UY41 Valve.

[Synchrodyne]

On a closer look, the original Philips data (provided in Book IIIA) is somewhat confusing.

It was said: “…whereas the UY41 is suitable for all conventional mains voltages up to 250 VRMS, the UY42 can only be used up to 110 VRMS.”

From this one would reasonably infer that the UY42 was not built to reliably handle voltages above 110 V.

But later on the same page it was said: “If it is intended to employ the UY 42 on mains voltages over 110 V, a limiting resistor should be included in the anode circuit to suppress sputtering (momentary flash-over between anode and cathode). At the same time, this completely counteracts all the advantages of the, valve, for which reason the UY 41 is the obvious choice for higher mains voltages.”

This suggests that although the UY42 was in fact quite capable of operating at higher voltages, the need to use a limiting resistor meant that its lower internal resistance was negated, and so it offered no advantage over the UY41, although perhaps there was no performance disadvantage, either. Possibly economics came into the preference for the UY41 at higher voltages, as it may have been cheaper than the UY42.

Note that the UY41 also required limiting resistors at higher voltages, 160R minimum at 220 V and 210 R minimum at 250 V. The values required for the UY42 at these voltages were not stated.

A reasonable deduction from the foregoing is that the UY41 and UY42 provided comparable performance at higher mains voltages, but that the UY42 was superior at lower voltages.


Cheers,

[Synchrodyne]

Originally Posted by Synchrodyne

Reconciling the different characteristics of the UY41 and UY42 in a single valve – if indeed it were done - does not look as if it would have been at all an easy task. I’d say that absent hard evidence that the combination was done, the safest assumption is that the UY41 and UY42 remained different until the end. That does not preclude interchangeability for some applications, but that was probably situation-specific.

This page from the Philips 1954 Electronic Tubes pocket book may well be the “hard evidence”:



Quite simply, it stated that the UY41 was the same as the UY42.

Evidently Philips standardized production on the UY42, relabelling it as the UY41 as required. This was logical, in that the UY42 matched UY41 performance at the higher voltages (where the limiting resistors were major determinants) but was better at the lower voltages.

The limiting resistor values shown for the UY42 at higher voltages were the same as those originally specified for the UY41, namely 16 R at 220 V and 210 R at 250 V.

Thus a UY42 would readily substitute for a UY41, with no differences at the higher mains voltages, but offering improved performance (with no apparent downside) at lower voltages.

From the previous posting, the UY42 evidently had higher voltage capability from the start, so the UY42-for-UY41 substitution would be valid for all UY42 production.

It turned out that it was not a case of trying to provide both sets of characteristics in a single valve, but choosing one over the other.

In the beginning, Philips may have thought it desirable that it be able to offer European setmakers the lowest possible pricing, hence the UY41, with the (assumed to be higher priced) UY42 available for lower-voltage only receivers where good performance at those voltages was a desideratum. (For multivoltage receivers, some drop in performance when operated on lower voltages seems to have been acceptable.) The production learning curve probably not only resulted in reduced costs for both, but also reduced the gap between the UY41 and UY42 to the point where the latter was viable for all applications.


Cheers,

[Synchrodyne]

Confirmation by way of a Philips datasheet labelled both UY41 and UY42:




The curves for the UY41 and UY41/UY42 may be compared:







The UY41/UY42 has a shallower curve at 110 volts, dropping to 115 V out at 100 mA as compared with about 98 V out for the UY41.

Note that the UY41/UY42 charts are marked as "UY42" on the graphs themselves, confirming that the UY41/UY42 was in fact a UY42.

It would appear that the UY41 had become a UY42 relabel by 1953 December 12, whilst the UY42 was still independent as of 1953 June 24. That puts the convergence as happening in 1953 second half.


Cheers,