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Old 25th Jan 2011, 7:04 am   #81
Synchrodyne
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Default Re: Valve Questions

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Originally Posted by kalee20 View Post
Don't forget also that Mullard chose the B7G base for the PC900 UHF triode!
Thanks – I had missed that one. And the PC95 and PC97 were also both B7G. Perhaps by that time (early 1960s?) Mullard’s attitude on valve bases had become “whatever”. As far as I know RAC did the initial work on those special VHF triodes and used a B7G base. Possibly the Mullard developments simply built on the RCA work, and followed its B7G base precedent.

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Originally Posted by kalee20 View Post
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.
Although the same argument could have been made earlier against the introduction of the EB41, which was simply a “rebottled” EB91. Perhaps Mullard was a tad less zealous about the B9A base than it had been with B8A. In the latter case it was the major sponsor in the promulgation of a new UK national standard for receiving valves. With the B9A it was a follower, although it seems to have seen the writing on the wall for the B8A standard fairly early on. I am not sure what was Mullard’s first B9A release, but my guess is the EBF80 or EQ80.

A pertinent question here – to which I don’t know the answer - is when was the last new type B8A-based valve released?

Nevertheless there was some continued use of B8A valves after the B9A types were well established and presumably the B8A types were not recommended for new designs. The Eddystone 670 and 840 receivers originated in the B8A era and so the initial versions had B8A valve lines-up. But these were retained through the model iterations, including for the final 670C and 840C variants released in the early 1960s.

Quite odd though was the Eddystone 820 FM/AM hi fi tuner of circa 1955, a then-new design that mixed B7G, B8A and B9A valves. Mixing of B8A with other types probably happened as original, pre-B9A designs were subject to partial updates. But inclusion of B8A types in a new B9A-era design is worthy of comment.

The 820 had a 6AM6 B7G FM RF amplifier followed by a 12AT7 B9A mixer-oscillator. So far it looks quite normal. Then followed an ECH42 B8A as AM mixer-oscillator and (hexode section) FM 1st IF amplifier. Considering that the ECH81 was available and optimized for such FM/AM applications whereas the ECH42 was from the AM-only era, the reason for that choice is far from obvious. 2nd FM IF amplifier and AM IF amplifier was another 6AM6, with a 3rd such serving as the FM limiter, feeding a 6AL5 B7G discriminator. The rectifier was an EZ41, B8A base, originally intended for car radio applications. In this case, maybe the EZ80 was viewed as being a bit oversized for the application. But the result was surely a curious mix of valve types.

I have found some interesting information on the B8A (Rimlock) valves at: http://scottbecker.net/tube/sheets/0...3a/021-026.pdf

I don’t know what (Mullard?) publication this was taken from, but as well as detailed pages for the B8A valves themselves, one can find late pages from it that refer to the EBF80 and EQ80, confirming that these were treated functionally as an extension of the series despite their B9A bases.

Since cinema equipment has been mentioned, I see that Mullard Outlook for June 1951 (Volume 1 No. 9) has a brief article on 35 mm projection equipment and the audio valves used in it. Interestingly it is the octal-based valves that are featured, EL33, EL37, ECC33, EF37A, etc. The EF37A had previously been mentioned in the November 1950 issue (Volume 1, No. 3) as new lower-hum version of the EF37. So it would seem that the improvements that came with the EF40 were a couple or so years later rolled back into to its octal counterpart.

Cheers,
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Old 25th Jan 2011, 12:28 pm   #82
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In a VHF/UHF triode unused pins are a nuisance, as you have to ground them to reduce unwanted coupling. You need at least 5 pins, and the grounded electrode (cathode or grid) benefits from using two or more pins in order to reduce lead inductance. You end up with a requirement for about 6 pins, or maybe 7. Hence B7G. I suspect that Philips just copied one or two of the American designs.

Having said all that, the PC88 etc used B9A bases so maybe there is less logic to it than I imagine.
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Old 30th Jan 2011, 12:47 am   #83
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Possibly EC88/PC88 design was partly informed by the American 6AM4, which had a B9A base and also had 5 grid pinouts. American practice was to use B7G bases unless more pins were actually needed, so it's reasonable to assume that they were in the 6AM4 case. The corresponding 6AF4A UHF oscillator had a B7G base. Were it not for the 6AM4 precedent, I would have been inclined to think that the EC88/PC88 had 5 grid connections simply to fill out a B9A base, choice of which was predetermined as the Philips/Mullard standard for domestic receiving valves. In fact I would have posted this thought alone had it not been for another look at:http://www.r-type.org/static/tv50.htm.k in connection with the concurrent ECC84/ECC81 thread (https://www.vintage-radio.net/forum/...ad.php?t=64857).

In that light the EC86/PC86 seems to have been something of a hybrid of 6AM4 and 6AF4A features, perhaps logical in the sense that it was intended for use as a self-oscillating mixer, whereas the 6AM4 was intended for use as an amplifier or a mixer, and the 6AF4A apparently as an oscillator only.

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Old 8th May 2011, 1:21 am   #84
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The thread EF50 the tube that helped to win the war (https://www.vintage-radio.net/forum/...568#post428568) pointed to the site http://www.dos4ever.com/EF50/EF50.html, which in turn pointed to a sidebar item at http://www.dos4ever.com/EF50/PTT_okt_1946_large_eng.pdf. The last mentioned is an October 1946 Philips Technical Review article about the origin of the Rimlock (B8A) valve series. It speaks to some of the questions that have been raised earlier in this thread.

A key point is that the envelope diameter for the Rimlock series was designed to be large enough to accommodate 8 pins and to handle the maximum dissipation required in a receiving valve without the risk of excessive bulb temperatures.

The choice of 8 pins was made in order to accommodate an indirectly heated triode-hexode type frequency changer “which is to be preferred owing to its inherent constancy of tuning on shortwaves”. That this was a pivotal issue for a new valve series clearly showed the very strong European preference for triode-hexode/heptode frequency changers as compared with the heptode type.
Maximum total dissipation was determined as 14 watts for a 9 W output pentode with a long cathode (for high mutual conductance) consuming 4½ watts. So the respective ECH41 and EL41 requirements were major determinants of the Rimlock valve series parameters.

In respect of the pin-count, Philips noted that the few valves that required 9 contacts could be accommodated in separate series, presumably at the time (1946) those with B9G bases. In the event, the choice of 8 pins proved to be one less than optimum, but it was a couple of years before that became apparent. Still, that Philips saw 8 pins as being not-quite-universal suggests that when it introduced the B9A-based EBF80 circa 1950, it wasn’t quite such a difficult departure for it as previously assumed. In fact, it might have quietly welcomed the fact that the B9A base had been developed in the USA, as a miniature double diode-pentode on a B9A base with the same envelope diameter as the Rimlock series would have been less incongruous than a larger diameter version on a B9G base. And in American practice the B9A series supplemented but did not supplant the B7G series, and so established the concept of mixed base miniatures in receiver valves lines-up.

The 1946 Philips article indicates that it was well aware of the American B7G series developments. It commented that such valves, having a maximum of 7 pins, precluded the possibility of including an indirectly heated triode-hexode in the series, and that output pentodes had to be of low mutual conductance or low output unless high working temperatures were accepted. That the B9A series was found to be necessary to supplement the B7G series was some vindication of Philips’ position.

One may wonder whether the American preference for heptode frequency changers, technically questionable though it may have been, was reinforced by the arrival of the B7G series which did not and could not offer frequency changer option other than the second kind of heptode. Or maybe it was that the alternatives in the octal series (e.g. 6J8-G and 6K8) had not made much impact on established practice, so were viewed as non-persuasive when it came to designing the new miniature series. Thus the 6BE6 became the standard AM receiver frequency changer in American practice until the end of the valve era. The advent of the B9A base allowed a triode-heptode, and one did appear in the form of the 12AH8. I wouldn’t be surprised though, if the 12AH8 was more important for Brimar than it was to the USA valve makers; Brimar might well have encountered some resistance from the UK setmakers to the 6BE6, although it was advertised as part of its standard radio receiver line-up.

As I think was mentioned earlier in this thread, the American “love affair” with heptode frequency changer led to the development of the 6BA7 for use in FM receivers, highly improbable though it may seem. This had a B9A base, which allowed for a separate suppressor grid pin rather than an internal cathode connection. The 6BA7 evidently had a second life as a colour TV subcarrier synchronous demodulator.

Notwithstanding Philips’ evident dislike of heptode frequency changers, it did embrace the B7G type for battery receiver valves, perhaps because the logic of using these smaller valves in this application was inescapable. Even so, there may have been some initial hesitation as indicated by the existence of the DK40 octode frequency changer, at least assuming that it was from Philips/Mullard. The DK40 raises other questions, though. Since 8 pins allowed a triode-hexode, why would a valve make with a self-declared preference for the triode-hexode choose an octode which, from a performance viewpoint, was little different to the 1st kind of heptode. Or are there difficulties with the triode-hexode when directly heated?

Amongst the Mullard Wireless World “Scroggie” series of advertisements, No. 17 (publication date unknown) refers to the DK91, and includes the comment: “In this country the triode-hexode is so popular that not everybody may be sure about how to use the heptode, or pentagrid, particularly as there are several different kinds.” Perhaps it was trying to rationalize a departure from its own standard, and doing it with a touch of arrogance.

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Old 8th May 2011, 3:18 am   #85
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Originally Posted by Synchrodyne View Post
Since 8 pins allowed a triode-hexode, why would a valve make with a self-declared preference for the triode-hexode choose an octode which, from a performance viewpoint, was little different to the 1st kind of heptode. Or are there difficulties with the triode-hexode when directly heated?
I've wondered that, too. In fact the DK91 and DK96, are rather different (I believe) - the DK91 has g2 and g4 strapped (and this works as oscillator anode), with g3 as signal grid, and a suppressor as g5, whereas the DK96 has g2 as oscillator anode, g3 screen grid (no AC on it at all), g4 signal grid, g5 suppressor. I say "I believe" because I haven't opened a couple up to verify that the data sheets are in sync with reality - occasionally they are not (such as the DL92 being shown as a pentode whereas all that I've seen are beam tetrodes).

There are triode-hexodes, directly heated - such as the TP25 (2V heater) used in the Pye 67A battery receiver. This is on a Mazda Octal base.

Regarding the pin count limitation of the B8A base, there is always the option of a top cap for an extra connection. I don't know of any B8A valves with a top cap, but if Mullard could do this with the B9A series then it could also have been done in the B8A series. And the EBF80 could easily have been an EBF40, with one connection (pentode control grid probably) brought out at the top.
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Old 8th May 2011, 8:48 am   #86
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Originally Posted by kalee20 View Post
I've wondered that, too. In fact the DK91 and DK96, are rather different (I believe) - the DK91 has g2 and g4 strapped (and this works as oscillator anode), with g3 as signal grid, and a suppressor as g5, whereas the DK96 has g2 as oscillator anode, g3 screen grid (no AC on it at all), g4 signal grid, g5 suppressor. I say "I believe" because I haven't opened a couple up to verify that the data sheets are in sync with reality - occasionally they are not (such as the DL92 being shown as a pentode whereas all that I've seen are beam tetrodes).
The heptode frequency changer seems two have existed in two basic forms. The “first kind”, such as the 6A8GT, had the grids as: oscillator grid, oscillator anode, screen (1), signal grid, screen (2). The octode was essentially the same arrangement with the addition of a suppressor grid.

The “second kind”, such as the 6SA7, 1R5 and 6BE6, had: oscillator grid, screen (1), signal grid, screen (2), suppressor, dispensing with the oscillator anode. Originally I think the idea was to tap the cathode into the oscillator coil for feedback, then came use of the screen grids as the oscillator anode. With indirect heating, the second kind was a forced choice when only 7 pins were available.

The DK91 seems to have followed the “second kind” pattern, perhaps more-or-less copying the 1R5. But the DK92 and DK96 differ again, taking advantage of the fact that with direct hearing, there was effectively an extra pin available. It looks as if the two screens, instead of being internally connected as was normally the case with heptodes and octodes, were taken to separate pins. This could have allowed the first screen to be used as the oscillator anode as well as a screen between the oscillator and signal grids, and the second screen to be used normally, with no AC on it.

Once the B9A base arrived, it would have been possible to revert to the first kind of heptode frequency changer, or even an octode with indirect heating, but I can’t trace that it was ever done.

As well as heptode self-oscillating heptode frequency changers, the American octal-base series included a heptode mixer, the 6L7G, which was intended for use with external oscillators. Here the grid order was: signal grid, screen (1), oscillator injection, screen (2), suppressor, that is the same as in the heptode portion of typical triode-heptodes. This concept was not replicated in the B7G series. It seems that the 6BE6 doubled as a standalone mixer, although later on the heptode portion of the ECH81 also served this purpose, at least in some British designs.

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Originally Posted by kalee20 View Post
There are triode-hexodes, directly heated - such as the TP25 (2V heater) used in the Pye 67A battery receiver. This is on a Mazda Octal base.
Thanks. So a “DCH40” would have been possible.

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Originally Posted by kalee20 View Post
Regarding the pin count limitation of the B8A base, there is always the option of a top cap for an extra connection. I don't know of any B8A valves with a top cap, but if Mullard could do this with the B9A series then it could also have been done in the B8A series. And the EBF80 could easily have been an EBF40, with one connection (pentode control grid probably) brought out at the top.
Empirically it is easy to get the impression that the use of top caps on miniature valves was generally not liked, and was practiced only where it was unavoidable for electrical reasons, such as for line output valves. Possibly top caps made manufacture more difficult and costly. Or maybe the setmakers preferred to avoid them. (It would be interesting to know why.) When more connections were needed, more pins seemed to be the chosen answer, hence the advent of 10-pin bases late in the valve era, as with the ECF200. As has been said earlier (I think by G8HQP Dave), we can know much about what was done, but have less access to why it was done.

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Old 9th May 2011, 1:21 pm   #87
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Thanks. So a “DCH40” would have been possible.
Definitely. Or a "KCH40" if you prefer a lead-acid accumulator rather than a dry battery.

In fact (keeping with Mullard valves and their excellent type numbering system) the KCH1 exists - as does KK2 (both using P bases). Whether they were also released as octals KCH31 and KK32 respectively, I don't know.
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Old 22nd May 2011, 7:13 am   #88
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Thanks. Also it establishes that a “DCH91” or “DCH96” could have been possible, as well. A directly heated triode-hexode or triode –heptode with triode grid directly connected to hexode (heptode) grid 3 needs only 7 pins.

Another question – were there any miniatures (B7G, B8A, B9A) at all with 2 volt heaters? Or was that technology obsolescent by the time that miniature valves arrived on the scene.

Re the use of top caps on miniatures, the “special” TV valves excepted, it does seem to have been avoided for domestic receiving valves. The only example I can find is essentially an industrial valve (at least according to the attached advertisement), namely the Brimar 6BS7 low-noise, low-microphony electrometer pentode, which has a top-cap grid connection and a B9A base.

But in the case of the B9A series, use of the top-cap for the TV valves was established very early on. For example the PL81 line output pentode was in the initial Mullard “World Series” of TV valves announced in 1950. I don’t think that there were any B8A valves with top-caps, though, and I am not sure about the B7G situation.

As previously noted, two of the Rimlock precepts were 8 pins in order to accommodate the triode-hexode, and an envelope diameter that would allow an output pentode with 9 W anode dissipation without excessively high operating temperatures. The Noval (B9A) series retained more-or-less the same envelope diameter as the Rimlock series so perhaps that was one parameter that Philips/Mullard did get right, at least for the majority of applications. For a while, the 9 W anode dissipation limit seem to be adhered to with valves such as the EL81 (TV line output), EL82 (TV field output) and EL83 (TV video output). But perhaps inevitably the boundaries were stretched and circa 1953 the EL84 audio output with 12 W anode dissipation and B9A base appeared as a member of the Mullard World Series Audio valves.

12 W seems to be as high as anode dissipation went with the B9A series. But the older 9 W number, established with the EL41, later resurfaced with the ECL86 triode-pentode. Above 12 W it was necessary to revert to the older octal base, as Philips/Mullard did with the EL34 when it added a 25 W anode dissipation audio output pentode to the World Series in 1955. But it seems that despite its octal base, the EL34 it did borrow some constructional techniques from the miniatures. I think that the same applied to the GEC KT88, which came after the EL34.

Presumably mains rectifiers were limited by the envelope size as well. The EZ40 had 90 mA capacity, deemed adequate for most domestic radio receivers, and the same rating was carried over to the EZ80. Later – I am not sure when - came the EZ81, with 180 mA capacity. I think that it must have been after the EL84 though, as originally Mullard had nominated the GZ30 rectifier (octal) for use with push-pull EL84 amplifiers. The GZ34 was associated with EL34 push-pull amplifiers – notwithstanding its octal base, was the GZ34 a new issue along with the EL34, and using similar construction techniques, or was it well-established, like the GZ32?

As far as I know, American practice in the later 1950s was to use octal-based TV line output valves where higher anode dissipation was required.

Still, this fairly ordered world where octals were used for applications where novals were simply not “big enough” did not last all that long due to the arrival of the magnoval type, of which I would guess the EL500 line output valve was the initial example circa 1960. Here it does not seem that the objective was to have a “big” valve with 9 pins in order to accommodate more connections, but simply to have a bigger version of the miniature valve construction that could accommodate higher anode dissipations. The rationale to do this when the octal type could do the same job might have been economic – perhaps magnovals were cheaper to produce than octals? A cost difference could have been important in price-sensitive mass-produced products such as television receivers, and most magnovals seem to have been television types, such as line and field output valves, booster diodes, EHT rectifiers and shunt stabilizers.

I know of only one magnoval type intended primarily for use as an audio output valve, namely the Brimar EL506, as used by Lowther in its L18 and L18S amplifiers from circa 1966. I imagine that these were L, not LL, as the EL506 suppressor grid was not independently accessible, so that the “Lowther Linear” (LL) circuitry was not possible. I am not aware of any mains rectifiers on magnoval bases. If economics did drive the use of magnoval valves in TV applications, then the reasons for using them would be less compelling in respect of the quality amplifier market.

Talking of output valves for audio amplifiers, it is interesting that Mullard seemed to dominate the UK market once its EL84 and EL34 were available. The EL84 seemed to push aside most other valves in or around the 12 W anode dissipation class, whilst the EL34 did the same in the 25 W class. For example, Leak switched from the KT66 to the EL34, and the latter was used by Armstrong, Chapman, Lowther, Radford and Rogers amongst others. However, Chapman did swing back to GEC in the later 1960s, towards the end of its amplifier production, using the KT77, which I think GEC saw more as an improved EL34 than as a KT66 successor. All the while Quad stayed with the KT66, though.

In the 35 W anode dissipation class, the GEC KT88 more-or-less had the field to itself, and was used by Leak and Radford notwithstanding their leanings towards Mullard for the smaller valves. One may wonder whether Mullard was simply more aggressive in selling into that market than GEC, particularly given that there is a body of opinion that the KT66 is potentially better than the EL34.

Another facet was the near-universal acceptance of the Hafler & Keroes Ultra-Linear distributed loading for amplifier outputs. Whilst this goes beyond being a valve issue, it is pertinent in that both GEC and Mullard featured Ultra-Linear outputs in their respective audio amplifier publications, which at some level were sales tools for their output valves. And both did the research work to determine optimum screen tapping points, etc., for their various output valves. Quad stayed with its own and earlier distributed loading system (and argued its superiority in the pages of Wireless World), and I think that Pye used a single-ended derivative for a while, whilst Lowther developed its “Lowther Linear” system that was an extension of the Hafler & Keroes system.

Cheers,
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Old 22nd May 2011, 1:41 pm   #89
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Another question – were there any miniatures (B7G, B8A, B9A) at all with 2 volt heaters? Or was that technology obsolescent by the time that miniature valves arrived on the scene.
Don't know - seems like I'll have to have a good look!

Don't forget that not all 'D' series 1.4V valves were intended for battery operation - notable exceptions being DY80 etc, in B9A envelope.

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Originally Posted by Synchrodyne View Post
12 W seems to be as high as anode dissipation went with the B9A series. But the older 9 W number, established with the EL41, later resurfaced with the ECL86 triode-pentode.
I don't know of anything with more than the EL84's 12W anode dissipation in a B9A envelope, either. What beats me is the EL90 with 12W anode dissipation, in B7G!

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Originally Posted by Synchrodyne View Post
Presumably mains rectifiers were limited by the envelope size as well. The EZ40 had 90 mA capacity, deemed adequate for most domestic radio receivers, and the same rating was carried over to the EZ80. Later – I am not sure when - came the EZ81, with 180 mA capacity.
In the B8A range, the UY41 had 100mA capability. I guess the demands on half-wave rectification from the mains were greater as the voltage couldn't be upped with a transformer, so the only way of getting plenty of volume was raise the current.
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Old 22nd May 2011, 3:13 pm   #90
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What beats me is the EL90 with 12W anode dissipation, in B7G!
Hence the Brimar 6BW6 which is the same valve on a B9A base.
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Old 22nd May 2011, 3:28 pm   #91
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Seems plenty of higher power Audio amps have been built with PL509 and PL519 to take advantage of the power. Of course higher power often means 500V to 5000V HT, so top cap anode needed. Though the larger pin spacing of B9G / Magnoval no doubt allows higher voltages between pins.
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Old 22nd May 2011, 4:50 pm   #92
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I believe the only B8A valve with a top cap is the UL44. It is a line output valve used in early post war Philips television receivers including the projection models [600A etc] Looks a bit like a PL81.
The post war 1946 range of battery valves did indeed have 2v versions of the 'red E' octal series. KK32 KCF80 KLL32. John.

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Old 22nd May 2011, 7:55 pm   #93
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Yes - but the KK32 and KLL32 weren't miniature valves in B7G, B8A or B9A which is what Synchrodyne wanted.

(It's interesting that Mullard had a 'K' range in octals as well as a 'D' range though. I have come across them).

The KCF80 - is this number correct? I had a search in the National Valve museum, as it would be a 2V jobbie in B9A, but it came up blank!
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Old 23rd May 2011, 8:42 pm   #94
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Notwithstanding Philips’ evident dislike of heptode frequency changers, it did embrace the B7G type for battery receiver valves... there may have been some initial hesitation as indicated by the existence of the DK40 octode frequency changer...
Looking last night at my valve data books to see if there were any 2V valves in B7G, B8A, B9A (I found none), I did also come across the DAF40 and DAF41, both 1.4V battery diode-pentodes in B8A envelopes. Again, puzzling when B7G has enough pins, and heat dissipation is a non-issue!
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Old 23rd May 2011, 10:00 pm   #95
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Despite the superiority in terms of conversion conductance of a frequency changer with a separate oscillator section, in a battery valve this is a real luxury in terms of filament power. When powered from a lead acid cell (Mazda TP25 for example) the enhanced performance is affordable, but not for dry cell operation.

A "DCH40" would have approximately one third of its filament allocated only to the oscillator section, whereas a "fully concentric" frequency changer such as the DK40 uses the whole filament for all jobs.

The B7G base was developed in the USA after Philips had introduced the B8A range, so a few B8A dry cell types were introduced in Europe before the B7G base was adopted universally for this range of valves.


12W is, in my view over the limit for anode dissipation in a B9A valve and the EL84 is in my experience, an unreliable device which is prone to grid current. When you add the screen and heater dissipations of about 2W and 4.8W respectively, the whole package runs far too hot.

The 6AQ5 survives a bit better because it has a lower dissipation heater (2.8W) and a better surface area to volume ratio in a smaller diameter envelope. The lower heater power for approximately the same anode current arises from the superior efficiency of the beam tetrode over the pentode due to its aligned grids.


I am in no doubt as to the superiority of the beam tetrode over the pentode in terms of both its linearity and its efficiency. Most, if not all of the high quality amplifier designers which were not tied to valve manufacture used them preferentially. The attraction of "on the plate" designs for makers without design expertise inevitably led to a profusion of EL84 and EL34 designs from Philips - who, of course, originally held the patent for the pentode and who were extremely sniffy about beam tetrodes. They made beam tetrodes (even a 6V6) and always described them in the data books as pentodes.

We don't know, of course, what price Philips made their pentodes available to the likes of Leak, Armstrong and Chapman etc. It's highly probable that with their high volumes and efficient manufacturing methods, they would have been able to undercut MOV.

For the record, there is a B7G type with a top cap - the R10 EHT rectifier. Quaintly, it has a 4V 0.5A heater...

Leon.
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Old 24th May 2011, 1:36 am   #96
Synchrodyne
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Thanks for the comments about filament power in respect of battery valves. I suppose that when the 25 mA series of battery valves was introduced to replace the 50 mA series in the early 1950s, there might have been the possibility of a triode-heptode with say a 38 mA filament, but then the drive to reduce battery drain was probably overwhelming.

I think that the B7G miniatures might have predated the B8A type. As I understand it, the first B7G valves, battery types, were introduced circa 1940, with the standard mains radio receiver range (6BA6, 6BE6, 6AT6, 6AQ5, 6X4) arriving in 1945. During WWII valves such as the 6AK5 had been developed. Philips certainly acknowledged their existence in its 1946 article on the Rimlocks, and presented its reasons for doing otherwise. Possibly it had the intention of developing a full Rimlock series of battery receiver valves, and actually started down this pathway before realizing that the B7G type, which it was making anyway for industrial applications, was in fact better-suited and more acceptable to its customers.

Regarding anode dissipation, maybe Philips’ original choice of 9 W (for a pentode) for the Rimlock series was about right. The EL84 could have been somewhat the result of commercial pressure – if 12 W could be done in B7G, why not in B9A? Plus some of the European receiver makers who had used the 6V6(G) in octal days might have been asking for a 12 W output valve.

It is interesting though that the magnoval series includes the EL508/PL508 TV field output valve, also listed as being suitable for audio output use. As far as I know this has 12 W anode dissipation, so maybe the choice of the larger magnoval envelope was informed by the EL84, etc., experience. Possibly having it homologous with the other valves in that part of the TV receiver was also a factor, though.

Quote:
Originally Posted by G8HQP Dave View Post
Hence the Brimar 6BW6 which is the same valve on a B9A base.
Was the 6BW6 a Brimar own-initiative, rather than an American development that Brimar took in as part of its “British made, American range” theme? If so, did Brimar do much of this in the 1950s? It makes me wonder if the 12AH8 (triode-heptode) was in fact a Brimar own-development. The previously-mentioned EL506 was from Brimar in the 1960s, but in this case it chose to use a European designation.

Quote:
Originally Posted by neon indicator View Post
Seems plenty of higher power Audio amps have been built with PL509 and PL519 to take advantage of the power. Of course higher power often means 500V to 5000V HT, so top cap anode needed. Though the larger pin spacing of B9G / Magnoval no doubt allows higher voltages between pins.
Were there any commercial hi-fi amplifiers that used the PL509 or PL519? Or were they used mainly for PA and guitar amplifier work? And did the valve makers support AF applications (and develop the requisite curves), or was their use in this role simply an amplifier builder choice. The PL509, at 30 W anode dissipation, offered an intermediate between the 25 W KT66 and EL34 and the 35 W KT88, and the PL519, at 35 W, equalled the KT88, but was probably lower cost (due to mass production for domestic TV receivers) although likely not as good.

Quote:
Originally Posted by Heatercathodeshort View Post
I believe the only B8A valve with a top cap is the UL44. It is a line output valve used in early post war Philips television receivers including the projection models [600A etc] Looks a bit like a PL81.
Aha, so Philips started very early with the top-cap for line output valves in its miniature series.

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Old 24th May 2011, 10:33 am   #97
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I believe the 6BW6 was a Brimar development. It seems to be relatively unknown on American websites, and never used in US equipment. Doubtless someone will now produce a counter-example! 6061 is the special quality version.
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Old 24th May 2011, 10:36 am   #98
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Default Re: Valve Questions

H Gents, I'm not sure if the later line output valves (PL519 etc) were used that much in Hi Fi amps; PA, instrument, etc possibly.
An examination of the Vg/Ia curves shows them to be pretty non-linear, exactly what is needed for valve pulse operation.
It is only latterly that the technique of applying the signal to G2 and the bias to G1 has been developed, where Vg2/ Ia is pretty linear.
Not too many curves around that show this though, and there is the drawback of a lower driving impedance and the signal needing to have a high standing DC.
Ed
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Old 24th May 2011, 12:22 pm   #99
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Quote:
Originally Posted by Ed_Dinning View Post
H Gents, I'm not sure if the later line output valves (PL519 etc) were used that much in Hi Fi amps; PA, instrument, etc possibly.
An examination of the Vg/Ia curves shows them to be pretty non-linear, exactly what is needed for valve pulse operation.
Quite right Ed. I remember working on some driver amplifiers for large vibration testers which used PL519s.

The requirement was to produce large pulses for applying vibration to large assemblies.
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Old 24th May 2011, 12:53 pm   #100
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Quote:
Originally Posted by Leon Crampin View Post
A "DCH40" would have approximately one third of its filament allocated only to the oscillator section, whereas a "fully concentric" frequency changer such as the DK40 uses the whole filament for all jobs.
Agreed - but in a concentric form (DK40) some of the electrons are intercepted and lost to the oscillator anode (grid g2). So there would not seem to be much benefit of a DK40 over a DCH40, with same length filament, a 2/3-height hexode section, and a 1/3-height triode section. Or is it down to the lost space necessary between the triode and hexode section, if configured one above the other (like DAF91 etc)?

Quote:
Originally Posted by Leon Crampin View Post
Philips ... were extremely sniffy about beam tetrodes. They made beam tetrodes (even a 6V6) and always described them in the data books as pentodes.
Such as the DL92! Beam tetrode even when having the Mullard logo!
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