[Synchrodyne]

The Philips initial release on the Australian Innoval series (2nd link in post #41) included a comparison between 6BD7 (EBC81) double diode-triode with the American 6AV6. The much lower diode-to-diode and diode-to-triode capacitances of the 6BD7, resulting from its internal screening, were stated to be advantageous in conventional domestic receiver circuits. (See page 10 pf the .pdf.) Given that the 6BD7 was essentially the EBC41 with a noval base, the same would have applied to the latter. The RMorg article (1st link in post #41) indicates that the EBC81 was not distributed in Europe until 1954 (I had guessed 1955), with the EBC41 offered until then. As well as for supply reasons, it appears that until the EBC81 was released, the British/European setmakers had technical reason to use the EBC41 rather than the 6AV6 or 6AT6. (I am assuming that the 6AT6 was similar to the 6AV6 in terms of its internal capacitances.)

It would appear that in Australia, the early Innovals, with the same internals as the initial Rimlock range, stayed in use until the end of the valve era, even though the later noval-only issues, such as the ECH81/6AJ8, were available. For example, the Audiosound AM100 wideband AM tuner, of c.1969, used a 6AN7 (ECH80, same internals as ECH42) as frequency changer.

The extended period over which novals progressively replaced Rimlocks in the European market did produce some interesting valve lines-up. The Ekco A182 export bandspread receiver provides a good illustration. I don’t know exactly when it was released, but c.1953 seems likely. Its valve line-up comprised 2 x EF41, ECH42, EBF80, EB91, 2 x ECC83, 2 x EL42, DM70 and EZ40.

The EF41, ECH42, EL42 and EZ40 were part of the original Rimlock range, and at the time were still current in Europe, with their noval replacements/counterparts not yet released in that region. Although the A182 might have been on the cusp of the ECH81 release. (The EF41, ECH42 and EZ40, but not as far as I know the EL42, already had Innoval counterparts in Australia by then.) The EBF80 was of necessity a noval valve from the start (and as the 6N8 was part of the initial Innoval range.) The EB91 had evidently superseded the EB41 in the European radio range. It [the EB91] had been part of the initial Philips World Series TV range, so it is logical that it also would have displaced the EB41 for new radio designs at about the same time. The ECC83 was a relatively new noval audio valve. It was somewhat different to the Rimlock ECC40, but a suitable, probably better successor for many AF applications. The DM70 was a new sub-miniature tuning indicator. There had been no tuning indicator in the Rimlock series, and the first noval version, the EM80 might still have been in the future, although not by much.

Reverting to the EBF80, this had been introduced in part to provide a combined IF amplifier, demodulator and AGC rectifier valve that allowed the use of conventional delayed AGC. Previously Philips/Mullard had recommended using the EAF42, with the pentode suppressor grid doubling as an AGC delay diode. But apparently this had not always worked very well. Perhaps ironically, in the A182, Ekco had used the EBF80 suppressor grid to provide a second delay for the RF AGC, the EBF80 AGC diode itself providing the initial delay for the IF AGC.


Cheers,