P-Series Valves, what to do with them?

[ppppenguin]

Can we try to clear up this PL84/EL84 equivalence question please. Ignoring heater voltage of course.

Trevor has asserted that they are equivalent David (Geordie) has said that PL84=EL86. Since the EL86 is different to the EL84 I don't see how both claims can be true.

[pwdrive]

Can we try to clear up this PL84/EL84 equivalence question please. Ignoring heater voltage of course.

Trevor has asserted that they are equivalent David (Geordie) has said that PL84=EL86. Since the EL86 is different to the EL84 I don't see how both claims can be true.

Philips PL84 valve data here:

https://frank.pocnet.net/sheets/030/p/PL84.pdf

Philips EL84 valve data here:

https://frank.pocnet.net/sheets/030/e/EL84.pdf

PL84 triode connected data, there's two lots of figures for two different Va and Vg, take one of them eg: Va = 100v, Vg = -ve 8v, Ia (no signal) = 30mA, now look at EL84 triode connected Ia-Va curves and try and make the above figures tally....I can't, that suggests to me that there is a difference if I've interpreted things correct?

Lawrence.

[Murphyv310]

A bag of worms then!!!
From what I've read the PL84 characteristics were taken as the HT available is less in AC/DC TV sets and that is the raison d'être for designing them in the first place. I'd suggest cutting open both types and do a comparison perhaps something will be gleaned that way. Thing is there are a number of references to say they are the same bar the heater.

[Murphyv310]

This supports David's reply.
https://en.m.wikipedia.org/wiki/EL84

[pwdrive]

Ref. Post#32: There's also the difference in the Ia-Va curves and the Ia-Vg curves, I realise that for those that the voltages (Va=Vg2) are different but at a 50 volt difference the difference in Ia seems disproportionate:

Ia-Vg curve for the EL84, Va=Vg2=250v...Vg1=-ve10volts Ia shows 22mA.

Ia-Vg curve for the PL84, Va=Vg2=200v...Vg1=-ve10volts Ia shows 160mA.

Lawrence.

[Murphyv310]

How about this quick and dirty test.
Mullard 3-3 running low HT at 244v.
Scope and audio power meter running 1Khz input sine wave.
EL84 2.7w RMS at the onset of clipping.
EL86 (NOS) 2.1w RMS at the onset of clipping.
PL84 (NOS) 2.6w RMS at the onset of clipping, (Heaters fed from Labpack)
No other tests done.

[davegsm82]

Dave, do you mean PCC83? The ECC83 can be used in 300mA series chains so there's no such thing as a PCC83 that I've ever heard of. Presumably given the context B9G is a typo for B9A.

Not sure about you constant pwoer idea. While it's probably true, it's a big hammer to crack a fairly small nut. Apart from a few small B7G triodes I think all P series valves need more than 6.3V heater. So easy enough to use a variable PSU and meters to see what's happening.

Hi Jeffrey, My apologies, I think I was thinking of the PCC84/85, but was probably staring at a ECC83 that's on my desk at the minute. And yes, I always make the mistake of B9G/A.

As for the heater power idea, having gone through the various envelope sizes Vs. Heater consumption I've realised that it might not be as easy to quantify them using this method, although I will add that this idea was mainly for testing unknown valves, possibly in an automated test jig.

I'm glad this thread has started a good debate, it's good to see everyone's ideas.

On the subject of Buck/Boost converters, this is a good idea, however I've noticed the heater consumption on startup can sometimes be 2-3x the normal rated current. An EL84 puts my L30/2 lab pack into current limit at 2A for a second or so then settles to about 0.7A so a converter would have to have plenty of overhead.

Dave.

[Refugee]

I would go for the increase in resistance as the filament heats up.
The resistance wire in them is pretty consistent even across manufacturers so it should increase by a percentage of the cold value that will be much closer than anything else.
It would not be as reliable for very old pre-war valves as some ran much hotter.

[Terry]

Dave, have you been able to identify some of your 'mystery' stock yet by decoding the etched codes?

[BusyBee]

With respect to heaters I suspect that it is far easier to deal with if you have the correct AC transformers for them. I have only one buck convertor running with very low demand so is not a problem at all. Running several heaters (especially big valves) would be more a problem. My bench PSU does have an LM338 (better than LM317) which is with heatsink sitting on a medium computer fan. It does run my TRF receiver Ok (6 average heaters).

Tracy