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Old 15th Jul 2010, 11:11 am   #61
G8HQP Dave
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Default Re: Valve Questions

I believe the 30L17 was in the same class as PCC189. As the advert says, it was a develoment of the 30L15. 30L17 was also known as PCC806. The 30C17 was also known as PCF87. However, I suspect that it was only Mazda who made these. Mullard already had the PCC189 and PCF86 to do the same jobs.

It looks to me that in the dying days of valves, Mazda decided to eat some of Mullard's lunch by producing valves which were not quite equivalents but did the same job. That made it easier to insist that only a Mazda replacement could be used.
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Old 25th Jul 2010, 4:41 am   #62
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Wireless World October 1961 has some additional comments about these Mazda valves in its Radio Show review section, as follows: “Thorn-AEI, who last year as Ediswan-Mazda introduced the first variable-mu television frequency-changer (30C17) this year showed a new range of valves for television including a cascode double-triode giving the highest gain achieved so far from a single valve of this type (30L17). Slope is 15 mA/V, using frame-grid construction, and to overcome instability an arrangement which harks back to the early days has been adopted. Two cathode connections are necessary, thus a ten-pin base would be necessary to allow earthing of the screening separately from the earthed grid. To avoid the introduction of a new base the screening is connected to one heater pin which must be isolated and bypassed to r.f.”

This commentary seems to overlook the fact that the ECC84/PCC84 also had two cathode connections for the input triode. And that the 30L17 had its inter-triode screen connected to the output triode grid, just as in the ECC84/PCC84. The actual point of difference seems to be that the 30L17 had an additional outer screen that was connected to one of the heater pins.

This “harking back” comment might refer in part to the EF80, discussed earlier in this thread, which also had two cathode connections (thus requiring a B9A base in what was the B8A era for Mullard), had a high slope for its time, and was widely used in early 1950s UK TV receivers.

The same WW item mentioned above also notes the ECH84 as a new valve: “Another valve from Mullard is a triode-heptode, Type (sic) ECH84, which is particularly suitable for sync separation in negative-modulation TV receivers. Noise pulses often rise well above the sync-pulse level of the signal and, with a normal separator, give spurious sync outputs and block off the proper pulses. One way of avoiding this is to use a dual-control valve, such as a heptode, the noise pulses being separated and used to cut off the sync-separator electron stream, so preventing the third grid, to which video and sync signals are applied, from drawing current and thus blocking the following sync pulses.”

That seems to confirm the design origins of the ECH84, although not whether it was, more-or-less, a non-vari-mu derivative of the ECH81. The triode function is unstated, although presumably Mullard would have selected its characteristics (e.g. mu of 50 as compared with 22 for the ECH81 triode) with a range of TV timebase functions in mind.

Given its negative modulation orientation, the introduction of the ECH84 was evidently timed for the expected introduction of dual-standard (625/405) TV receivers in the UK. Thus its use by the UK setmakers would have coincided, more-or-less, with their adoption of the EH90 as a locked-oscillator FM sound discriminator. Yet as noted in the thread “Mixer valves: hexodes and above”, at: https://www.vintage-radio.net/forum/...highlight=EH90, the EH90 was the European version of the American 6SC6, which was originally designed for use as a noise-gated TV sync separator; that is exactly the same function as the heptode section of the ECH84!

That points to a question – did any of the UK setmakers use the EH90 as a sync separator? Or was it used solely as an FM discriminator?

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Old 29th Aug 2010, 4:14 am   #63
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Default Re: Valve Questions

Some more on pentodes and heptodes……

I recently read that some of the earlier (1950s) American colour television receivers used 6AS6 (pentode) or 6BA7 (heptode) valves as low-level synchronous demodulators for the colour subcarrier.

The use of a dual-control heptode in this role seems logical enough. But I wonder what was the rationale for using a pentode? At 3.58 MHz, it would seem that the frequency is not high enough that a reduction in valve grid count would make a material difference in noise level, and the typical signal levels would probably be high enough that this would not be much of an issue anyway.

Anyway, this prompted an internet search for background data on these two valves. The 6BA7 seems to have originated circa 1948 for use an FM frequency changer, either self-oscillating or with an external oscillator. So its use in colour television decoders was probably not envisaged in its original design brief, although evidently it was found to be satisfactory as such. And its period of use as an FM frequency changer was probably quite brief; one would expect that it might have been a bit too noisy as compared to triodes and even pentodes. Possibly it was simply a projection of established AM receiver practice into FM. Some early US FM tuners in fact used the 6BE6 as frequency changer, so the 6BA7 might have been the result of optimizing the basic concept for FM use at around 100 MHz.

The 6SA6 apparently dates from 1949, and was designed as a sharp cutoff pentode in which the suppressor grid could be used as a second control element, mostly by changing the current division between screen and anode rather than by modulating cathode current. As with the 6BA7, it predates colour television.

So maybe the colour television circuit designers simply looked for existing valves that would work as colour subcarrier synchronous demodulators.

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Old 30th Aug 2010, 9:49 pm   #64
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Quote:
At 3.58 MHz, it would seem that the frequency is not high enough that a reduction in valve grid count would make a material difference in noise level
I'm not quite sure what you are saying here. More partition of the current means more partition noise whatever the frequency. At VHF and up you also get grid input noise current, but that does not depend on how many grids there are.

The reason multi-grid valves can be used OK at lower HF frequencies is that the incoming signal is very noisy anyway if it comes from an antenna. If it is generated internally (e.g. as a subcarrier) then the antenna noise is not an issue so the only question is, as you said, what the signal level is. Would a pentode have been cheaper or easier to make than a multi-grid? 6AS6 and the like were generally based on a normal pentode (6AS6 is a modified 6AK5?) so might even have been made on the same line just by using a different suppressor grid?
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Old 12th Sep 2010, 12:26 am   #65
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Thanks Dave! For the longest time I have laboured under the misapprehension that somehow valve shot and partition noise worsened as frequency increased - a misinterpretation made many years ago and never questioned meanwhile. Your comments prompted a review of the topic, and so discovery of my error.

Re my previous post, maybe the choice between 6SA6 and 6BA7 was just a case of designer preference.

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Old 12th Sep 2010, 3:11 pm   #66
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I'm always glad to correct a misapprehension! Strangely, I have also seen some comments which lead me to believe that some people think partition noise gets worse at low frequencies, and is 1/f in character. So for the avoidance of doubt: partition noise, like shot noise, is white i.e. flat with frequency. Grid current noise, sometimes called induced grid noise, gets worse as the frequency increases so is a major issue at VHF. 1/f noise, or flicker noise, appears at low frequencies (e.g. low audio) and is probably due to the details of the cathode construction.
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Old 15th Dec 2010, 4:57 am   #67
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The Mullard “Valves, Tubes & Circuits” series kindly posted by “Valvepower” in the thread Mullard Valves, Tubes & Circuits and Frame Grid Valves (https://www.vintage-radio.net/forum/...ad.php?t=62844) has thrown a lot of light on many of the topics previously discussed in this thread.

For example, the origins of the EF89, and the reasons for its low anode-grid capacitance and smooth AGC curve are apparent in VT&C #29.

Therein it is presented as an improved IF amplifier valve for FM/AM receivers, and particularly for use in conjunction with the ECH81. Strangely though, no mention is made of the EF85 that was its immediate predecessor for the same application. Rather the EF41 is cited as the prototype from which the EF89 was derived. It’s almost as if the EF85 interlude had not existed.

Yet VT&C #18 clearly shows the EF85 as the designated IF amplifier valve in the line-up of six then-recently developed valves for AC Mains-Operated FM/AM receivers. And #20 discusses the role of the ECH81 and EF85 in such receivers.

One may wonder whether the EF85 was designed mainly with FM/AM receiver applications in mind, or for TV receiver IF stages. Possibly in UK domestic TV receiver practice, use of the EF85 as a gain controlled 1st vision IF stage did not become common until the advent of Band III transmissions and the standard 34.65 MHz IF? That would have put the TV application on pretty much the same timeline as the FM/AM application.

The rationale for the ECC85 – very low anode-to-anode capacitance - is given in VT&C #19. Its anode-to-anode capacitance is quoted as less than 0.04 pF, an order of magnitude less than that of the ECC81, which is 0.4 pF. Whilst the existence of the ECC85, like that of the EABC80, can be seen as promoting overly economized receiver designs, at least one has the impression that quite a bit of careful thought went into the valve and its applications. But nowhere in the VT&C series is there mention of the better FM front ends that could be achieved with the use of two valves, say an ECC84 with an ECC81 or ECC85. Maybe Mullard didn’t do any focussed work here, which in turn might explain the paucity of British FM tuners that used cascode RF amplifiers.

On the other hand the PCC84 and its companion PCF80 as used in VHF TV tuners are well-covered in VT&C 15, 16 & 17. And the various other TV receiver applications for the PCF80 are detailed in VT&C #26 & 27. It looks as if the PCF80 was a favourite of Mullard’s.

The frame-grid valve article also provided by Valvepower provided some insights not readily available elsewhere. The frame grid valves listed are correlated and compared with their predecessors and interestingly, the apparently rare EF42 is mentioned in the EF184/EF80/EF50 group. Was the EF42 ever actually used in British TV receivers?

An interesting aspect of the PCC89 is that it had a signal handling capability five times that of the PCC84. I wonder if that was the improvement that enabled the use of cascode 1st RF stages in some HF receivers, such as the Eddystone 880 series (which used an ECC189, an idea then cascaded to the 830 series and the 940). I would imagine that the lower noise of the cascode would have been beneficial above around 20 MHz at least, but perhaps the ECC84 wasn’t otherwise as good as say an EF93 in other departments, and so not really usable, whereas the ECC189 did bring all-round improvement.

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Old 15th Dec 2010, 9:01 am   #68
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Originally Posted by Synchrodyne View Post
But nowhere in the VT&C series is there mention of the better FM front ends that could be achieved with the use of two valves, say an ECC84 with an ECC81 or ECC85
An extra valve! Shock, horror. The drive at the time was to cut down on them not add more.
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Old 15th Dec 2010, 11:58 am   #69
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I always assumed the EF85 was intended for TV, as the combination of high gm and highish Cag means reasonable gain in a wide bandwidth circuit. It was used in lots of radios too, as it had more gain than the EBF80 and Europeans tended to avoid B7G valves in domestic sets.

The low Ca-a in the ECC85 was simply because of the screen. This seems to be the only fundamental change from the ECC81.

My guess is that the PCC89 beats the PCC84 on signal handling when AGC is used, but if used 'straight' I suspect the '84 would win as it has less gain. A normal valve has good signal handling at one optimum bias point, and poor when biased back. Remote cutoff valves are slightly poorer at optimum bias, but relatively much better when gain is redced. The ECC189 is a strange choice for a general-purpose HF receiver, as it has far too much gain (and so poor signal handling) for the noisy LF end of the spectrum - but fine above 20MHz. But maybe a reasonable balance for use with a very short antenna?
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Old 18th Dec 2010, 9:11 am   #70
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Originally Posted by G8HQP Dave View Post
I always assumed the EF85 was intended for TV, as the combination of high gm and highish Cag means reasonable gain in a wide bandwidth circuit. It was used in lots of radios too, as it had more gain than the EBF80 and Europeans tended to avoid B7G valves in domestic sets.
There is certainly evidence that the EF85 was intended to be the TV IF vari-mu counterpart to the EF80, such as at: http://www.r-type.org/exhib/aaq0029.htm.

It has the same pinouts as the EF80, and likewise two cathode connections.

Although it predated the real Mullard B9A era, the EF80 had a B9A base, simply I think because with two cathode connections and a separate internal screen connection, it needed nine pins. Thus like the EBF80, it was somewhat anomalous in what was generally a B8A range.

It seems that whether by happenstance or design, by the time that the EF85 was developed, the B9A era had arrived for Mullard. At the time Mullard would have been considering its B9A radio valve range that would supersede the EF41, ECH42, EAF42, EBC41, EL41, etc. In fact the EF41, ECH42 and EBC41 had direct B9A replacements in the form of EF81, ECH80 and EBC81 respectively. Of these the EF81 and ECH80 were probably little used. The EBC81 might have been less common in the UK, but it was legion elsewhere, such as in New Zealand.

Coincident with arrival of the B9A era was the need to address FM/AM receiver requirements, which required a combination of new and improved valves. Hence the development of the ECC85, ECH81, EABC80 and EL84, as well-covered in the Mullard literature. For the RF/IF pentode, something better than the EF41/EF81 was evidently perceived as necessary, and quite possibly as a matter of convenience the EF85, then also new, was seen to be close enough and so pressed into radio service, and in that context simply treated as part of the new range. Thus for example one finds data sheets that show the EF85 paired with the ECH81 and sharing a common screen grid decoupling capacitor.

Then when the EF85 was found to be less than ideal in some radio applications, the EF89 was developed as an improved EF41 that retained its basic virtues. In contrast to the EF85, the EF89 has one cathode connection, which I think is what one might expect for an HF/MF valve that would not normally be used at above 30 MHz.

The EBF89 was the double diode pentode derivative of the EF89, and so more-or-less the successor to the EBF80, which was counterpart to the EF41. The EBF80, already having a B9A base, simply moved into the initial B9A range as it was, and it shows up paired with the ECH81, sharing a common screen grid decoupling capacitor, in some of the literature for the latter. There does not seem to have been an EBF counterpart to the EF85 – to start with a B9A base would not have had enough pins to accommodate two cathode connections for the pentode cathode. There was no B9A successor to the EAF42, nor would there seem to have been a real need for one.

Quote:
Originally Posted by G8HQP Dave View Post
The low Ca-a in the ECC85 was simply because of the screen. This seems to be the only fundamental change from the ECC81.
There is some interesting data on triodes at: http://www.r-type.org/static/tv50.htm. It’s a pity that the ECC85 was not included in that comparison of the “mechanical” details.

Quote:
Originally Posted by G8HQP Dave View Post
My guess is that the PCC89 beats the PCC84 on signal handling when AGC is used, but if used 'straight' I suspect the '84 would win as it has less gain. A normal valve has good signal handling at one optimum bias point, and poor when biased back. Remote cutoff valves are slightly poorer at optimum bias, but relatively much better when gain is redced. The ECC189 is a strange choice for a general-purpose HF receiver, as it has far too much gain (and so poor signal handling) for the noisy LF end of the spectrum - but fine above 20MHz. But maybe a reasonable balance for use with a very short antenna?
Eddystone provides only a qualitative rationale for its use of the ECC189 1st RF stage.

In respect of the 880/2:

“The first stage is a high-gain RF amplifier which uses a low-noise double-triode in a series cascode circuit. This arrangement is used in preference to the more conventional pentode because of its superior performance with respect to blocking, cross modulation, etc.”
And for the 940:

“The cascode amplifier maintains excellent signal-to-noise characteristics throughout the entire tuning range and is superior to the more conventional pentode amplifier usually found in this position.”

and:

“The first RF amplifier is of the cascode type and, as a result, the figures for noise, cross-modulation and inter-modulation are exceptionally good.”

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Old 18th Dec 2010, 11:35 am   #71
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Eventually there was a successor to the EAF42, namely the EAF801. This was introduced in the early '60s, right at the end of the valve era. The EAF801 was used in AM/FM receivers of German and east European origin where germanium diodes were used in the FM detector.

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Old 18th Dec 2010, 12:40 pm   #72
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The data sheets show that the ECC189 had poorer signal handling than the EF89, but lower noise. I suppose in a general coverage set, where good tracking is needed, you could have low antenna coupling (and so good tracking, but also low input step-up) and still have reasonable dynamic range by using a low noise valve.

I don't think there is any reason why the cascode is intrinsically better for crossmod than a pentode. In both cases you are largely relying on the change in gm with signal voltage being linear (straight valve) or logarithmic (remote cutoff). There is no anode feedback to create linearity as you get with a triode, so it is all down to the grid.

The cascode is less noisy than a pentode as there is no partition noise. You can take advantage of this by having less step-up from the antenna.

As I said in an earlier post, the best valve HF front-end would be a lower gain remote-cutoff triode (or triode-connected pentode) in a cascode circuit. Then you need a decent low noise mixer.
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Old 19th Dec 2010, 7:02 am   #73
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Originally Posted by jjl View Post
Eventually there was a successor to the EAF42, namely the EAF801. This was introduced in the early '60s, right at the end of the valve era. The EAF801 was used in AM/FM receivers of German and east European origin where germanium diodes were used in the FM detector.
Thanks for that, John. It prompted a quick internet search, wherein I found that there was also an EAF81. What little data I could find suggests that the pentode section is more like that of the EF89 than the EF41. So it looks as if the EAF81 was counterpart to the EF89 and EBF89, and direct descendant of the EAF42.

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Old 24th Dec 2010, 10:28 am   #74
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The Mullard Outlook issues kindly made available by Jon (Nuke_Nukem), see: https://www.vintage-radio.net/forum/...ad.php?t=62609, add some good insights to valve development in the period at interest.

It would seem that Mullard’s large-scale adoption of the B9A base started with its “World Series” television valves described in Outlook #6, February 1951. Apart from two existing valves taken into the series, EB91 and EY50, all of the others had B9A bases. They were: ECC81, EF80, EQ80, PL83, PL82, ECL80, PL81, PY80 and PY82. At that time there was no vari-mu RF pentode in the series.

The EF80 itself was described in Outlook #8, April 1951. Therein pretty much all that has been said about it earlier in this thread is confirmed. RF amplification at Band I frequencies (41 to 68 MHz) was one of its roles. It was said to be superior to earlier pentodes in terms of its VHF performance. In just the previous issue, Outlook #7 of March, 1951, in an article on grounded grid RF amplifiers and the EC91 in particular, it was noted that pentodes were reasonably efficient up to 50 MHz, but that triodes were better (quieter) at higher frequencies.

But although Mullard had by early 1951 adopted the B9A base for its TV valves, for the time being it was evidently staying with the B8A base for other purposes. In Outlook #11, August 1951, an article on valves and photocells for 16 mm film projectors lists the EF40, ECC40, EL41 and EZ40, all with B8A bases, and essentially the standard Mullard AF line-up of the time. And the EF40 is mentioned again in Outlook #12, September 1951, in connection with amplifiers for long-playing records. Basis available information, 1953 was the year when Mullard started promoting its B9A AF and radio receiver valves.

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Old 27th Dec 2010, 8:58 am   #75
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From further review of the wealth of Mullard information, particularly the Mullard Valves, Tubes & Circuits (VT&C) and Mullard Outlook series recently made available to this forum:

As well as the “World Series” of television valves, Mullard also had a “World Series” of audio valves, although apparently it was not as well publicized. It showed up in the “additional notes” section of VT&C #28 (April 1955), introducing the EL34. Therein it was stated that the EL34 belonged to the Mullard “World Series” of audio valves whose other important members included the EF86, ECC83 and EL84. Working back from that, then although not explicitly stated, the inference is that the “World Series” of audio valves was introduced by VT&C #10 (October 1953) entitled “Noval-Based Valves for Audio Amplifiers”, and which covered the EF86, ECC81, ECC82, ECC83, EL84 and EZ80. These were all discussed in more detail in following VT&C issues.

The EF86 was described as the direct successor to the EF40 and EF37A, and the EL84 as a higher anode dissipation successor to the EL41 and EL33. The EZ80 was not correlated with a predecessor, although the latter was almost certainly the EZ40. Similarly none of the double triodes was noted as succeeding an earlier valve, there being no mention of the ECC40 (or ECC33). The ECC81 was already an original member of the “World Series” of television valves, so was not really new in 1953. In this case, rather the develop a direct successor to the ECC40, it looks as if Mullard simply adopted counterparts to the American 12AT7, 12AU7 and 12AX7, perhaps with some improvements in the case of the 12AX7-to-ECC83 transition. The three American valves had been advertised by Brimar as being available in the UK at least since January 1950.

Looking through the list of Mullard Outlook topics I see that the EF86 was in the new products list for V3, #7, July 1953, and that V3, #8, August 1953 included the topic “New Mullard Valves for Audio Amplifiers”. I would guess that it correlated with VT&C #10, and so referred to the same set of valves.

As mentioned, the ECC81 was in both the television and audio “World Series”. Curiously, Wireless World October 1953, as well as including VT&C #10, listing the three double-triodes in an AF application context, also included a Mullard advertisement: “Three New Double Triodes”, covering the full range of applications for the ECC81, ECC82 and ECC83.

Back to the TV “World Series”, although this was announced in Outlook #6, February 1951, according to “Valves and their Applications” entry in Wireless World August 1952 (which announced the PY81), it actually dates back to 1950. The PCC84 and PCF80 were announced in VT&C #15, March 1954 as additional members of the “World Series”. The Outlook topic list shows “Band III Television - Two New Mullard Valves” in V4, #2, March 1954, which would I think cover the same pair. Not apparent as yet is when the EF85 joined this group. I suppose a pertinent question is – did any UK Band I-only TV receivers employ the EF85? Or for TV applications did it arrive only with 13-channel receivers in 1955, when agc was more of a necessity than an option? But even in the latter case, one might expect that it would have been featured soon after the PCC84 and PCF80, which were also aimed at 13-channel receivers.

From the materials available, there is no evidence that there was a Mullard “World Series” of radio valves. Still, one might say that the FM/AM Receiver valves mentioned in VT&C #18 of June 1954, constituted a de facto series, these being the ECC85, ECH81, EF85, EABC80, EL84 and EZ80. To this list might have been added the EBC81, and possibly the EBF80 and the EB91, and the U-series counterparts to all of these. The EF89, announced in VT&C #29, May 1955, would have been a later addition, along with the EBF89.

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Old 31st Dec 2010, 3:28 am   #76
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Originally Posted by G8HQP Dave View Post
As I said in an earlier post, the best valve HF front-end would be a lower gain remote-cutoff triode (or triode-connected pentode) in a cascode circuit. Then you need a decent low noise mixer.
Could the cascode double-triode be used as a low-noise mixer? Either additive, with RF and oscillator inputs both to the 1st triode grid, or multiplicative, with RF input to the 1st triode grid and oscillator input to the 2nd triode grid? In the latter case it would be analogous to the typical dual-gate mosfet mixer. Still, if this idea had worked, then I imagine that it would have been used in at least some HF receivers, and that does not appear to have been the case. In the multiplicative case, that the 2nd triode grid could relatively easily modulate the output seems to be indicated by the fact that the DC bias supply to same need to be very hum-free to avoid any hum modulation of the output. If one extends the dual-gate mosfet analogy, then with a cascode RF amplifier, it might have been possible to apply AGC bias to the 2nd triode grid rather than the 1st. But again this arrangement doesn’t appear to have been used in practice, which suggests that it would have a fatal flaw. (The only example of “multiplicative” agc with valve circuits that comes to mind is from hybrid car radio practice – I recall that one or two manufacturers, when using the ECH83 heptode as RF amplifier, applied the agc bias to grid 3 rather than to grid 1, although I do not have any references on hand.)

Quote:
Originally Posted by G8HQP Dave View Post
I don't think there is any reason why the cascode is intrinsically better for crossmod than a pentode. In both cases you are largely relying on the change in gm with signal voltage being linear (straight valve) or logarithmic (remote cutoff). There is no anode feedback to create linearity as you get with a triode, so it is all down to the grid.
So it would be interesting to know what was in the Eddystone designers’ minds when they chose the ECC189 for the 1st RF stage in the 880 and other receivers. In the case of the 880 and 940, it was followed by an EF93 2nd RF stage, thence to the EF95 1st mixer for the 880, and the ECH81 mixer for the 940. In the 830/7, the ECC189 fed the 1st mixer, an EF95. The practice of using a cascode 1st RF stage in HF receivers does not appear to have been widespread, though. I am not sure about this, but I think that some versions of the Racal RA17 might have had an ECC189 RF amplifier in place of the E180F (?) pentode.

It’s rather tangential to this thread, but Eddystone carried over the cascode RF amplifier idea to the next generation of solid-state receivers. The EC958 had a jfet/mosfet (single-gate) cascode RF amplifier that was also cascaded to the 1830 and 1000 series receivers.

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Originally Posted by G8HQP Dave View Post
I don't think there is any reason why the cascode is intrinsically better for crossmod than a pentode. In both cases you are largely relying on the change in gm with signal voltage being linear (straight valve) or logarithmic (remote cutoff). There is no anode feedback to create linearity as you get with a triode, so it is all down to the grid.
I found an interesting comment in Keller (1) in respect of the series cascode circuit (as compared with the shunt cascode circuit), to the effect that the application of AGC voltage to the stage increases the anode-cathode voltage of the lower valve, and thereby increases the value of grid bias required for anode-current cut-off, effectively giving the advantages of a variable-µ valve, i.e. good cross-modulation performance.

Quote:
Originally Posted by G8HQP Dave View Post
The cascode is less noisy than a pentode as there is no partition noise. You can take advantage of this by having less step-up from the antenna.
More interesting comparative data: The Cyldon TV.5 Band I 5-channel TV tuner, with EF80 RF amplifier, was quoted as having a noise factor of 10.5 dB across Band I. For 12-13 channel tuners with PCC84 RF amplifier, around 6dB on Band I and 9 dB on Band III was typical as far as I know.

In terms of pentode RF amplifier choice for MF/HF receivers, Hawker (2), in describing what was a Murphy export MF/HF/BS receiver, states: ”The 6F1 valve, having a high slope (9 mA/volt) yet moderately low anode current, produces less noise than the variable-mu type, which also has much lower slope. This results in quite a good signal-to-noise ratio (e.g. 20 dB for a signal of 7 µV at 15 Mc/s.)” I imagine that accommodating a non-agc RF amplifier might have been easier for a domestic receiver than for a communications receiver where maximum agc range was required. Murphy might not have been alone in using a high-slope pentode as RF amplifier – I think that the Ambassador Viscount (also MF/HF/BS) had much the same arrangement, but using an EF80.

The Quad FM tuner started with a 6BJ6 (variable µ) RF amplifier with smoothed agc from the limiter grid, but from # B8677 onwards, a 6BH6 (high-slope) was used without agc; at the same time the 1st IF stage was changed from a 6BH6 without agc to a 6BJ6 with unsmoothed agc.) One may wonder whether this change was made to obtain an incremental improvement in noise factor (as well as better AM rejection).

Quote:
Originally Posted by AlanBeckett View Post
An extra valve! Shock, horror. The drive at the time was to cut down on them not add more.
Well yes, it certainly would have been swimming against the tide. But on the other hand, Mullard did develop high quality audio applications for its valves as well as those for cost-conscious domestic radio and TV receivers. So in that context a high-performance two-valve, 3- or 4-gang FM front end using the ECC84 as RF amplifier would not have been totally out of place. Still, Leak (starting with the Troughline II, 1959) appears to have been the only British FM tuner maker to use a cascode RF amplifier. The paradox is though, that the PCC84/PCF80 (and later iterations of this front end combination) was used for FM, in the form of many TV/FM receivers. Surprisingly (to me, anyway), Valradio was very early with a Band I/II/III TV/FM tuner, per the attached page from Wireless World September, 1954. Somehow I would have expected Cyldon to have been first in the UK with such a device.
References in Keller (1) show that there were a couple of Mullard Technical Communications on the subject, “Valves for use in Band III TV tuners”, May 1954, and “TV tuner design”, July 1954. No doubt these feature the PCC84 and PCF80. If these can be tracked down, it would be interesting to see if they cover the TV/FM case as well.

Cheers,


References:

(1) Keller, P.R.; V.H.F. Radio Manual; Newnes, 1957; p.15ff
(2) Hawker, J.P (Ed); Radio and Television Engineers’ Reference Book, Third Edition; Newnes, 1960; p.14-33ff.
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Old 4th Jan 2011, 2:10 pm   #77
G8HQP Dave
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Default Re: Valve Questions

A cascode mixer with both signal and LO to the first grid would work, although I am not aware of any circuit which uses it. The second grid is not a good place to apply LO, as to get a good swing of gain up and down through the LO cycle you are actually swinging the first anode up and down which might affect signal handling.

I suspect Eddystone were aiming at sensitivity specs when they used the ECC189. A low uV figure looks good in an advert. They may have deliberately used low antenna coupling to get some signal handling back, though.

To get the AGC improvement from a cascode you have to use cathode bias for the upper valve, rather than using a fixed grid supply for it.
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Old 22nd Jan 2011, 5:01 am   #78
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Default Re: Valve Questions

Quote:
Originally Posted by G8HQP Dave View Post
A cascode mixer with both signal and LO to the first grid would work, although I am not aware of any circuit which uses it. The second grid is not a good place to apply LO, as to get a good swing of gain up and down through the LO cycle you are actually swinging the first anode up and down which might affect signal handling.
Thanks for the clarification, Dave. Then that is one case where one may not “read back” from solid state practice to valve practice. Thus notwithstanding the common analogy that mosfet circuitry is more akin to valve practice than to that associated with bipolar transistors, the dual gate mosfet was quite an innovation, facilitating more possibilities than could be done with valves, such as multiplicative mixing (using g1 for signal and g2 for local oscillator) at VHF without apparent noise penalty.

Quote:
Originally Posted by Synchrodyne View Post
Back to the TV “World Series”, although this was announced in Outlook #6, February 1951, according to “Valves and their Applications” entry in Wireless World August 1952 (which announced the PY81), it actually dates back to 1950.
Well, I should have read more carefully. The World Series of TV valves was mentioned in the first edition of Mullard Outlook (V1, #1, 1950-09).

Although the B9A base was a key feature of the World Series, there were exceptions. The initial TV range all had B9A bases except the EY51 and the EB91. In the case of the EY51, that “deviation” was probably explained by its special nature as an EHT rectifier, as well as the fact that it was already established. Later, when an improved EHT rectifier was required, the B9A-based EY86 emerged.

But in the case of the double-diode, Mullard evidently resisted the temptation to produce a B9A version of the EB91, and instead settled for the original B7G item. This was out-of-character; after all, it did offer an EB41, essentially the EB91 in B8A guise. Maybe Mullard saw that there would be a move to using germanium diodes as envelope demodulators in TV receivers, so that TV applications for the EB91 would diminish to the extent that a B9A rework was not justified.

Generally Mullard “talked-up” the B9A base quite a bit. VT&C #10 (October 1953) was entitled “Noval-Based Valves for Audio Amplifiers”. And VT&C #18 (June 1954) “Valves for A.C. Mains-Operated F.M./A.M. Receivers included the comment in bold type: “These Mullard valves for A.C. mains operated F.M./A.M. receivers are all mounted on the B9A (noval) base.”

There were some later exceptions to “B9A rules”, though. The EL34 had an octal base, presumably because of its size and perhaps because such was still viewed as standard for the larger output valves.

The EF97 and EF98 12 V HT car radio valves of 1957 were both B7G, but they were part of a new series that was otherwise B9A. Quite why they were B7G is hard to fathom. Neither seems to have had a prototype in the regular EF9x series; perhaps they were derived from American types? American practice of the period was to use the B7G base except where the required pin-count indicated B9A; there seems to have been little or no duplication between the two bases, and mixing them was normal practice. Of course, the question might be the wrong way around. Perhaps Mullard saw the smaller B7G valves as more appropriate for car radio receivers (as it did for dry battery receivers) and it was the ECH83 and EBF83 that were the outliers by virtue of their required pinouts (and their derivation from the ECH81 and EBF89 respectively).

With the arrival of the UK dual-standard TV era, Mullard released the B7G base EH90 as a locked oscillator FM discriminator. Perhaps it was simply easier to replicate the American 6CS6 than to develop a B9A version, hence the retention of the B7G base.

Cheers,
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Old 22nd Jan 2011, 12:48 pm   #79
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Default Re: Valve Questions

Quote:
Originally Posted by Synchrodyne View Post
But in the case of the double-diode, Mullard evidently resisted the temptation to produce a B9A version of the EB91, and instead settled for the original B7G item. This was out-of-character; after all, it did offer an EB41, essentially the EB91 in B8A guise. Maybe Mullard saw that there would be a move to using germanium diodes as envelope demodulators in TV receivers, so that TV applications for the EB91 would diminish to the extent that a B9A rework was not justified.
I wouldn't have thought the re-work involved much - just larger micas and then stuff into a small B9A bottle.

More likely the Americans had got there first with the 6AL5 and Mullard saw that set designers would rather avoid something new that couldn't be second-sourced if Mullard ever had supply problems.

Don't forget also that Mullard chose the B7G base for the PC900 UHF triode!
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Old 22nd Jan 2011, 6:23 pm   #80
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Default Re: Valve Questions

Quote:
Cinema 1 said;.... "I am after information oN THE RANK GAUMONT DUO-SONIC KALEE valve amplifiers of the 1950s , such as the valve line up -----wattage out put from these kalee amplifiers, also did the rank gaumont make there own amplifiers".....
I worked at the Odeon cinema Richmond for a few years in the early 1960’s and Kalee Duophonic sound was in use there.
Unfortunately I remember little about it.
There were four main amplifiers mounted in racks inside a cabinet. There was also a monitor amplifier to supply the loudspeaker inside the projection box.
I seem to recall that the main amplifiers had 4 KT88s in Parallel Push-pull as the output. The monitor speaker had a single ended 6V6 valve driving it.
I cannot remember the other valves inside the cabinets. The power output was only about 30 watts as the equipment was designed for reliability not high power output. Cinema sound in those days did not overpower you as it does now.
We had the 4 amplifiers as the cinema had 4 track magnet sound although in those days most films were a mono optical track. So normally only one main amplifier was in use. One other 3 could be use as a stand by if the mono amp failed.
The optical sound head had I think an EF37 as the pre amp, and the magnetic sound heads had EF86 pre amps.

You can see a photo of similar cabinets fitted with Duophonic amplifiers via the link below although in this case they are being used with six-track magnetic sound (70mm film).

http://www.in70mm.com/newsletter/200...es/kalee_4.jpg

If you go to the Projected Picture Trust at Bletchley Park you may find some old amplifiers there.

I think there is another member on this group who may come forward with a lot more accurate information than I can remember.

John
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