In post #21 there was a claim that series link ( 300mA) and voltage ( 6.3V) used different materials in the filament
making them unsuitable for exchange
I don't know that, I just answered that it could be. I'm not very interested in what materials they use for the heaters.
One more thing bothers me, if filaments have a positive temperature coefficient, which means if they are a little hotter, they will have higher resistance and more power and will heat up even more if they are powered with CCS, and vice versa with constant voltage supply. That's certainly not good for the tubes. Does this mean that materials with a negative temperature coefficient for the filament are used for PCC tubes? In that case, they should not be powered with constant voltage.
One more thing bothers me, if filaments have a positive temperature coefficient, which means if they are a little hotter, they will have higher resistance and more power and will heat up even more if they are powered with CCS, and vice versa with constant voltage supply. That's certainly not good for the tubes. Does this mean that materials with a negative temperature coefficient for the filament are used for PCC tubes? In that case, they should not be powered with constant voltage.
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These different filaments are there for the specified purpose. They are made of different materials as P series tubes were always in a series chain (BY DESIGN, RTFM) and it is undesired these have different warmup times and therefor tubes that heat up irregularly. Make a drawing with a few P type tubes in series at 300 mA and calculate what happens if one in the chain deviates in cold and warm resistance. If possible think of (next level **** 🙂) Christmas series light bulb chains and what happened if you screwed in a wrong bulb. This was much less a real concern with E series tubes in parallel. Of course series filaments was tried out with E tubes too in large tube quantity devices, that is why the P series was developed 😀 Take a well working existing part and adapt it to real world requirements. That is why they both have "88".
Contrary to what has been written they are not drop in replacement tubes and never were. If I recall correctly also the maximum cathode-filament voltage differs between E and P tubes because of series connection.
Contrary to what has been written they are not drop in replacement tubes and never were. If I recall correctly also the maximum cathode-filament voltage differs between E and P tubes because of series connection.
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Please read my post again and ask if something is not clear.
I don't think it's hard at all, but I might be wrong. sigh 🙄
If this thread does not steer towards some sanity I'll ask the mods to lock it.
I built a HP amp with ECC88/PCC88 once. I used an old power transformer with a 220V primary. Our mains voltage was at least 235V then. Filament windings output was 7V, good for PCC88. I used a switch for ECC88 with two 0,25 Ohm resistors IIRC, that gave 6,3V.
The Philips datasheet was confusing indeed, it did say 7,6V at first (with a little pencil mark), and then later 7V.
The Philips datasheet was confusing indeed, it did say 7,6V at first (with a little pencil mark), and then later 7V.
Yes, Philips datasheet lists both data, 7V and 7.6V both for 300mA current. It is possible that these are min. and max. values, although it is not emphasized anywhere. And in the first post, an average of 8.09V (7.98-8.13) was measured for 300mA constant current. For 7.6V average, the current is 290mA, that's quite OK. For 7V average current is lower, a little above 270mA. If I were to use the PCC88, I would make an adjustable power supply 6-8V and check that the current does not exceed 300mA for PCC88, and 6.3V would allow the E88CC to be safely used. These variants with a higher supply voltage and a series resistor for PCC/ECC88 do not seem appropriate to me, because there are apparently some discrepancies between measurements and datasheets.
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thr photo is a proto of Italian airplane of the Fascism era.
Then, 4 pages of posts around a non-problem
Each test done on stuff where the Ecc88 and Pcc88 are used alternatively with 6,3 volts gave the same results
And it is evident that some little differences comes from different brand and selections but basically are perfectly the same
The problem is that few years ago the PCC88 are very cheaper, I bought 100 pcs of Tungsram nos/nib fro 100 euro!!!!!!!!!!!!!!
Now the quotations are almost similar to the ECC88 regal brand
Walter
The photo is metaphorically like average tube DIYers selecting the "right" (read random) tube as suitable engine and their way of constructing/working with tubes. Make it a fascist subject if you feel like it but that was not the intention (should be clear). If you look carefully you will see an airplane in the picture, not Mussolini. Outside Italy no one will recognize the symbols contrary to a swastika.
Of course the PCC88 were cheap (that was really NOT a problem), just look at this thread to read how well they are understood. Empirical evidence without brand name, year of production, manufacturing stamps on the tube, pictures of the tubes etc. versus clear datasheet reality by those that actually produced them.
Voltage droppers only talk in voltages. Last post in this thread, ciao!
Of course the PCC88 were cheap (that was really NOT a problem), just look at this thread to read how well they are understood. Empirical evidence without brand name, year of production, manufacturing stamps on the tube, pictures of the tubes etc. versus clear datasheet reality by those that actually produced them.
Voltage droppers only talk in voltages. Last post in this thread, ciao!
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I mentioned the airplane to show how in a dark era of our history some good ( and strange) things were done.
Walter
The plane looks great, and the colors are great, like from the cartoons, and it could certainly fly. They did that to increase the efficiency of the propeller, and that's how it works today.
Looking at the dates of the various pages, it looks to me like they originally thought 2.1 W of heater power would suffice, but found in characterization or production that they needed a bit extra and redesigned the heater for a slightly higher voltage. The maximum voltage between cathode and heater with the cathode positive was also updated, as was the grid to heater capacitance without external shield.
During the years of production, there must have been some changes. If I ever come across a PCC88, I'll check their filament first.
The way I see it, this is DIY, not about producing devices in quantities for sale. What I usually do with this is just to test the tube with the settings I need. In this, particular case, if I had a bunch of PCC88, then I would just test them in a circuit with 6.3V. If the measurement is within the datasheet curves, then I use it as a ECC88.
Nope, I have tested both E and P (CC88) and some Ps are closely matched to Es. It is a lotery. But hey, If I have good PCC88 then I won't definitely buy some new production ones. But that is me.
What you get in a datasheet are average values, I do not know how many tubes a manufacturer would test to create the datasheet curves. Get a bunch of new tubes, even from the same manufacturer, and you will see plenty of deviation.
As I mentioned the testa on stuff with the two types are same
If the selection of tubes is good in terms of gain and curves for both sections
Walter
I agree that every tube should be checked. Let's say for the E88CC the voltage is 6.3V and in datasheets some of them have a current of 300mA and some 365mA. I have a lot of different tubes, Siemens E88CC gold pins, Amperex 6922, 6N23P. I also had some 6922 and EI ECC88. I should now sit down and carefully measure how much current each consumes at 6.3V and make a spreadsheet.
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