[Synchrodyne]

Originally Posted by G8HQP Dave

I always assumed the EF85 was intended for TV, as the combination of high gm and highish Cag means reasonable gain in a wide bandwidth circuit. It was used in lots of radios too, as it had more gain than the EBF80 and Europeans tended to avoid B7G valves in domestic sets.

There is certainly evidence that the EF85 was intended to be the TV IF vari-mu counterpart to the EF80, such as at: http://www.r-type.org/exhib/aaq0029.htm.

It has the same pinouts as the EF80, and likewise two cathode connections.

Although it predated the real Mullard B9A era, the EF80 had a B9A base, simply I think because with two cathode connections and a separate internal screen connection, it needed nine pins. Thus like the EBF80, it was somewhat anomalous in what was generally a B8A range.

It seems that whether by happenstance or design, by the time that the EF85 was developed, the B9A era had arrived for Mullard. At the time Mullard would have been considering its B9A radio valve range that would supersede the EF41, ECH42, EAF42, EBC41, EL41, etc. In fact the EF41, ECH42 and EBC41 had direct B9A replacements in the form of EF81, ECH80 and EBC81 respectively. Of these the EF81 and ECH80 were probably little used. The EBC81 might have been less common in the UK, but it was legion elsewhere, such as in New Zealand.

Coincident with arrival of the B9A era was the need to address FM/AM receiver requirements, which required a combination of new and improved valves. Hence the development of the ECC85, ECH81, EABC80 and EL84, as well-covered in the Mullard literature. For the RF/IF pentode, something better than the EF41/EF81 was evidently perceived as necessary, and quite possibly as a matter of convenience the EF85, then also new, was seen to be close enough and so pressed into radio service, and in that context simply treated as part of the new range. Thus for example one finds data sheets that show the EF85 paired with the ECH81 and sharing a common screen grid decoupling capacitor.

Then when the EF85 was found to be less than ideal in some radio applications, the EF89 was developed as an improved EF41 that retained its basic virtues. In contrast to the EF85, the EF89 has one cathode connection, which I think is what one might expect for an HF/MF valve that would not normally be used at above 30 MHz.

The EBF89 was the double diode pentode derivative of the EF89, and so more-or-less the successor to the EBF80, which was counterpart to the EF41. The EBF80, already having a B9A base, simply moved into the initial B9A range as it was, and it shows up paired with the ECH81, sharing a common screen grid decoupling capacitor, in some of the literature for the latter. There does not seem to have been an EBF counterpart to the EF85 – to start with a B9A base would not have had enough pins to accommodate two cathode connections for the pentode cathode. There was no B9A successor to the EAF42, nor would there seem to have been a real need for one.

Originally Posted by G8HQP Dave

The low Ca-a in the ECC85 was simply because of the screen. This seems to be the only fundamental change from the ECC81.

There is some interesting data on triodes at: http://www.r-type.org/static/tv50.htm. It’s a pity that the ECC85 was not included in that comparison of the “mechanical” details.

Originally Posted by G8HQP Dave

My guess is that the PCC89 beats the PCC84 on signal handling when AGC is used, but if used 'straight' I suspect the '84 would win as it has less gain. A normal valve has good signal handling at one optimum bias point, and poor when biased back. Remote cutoff valves are slightly poorer at optimum bias, but relatively much better when gain is redced. The ECC189 is a strange choice for a general-purpose HF receiver, as it has far too much gain (and so poor signal handling) for the noisy LF end of the spectrum - but fine above 20MHz. But maybe a reasonable balance for use with a very short antenna?

Eddystone provides only a qualitative rationale for its use of the ECC189 1st RF stage.

In respect of the 880/2:

“The first stage is a high-gain RF amplifier which uses a low-noise double-triode in a series cascode circuit. This arrangement is used in preference to the more conventional pentode because of its superior performance with respect to blocking, cross modulation, etc.”
And for the 940:

“The cascode amplifier maintains excellent signal-to-noise characteristics throughout the entire tuning range and is superior to the more conventional pentode amplifier usually found in this position.”

and:

“The first RF amplifier is of the cascode type and, as a result, the figures for noise, cross-modulation and inter-modulation are exceptionally good.”

Cheers,