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#1
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ECL86/6GW8/PCL86/14GW8 pentode section triode strapped data
Gentlemen,
ECL86/6GW8 or PCL86/14GW8 pentode section triode strapped data now is available he http://www.tubes.mynetcologne.de/roe..._as_triode.pdf As usual, three samples (Mullard 6GW8, ITT/SEL mil spec PCL86, EI PCL86) were measured and the data was averaged. While ECL86 gets scarce nowadays, the 300mA heater versions PCL86/14GW8 still are plenty and cheap, even from "top" brands. The triode section of this tube is exactly 1/2 of ECC82/12AX7 (nitpickers will say 1/2 of ECC808, with even better data). The triode strapped pentode section is very linear, it is almost identical to triode strapped EL84/6BQ5, except that the allowed Pd is a bit lower (9 watts instead of 12). Like triode strapped EL84/6BQ5, the trioded pentode section of this tube will make a bombastic SE driver stage or PP "power LTP" splitter/driver stage. Two of them will make a complete front end even for the most swing demanding PP output tubes: For example use the triode sections as a diff amp input/splitter stage, and the trioded pentodes as sort of diff amp / driver like the third stage in the Williamson. The combined gain of the sections is very high (expect easily up to, say, 500 times in real world apps). Thus take care to prevent parasitic oscillations ... Here is a tip I got from an old HAM: Have a close look how the sections are wired to the base pins and you will see, that using a very tiny earthed metal sheet at the socket at the right place, acting as a static shield, would .... ;-) Tom -- When in doubt, use brute force. - Ken Thompson |
#2
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Tom Schlangen wrote: Gentlemen, ECL86/6GW8 or PCL86/14GW8 pentode section triode strapped data now is available he http://www.tubes.mynetcologne.de/roe..._as_triode.pdf As usual, three samples (Mullard 6GW8, ITT/SEL mil spec PCL86, EI PCL86) were measured and the data was averaged. Thanks Tom. The Ra = 2.5k at Ia = 30 ma, Ea = +300v, u = 14.3, so gm = 5.72 mA/V. ( 6BQ5 triode u = 20, Ra slightly less.) 1/2 12AX7 are not regarded as good triodes any more these days for power amps but they work OK in these tubes in a circuit like the one at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm Patrick Turner. While ECL86 gets scarce nowadays, the 300mA heater versions PCL86/14GW8 still are plenty and cheap, even from "top" brands. The triode section of this tube is exactly 1/2 of ECC82/12AX7 (nitpickers will say 1/2 of ECC808, with even better data). The triode strapped pentode section is very linear, it is almost identical to triode strapped EL84/6BQ5, except that the allowed Pd is a bit lower (9 watts instead of 12). Like triode strapped EL84/6BQ5, the trioded pentode section of this tube will make a bombastic SE driver stage or PP "power LTP" splitter/driver stage. Two of them will make a complete front end even for the most swing demanding PP output tubes: For example use the triode sections as a diff amp input/splitter stage, and the trioded pentodes as sort of diff amp / driver like the third stage in the Williamson. The combined gain of the sections is very high (expect easily up to, say, 500 times in real world apps). Thus take care to prevent parasitic oscillations ... Here is a tip I got from an old HAM: Have a close look how the sections are wired to the base pins and you will see, that using a very tiny earthed metal sheet at the socket at the right place, acting as a static shield, would .... ;-) Tom -- When in doubt, use brute force. - Ken Thompson |
#3
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Hi Patrick,
The Ra = 2.5k at Ia = 30 ma, Ea = +300v, u = 14.3, so gm = 5.72 mA/V. thank you for adding this data. May I include it as an example in the sheet? ( 6BQ5 triode u = 20, Ra slightly less.) I agree on 6BQ5 Ra (say, 2k), but I have a hard time to get mu in excess of, say, 15 from trioded 6BQ5. But I don't nitpick: Be it 15, 17,5 or 20 under optimal circumstances, it doesn't matter much under real world circuit conditions. 1/2 12AX7 are not regarded as good triodes any more these days Probably it just ain't "fashionable" nowadays :-) On the other hand, the absurd prices (of certain brands) on Ebay tell another story. Personally, I never used 12AX7 in a DIY project myself, I admit. No hard reasons, but my finger just automagically grab an octal based 6SL7 out of the drawer when highish mu is needed. Tom P.S: Next on the bench probably will be triode strapped EF184/6EJ7 frame grid pentode. -- The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth. - Niels Bohr |
#4
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Tom Schlangen wrote: Hi Patrick, The Ra = 2.5k at Ia = 30 ma, Ea = +300v, u = 14.3, so gm = 5.72 mA/V. thank you for adding this data. May I include it as an example in the sheet? ( 6BQ5 triode u = 20, Ra slightly less.) I agree on 6BQ5 Ra (say, 2k), but I have a hard time to get mu in excess of, say, 15 from trioded 6BQ5. But I don't nitpick: Be it 15, 17,5 or 20 under optimal circumstances, it doesn't matter much under real world circuit conditions. The u of all the EL84/6BQ5 I have tested had u = 20. Circuit gain was about 18,19 with high value RL. See the 2.5 Mb of data from STC at http://www.retrovox.com.au/STC6BQ5.pdf The triode curves there show the gain with CCS load is 18.2 at 20 mA Ia, and 20 at 40 mA. Samples I tested were Sovtek and other Oz made tubes and they went u=20 at 14 mA. These EL84 are extremely linear with a CCS load. 1/2 12AX7 are not regarded as good triodes any more these days Probably it just ain't "fashionable" nowadays :-) OK in preamps. But the " in brigade " likes more in everything, so all triodes are expected to have high current, high gm and low Ra, regardless of where they are used, but it does not necessarily follow that the sound will be better and the measurements are better. The 12AX7 was a cheap high gain signal triode invented at a time when the need for such a creature came with demand for electronic equipments to do more than just put a radio voice on the mantle piece. I think they were used even in V2 rockets in WW2. On the other hand, the absurd prices (of certain brands) on Ebay tell another story. Personally, I never used 12AX7 in a DIY project myself, I admit. No hard reasons, but my finger just automagically grab an octal based 6SL7 out of the drawer when highish mu is needed. I have used 12AX7 often, and they are great for the first stage of a phono amp for MM. Hopeless for a low output MC; you need the step up tranny, or a 6C45pi, but then ppl argue about what sounds best.... I have only used 6SL7 in the front end of SEUL amps, with 6SL7 or ECC35 for V1, ECC32 or ECC33 for V2, and then 13E1 for output. I had to pick through the SLs though to get a quiet one. I'll have to work more at training my finger to be automagical. Tom P.S: Next on the bench probably will be triode strapped EF184/6EJ7 frame grid pentode. There must be 100 tonnes of EF80 or 6BX6 lingering forgotten and unwanted around the world. Many were made for the TV IF stages of tube TVs. But they make fabulous triodes, imho. Any chance of doing a test on those? Patrick Turner. -- The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth. - Niels Bohr |
#5
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Hi Patrick,
There must be 100 tonnes of EF80 or 6BX6 lingering forgotten and unwanted around the world. Many were made for the TV IF stages of tube TVs. But they make fabulous triodes, imho. Any chance of doing a test on those? I don't have a single one in the drawer, but that might change soon ;-) I'll do the test after having obtained a few. Tom -- Falling in love is a lot like dying. You never get to do it enough to become good at it. |
#6
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There must be 100 tonnes of EF80 or 6BX6 lingering forgotten and unwanted around the world. Many were made for the TV IF stages of tube TVs. But they make fabulous triodes, imho. Any chance of doing a test on those? Just be sure that you use "sharp cutoff pentodes". Some TV IF pentodes were "remote cutoff". Variable gain depending on bias. Great way to do AVC, but not good for audio work. Some TV tubes were "dual control" pentodes, and heptodes (pentagrid). One could use one grid to feed audio, and the other grid to vary the gain via a DC bias of the plate circuit. http://pw2.netcom.com/~wa2ise/radios/elvctube.jpg http://pw2.netcom.com/~wa2ise/radios/6be6vol.html |
#7
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Behold, robert casey signalled from keyed 4-1000A filament:
There must be 100 tonnes of EF80 or 6BX6 lingering forgotten and unwanted around the world. Many were made for the TV IF stages of tube TVs. But they make fabulous triodes, imho. Any chance of doing a test on those? Just be sure that you use "sharp cutoff pentodes". Some TV IF pentodes were "remote cutoff". Variable gain depending on bias. Great way to do AVC, but not good for audio work. Hi Robert, Why is that anyway? -- Gregg t3h g33k "Ratings are for transistors....tubes have guidelines" http://geek.scorpiorising.ca |
#8
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Just be sure that you use "sharp cutoff pentodes". Some TV IF pentodes were "remote cutoff". Variable gain depending on bias. Great way to do AVC, but not good for audio work. Hi Robert, Why is that anyway? These tubes have variable gm (or mu if triode), depending on the DC bias on the control grid. Which means that the output will not be linear. Not an issue if you are using such a tube in an IF amplifier (signal level in the millivolts, and most distortion products fall outside the IF amp's passband). Bad for audio, which is a wide band signal and higher levels. Excessive 2nd harmonic for sure. If you have an audio amp using a 6AU6 try subbing a 6BA6. It's sure to sound bad. A 6AU6 is a sharp cutoff pentode, the 6BA6 is a remote cutoff pentode. |
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