a standard Eddystone inventory item, although of course it was well-known in industrial/commercial and military equipment, often as the CV138.

The EF91 was also used in some of the Racal outboard SSB/ISB adaptors that were intended to work with the RA17 and RA117 HF receivers. These probably date from the late 1950s or early 1960s, but that is unconfirmed.

I have also looked for cases where the EF91 and EF80 were both used in the same piece of equipment, finding only one, that being an FM tuner from Jason. This was the Jason (built)/Jasonkit (kitset) fringe area model announced at the end of 1954. It was derived from the local-area model released a few months previously. That had used four Z77s, as RF amplifier, autodyne mixer, IF amplifier and limiter. The fringe area model added a second Z77-based IF stage, and the RF amplifier used a Z719 in place of the Z77, said to provide extra RF gain. This was superseded in 1958 by the Jason/Jasonkit FMT3, which used five EF80s in the signal path. At this time, the original local-area circuit, by then in Jasonkit form only, was renamed as the FMT1, still using four Z77s, and thereafter lasting until the end. Also introduced at that time was the Jasonkit FMT2, using the FMT1 circuit but with four EF80s for better overall performance. Thus Jason did differentiate between the EF80 and EF91 on a performance basis. An interesting point is that the Jason FMT4, which in 1960 superseded the Jason FMT3 (but not the Jasonkit FMT3, which stayed until the end) abandoned the all-EF80 IF strip for one with two EF89 gain stages followed by an EF80 limiter. That was part of a more general trend in FM-only IF strips, where the EF89 was preferred over the EF80 for the gain stages, even where they were not agc’d, and where the 2nd IF stage might also be a partial limiter. The EF80 remained the preference for the full limiter application, although there was at least one example where the EF184 was used, namely the Pye HFT113 FM-AM unit of c.1961. Quite late as new-design valved FM tuners went was the Radford FMT1 of c.1962. This had an IF strip comprised of three EF89 and one EF80.

The preference for the EF89 in the FM IF amplifier role was note by Philips in an article “The F.M. Section of Modern Broadcast Receivers” in Philips Technical Review 1956 December. This was because the EF89 had the highest slope (gm) to Cag ratio. Also stated was that the EF85 had the most favourable characteristics for the limiter stage. This I find puzzling; better than the EF89 because of its higher slope seems reasonable, but I was under the impression that the shorter grid base of a sharp cutoff valve such as the EF80 would have been preferable for limiter service. The standard FM limiter valve in American practice was the 6AU6, a medium-high slope sharp cutoff HF pentode.

Based upon a rather limited body of evidence, it is possible to deduce that the EF80 last a little longer than the EF91 as a current type suitable for new designs, but if so, then not by very much.


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Old 20th Jul 2019, 3:28 am   #33
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Default Re: EF91 to EF80

Quote:
Originally Posted by Synchrodyne View Post
I have looked through data on hand to find confirmed late applications of the EF91 in newly designed equipment. The most recent of those was in the Eddystone 880 HF receiver of 1959, where it was used under the 6AM6 moniker as the 3rd and final 500 kHz IF amplifier, the first two stages using the 6BA6 (EF93). The Eddystone 880 was also the basis for the Marconi H2301 of later 1964, retaining the EF91. I don’t think that Eddystone had previously used the EF91 very much, so one assumes that it was chosen as the best fit for the specific role rather than because it was a standard Eddystone inventory item, although of course it was well-known in industrial/commercial and military equipment, often as the CV138.
That needs to be amended somewhat. The 6AM6 (EF91) was used as the 3rd 500 kHz IF amplifier in the Eddystone 880/2, of 1962, whereas the 1959 original 880 had used the 6BA6. That looks like a deliberate change for improved performance. And the 6AM6 had been used in some earlier Eddystone equipment. One application was in the 820 FM/AM tuner of 1955, which was a consumer product. There the 6AM6 was used for the FM RF amplifier, FM 2nd IF amplifier/AM IF amplifier and FM limiter. Its used as an agc’d AM IF amplifier in a consumer item was probably quite unusual. In contrast, Rogers had used it as a sidechain AM IF amplifier (non-agc’d) for amplified AGC in its RD Junior AM tuner of 1953.

Perhaps unexpected was that RCA UK had used the EF91 as mixer in its New Orthophonic FM tuner of c.1956. In this the IF strip (3 x 6AU6) had followed RCA US practice, but the front end did not. As well as the EF91, it had an EF95 (6AK5) RF amplifier and ECC81 (12AT7) oscillator and AFC valve. Typically RCA USA would have used a 6CB6 RF amplifier and a 6X8 triode-pentode mixer oscillator, with the pentode triode-strapped.

I understand that the initial FM tuner from Pamphonic used four EF91/Z77 valves, but I have not seen a schematic to confirm this.

To recap, in respect of the high-slope pentode domestic receiving valves offered by the British valvemakers, the Osram Z77 (presumed progenitor of this series) was replicated by all of the major players, Brimar 8D3 (later 6AM6), Cossor 6AM6, Mazda 6F12, and Mullard EF91.

In parallel, Mazda offered the 6F13 and Mullard the EF42 as part of their respective new Rimlock domestic receiving ranges.

Within a couple of years, the Mazda 6F13 begat the improved 6F1, still on the Rimlock base, whereas Mullard offered the reworked EF80, on the noval base. The Osram Z719 was a clone of the EF80.

The EF80 had the American designation 6BX6. I am not sure who did the registration, but my guess is that it was Philips, in part for the Australian market.

Brimar did use the 6XB6 designation for an EF80 clone, but its primary offering in this sub-class, i.e. high-slope, two cathode pinouts, lowish anode voltage, was the 6BW7, which had a higher slope than the EF80, 9.3 mA/V at 180 anode volts, as compared with 7.4 mA/V at 170 volts. Although the 6BW7 and EF80 were probably interchangeable in many applications, there were some where the 6BW7 appeared to have been preferred. (If not, why the higher slope?)

A curious example is that of the first Lowther FM tuner, released in mid-1953. This was of the VHF-AM/FM type, covering both forms of the Wrotham experimental broadcasts of the time. It had a 6BW7 RF amplifier, 12AH8 mixer-oscillator, EF80 IF amplifier, EF42 limiter and AM demodulator, EBC80 FM demodulator and AF amplifier, EM34 tuning indicator. The front end was wideband, and one may see that Lowther wanted to use the highest slope pentode available in the domestic receiving series. Why then also an EF80 and an EF42 is hard to fathom. Perhaps the lower slope of the EF80 made the IF amplifier more stable. And possibly the choice of the EF42 for limiter and AM demodulator followed the precedent of the Fitton (Ambassador) BBC Comparator receiver.

Digressing, the use of the 12AH8 triode-heptode as an FM frequency changer seems odd, but not inconsistent with early practice. In the US, the 6BE6 pentafrid was envisaged as an FM as well as an AM frequency changer. It was rather noisy at FM, so the quieter 6SB7-Y was developed by RCA (at the time when the presumption was that the octal base would sustain where more than 7 pinouts were required), and quickly succeeded by its noval version, the 6BA7. Before the 6BA7 appeared though, GE had changed the game by introducing its 12AT7 double triode specifically for FM (and TV) frequency changer work. Some setmakers, notably Zenith, also used the 12AT7 as an AM frequency changer, in order to retain front end commonality in FM-AM receivers. In 1951, triode pentodes were developed for TV frequency changing, RCA’s 6X8 being the first. This was also specified for use as an AM and FM frequency changer, with the pentode operated triode-strapped for the FM case. I guess that the RCA, having been blind-sided by GE, was now upping the ante. (In the interim, it had used the rather microphonic 6J6 for some FM frequency changers.) GE stayed with the 12AT7 FM frequency changer until specialized unit FM front ends came into American use, but did use one triode as AM oscillator, with the first pentode in the IF chain (usually a 6AU6) used as an AM mixer and an FM IF amplifier. When unit FM front ends were used, that first IF chain pentode was used as a self-oscillating AM mixer and FM IF amplifier.

Parallel to the US use of pentagrids for FM, there was some use of triode hexode/heptodes for FM frequency changing in Europe, including the ECH42 and ECH81. (An “official” use of the ECH81 triode was as a self-oscillating FM mixer.) So given the background, it seems possible that Brimar included the FM application when it worked up the 12AH8. Still, by 1953, one might have expected Lowther to have found a better solution, and for example Brimar was offering the 12AT7 for this role.

Also still in digress, the use of the limiter grid for AM demodulation was uncommon but not unknown. Lowther may have followed the Fitton precedent. GE in the USA appears to have been a major proponent, using it at least as early as its immediate post-WWII X415 receiver and then on some models through to the early 1960s.

Returning to the main theme, Lowther retained the use of both the 6BW7 and EF80 in its FM tuners through to the end of the valve era, although the EF42 was dropped. The later line-up, FM-only, was 6BW7 RF amplifier, EF80 mixer, 6C4 oscillator, EF80 IF amplifier, ECF82 limiter and AF cathode follower, 6AL5 FM demodulator.

Armstrong used the 6BW7 in its first FM tuner, the FM56. It had a conventional ECC85 single-valve front end with EF85 1st IF amplifier (with suppressor grid AGC from the demodulator), 6BW7 2nd IF amplifier/limiter, EABC80 FM demodulator, EM34 tuning indicator. The FM56 was soon superseded by the FM61 whose circuit details remain elusive. At the time that the FM56 appeared, Armstrong looks to have been in the process of a slow change from Mazda to Mullard valves. Thus the use of the Brimar 6BW7 was probably driven less by supply considerations and more by technical requirements.

Mazda introduced the 6F23 in 1959. This seems to have been comparable, but not identical to the Brimar 6BW7, with a slope of 9.2 mA/V at 170 anode volts. I suspect that it was used mostly in TV applications.

Interesting how an apparently straightforward question can result in much rabbit-chasing…..


Cheers,
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Old 20th Jul 2019, 11:44 am   #34
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Default Re: EF91 to EF80

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Originally Posted by Synchrodyne View Post
The preference for the EF89 in the FM IF amplifier role was note by Philips in an article “The F.M. Section of Modern Broadcast Receivers” in Philips Technical Review 1956 December. This was because the EF89 had the highest slope (gm) to Cag ratio. Also stated was that the EF85 had the most favourable characteristics for the limiter stage. This I find puzzling; better than the EF89 because of its higher slope seems reasonable, but I was under the impression that the shorter grid base of a sharp cutoff valve such as the EF80 would have been preferable for limiter service.
Yes I would have thought the EF80 short grid-base would have been preferable, too.

Interesting the choice of valves for FM front-end, too. The British, Eddystone 820 used the 12AT7 (ECC81) as FM frequency changer, but followed this by 6AM6's (EF91's). Why not EF80's or was the 820 just a bit too early? It certainly uses a mixture of valve bases, B9A, B7G, and B8A (for the AM frequency changer). And then has a germanium diode for AM detector - the purist in me wants to replace mine with an EA51 wired-in diode, which would make four different bases.
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Old 20th Jul 2019, 11:53 am   #35
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Default Re: EF91 to EF80

6F23 is also known as EF812 and 6EL7. There was a very similar 300mA heater valve called 30F5/PF818/7ED7 - only minor difference in characteristics. Curiously, I have seen the same Brimar factory code (1291) on both types.
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Old 20th Jul 2019, 12:03 pm   #36
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Default Re: EF91 to EF80

EF80, EF85, EF183, EF184, 6F23, 30F5 were mainly TV valves.

Lawrence.
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Old 21st Jul 2019, 6:34 am   #37
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Default Re: EF91 to EF80

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The British, Eddystone 820 used the 12AT7 (ECC81) as FM frequency changer, but followed this by 6AM6's (EF91's). Why not EF80's or was the 820 just a bit too early? It certainly uses a mixture of valve bases, B9A, B7G, and B8A (for the AM frequency changer). And then has a germanium diode for AM detector - the purist in me wants to replace mine with an EA51 wired-in diode, which would make four different bases.
The Eddystone 820 dated from 1955 – it was full described in WW 1955 July p.347ff – so it was well after the EF80 became available. Thus I think we may conclude that the EF91 was a deliberate choice in this case. As to AM demodulation, possibly demodulated AM could be taken from the limiter grid. As previously noted, this was an established technique, and as Fitton demonstrated, it could be low distortion, as well. FM frequency changer was a primary raison d’être for the ECC81 (12AT7), as shown by this GE advertisement:

Anyway, an interesting question is: EF91 or EF80 for FM work, in those positions where a high-slope valve was desirable? Given that the EF80 was in widespread used in TV receivers, then setmakers also in the TV business would have a good non-technical reason to use it rather than the EF91. That the EF80 was also a standard-stock replacement valve might be more generally persuasive, although I think that in the mid-1950s, the EF91 would not have been uncommon.

On the performance side, as already noted upthread, we have Fitton’s position in respect of the BBC Comparator receiver, which was that it would have used the EF80 or the 6F1 for a lower noise RF amplifier had either been available at the time. (It used the EF42). But the EF91 was found to be satisfactory for the mixer and for the 3rd IF amplifier. It used the EF42 as limiter, but here it was probably going for maximum slope.

There was also Jason’s position, wherein it used an EF80 as RF amplifier for its fringe area tuner in place of the EF91 used in its local area model because it provided greater gain. The EF91 was retained for the mixer and all IF stages. But following Jason practice favoured the EF80; I’ll comment upon this later.

So let’s posit that the EF80 was better than the EF91 as an FM RF amplifier, so might be chosen for tuners intended to work well at the edges of the service areas.

I have since found some additional information pertinent to this matter, both directly and indirectly. I’ll work through it and distil it into a posting shortly.


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Old 24th Jul 2019, 9:24 am   #38
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Default Re: EF91 to EF80

In that period the domestic appliance market was subject to maximum quotas, the rest being reserved for the export market as part of the Attlee government's flawed plan to boost foreign trade. The rest of the world mostly did not use 7-pin valves so there may have been pressure on the BVA to encourage the use of 9-pin valves to make products more attractive to foreign markets. Just a thought.
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Old 30th Jul 2019, 3:36 am   #39
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Default Re: EF91 to EF80

Some comparative performance data on “TV” pentodes is provided in this excerpt from Fisher, “VHF Television Tuners”:

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This shows that the EF80 had a higher input resistance, 10k at 50 MHz, than the EF91, 7k2 at 50 MHz. This parameter decreases with frequency on an inverse square basis. It is an important parameter, but not the only one of interest.

The Radio and Television Engineers’ Reference Book (R&TVERB) set out the key requirements for TV IF valves, as shown in this excerpt:

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An input resistance of 10k or greater was one of the desiderata. So on that basis the EF80 was ahead of the EF91.

An interesting commentary on the EF80 as compared with the EF91 for the FM case was provided by Jason in respect of its Jasonkit FMT2 of 1958. The FMT2 was essentially a self-powered version of the FMT1 in the same case as used for the then-new FMT3. The FMT1 was in 1958 the new name for the original Jason/Jasonkit local-area FM tuner circuit that used four Z77 (EF91) valves, by then available only in Jasonkit form. The FMT2 had essentially the same circuit but used four EF80 valves. (The Jasonkit FMT3 also of 1958 used five EF80 and one ECC81; it was different to the Jason (built version) FMT3.)

“The valves have been changed to EF80, and this results in an improved sensitivity. In the RF and FC stages the fact that there are two cathode leads reduces the feedback which is experienced at this point and gives a slight increase in gain. In the IF stage advantage has been taken of the slightly lower anode-to-grid capacity which is found when the valveholder capacities are also included. Therefore less damping may be used across the coils and more gain results.”

From that one could say that the EF80 was directionally better than the EF91 in FM applications, both RF and IF, but probably not startlingly so.

Another datapoint comes from the Amos & Johnstone (BBC) FM tuner described in WW 1952 September and October. This used an EF95 (6AK5) RF amplifier, EF91 autodyne mixer and a single EF91 IF stage ahead of a ratio detector. It was said: “An EF95 was chosen as r.f. amplifier because experiments showed it capable of substantially greater gain at 90 Mc/s than the EF91-type used in the other two stages; the improvement is due to the higher input impedance of the EF95.” Given that there was only one IF stage, RF gain was probably at a premium. The Fisher data showed the 6AK5 as having an input resistance of 32k at 50 MHz. The EF95 was the European version of the American 6AK5 from the WWII era. The release of the EF95 by Mullard was announced in WW 1952 December. It was probably a relatively expensive valve; Amos & Johnstone presented an alternative circuit with an EF91 RF amplifier in WW 1953 February, at the suggestion of some would-be constructors.

The Brimar 6BW7 was announced in WW 1952 October, and was said to have an input impedance of 14k at 50 MHz. So it was a step-up from the EF80 in that regard, and one imagines would provide higher gain when used as an FM RF amplifier, as well as being an improvement for TV IF stages. On the other hand, in tuners/receivers that had sufficient IF gain, extra RF gain, beyond that required to prevent mixer noise from being an issue, was probably not needed.

In respect of conventional FM limiters, it would appear that high slope was desirable. At least that would explain the choice of the EF42 for that role, at least up until the time that it was moved from current to replacement type status, probably in the mid-1950s. Input impedance might not have been a major issue, given that the RC network at the limiter grid provided significant damping of the preceding tuned circuit anyway. But the EF80 was evidently satisfactory as a limiter; so was the EF91 and also the pentode section of the ECF80. The 6BW7 was also found as a limiter, e.g. in the Armstrong FM56. In that case it may have been chosen for its high slope.

Philips’ apparent preference for the EF85 as FM limiter, noted in post #32, might in fact have been situation-specific, applying to the case where a conventional ratio detector was used. This excerpt from R&TVERB provides a possible rationale:

“By using an extra pentode in front of the ratio discriminator, several advantages accrue. The gain of each stage does not need to be so high, so that larger capacitors (of the order of 30-40 pF) can be used for tuning the primary and secondary inductors of the intermediate-frequency transformers. There is then unlikely to be any trouble, such as distortion of the response curve due to feedback, or shift of tuning duo to the change of valve-input capacitance with grid-current bias under strong signals or with A.G.C. if used.

“Limiting.—In addition, the extra valve can be made to act as a limiter for stronger signals, while still behaving as a high-gain amplifier for weaker signals. The amplitude-rejection properties of a ratio discriminator are not perfect—as will be shown later—so that pre-limiting is an advantage.

“For this system of partial limiting the pentode, a high-variable-slope type, is not run with low anode and screen voltages as in the saturated-amplifier type of limiter frequently employed before the Foster-Seeley phase discriminator (see Section 8), but differs from an ordinary amplifier merely in having a resistor shunted by a capacitor connected in series in the grid circuit. Typical values for the capacitor and resistor are 0.1 MΩ and 100 pF; these providing a time constant of 10 µS. Too small a time constant would not allow the A.M. voltages to develop enough bias to cut down the gain of the valve sufficiently, while too large a time constant would not cope with the short rapid pulses of ignition interference.”


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I think that the EF85 would have been a prime example of the high-variable-slope pentode. Nonetheless, conventional limiters were also ahead of ratio detectors, and as far as I know the wideband type, chosen for very low distortion, required good prior limiting.


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Old 30th Jul 2019, 9:51 am   #40
kalee20
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Default Re: EF91 to EF80

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From that one could say that the EF80 was directionally better than the EF91 in FM applications, both RF and IF, but probably not startlingly so.
That is almost what I was hoping to read.

The EF91 had room for improvement. But at the time of its introduction, no doubt it was such a massive leap forward (from the octal EF36?) that it accrued legendary status. Vastly smaller, with the reduction in the crippling cathode-lead inductance (and interelectrode capacitances) to match, I am sure it was the answer to the HF wideband amplifier designer's prayers.

The EF80, with dual-lead cathode, allows separation of input-circuit and output-circuit return paths to cathode, so another big step forward from the EF91. The internal mesh screen means you don't need a screening can - cost saving, and the valve envelope can run cooler so longer life.

Only down side - put them side by side and (especially Mullard's EF91 with the blue internal coating) the EF80 just doesn't look as cute.
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