GZ34 data sheet discrepency?
 

Looking at the data sheet for the GZ34:
http://www.r-type.org/pdfs/gz34.pdf
Pages 5 and 6 appear to show the anode chaarcteristic, except they're different? So what are they supposed to be showing??

Re: GZ34 data sheet discrepency?
 

Better performance of a later valve?

p5 plot is dated 1952, p6 plot, 1958.

Re: GZ34 data sheet discrepency?
 

Several other sheets appear to be similarly paired.

It seems a bit strange really - I'd have thought that if significant improvements were made, the valve would have been redesignated, perhaps GZ34A, or GZ304.

Will Synchrodyne have any insight, I'm wondering? He often does when valve development is concerned.

Re: GZ34 data sheet discrepency?
 

I wonder if this could be a case of "rationalisation" by the manufacturer - different and upgraded internals (shared with some other more-popular valve?) but still badged the same as the original version?

In the same way as the original 5Y3 was directly heated but later started appearing as an indirectly-heated version with the cathodes tied to one filament-pin.

Re: GZ34 data sheet discrepency?
 

I've been surprised too at the range of data in the GZ34 sheets. But I'd just assumed that it did represent a steady improvement in performance. I have other versions of the GZ34 sheets and they do generally seem to show such an improvement as their dates get steadily later.

Cheers,

GJ

Re: GZ34 data sheet discrepency?
 

Just a query... What is the purpose of having one side of a heater wired to the cathode (hence HT line) doesn't make any sense to me but there's obviously a reason?

Mike.

Re: GZ34 data sheet discrepency?
 

The original 5Y3 was a directly-heated valve - the two flat 'ribbon' filaments were coated with emissive material and served directly as the cathodes.

The "later" 5Y3 was indirectly-heated - but to make it plug-compatible with the original version the indirectly-heated cathode tubes were linked to the heater-pins.

Re: GZ34 data sheet discrepency?
 

I presume the need to remain pin compatible and a "fast heat" device meant that little heater to cathode insulation could be included.

Re: GZ34 data sheet discrepency?
 

Ah, thanks, I knew there must be a reason somewhere. :)

Mike.

Re: GZ34 data sheet discrepency?
 

It also avoids potential (no pun intended) heater-cathode breakdown problems if the heater supply should somehow end up close to 0V. With the heater and cathode tied together that would blow the fuse, not the valve.

A few rectifiers (the EZ80 for example) were designed to withstand a large h-k voltage, thereby allowing a single common heater supply for all the valves in a set. In those cases the heater and cathode aren't internally connected, obviously.

Cheers,

GJ

Re: GZ34 data sheet discrepency?
 

I suppose the only downside of a directly heated rectifier is having to have a separate winding for the heater of that valve, and a well isolated winding as well, or some serious problems could arise should that winding short over to the other heater wiring or HT winding. 8-o

Mike.

Re: GZ34 data sheet discrepency?
 

There's another downside to being directly heated - the warm-up time is much faster, so the HT electrolytics charge up to practically the peak voltage for several seconds, before the other valves in the equipment start passing current and drag the voltage down.

That's one reason for an indirectly heated cathode - even if it is internally commoned to one of the heater pins.

Re: GZ34 data sheet discrepency?
 

Sorry to say that in this case I do not have any insights. I'd say that GrimJosef has summed it up - progressive improvment.

As long as the characteristics changes brought by the improvements did not disqualify the improved versions from applications for which the original versions were recommended, redesignation would not appear to have been imperative. Apart from lack of back serviceability, another trigger for redesignation would be that the improved version was intended to suitable for applications beyond the reach of original, i.e. what might be called lack of forward serviceability.

Was the GZ34 of what might be called "late octal" form, that is with a glass button base/foot that was fitted into an octal "boot", as was done with the EL34?

Cheers,

Re: GZ34 data sheet discrepency?
 

Yes it was :thumbsup:.

Cheers,

GJ

Re: GZ34 data sheet discrepency?
 

What I'd have been worried about in that case, is a design engineer using the 'new' data sheet, with the improvements, designing-in a GZ34 in an application which really does need the new ratings, , and then at some time in the future an 'old' type GZ34 being plugged in.

Sounds a recipie for disappointment.

When Mullard/Philips improved the PCL85, they rebranded it as PCL805 to guard against this happening. You can use a PCL805 in circuits designed for PCL85, but not the other way round. I've even seen valves laballed 'PCL85/PCL805'.

Maybe this thinking wasn't around in the GZ34 days?

Re: GZ34 data sheet discrepency?
 

I suppose the time-span of GZ34 manufacture represented an era of tightening tolerances and repeatability and improving understanding of things like cathode materials/preparation, so incremental improvement was possible with little or no expense in unit cost, so no perceived need to trumpet it.

Also, the PCL85 had become notorious, so a definite statement of improvement was needed- or "re-brand" as we hear nowadays- to re-assure users. Presumably, the GZ34 was seen as a good 'un from the outset- (slightly) lower cathode heating power than the established 5Z4 workhorse but improved ratings all round, so no need for change of identity as it got better over a few years- when folk trust something, they like stability.. Indeed, an extra 10-20V of HT with later versions might not have been shouted about in case it worried nervous consumers. Most of the time, it would have been fine- slightly hotter output valves, a bit more undistorted output power. Shunt voltage regulators could have been a little over-run, but perhaps we're now getting into expected component lifetimes versus consumer turnover rates and the stats said "not an issue".

Re: GZ34 data sheet discrepency?
 

Maybe that is why Philips included data for both the original and the latest variants in the data sheet at interest? That way designers could take account of the differences between old and new. Still, if that were so, and inclusion of the old data was not simply an editing error, including a few words of explanation would have been not unreasonable.

Hard to say. There were some examples from that period or earlier of designation differentiation as the result of improved performance and/or better construction. The ECH42 was an ECH41 with higher conversion transconductance (maybe after Philips had miscued with the original), and the UL46 was a more robust UL41, suitable for TV field output and video output service. But in these cases Philips had a strong element of self-interest pointing to differentiation.

Cheers,