The Radiomuseum.org site allows one to do a “reverse lookup” on valve types to see which equipment each was used in. A cursory use of this facility shows that the EF91 was not very common at all in European domestic receivers, although it was found in some instruments. But it was quite common in British domestic receivers. On the other hand, the E/UF42 was widely used in European domestic receivers, but less so in British models. Of course, the EF80, once it was available, was very widely used in Europe and the UK.
This limited survey does at least directionally support the notion that Mullard did differently to the parent organization. There might have been an element of doing differently to headquarters simply for its own sake. A possible example of that was its (semantically illogical) renaming of the EQ80 enneode as a nonode. As already mentioned, the UK competitive scene might have been a factor, but also perhaps what might be called the “non-competitive” scene that arose from the cartel of the time. That may have fostered a situation where it was desirable that all suppliers offered a common high-slope pentode, namely the Z77 and its clones. If so, Mullard could well have deemphasized the E/UF 42. On the other hand, it took the lead with the EF80 generation, with most of the other UK valve makers cloning it, e.g. the Osram Z719 and Brimar 6BX6.
Quote:
Originally Posted by G8HQP Dave
I read somewhere that the EF80 could provide performance with 170V supply rail which an EF91 needed 250V to deliver. The two cathode pins means that you can optimise either in-out isolation or input conductance, whichever is most important for your design.
|
Looking at the numbers, those for the EF42 and EF91 were quoted only for an anode voltage of 250, at which the respective slopes were 9 and 7.65 mA/V both at 10 mA anode current.
The UF42 was the same as the EF42 except for its heater, and its performance was quoted at an anode voltage of 170, at which its slope was 8 mA/V, still at 10 mA anode current, a bit lower than what the EF42 achieved at 250 volts. That suggests that the valve was optimized for 250 volts, and that the fall-off – not that large - when operated at 170 volts was simply accepted. By extension, the EF42 at 170 volts would have given 8 mA/V.
EF80 data was quoted at 170, 200 and 250 anode volts, with respective slopes of 7.4, 7.1 and 6.8 mA/V, all at 10 mA anode current. So clearly it was optimized for the 170-volt case, typical of AC-DC chassis that might have to operate on supply voltages as low as 200.
For the 6AM6 Brimar quoted a slope of 7.5 mA/V at both 200 and 250 anode volts and respective anode currents of 9 and 10 mA. Osram gave 7.5 mA/V at 250 volts, 10 mA for the Z77, the same when triode-strapped at 250 volts, when the µ was 75.
Cheers,