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Old 30th Mar 2009, 2:39 pm   #21
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Default Re: Valve Questions

I agree that the EABC80 was most likely used to keep costs down.
Some more sophisticated sets used separate double diode valves for the FM detector. The Grundig 5080 that I mentioned earlier uses an EAA91 in a Foster-Seeley discriminator arrangement with an EF80 as the limiting amplifier. AM detection and AGC is taken care of by the pair of diodes in an EBC41.

John
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Old 30th Mar 2009, 2:43 pm   #22
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Default Re: Valve Questions

Neil,
That's why I baled out of the TV industry 40 years ago. I just couldn't see spending the rest of my (working) life trying to replace a valve or transisor with a couple of resistors and a cap just to knock a few pence off the cost.
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Old 1st Apr 2009, 10:55 am   #23
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Default Re: Valve Questions

Quote:
Originally Posted by paulsherwin View Post
That's a very interesting document which I hadn't seen before. My suspicion is that the circuit doesn't work as well as Mullard suggest. I don't know of a single short superhet which uses that arrangement.
Indeed. There is a brief comment to this effect in "Radio and Television Engineers' Reference Book", 4th Edition, 1963.

In discussing the use of separate AGC delay diodes, it is stated that sometimes a variant of this circuit is used in which the intermediate frequency valve suppressor and cathode are used instead of a separate diode, but that this method has given trouble due to large variations in "diode" resistance from valve to valve.

Quote:
Originally Posted by Neil Breward View Post
That might be one reason why so many AM/FM sets are pretty mediocre on AM.

The use of the EABC80 implies economic rather than technical considerations were paramount. Not only does it deny the use of delayed AGC,
As well as economics, it may have been the beginning of a general disregard for AM performance in FM/AM receivers. One argument made in favour of simple AGC from the detector diode was that it avoided the differential distortion that came with conventional delayed AGC. But that strikes me as a post facto rationalization. Differential distortion was probably more of a minor irritant than a major problem in domestic receivers where the delay was small, say around 2 volts.

Cheers,
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Old 9th May 2009, 4:10 am   #24
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Default Re: Valve Questions

Earlier in this thread it was noted that the EBF80 was, of necessity, a B9A base valve in the (relatively short) era when Philips and Mullard were pushing the B8A type. Although it had a B9A base, it had characteristics that aligned it more with the EF41, ECH42 group than with the later B9A family. The EBF89 might be viewed as its nominal replacement, although interestingly, Chapman used the EBF80 until the end of valve AM tuner production, even though it had otherwise switched from the EF41, ECH42 combination to the EF89 and ECH81.

Another early B9A valve released in the B8A era was the EF80 high-slope pentode, evidently intended primarily for TV use, although also finding other applications. The B8A series included a high slope pentode, namely the EF42, that I think saw some application in TV receivers, so the EF80 was not breaking completely new ground. And the EF43 might have been the vari-µ counterpart to the EF42. The EF80 did use all 9 pins, however, having two cathode connections - perhaps to minimize cathode lead inductance in certain applications? Whether or not this feature was widely used, the EF80 seems to have overshadowed the EF42 very early on. But the EF80 did not get a vari-µ counterpart until the EF85 arrived, by which time the B9A base was well in vogue. Their nominal successors, the EF183 (vari-µ) and EF184 (high-slope) seem to have arrived at more-or-less the same time.

Also as noted previously, in radio applications, the advent of FM/AM receivers pretty much forced the use of B9A bases with valves like the ECH81 and EABC80. In the TV case, I wonder if the die was cast when it was seen that triode-pentode frequency changers, such as the ECF80, would be needed for receivers with the higher standard intermediate frequencies then on the horizon?

Cheers,
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Old 9th May 2009, 1:40 pm   #25
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Default Re: Valve Questions

I think I read somewhere that the EF80 was introduced in order to provide from a 170V HT a similar performance to that which the EF91 could already provide from a 250V HT. Was the lower HT forced by some DC mains supplies still used in rural areas at this time?

Two cathode pins can be used to minimise lead inductance and hence raise input impedance at higher frequencies, or to help separate the input circuit from the output circuit. The data sheet doesn't seem to give any guidance on which might be the best option.
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Old 9th May 2009, 7:56 pm   #26
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Default Re: Valve Questions

Quote:
Originally Posted by Synchrodyne View Post
However, the pentode suppressor grid had its own pin, hence the need for 9 pins. It was normal for RF pentodes to have the suppressor grid brought out to a separate pin, rather than being connected to the cathode internally. I must admit I've forgotten exactly why, but it was considered to be good practice.
Cheers,
One radio that I know of uses the supressor grid of the last IF amp (UF89)with effect, on FM to provide limiting. Have a look at the circuit for the Bush VHF80. There is feed back from the ratio detector to supressor grid so that the last IF limits to prevent overload. This set uses two IF amps on FM and has more gain than usual so limiting the input to the ratio detector becomes necessary. The extra IF amp is used as an RF amp on AM so this little radio gives an excellent performance.

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Old 10th May 2009, 4:06 am   #27
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Default Re: Valve Questions

Quote:
Originally Posted by G8HQP Dave View Post
I think I read somewhere that the EF80 was introduced in order to provide from a 170V HT a similar performance to that which the EF91 could already provide from a 250V HT. Was the lower HT forced by some DC mains supplies still used in rural areas at this time?
Ah yes, the AC/DC factor - that makes sense. I think that many UK TV receivers were of the AC/DC type, even after DC mains had more-or-less disappeared.

That led to a check of the lowest anode voltages quoted for a selection of RF pentodes, as:

EF41 100 V
EF42 250 V
EF43 100 V
EF80 170 V
EF85 170 V
EF89 100 V
EF91 250 V
EF93 90 V
EF183 170 V
EF184 170 V

So, it seems that the ability to work at 170 V anode voltage was a requirement for AC/DC TV receivers in the UK. The EF80 evidently anticipated the widespread use of such receivers, inclusive of 300 mA series heater chains. Of the above list, all have 6.3 V, 300 mA heaters except the following:

EF41 200 mA
EF42 330 mA
EF43 330 mA
EF89 200 mA

In this context, the EF42 and EF43, with 330 mA heaters, were not a fit to the expected TV future. And one might also deduce that the EF89, with a 200 mA heater, was clearly intended for (AC only) radio, and not TV applications. The “radio” pentodes also could operate at low (100 V or 90 V) anode voltages, something that strikes me as more likely to have been a consequence of their having U-series 100 mA heater counterparts that were used in AC/DC receivers that could operate on mains voltages a slow as say 110 V.

Cheers,
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Old 4th Apr 2010, 3:13 am   #28
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Default Valve Questions - More

The EABC80 triple diode triode was one of several valves introduced circa 1953 to facilitate the design of combined FM-AM receivers whilst minimizing the valve count. But as has been outpointed on the above-mentioned thread, it also had a constraining effect on receiver design.

It was intended to combine FM demodulator, AM demodulator and 1st AF amplifier in one valve. But having only one independent diode, with the other two sharing their cathodes with the triode forced the use of unbalanced ratio demodulators. And with only one diode available for AM functions, delayed AGC was not possible, notwithstanding its desirability, as evidenced by its general use in the pre-FM era, and continued use in even relatively simple AM-only receivers.

Presumably some receiver makers were happy with the kind of circuitry that valve availability dictated. But those who did not want to be constrained by the EABC80 limitations may nevertheless have resisted the idea of using say an EBC81 for the AM demodulator, AM delayed AGC and 1st AF amplifier, and a separate EB91 for the FM demodulator in their standard receivers on the basis that it increased the valve count.

That being the case, one may wonder then why did not Mullard introduce what I’ll call an “EAAC80”, combining an AF triode with a pair of independent diodes? This could have been done on a B9A base. (Three cathodes, three anodes, one grid and the heater pair sum to nine connections.) This would have allowed designers full flexibility in FM demodulator design, and also in 1st AF stage design. The AM demodulator and delayed AGC functions could have been provided by using an EBF80 (or EBF89) in place of an EF85 (or EF89) for the FM 2nd IF/AM IF amplifier stage, with no increase in valve count.

Thus, instead of the customary FM/AM receiver valve line-up of ECC85, ECH81, EF85 (or EF89), EABC80, EL84. the alternative would have been ECC85, ECH81, EBF80 (or EBF89), EAAC80, EL84.

An “EAAC80” would also have been useful for FM-only receivers, which might have had a line up like ECC85, EF85, EF80, EAAC80, EL84.

With hindsight, it seems strange that in this case valve type availability was quite a constraint on economic (i.e. reasonable valve count) receiver design and performance when on the face of it, quite simply it could have been otherwise.

Cheers,

Last edited by Station X; 4th Apr 2010 at 8:48 am. Reason: Threads merged.
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Old 4th Apr 2010, 8:12 am   #29
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Default Re: Valve Questions

I suppoe the simplistic answer is "valve base".

The separate cathodes would have required a 10 pin base and although this was later available for some special valves with the addition of the central pin in the B9A configuration, this would have considerably added to production costs for a mass-produced valve.

I suspect that it was more valve maker driven than technology. And hence financial considerations than inhibited the set designers.

I should have added that a top cap could have been used, but such valves were not favoured by set makers once the use of printed wiring became common. The use of top cappped valves added to production costs both in wiring and final assembly.

Interesting question!

Roy
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Old 4th Apr 2010, 10:10 am   #30
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Default Re: Valve Questions

OK, forget the EAAC90 and its B9a base, how about an EAAC200 with a B10b base, fine for PCB manufacture (like the PFL200 which was used in fair quantities in TV sets)?

Not that I can think of anyone introducing it these days, but it's a nice thought!

Incidentally, why are we going for 'AA' rather than 'B'? Sure, it emphasizes the separate cathodes. But 'B' was good enough for Mullard, with their separate-cathode EB91!
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Old 6th Apr 2010, 5:06 pm   #31
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Default Re: Valve Questions

So, is there any difference between EB91 and EAA91? Both exist, and are often listed as equivalents, but is there some subtle distinction?
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Old 6th Apr 2010, 5:45 pm   #32
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Default Re: Valve Questions

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Originally Posted by G8HQP Dave View Post
So, is there any difference between EB91 and EAA91? Both exist, and are often listed as equivalents, but is there some subtle distinction?
No. They are identical.

The "EAA91" designation seems to be restricted to valves distributed in Germany and the Continent; Siemens, Telefunken etc. Although examples exist from the Philips chain, labelled Valvo and Philips, those labelled Mullard all seem to be EB91.

The EB91 from 1949 would seem to predate the EAA91 which appeared in 1951.

Probably it was a marketing decision (Telefunken?) to sell their valves in their sets.

Roy
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Old 6th Apr 2010, 6:44 pm   #33
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Default Re: Valve Questions

You have confirmed what I suspected - that it was just a Continental naming variation.
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Old 7th Apr 2010, 11:12 am   #34
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Default Re: Valve Questions

My reason for choosing “EAAC80” for the notional double diode triode was simply to emphasize the fact that both diodes were completely independent. The “EBC” prefix was well-established for double diode triodes with common cathodes, such as the EBC41 and EBC81. Quite possibly Mullard would have used a name like “EBC82” had it introduced such a valve. Or perhaps it would have used the EAAC80 designation in order to differentiate it from the EBC series, and to align with the EABC80, wherein the “A” presumably referred to the independent diode. It’s a hard call to make in retrospect.

The use of different second letters to indicate different functionalities in otherwise similar valves does have some precedents. For example, the EK90 and EH90 are both heptodes and have the same pinouts. But the EK90 is a essentially a pentagrid converter (of the second kind, I think), although sometimes used as a dual-control heptode mixer, whereas the EH90 is basically a dual-control heptode, albeit of a special kind optimized for use as a locked oscillator FM demodulator (apparently of the fully synchronous quadrature kind, whereas the earlier EQ80 looks more like it was of the quasi-synchronous quadrature kind).

Re the EB91 and EAA91 designations, I too had wondered whether there was any difference. To indulge in pedantry (it comes easily, along with brevity of Polonian proportions) I suppose it might have been more logical had the “A” been reserved for independent diodes, and the “B: used for common cathode diode pairs, but it wasn’t so - every language has its irregular verbs.

By the way, I think that the notional EAAC80 could have been done on a B9A base without a top cap. Two heater pins, three cathode pins, one grid pin and three anode pins seems to sum to nine., although admittedly that sum was done using base 10 arithmetic.

Cheers,
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Old 7th Apr 2010, 11:35 am   #35
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Quote:
Originally Posted by Synchrodyne View Post
..... seems to sum to nine., although admittedly that sum was done using base 10 arithmetic
But it would be OK with any base above 9.
It would have been amusing if valve pins were numbered in Binary or Octal
Alan
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Old 9th Apr 2010, 3:42 am   #36
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Default Re: Valve Questions

Well, octal would be octimal for valves like the KT88. (I remember the term “octimal” from what I think was a science-fiction book many years ago that dealt with an eight-oriented world, but have forgotten what the book was.) Then we could add in the “power of zero” and number the pins from 0 to 7. (“Power of zero” – or something similar – was an SF short story that was in that UK series that ran on New Zealand television Monday nights circa 1967 - the Asimov neutrinics and chronoscopy story was another one in the same series; halcyon days – we had The Avengers, The Prisoner, maybe the first Star Trek series was a little later, and we could still watch Maverick on Saturday afternoons, although live telecasts of the All Blacks thumping the Wallabies were still some way in the future.)

Back to the “EAAC80”, I have since discovered that valves of this basic type actually did exist in the American series, examples being the 6BJ8 and 6BN8, links below. Apparently they were designed for TV flywheel line timebase use, with the pair of diodes forming the phase-discriminator. This just goes to show that when dealing with technology history, if you can think of something that might have/should have been tried/done in a given era, it probably was, and you’ll find it if you look hard enough. And if you can’t find it, it was probably tried and found to have a fatal flaw that you haven’t thought of.

http://www.shinjo.info/frank/sheets/137/6/6BN8.pdf

http://scottbecker.net/tube/sheets/127/6/6BJ8.pdf

Cheers,
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Old 14th Apr 2010, 10:45 pm   #37
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Default Re: Valve Questions

An interesting aspect of the September, 1954 Wireless World article on FM/AM receiver design, apparently by Mullard, is that amongst the “special” valves intended for this application, the ECC85 is not mentioned. The list was ECH81, EF85 and EABC80. The EF85 – with its TV IF application origins – was even then recognized as perhaps having too high of a slope, which is why the EF89 was developed, as discussed earlier in this thread. Re the ECC85, perhaps this came a bit later on, or was originally developed by another valve maker? Anyway, more on that later on. Meanwhile, having impugned the EABC80, or at least the design constraints that attended its use, balance might be restored by considering the ECH81, which seems to have been something of a gem. Taking a detailed look at the ECH81 was prompted by the concurrent thread on hexodes: https://www.vintage-radio.net/forum/...ad.php?t=52497.

The ECH81 was more-or-less a replacement for the ECH42 triode hexode, although the latter was replicated in B9A form as the ECH80, although I suspect little used.

The key design requirements for the ECH81 seem to have been that it be a very good AM frequency changer, as well as the heptode section being a good FM 1st IF amplifier at 10.7 MHz. Perhaps the latter requirement is why it was configured as a heptode, with suppressor grid, rather than a hexode, without. Admittedly the suppressor was connected to the cathode – there being not enough base pins to allow otherwise – which is eschewed in RF pentode practice, but such connection seems to be less of an issue with heptodes. Perhaps the multiplicity of grids eases the potential feedback problem.

Another difference from the ECH42 was that the triode grid was not internally connected to the heptode injection grid, g3, the latter having its own pin. This feature was not unique to the ECH81; although it was not common in triode-heptode and triode-heptode practice. That the triode and heptode could be used independently was noted as a feature by Mullard, as shown in the 1953 Wireless World advertisement, copy attached. For example this allowed the triode to be used as an AF amplifier in the FM mode, and this possibility was noted in the September 1954 Wireless World article.

Whether by accident or design, the combination of accessibility and performance seems to have resulted in the ECH81 becoming the valve of choice where heptode HF mixers driven by separate oscillators were required, even to the extent that the triode section was sometimes unused. Apparently the B7G and B9A valve series did not include a standalone dual-control vari-mu heptode, so there was no direct successor to the octal base 6L7. To some extent the EK90, designed as a pentagrid converter, was used in this role. But once available, the ECH81 heptode was preferred.

One example was the Marconi Atalanta marine HF receiver. This used the ECH81 heptode as the 1st mixer, without agc, driven by a (triode-connected) EF85 oscillator, with the ECH81 triode unused. Another ECH81 was used as the 2nd oscillator and mixer, again without agc. This receiver was unusual – for the valve era – in having the RF agc delayed with respect to the IF agc. A 3rd ECH81 was used as the BFO, with the triode as oscillator and the heptode as an amplifier, but fed via g3 rather than g1.

Eddystone had previously used the EK90 as an HF mixer, for example in the 730 series, but moved over to the ECH81 in later models. The 830 series used the ECH81 heptode as 2nd mixer, in this case with agc, fed by an EC90 oscillator, but using the ECH81 triode as a buffer amplifier. On the other hand, the 940 omitted the buffer stage, the EC90 driving the ECH81 heptode directly, with the triode unused. The 850 series LF receiver used the ECH81 in its “normal” frequency changer mode, albeit without agc.

The above applications also illustrate various approaches to addressing the issues of oscillator stability and oscillator pulling. At the upper HF frequencies anyway, it was easier to obtain stability by using a separator oscillator. Even with a well-designed triode heptode in its normal mode, oscillator pulling could still occur, albeit less so than with a pentagrid converter. And pulling could be worse with agc. So using a separate oscillator and/or avoiding agc were two pathways to reducing pulling.

Where agc was not required, then possibly the heptode section of the ECH84 would have been a possible alternative. But perhaps its characteristics were non-ideal for the role, or perhaps it arrived on the scene too late.

On the face of it, that a standalone vari-mu heptode mixer more-or-less equivalent to the heptode section of the ECH81 was not produced seems a little odd, particularly when one considers the existence of valves such as the EH90, ECH83 and ECH84. But then the total market for use in specialized HF receivers was probably very small as compared with the TV receiver (EH90 and ECH84) and car radio (ECH83) markets.

Domestic receiver use of the ECH81 was probably mostly as originally suggested by Mullard, even in more upmarket tuners. The Chapman S6BS (2nd iteration) and Quad AMII (which looks very much like a textbook – Langford-Smith – design) both used the ECH81 as a normal frequency changer with full agc. The (very elaborate) Dynatron T139 is the only domestic AM tuner that I know of which used a separate oscillator, in this case an EC90 driving the heptode section of an X79, with agc, and with the triode unused. There might have been others, such as the Lowther DT/4 and DT/5 (https://www.vintage-radio.net/forum/...ad.php?t=49684).

As far as I know the ECH81, or a very similar triode-heptode, was used as the 2nd frequency changer in the Murphy TV/FM receivers that had dual conversion (38.15 and 6.31 MHz) sound IF strips. Dual-conversion was an advertised feature, e.g. see: http://www.murphy-radio.co.uk/murphy...59t_inside.jpg.

The ECH83 was the car radio 12 volt HT derivative of the ECH81, perhaps being identical or selected production. The original Mullard LF/MF receiver circuit used a pair of ECH83s. One was a conventional frequency changer, with full agc. The heptode section of the other ECH83 was used as an RF amplifier, with g3 strapped to g2 and g4, and with full agc. I also saw many years ago a circuit in which RF agc was applied via g3. (It was in one of those books from the late 1950s/early 1960s, probably published by Newnes, about quarto size, with maroon covers that I have not been able to trace. Would that I had kept a list of all of the library books that I read way back then.) But even a good triode heptode has its limits, at least when there is only 12 volts HT available. The corresponding Mullard MF/HF car radio circuit used an EF97 RF amplifier to obtain greater freedom from cross-modulation and better strong signal handling capability. Thus it used only one ECH83. But as it required an external oscillator (a triode connected EF98) the ECH81 triode section was still available for use as the 1st AF amplifier.

The ECH84, with a sharp cutoff heptode section was designed for use in TV receiver noise-gated sync separator circuits, evidently as a replacement for the ECH81 in this role. Perhaps receiver makers had adopted the ECH81 outside of any Mullard application recommendations, following which Mullard saw an opportunity for improvement. To a first approximation the ECH84 is the sharp cutoff counterpart to the ECH81, but I suspect that there were other differences.

Cheers,
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Old 15th Apr 2010, 11:30 pm   #38
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Thanks Synchrodyne, for a very interesting post!
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Old 25th Apr 2010, 2:03 am   #39
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Default Re: Valve Questions

Thanks for the kind words, Kalee20!

Going back to the EABC80 design constraint theme, I was initially inclined to place the ECC85 in the same class. It was evidently developed in the pursuit of valve-count economy in FM receivers, facilitating single-valve FM front-ends.

But set-makers who wanted to use a more elaborate two-valve FM front end were not deprived of suitable valves. They could always choose from the range developed for TV applications, including the ECC81, ECC84, ECF80, EF80, etc. And even without ECC85 availability, the ECC81 could have been used as a single-valve FM front end, with triode RF amplifier (earthed grid or neutralized) and triode self-oscillating mixer, although its more usual VHF role was as a mixer with separate oscillator. In that context, the ECC85 could be seen as an optimized version of a valve type that already existed. On the other hand the EABC80 was a new type that facilitated FM-AM receiver design but at the same time imposed significant constraints.

Unlike the TV RF and FC valves, I am not aware that the ECC85 had a higher slope, frame grid direct successor. The ECC86 seems to have been its car radio (12 V HT) counterpart.

Mostly the ECC85 seems to have been used as intended, as a combined Band II RF amplifier and frequency changer. One exception was in the Leak Troughline II FM tuner. This had an ECC84 cascode RF amplifier, with one half of the ECC85 used a mixer, fed from a separate oscillator (the triode section of an ECF80). The other half of the ECC85 was used as the AFC reactance valve.

Cheers,
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Old 25th Apr 2010, 6:08 pm   #40
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Default Re: Valve Questions

One essential feature of the ECC85 which other non-VHF specific valves such as the ECC81 lack, is the screen between the two sections. As has been pointed out, it's also of much higher slope.

In order to meet strict oscillator radiation limits (via the aerial) the screen is essential. This is because the RF amplifier and mixer/oscillator were combined in one envelope, which was necessary to reduce the valve count. Separate B7G triodes can live in their own cans.

Remember that with the oscillator running high, the third harmonic lies within band III, although most later sets were arranged to have the oscillator running below the input frequency to minimise problems.

I have found that ECC85s run cooler, last longer and drift less if you fit them with a blackened can.

Leon.
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