[Synchrodyne]

Re the double-diode triode case, Philips included the EBC41 in its initial Rimlock range, announced in 1946. It would appear that Philips wanted to have all of the core domestic receiving valves in Rimlock form, even though some would have fitted on the B7G base. The initial Rimlock range also included the EB41 double diode.

The EBC41 was probably available from UK production (Mullard) at about the same time as the American B7G-based 6AT6, as such from Brimar and probably Cossor, and as the DH77 from Osram. It seems likely that the EBC41 and 6AT6 established themselves in parallel in UK setmaker practice as the changeover was made to miniature valves of one kind or another.

Philips initial noval-based radio receiving valve range of 1949 also included a double-diode triode, namely the 6BD7/EBC81. Again it would appear that Philips preferred putting this valve type on a noval base, even though it could instead simply have picked the EBC90 (6AT6) from its industrial range. One could infer that it preferred to have an internally screened double-diode triode for receiving applications (as with the EBC41) and that as far as reasonably possible, it now wanted to standardize on the noval base.

Of the four novals in this initial release, the available evidence is that all four (6AN7/ECH80, 6N8/EBF80, 6BD7/ECH81 and 6M5/EL80) were made available in Australia right away, but only the EBF80, which perforce had no Rimlock counterpart, was offered in UK/Europe. Given that the ECH42, EBC41 and EL41 were established in UK/Europe, Philips elected to delay the changeover for that region. Possibly in 1949 it had the ECH81 and EL84 in view, and did not see any benefit from an intermediate change in those two categories. It may also have had the EABC80 in view, and saw that as largely displacing the EBC41 as receivers moved from AM-only to FM-AM configuration. Of course, it could have been a ploy to extend somewhat the “frontline” life of its Rimlock range. An odd facet is that the key Rimlocks eventually received American registrations and type numbers, but this did not happen until later in 1955. What that was about I do not know; perhaps for replacement supply in American designation-oriented markets into which Rimlock-equipped receivers had nonetheless found their way.

An early addition to the noval range was the 6BH5/EF80, essentially a noval version of the Rimlock EF41, and initially released for Australia but not for UK/Europe. Philips’ initial thinking was that the EF41 would be displaced by the EF85 in FM-AM applications. Apparently it was not the best option for the IF gain stage(s), so there was a rethink that resulted in the EF89/6DA6 c.1955 as the direct and improved successor to the EF41. The arrival of the EF89 meant that there was now a nearly complete set of novals for FM/AM and AM-only applications in UK/Europe, with the EBC41, now much less used, as the only outlier. Thus it was time to release the EBC81 in UK/Europe in order to complete the noval series.

Pye was in the Mullard Rimlock camp when it came to its first wave of miniature valve domestic receivers, and thus used the EBC41 amongst others. Thus it was logical that when it (unusually) required a double-diode triode for its FenMan II FM-AM receiver, it would use the EBC41. On the other hand, given that the FenMan II otherwise used noval valves, it is also reasonable to assume that it would have used the EBC81 had it been available from Mullard UK when the receiver was designed.

Notwithstanding the precedent of the EB41, Philips did not issue a noval-based double-diode. Rather it drew the EB91/6AL5 B7G-based double diode from its industrial series into its domestic radio and TV receiving range.

Re Australian post-WWII practice, notwithstanding the dominance of American influence, there were also UK/European elements. These included some use, possibly quite extensive, of the triode-hexode/heptode AM frequency changer rather than the American pentagrid. The valves concerned, e.g. ECH80/6AN7, 6AE7/X79 and ECH81/6AJ8 were all of European origin. Another was the use of the double-diode pentode, such as the 6N8/EBF80. The use of noval-based HF pentodes, such as the EF89/6DA6 was also European, as the American miniature HF pentodes all used the B7G base.

The triode-hexode/heptode case suggests that the Australian setmakers did not all share the American “love affair” with the (relatively noisy) 6BE6. Possibly there was greater inclusion of shortwave bands in Australian-made receivers (bearing in mind that SW was used for some Australian domestic broadcasting back then), and that was where the 6BE6 shortcomings were more likely to show up. But to be fair, some American setmakers avoided using the 6BE6 by other means that were facilitated by the need to offer FM-AM receivers. GE, having developed the 12AT7 double-triode for use as an FM and TV frequency changer, used it in its radio receivers, where it was used not only for FM, but also for AM, on which band one triode served as oscillator, with the FM 1st IF stage, often a 6AU6, serving as AM mixer. So effectively GE used a triode pentode AM frequency changer. Zenith also adopted the 12AT7 as FM frequency changer, and then used it as such (both sections) for AM. RCA used the 6X8 triode pentode as both FM and AM frequency changer. The 6X8 was developed as a VHF TV frequency changer, but was also designed from the start to be suitable for FM-AM applications. RCA triode-strapped the pentode mixer section on FM, but not on AM.

New Zealand was much more of a mix in terms of valve types used, and during the 1950s and 1960s one saw equipment with American-numbered (and usually American-type) valves and European-numbered valves, including Rimlocks. I recall seeing more European than American valve numbers, but whether that reflected the actual split I don’t know. But a typical radio receiver of the later 1950s/early 1960s from the Waihi factory (which supplied several brands) was ECH81, EF89, EBC81, EL84, EZ80. There was some use of American-numbered European-type valves. AWA made a wideband AM tuner (MW-only) to match the RCA UK Orthophonic hi-fi equipment for which it was the NZ agent. This had a 6BY7 (EF85) RF amplifier, 6AJ8 (ECH81) frequency changer and 6DA6 (EF89) IF amplifier. (The use of the EF85 as an AM RF amplifier was I think unusual, but then Marconi used two of them in its NS702/2207C Atalanta HF receiver).

Generally, I have found that to make sense of the receiving valve ranges that were offered in different parts, and they way they were used, one has to drill down quite a way to find otherwise obscure reasons, or at least plausible rationalizations, not always technical.


Cheers,