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Old 23rd Jun 2015, 2:44 am   #361
Synchrodyne
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Default Re: Valve Questions

The top-cap anode sounds like the kind of thing that Brimar might have done.

Doing the variant count for each of the 6V6 and 6Q7 cases would be quite a daunting task. Easier I suppose if one limits the counts to domestic receiving variants, but even so.....

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Old 23rd Jun 2015, 6:53 am   #362
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Default Re: Valve Questions

An audio output stage is needed in just about all radios, and the amount of power needed is going have a spread, but the 6V6 is right at the level with the biggest demand. The emissivity of cathodes for an acceptable heater power sets the max current, which along with the power needed sets the HT requirement. Into all these relationships, the 6V6 came along as the beam tetrodes swept all before them. Standard voltages for smoothing capacitors tended to stabilise the choices of HT voltage. So even without any other factors, there was going to be a bunch of fairly similar valves. Once one type becomes particularly popular, the "me too" effect has competitors vying to get their brand in the socket. On top of that valve manufacturers don't see any reason to do completely new designs when it's quicker and cheaper to stick a different voltage/current heater in an existing design, or to stick that existing design in a different bottle and base. Both happened and the successful types expanded into a 3-dimensional matrix with varieties of brand, base and heater.

An interesting question would be just how many really different valve types were there?

The data books catalogue zillions of transistors, but a much more moderate number could replace the whole lot.

And then there's opamps...

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Old 23rd Jun 2015, 10:06 am   #363
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Default Re: Valve Questions

The whole proliferation of 'similar but different' valves thing has always intrigued me; I see there having been a number of distinct drivers.

Some of this was done purely for marketing reasons: it's well-documented that Philco and RCA had an ongoing war in the 1930s/1940s where one offered radios using their "all-metal" tubes [both Octal and B7-type bases] the other all-glass (Loktal) valves developed originally by Sylvania; both indulged in high-profile campaigns in the popular press 'dissing' their competitor's choice.

Philco even managed to get the RMA to *******ize their numbering-system to accomodate Loktals - and in doing so broke the consistency of the first digit(s) being the heater volage.
Hence we have the likes of the 7C5 which is a Loktal version of the 6V6. The "7" would normally imply a 7V heater but it has a good old 6.3V one same as the 6V6.

"Manufacturer lock-ins" between set- and valve-makers caused yet more proliferation of "similar but different" valves. The 1930s 'continental' side-contact base, the Mazda Octal and subsequent B8A base (again promoted hard by Mazda) could be seen as a not-so-covert way to ensure replacement valves would only be provided by the same small circle of manufacturers [BVA] that produced the originals.

Same wine, different bottles!
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Old 23rd Jun 2015, 11:05 am   #364
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Default Re: Valve Questions

But incompstible corkscrews

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Old 24th Jun 2015, 3:21 am   #365
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A point with the 6V6 and 6Q7 that probably has much to do with their respective multitudinous progeny is that, amongst the “common core” receiving valves, their immediate post-WWII miniature successors, the 6AT6 and 6AQ5, retained essentially the same innards and delivered the same performance, excepting for anode voltage restrictions in the case of the 6AQ5 due it its small envelope size. This was not the case for the others in that core group, namely the 6BA6, 6BE6 and 6AU6. They all had non-negligible performance improvements as compared with their pre-WWII octal predecessors. In part this enhanced performance anticipated their use in FM and FM/AM receivers. Their timing suggests that they may have been designed around 45 MHz FM needs, not 100 MHz, and that better, although basically similar VHF valves soon followed is perhaps empirical evidence in support of this notion.

As it happened, the 6V6 and 6Q7 characteristics were good enough to survive right through to the end of the valve era. The 6Q7 was largely displaced by the miniature 6AT6, because there was no good reason to use other than a miniature for its functions. There was also the 6AV6, with a 100 µ triode, but this was also a miniature version of a pre-WWII octal, namely the 6SQ7. But the 6AV6 did not overshadow the 6AT6. Perhaps the 6AV6’s main claim to fame was that it bequeathed its triode to the 12AX7 and ECC83. There were a plethora of later double diode-triodes and some triple diode-triodes in the Americans series, variously for TV, FM and FM-AM purposes, but none of these displaced the 6AT6 in the erstwhile AM demodulator/AGC rectifier/AF amplifier application.

Apparently the 6AQ5 was initially released with car radio applications in mind, although of course it was much more widely used. Nevertheless, in American practice there was also continued use of octal valves in “power output” positions, particularly in TV receivers. Thus the 6V6 was not fully displaced by the 6AQ5 and other miniatures, so it survived until the end, and spawned the diversity of heater variants as previously noted.

As it turned out, the 12 watt anode dissipation output valve was something of a “goldilocks” choice for domestic radio receivers. European practice generally got there with the EL84 in 1953. Some smaller valves were issued in the American series, such as the 8.5 watt 6AR5 for car radio applications, but the dominance of the 6V6 family seems not seriously to have been challenged.

The use of these valves also overlapped with the early part of the IC age. The CA3041 and CA3042, from late 1967 or early 1968, I think, were RCA’s second generation of TV intercarrier IF amplifier/limiter/demodulator/AF driver ICs, the first generation having been the CA3013 and CA3014 in 1966. The AF amplifier section of the CA3041 was described as “specifically designed to drive directly a 6AQ5 beam power tube or other audio output tube of similar characteristics.” So, a state-of-the-art 1967 solid state device was designed to drive a valve of basically 1936 design.

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Old 24th Jun 2015, 7:48 am   #366
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Default Re: Valve Questions

That's quite funny. During an overlap period we had TVs that were all-semiconductor right up to the line output stage. Similarly amateur HF transceivers were appearing with transistors, but still a valve driver and PA, while at the same time some older car radios were still in service with a complement of 12v anode valves and one big germanium power transistor for the audio output.

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Old 24th Jun 2015, 12:43 pm   #367
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Yes, ironic that the hybrid arrangement was in use both ways round!
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Old 24th Jun 2015, 3:55 pm   #368
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The "hybrid" approach was standard in the 1960s for mobile two-way VHF/UHF stuff too: look at something like a Pye Vanguard or Cambridge. On the receive side the early versions used valves for the RF-strip (EF95 etc) with semiconductors for the IF and audio; later versions had all-semiconductor receivers. On transmit, the RF stages were valves throughout (QQV03/10, QQV06/20 or 6/40 PA) with a semiconductor modulator (either AM or FM).

An invertor to generate the HT.

Germanium transistors throughout - an interesting mix of Mullard OC170/171 for the receiver VHF stages and 10.7MHz IF, the nice gold-plated TO5-with-a-central-flange GEC "GET" types for the Rx 2nd IF/low-level-audio, and TO-3 cased Newmarket NKT404 or odd "top-hat" Mullard ADZ11 for the audio output and invertor.

It was quite something in the early-1960s to have a 100-Watt-output mobile VHF radio.
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Old 24th Jun 2015, 4:23 pm   #369
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Default Re: Valve Questions

QQV03-40?

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Old 24th Jun 2015, 4:35 pm   #370
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The 3/10 was used as driver in the FM Vanguard and as output in the Cambridge; the 6/20 and 6/40 were outputs on the Vanguards. Not a lot of people had a Vanguard FM100B!
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Old 2nd Jul 2015, 2:55 am   #371
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In respect of hybrid car radio practice, it may be noted that in the American 12-volt HT valve series, the 12K5 space-charge tetrode was developed specifically as an audio driver for transistor output stages, and probably had few other applications. In Europe the EF98 pentode, but tetrode-connected, was used for the audio driver function. The EF98 was basically the sharp cutoff RF pentode in the European 12-volt HT series, counterpart to the remote cutoff EF97. However, prior to the availability of the 12-volt HT valves, Pye had used a PCL83 as audio amplifier and driver in its TCR16 car radio receiver, which had a push-pull transistor output, with HT for the regular valves (12BE6 and 12BA6 as well as PCL83) derived from a single transistor oscillator with transformer and rectifier. I assume that the rectifier was solid state. But Delco in the USA had an early hybrid car radio in which a 12X4 valve rectifier was used following a push-pull transistor oscillator to supply HT to regular valves. It is strange too that hybrid car radios first appeared at about the same time as – or maybe even just after - all-transistor types. And not only that, the prognosis for the continued use of valves in the RF and IF stages was good enough to justify the development of a new series of 12-volt HT valves.

Re the PCL83, one wonders if its 12.6-volt heater was just happenstance or whether it was a deliberate choice. Primarily it was designed to fit 300 mA heater chains. And unlike the American case, the European valve series did not appear to include a complete 12.6 volt heater group, although some here and there fitted that class. Possibly when the designers saw that the PCL83 heater would come out somewhere around 12 volts, the design was adjusted for an exact fit on the basis that this would incrementally increase its utility without detracting materially from its primary mission.

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Old 2nd Jul 2015, 12:57 pm   #372
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Quote:
Originally Posted by Synchrodyne View Post
In Europe the EF98 pentode, but tetrode-connected, was used for the audio driver function.
Now that's interesting from a circuit point of view - presumably the driver stage needed to supply some base drive power to the O/P transistor base, via the drive transformer. So there would be significant anode voltage swing... what about the tetrode kink?
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Old 2nd Jul 2015, 11:39 pm   #373
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Well, at least according to the published curves – attached - the tetrode kink was negligible.

My rather simplistic rationalization is thus. Strapping the suppressor grid, g3 to the anode created a virtual anode at the position of g3. Being a coarse-wound structure, it was probably not a prolific emitter of secondary electrons. Secondary electrons emitted from the anode surface proper would find themselves inside the “anode space”, as it were, and so would not have had high velocities, in turn meaning that not so many would have gotten through the suppressor grid and moved on to the screen grid. Possibly the anode/g3 combination behaviour was a little like that of the Cavitrap anode in the PL500.

With a virtual anode at g3, the effective electrode spacing proportions would have changed, with cathode-to-g1 distance becoming a larger fraction of the cathode-to-anode distance. That may have better equipped the EF98 for the driver role. In the original Mullard circuit, it was required to deliver 13 mW from an input of 1.8 volts rms.

Maybe Philips or Mullard published a proper explanation, but so far I haven’t come across such.

The EF98 (in pentode mode) probably had application as an IF amplifier in FM car radio receivers. Mullard also used it, triode-strapped, as the oscillator in its initial MW-SW 12-volt HT design, as the ECH83 triode was not up to the job at higher HF. That design also used an EF97 RF amplifier, which was evidently better in the cross-modulation department than the ECH83 heptode section used as RF amplifier in the LW-MW circuit.

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Old 5th Jul 2015, 4:21 am   #374
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Something that I have never come across is a paper or article that addresses in detail the introduction of noval-based miniature valves, and the reasons for the specific choice of pinout number and dimensions. As compared with the 7-pin miniatures and the Rimlocks, both of which had learned subject articles published, the novals seemed to have had a rather quiet introduction.

The first noval, the 12AU7, was mentioned almost in passing in the RCA article “Miniature Tubes in War and Peace”. (See RCA Review 1947 June, p.331ff, recently available at: http://www.americanradiohistory.com/..._Issue_Key.htm.) This essentially covered the inception and early development of the 7-pin miniatures. Therein the noval form was presented simply as a logical development with a greater pinout count and larger envelope size. Which of course it was, but no elaboration was provided. In hindsight one might say that the parameters were well-chosen.

It could have been that introduction of the noval form was done fairly quickly, and that it was not part of the original post-WWI American plan for receiving valves. That seems to have been based upon the general use of 7-pin miniatures for small-signal valves, the use of octals for “power” valves that required larger envelopes than the 7-pin miniature format allowed, and also the use of octals for small-signal valves that required more than seven pinouts.

The first and second points of that putative plan are self-evident. Development of octal “power” valves, particularly for TV applications, continued into the 1960s. (Relatively speaking, the novar type seems to have had less of an impact on American TV "power" valve practice than did the magnoval type in Europe.) The third point is supported by the empirical evidence of octal signal valves developed post-WWII. Two examples were the 6S8GT triple diode-triode (Tung-Sol), and the 6SB7 pentagrid converter (RCA). Both were intended for use in FM-AM receivers, the 6S8GT as FM demodulator, AM demodulator and AF amplifier, and the 6SB7 as a mixer, either separately excited or self-excited. The initial data for the 6SB7 specifically mentioned operation in the 88 to 108 MHz FM band.

Interesting is that the 6BE6 miniature pentagrid was also said to have been suitable for FM applications, but the inference is that the 6SB7 was more suitable. As mentioned upthread, I suspect that the FM suitability for the 6BE6 may have been predicated on the older 42 to 50 MHz FM band. The 6SB7, whilst being of the heptode-type, like the 6BE6, and so using grids 2 and 4 as both screens and oscillator anode, had a separate pinout for its suppressor grid, and so required eight pinouts. The 6S8GT required 9 pinouts, and so used the topcap as well as the 8 octal pins.

It does seem unlikely that RCA would have released a new octal small-signal receiving valve, particularly one intended for use in FM receivers, if at the time the decision to develop the noval type had already been made. So we’re probably looking at 1946 as the year in which the noval was conceived and committed to production. Quite early in the noval era, RCA introduced the 6BA7 (and 12BA7) which repackaged the 6SB7 in a noval envelope.

The 6T8 (and 19T8) triple diode-triode was also an early noval release. It was not quite the same as the 6S8GT, in that it had a 70 mu rather than a 100 mu triode, but it was generally regarded as the miniature successor to the 6S8GT.

So one may see that novalization of small-signal receiving valves (those that wouldn’t fit on a B7G base) proceeded quite quickly, notwithstanding the comparable octal releases of but two or three years previously.

These two examples also illustrate the progression and proliferation of American valve types. The 6BA7 and 12BA7 respectively met the needs of AC and car radio receivers with 6.3-volt heater systems and AC/DC receivers with 150 mA heater strings. The 12BA7 would also have served the slightly later need for car radios with 12.6 V heater systems, had anyone wanted to use it in AM service.

The 6T8 and 19T8 also met the respective needs for 6.3-volt and 150 mA heater systems. In the mid-1950s, the 5T8 was released with 600 mA heater, for TV receiver series strings. The original version had a 450 mA heater, and in 6T8A form, with controlled warm-up both replaced the original 6T8 and was suitable for use in TV receiver 450 mA heater strings. As best I can determine, there was no 12T8 version, which would have been suitable for use in car radio 12.6-volt heater strings. By the time FM and FM-AM car radios arrived in any numbers, so had 12-volt HT valves and the use of germanium diodes for FM demodulators. As best I can determine, the American 12-volt HT valve range included double diode-triodes but not triple diode-triodes.

On the other hand there were not 600 mA or 450 mA versions of the 6BA7, nor a controlled-warmup version of it. The 6BA7 did find application as a synchronous demodulator in early colour TV circuits (along with the 6AS6), but quite early on RCA introduced the 6BY6 sharp cutoff heptode as being more suitable for this work. Although depending upon source, the 6BY6 was either introduced for this purpose or for use as a noise-gated sync separator. There was a 3BY6 600 mA version, but apparently not a 450 mA (“4BY6”) version. Given that 600 mA strings were used in colour and larger monochrome receivers, whereas 450 mA strings were developed for smaller monochrome receivers, then the evidence does lean towards the 6BY6’s being a “colour TV” valve.

The 6BE6 also had some TV applications as a noise-gated sync separator, in which role it was nominally superseded by the sharp cutoff 6SC6. But 3BE6 (600 mA) and 4BE6 (450 mA) versions were also issued, so it must have had ongoing TV applications. The 6CS6 had 3CS6 (600 mA), 4CS6 (450 mA) and 12CS6 (150 mA; 12.6 V) counterparts. One wonders what applications were envisaged for the last-mentioned, since it wasn’t a TV valve.

But a pointer may be found in the form of the Heathkit Mohawk dual-conversion amateur band HF receiver of the late 1950s. (See Radio-Electronics 1958 December, p.98ff, available at: http://www.americanradiohistory.com/...aster_Page.htm). The Mohawk employed three 6CS6, one as first mixer, another as second mixer, and a third as self-oscillating product demodulator. Given that some amateur HF equipment used “12”-series valves, and if the Heathkit deployment was within the ambit as seen by the valve makers, and so not unique, then it is not so surprising that there was a 12CS6.

At first glance it seems surprising that a sharp cutoff heptode was used in functions where one would usually expect the remote cutoff (with respect to signal grid) type, but then it was not too unusual to find sharp cutoff pentodes in mixer service in more elaborate HF receivers. So why not a sharp cutoff heptode where better isolation between oscillator and signal isolation was desired. Looked at from the other side, so as to speak, the use of remote cutoff heptodes in domestic receivers was a necessity occasioned by the paucity of stages to which agc could be applied, so was something as a trade-off. Against that background, one may see the logic of the Mazda 6H1 sharp cutoff heptode, mentioned by turretslug upthread.

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Old 6th Jul 2015, 9:54 am   #375
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Quote:
At first glance it seems surprising that a sharp cutoff heptode was used in functions where one would usually expect the remote cutoff (with respect to signal grid) type
Heathkit made a habit of using sharp cutoff valves where everyone else would use a remote cutoff type. Perhaps an individual designer with a bee in his bonnet? Of course, if AGC is not applied then the sharp cutoff is better but Heathkit often applied AGC to them.
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Old 6th Jul 2015, 6:26 pm   #376
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Considering that some valve types managed to use all eight pins of the IO base, and even extend to a top cap connection, it might seem odd that the first widely introduced miniature type was the B7g with only seven connections- even more so considering the awareness that multiple cathode etc. connection had benefit as regards the ever-higher frequencies that valves were finding themselves used at. Perhaps B7g was only ever regarded as one of several possible, indeed forthcoming, formats. It offered notable size reduction over IO, which maybe meant that it was regarded as particularly useful in the burgeoning war-time fields of VHF comms and radar, which brought new demands in the contradictory necessities of compactness and complexity, possibly pushing it to the fore. Double-diodes and compact VHF pentodes were possible in B7g, but the 6J6 double triode was notable for its common cathode, which inevitably would have hobbled its use in some applications. All the same, the isolated double-triode would seem to be sufficiently useful a concept in many applications that it's surprising that B9a wasn't offered somewhat sooner, if not simultaneously with B7g- especially as 6SL7, 6SN7, VR102 etc. were established in IO and other "large" formats.
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Old 9th Jul 2015, 6:25 am   #377
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The full background as to the development of the B7G and B9A based valves seems to be elusive, but there is some additional information available.

As well as the 1947 RCA Review article already mentioned, there was an earlier article in the 1940 April issue, p.496ff, “Development and Production of the New Miniature Battery Tubes”.

And Radio Craft for 1940 February (http://www.americanradiohistory.com/...Page_Guide.htm) had an article entitled “Radically New Miniature “Button” Bottom Tubes”, p.465ff. The 1940 December issue had another article “Circuit Applications for the Miniature Tubes”, p.358ff.

There is little doubt that the B7G type was originally developed to facilitate the mass production of much smaller valves for battery operated receivers, and so was probably as small as could reasonably made given the starting parameters. The initial range consisted of the 1R5, 1S4, 1S5 and 1T4.

I have not found anything about the choice of pin count, though. Possibly there was an ab initio workup that gave seven as the answer. Or maybe the desired dimensions and resultant pin pitch circle indicated eight maximum, less one to allow easy location without additional devices. And seven was enough to accommodate the 1R5 heptode, which was probably the highest pin count valve likely to be required for use in battery receivers.

The initial RCA post-WWII release of heater-cathode miniatures was covered by a half-page item in Radio Craft for 1946 October, p.46. The nine valves were: 6AT6, 6AU6, 6BA6, 6BE6, 12AT6, 12BA6, 12BE6, 36W4 and 50B5. The emphasis seemed to be on their suitability for use in compact receivers. By then, the use of the 6AG5, 6J6 and 6AL5 in domestic TV receivers (and some FM receivers) had probably started, so miniatures in and of themselves in mains-operated domestic equipment were nothing new.

Of that initial post-WWII release it was said: “The r.f. amplifier pentodes are particularly suitable for use in FM and television receivers. The high mutual conductance of the 6BA6 and 12BA6 reduces the signal-to-noise ratio while the low grid-to-plate capacity adds to the inherent stability of the tube. The sharp cutoff feature makes it an ideal tube for FM limiters.” The 6AU6 was very widely used as an FM limiter, but that’s the first reference I have seen that indicates that the FM limiter application was a design target.

What is interesting is that the initial release included a full set of AM radio AC/DC valves inclusive of audio output and half-wave rectifier types, whereas the corresponding AC series lacked the latter two types, although it did include an FM limiter that the AC/DC series lacked. Perhaps it was thought that the initial demand for miniatures would be for use in compact AM-only radio receivers. But the gaps were soon filled, with the addition of the 6AQ5, 6X4 and 6BF6. Initially these were nominated as completing the set for car radio receivers, so that may also have been seen as a significant initial market. I haven’t fathomed the specific utility of the 6BF6 double diode-triode, with its 16 mu triode, as compared with the 6AT6, with its 70 mu triode. The 12AW6 and 12AL5 were added to complete the AC/DC set. Why the 12AW6 and not a 12AU6 is not clear, and in any event a 12AU6 was released a couple or so years later.

Then Radio Craft for 1947 December had an article entitled “New Tubes Improve FM”, p.28. This covered the 19T8, 6T8 and 12AT7, then just released by GE. As best I can determine, this was the second noval-based release following the RCA 12AU7. The article focused on the 19T8, gave its dimensions, and mentioned that it was on the “new 9-pin base”, without further elaboration – very low key. The 12AT7 was described as being suitable for use as an RF amplifier or frequency changer up to 300 MHz. Actually, despite its advantages, I don’t think that it generally displaced the 6J6, which remained widely used in TV circuits, and probably some FM circuits until the arrival of the 6BQ7, 6BK7, 6X8 and 6U8. The 6J6 seemed to have staying power, and was available in 19T8 (150 mA heater) and 5J6 (600 mA heater) variants. The latter would have been a mid-1950s addition, when 600 mA series-string haters were introduced to American TV practice. I think also that there was a 9J6 in Europe, for 300 mA heater strings.

If Radio Craft covered the release of the 12AU7 or the advent of the noval base more generally, then I can’t find the articles/items. In respect of the noval, one may ask why nine pins, and how was the envelope size determined. On the pin count, a worthwhile increment over the B7G probably indicated 9 minimum, 9 was the same as an octal with a top-cap, and 9 covered most contingencies including double triodes with separate cathodes, triode-pentodes with separate cathodes and triple diode-triodes. Possibly envelope diameter was more of a consequence than a cause. The pin pitch circle for the B7G was 0.375 inches, that for the B9A was 0.468 inches. If one does the arithmetic (or cheats by using http://rechneronline.de/pi/decagon.php), then it happens that the B9A pitch circle , which inscribes a decagon, maintains very close to the same pin-to-pin spacing as the B7G pitch circle, which inscribes an octagon. Just maybe the pin-to-pin spacing worked out for the B7G case was the main determinant of the B9A pin pitch circle diameter and in turn, to the first approximation at least, its envelope diameter. Whilst one might expect that heat dissipation capacity would have come into the envelope size equation, it is also possible that the approach was more towards “let’s design it for signal valve applications that require nine pins, and use it for power applications up to the level that its resultant envelope size allows.

The early releases of miniature domestic receiving valves do seem to have been application-themed: very small battery receivers for the initial B7G range, compact mains-operated receivers for the immediate post-WWII B&Gs, and FM receivers for the early novals.

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Old 9th Jul 2015, 8:07 am   #378
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"The high mutual conductance of the 6BA6 and 12BA6 reduces the signal-to-noise ratio"

As marketing claims go, it's a bit of a home-goal.

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Old 9th Jul 2015, 9:12 am   #379
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Default Re: Valve Questions

Yes, that's a classic. I thought about putting a [sic] next to it, then a sarastic comment, but finally decided it was more fun to quote verbatim without comment......and then see who was first to notice.
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Old 10th Jul 2015, 6:35 am   #380
Synchrodyne
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Default Re: Valve Questions

The attached General Electric (G-E) advertisement from Radio News 1947 October (http://www.americanradiohistory.com/...Page_Guide.htm), which I have just found, provides a significant piece of the puzzle in respect of the noval valves.

Essentially it announced “4 Nine-Pin Miniatures for FM and Television Receiver Applications”. These were the 6T8, 19T8, 12AT7 and 12AU7. As already noted, the first three of these were GE originals. The 12AU7 was an RCA original. At the time of the advertisement, the four probably represented the sum total of noval receiving valves then issued. Depending upon how one reads the text, it is possible to interpret “designed and developed by General Electric” as applying to the noval concept as well as the valves themselves.

Their multi-unit nature was stressed, as might be expected. But G-E also outpointed that they are true miniatures. I guess this was to head-off any thoughts that these were “big miniatures” that were somewhat reinventing full-sized valves.

That the pin spacing was the same as for the seven-pin types is stated, confirming what my back-of-the-envelope calculations suggested. It is also noted that the use of nine pins required a slightly larger base diameter.

At that stage G-E was evidently not yet using the “noval” moniker, but rather the “nine-pin” descriptor. Otherwise it might have advertised “novel novals”.

G-E does not seem to have been the originator of any of the prominent B7G receiving types issued by late 1947, so it evidently took the opportunity to be a publicity leader with the noval type. Against that background, it could be that RCA, indelibly associated with the B7G miniatures which it had pioneered and then had led the way with the post-WWII additions, was not anxious to promote novals as a new type, but simply as individual additions to its existing miniature range. At that time, Sylvania was still pushing hard its lock-in (Loctal base) valves, stressing their suitability for FM and TV applications. And Raytheon was about to start advertising its Bantal types. So G-E had a relatively clear field.

G-E’s positioning of the 12AT7 as being suitable for use as an FM mixer-oscillator visibly put the triode argument into play in the way that the 6J6, a WWII valve pressed into domestic receiver service, did not, even if in fact the 12AT7 did not sideline the 6J6. At the time, RCA still favoured the heptode for this job, and in fact its 6BA7 was yet to come. I suppose that RCA’s final capitulation on that front came with its 6X8 triode-pentode in 1951, which as well as its TV application, was also offered for FM mixer-oscillator applications, in which the pentode could be used either au naturel or triode-strapped.

Cheers,
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