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PCC88 heater current vs. voltage

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#42
jean-paul said:
Make it 300 mA. Stop thinking in filament voltage with P tubes.

ECC88 filament voltage is 6.3V not 7V.

So E: 6.3V @ xmA, P: 300 mA @ xV. Simple. No assumptions. Just correct usage as per datasheet/common knowledge. Certainly with meanwhile rare western made quality tubes instead of todays knockoffs.
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You skipped to answer what source you have regarding "different materials" ( post #21 )
 
#45
Those TV sets simply had different P series tubes but all for the difficult mystery 300 mA. This with tubes having totally different filament voltages at that current. PL519 for instance. 300 mA resulting in around 40V. The total voltage was not interesting or even relevant.

I tried to explain that with subtlety 😉 Old enough to have scrapped them, old enough to have played with christmas series light bulb chains.
 
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#46
This Philips datasheet that consists of old and newer pages has both 7 V and 7.6 V as typical voltage at 300 mA heater current: 7 V in the preliminary data, 7.6 V on the later pages. In all cases, it specifically specifies that the PCC88 is meant for series supply, it doesn't say anywhere that it is suitable for series as well as parallel supply (like some other Philips valve datasheets do).

http://www.r-type.org/pdfs/pcc88.pdf
 
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#49
MarcelvdG said:
This Philips datasheet that consists of old and newer pages has both 7 V and 7.6 V as typical voltage at 300 mA heater current: 7 V in the preliminary data, 7.6 V on the later pages. In all cases, it specifically specifies that the PCC88 is meant for series supply, it doesn't say series or parallel anywhere (like some other Philips valve datasheets do).

http://www.r-type.org/pdfs/pcc88.pdf
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Now you've posted that, I remember seeing it before, which added to the confusion at the time.
 
#51
as_audio said:
Somebody should go to his stock, grab a number of different PCC88 and check for filament voltages using a ccs supply.
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Already done that a few year ago on my stock of about 50 PCC88 pulled from scrapped bw TV sets. Many are service types (rebranded by the distributor). Only a few are Philips branded. On about half of the tubes, the filament draws 300mA at 6.3V exactly. This means, on that tube they printed either ECC88 or PCC88 according to market needs. On the other half of the tubes, the required voltage for 300mA is 7V or slightly more.
 
#53
Tip: if it are just a few P series tubes like PCCxx some use 300 mA LED drivers for the filaments. LEDs are like P series tubes current controlled. Usually these are able to feed 2 x PCC88 in series. This adds nicely to the SMPS for B+.

P (300 mA) C triode C triode is a double triode for 300 mA chains.

E (6.3V) C triode C triode xx is a double triode for 6.3V heater windings.

E (6.3V) L xx is a pentode for 6.3V heater windings.

P (300 mA) C triode L pentode xxx is both a triode and a pentode in one envelope for 300 mA chains.

U (100 mA) L xx is a pentode for 100 mA chains.

E (6.3V) C triode L pentode L pentode xxx like ECLL800 is a triode with 2 x pentode in one glass envelope for 6.3V windings. Dinosaur chip amp 😉

The letters are quite clear in what the tube is. Maybe unknown info!?
 
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#54
as_audio said:
I wanted to suggest to check different fresh original tubes.
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I will check if at least some of the "universal filament" tubes I've measured bear a known brand label. I guess that ECC88 and PCC88 started with different filaments, but later on the 300mA 6.3V filament seems to have been quite popular here on the last iteration of tube TV sets, maybe due to cost optimization or dwindling tube demand.
 
#55
If there is an A brand (Philips, Telefunken, Siemens..) datasheet to support that I want to see it. They sure don't have different type names without a reason as manufacturers of both tubes and TV sets had quite another interpretation of what quality was then. Even normal consumers that in their opinion got a questionable tube at the counter were given replacements as tubes were then also not cheap let alone TV sets. It were mostly passive parts like flyback transformers that broke down and HV leakage if I recall correctly. The Philips picture tubes often measured fine even after 20 years of daily service.

Maybe it is more a matter of the rebranding at Berlusconi S.r.l. Beware of double crown stamps 🙂
 
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#57
patrickblue said:
Strangely enough we had this very debate on the Bigbottle Phonostage Builders thread. It seems that only Phillips give a voltage of 7.6 in their spec sheets, everyone else gives 7.0v.
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Uhm, well, that's an awkward way read the datasheet(s). By convention in (natural) sciences and engineering, numerical values are given using the concept of "significant digits". If the datasheet says "7 V", it just that. Not 7.0 V, or 7.00 V. The implied uncertainty of "7 V" is such the value is not at all different from "7.6 V". The tubes I tested (first post) had 8.1 V, which is well within the "7 V" spec. The 8.1 V reading is also consistent with the "7.6 V" spec, if you ask me.
patrickblue said:
...the Bigbottle preamp, which I built a few years back, and which I'm currently using, was originally designed for 7.6v ... then modified (with a lower voltage zener) to 7v, the assumption being that the Phillips either ran at a higher voltage, or there was a mistake in the Phillips data sheet, and the normal ECC88 heater voltage is 7v.
I'm now wondering whether to change it to 7.6v.
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Given my above comment, this design approach does not make much sense to me.
Also, as @jean-paul rightly insisted, designing a heater supply for a PCC tube should focus on the heater current, not voltage.
 
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#58
The 8.1V you measured cannot possibly be in the 7V specification, then the 6.3V is also in that specification, it's even closer. But let's say 8.1V can be in the 7.6V specification, although even that is with a lot of deviation. There is a lot of ambiguity here, why is it measured around 8V when the datasheets refer to 7V or 7.6V for 300mA? If we look at the power of the heater, and we consider that the PCC88 and ECC88 are the same tubes, then it is correct 7.6V and 300mA or 2.3W of dissipation on the heater. I might measure my E88CC, 6922 and 6N23P tubes to see how things stand there.
 
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#60
Is it THAT hard to understand datasheets and correct information explained in tedious detail? The voltage follows prime parameter current. Longevity is best at the optimal current too. With E tubes at 6.3V that is as these have filaments wound for voltage.

Tube pilots feeding the P series tube 7.6V without measuring/knowing/controlling current don't understand a jota of stuff. Who knows what the tubes filaments current is at start up and after an hour? After a week? A month?
 
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