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#1
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favourable triode section
http://www.mif.pg.gda.pl/homepages/f...10/e/ECC82.pdf
With reference to the Remark on page-1 of the above datasheet, does anybody know the reason? Rgds, Gio |
#2
Posted to rec.audio.tubes
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favourable triode section
"GRe" http://www.mif.pg.gda.pl/homepages/f...10/e/ECC82.pdf With reference to the Remark on page-1 of the above datasheet, does anybody know the reason? ** Pin 5 is adjacent to the plate pin of the " favourable " triode while parallel connected heater pin 4 is adjacent to the cathode pin of the other triode. So any leakage from the 3.15VAC on pins 4 & 5 will not get amplified by the " favourable " triode. .... Phil |
#3
Posted to rec.audio.tubes
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favourable triode section
"Phil Allison" wrote in message ... "GRe" http://www.mif.pg.gda.pl/homepages/f...10/e/ECC82.pdf With reference to the Remark on page-1 of the above datasheet, does anybody know the reason? ** Pin 5 is adjacent to the plate pin of the " favourable " triode while parallel connected heater pin 4 is adjacent to the cathode pin of the other triode. So any leakage from the 3.15VAC on pins 4 & 5 will not get amplified by the " favourable " triode. OTOH, pin 9, with antiphase 3.15Vac, is adjacent to the cathode pin(8) of the "favourable" triode. What am I missing? Rgds, Gio |
#4
Posted to rec.audio.tubes
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favourable triode section
In article ,
"GRe" wrote: "Phil Allison" wrote in message ... "GRe" http://www.mif.pg.gda.pl/homepages/f...10/e/ECC82.pdf With reference to the Remark on page-1 of the above datasheet, does anybody know the reason? ** Pin 5 is adjacent to the plate pin of the " favourable " triode while parallel connected heater pin 4 is adjacent to the cathode pin of the other triode. So any leakage from the 3.15VAC on pins 4 & 5 will not get amplified by the " favourable " triode. OTOH, pin 9, with antiphase 3.15Vac, is adjacent to the cathode pin(8) of the "favourable" triode. What am I missing? Probably nothing, I suspect that Phil, although probably on the right track, is not looking deep enough. I suspect that the difference in hum susceptibility between the two triode sections isn't to be found in the base layout as Phil suggests, but rather is in the internal layout of the tube, with the coupling more likely being into the grid circuit than the cathode. If it is the internal layout rather than the base layout suggested by Phil, then there is the possibility that this "remark" applies only to Philips tubes and may not be applicable to tubes from other manufacturers. As a designer I'm not sure that I would count on this remark to hold for all ECC82 variants, it may be that the other triode is the "favorable" one in some variants. -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
#5
Posted to rec.audio.tubes
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favourable triode section
"John Byrns" wrote in message ... In article , "GRe" wrote: "Phil Allison" wrote in message ... "GRe" http://www.mif.pg.gda.pl/homepages/f...10/e/ECC82.pdf With reference to the Remark on page-1 of the above datasheet, does anybody know the reason? ** Pin 5 is adjacent to the plate pin of the " favourable " triode while parallel connected heater pin 4 is adjacent to the cathode pin of the other triode. So any leakage from the 3.15VAC on pins 4 & 5 will not get amplified by the " favourable " triode. OTOH, pin 9, with antiphase 3.15Vac, is adjacent to the cathode pin(8) of the "favourable" triode. What am I missing? Probably nothing, I suspect that Phil, although probably on the right track, is not looking deep enough. I suspect that the difference in hum susceptibility between the two triode sections isn't to be found in the base layout as Phil suggests, but rather is in the internal layout of the tube, with the coupling more likely being into the grid circuit than the cathode. A close look at a Philips ECC82, trough the glass above the base but below the two triode structures, shows a "topographic" symmetrical layout for the A/G/K stucture-to-base interconnections for both the 1/2/3 triode and the 6/7/8 triode. IOW, if you'd be able to disconnect the 1/2/3 triode from it's position, than, after 180 degrees of rotation, you'd be able to reconnect it to the 6/7/8 position WITHOUT the necessity of re-shaping/bending the interconnections. Only the filament-to-base interconnections are assymmetrical, a long connection from 9 to filaments common, a long connection from 4 to the 1/2/3 filament, but a short connection from 5 to the 6/7/8 filament. If it is the internal layout rather than the base layout suggested by Phil, then there is the possibility that this "remark" applies only to Philips tubes and may not be applicable to tubes from other manufacturers. That may well be true, I did'nt have a look at other ECC82's, simply too troublesome figuring out 3-D structures trough a loupe. As a designer I'm not sure that I would count on this remark to hold for all ECC82 variants, it may be that the other triode is the "favorable" one in some variants. For the "variant" ECC83, different tube but identical base/pin-out, the Philips datasheet of the same era (1965) holds the same remark: http://www.mif.pg.gda.pl/homepages/f...10/e/ECC83.pdf .... as well as for a different era (1947-1964). http://www.mif.pg.gda.pl/homepages/f...30/e/ECC83.pdf (.pdf page 6) .... which page gives some more clues. After reading the last .pdf it now seems to me that: -with pin 9 to GND and pin 4+5 in parallel to 6.3V is "best".(... -60dB when the center tap of the heater has been earthed...) -with Vf to pin 4+5 and pin 9 and the transformer center tap to GND is not "best", but, in this case, triode 6/7/8 is "favourable". Right? Rgds, Gio -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
#6
Posted to rec.audio.tubes
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favourable triode section
On Friday, 1 February 2013 18:09:09 UTC+11, GRe wrote:
http://www.mif.pg.gda.pl/homepages/f...10/e/ECC82.pdf With reference to the Remark on page-1 of the above datasheet, does anybody know the reason? Rgds, Gio I've just read the other replies which explain that noise can more easily leak into one tride than the other, and this would have relevance in a sensitive preamp. But in all my years playing with 12AU7/ECC82, I've never noticed the difference in hum levels. But, I've never used AC heating in any preamp or power amp input stage that I have sold to anyone, because people expect amps to be utterly quiet. If one uses a 12AU7 for a driver stage before a power tube, either SE, or as as an LTP, usually any hum is negligible to the signal level and is reduced by the NFB. Many tubes hum, and tubes for phono or microphone amps usually need very careful selection for low noise - hisses, hums, and sputtery barbecue noise can vary a lot, plus of course microphony, and so, never take any tube for granted, and always remember that noise is always possible regardless of the REMARKS made in manufacturer's optimistic data sheets. But hums due to leakage or stray C from heaters is best avoided with DC heating, so easy these days. For exceptionally low noise from a tubed phono amp, do not use a tube at the input, use a j-fet instead, and all noise can be 20dB lower than any tube you have selected, despite theory saying that its noise should be low, due say to its high Gm. They say the higher the Gm, the lower is the input noise so a 6DJ8 with both halves paralleled should be much quieter than 1/2 a 12AX7 but in practice I've found this is not the case, and there's only a 6dB betterment in SNR if you are lucky. Hence MC carts with say 0.2mV rated output need a step up tranny but at least this is easy because the MC cart is a very low Z generator so stepping up its output x 10 is easy. But a j-fet beats any 6DJ8 by a country mile. BUT, j-fets are prone to magnetic fields, and they can hum too, so one has to be extremely careful about how and where the power tranny is located about potting the trannies, and how other gear nearby is located or shielded. I have found j-fets to be far less microphonic than any tube. I have had to chase tube and solid state amp hum and hisses and sputters around the paddock for the last 20 years, and that data REMARK is a quaint naeive statement if ever there was one because usually, there are many other things concerning noise minimization one has to worry about. Usually, one is doing well to make any power amp with noise 0.25mV, even a preamp with that much noise with input shunted, and gain turned down is usually OK, if the signal level is a volt. 0.25mV of 50Hz hum is -60dB if signal = 0.25V. Its -72dB with 1V, and -80dB with 2.5V, and -100dB with 25V signal. Many amps quote SNR relative to the maximum Vout and figures then look impressive, and they don't mention noise levels at idle. Headphone amps also need extremely low noise&hum levels, preferably less than 0.05mV, ( 50uV ) and many I have tested are too noisy. One MingDa phone amp and a Glow Audio phone amp were hopelessly noisy, and the only way to fix them was to put in a resistance divider after the OPT to force the owner to raise signal levels about +15dB which is OK because the level is still extremely low and in the very low THD range. Plus the resistance load using say 22r + 4.7r is benign for the amp. There are ways to get around some noise. Patrick Turner. |
#7
Posted to rec.audio.tubes
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favourable triode section
On a semi-related subject - do you know if the 5751 is equivalent to
the ECC82? Thanks - af On Fri, 1 Feb 2013 08:09:09 +0100, "GRe" wrote: http://www.mif.pg.gda.pl/homepages/f...10/e/ECC82.pdf With reference to the Remark on page-1 of the above datasheet, does anybody know the reason? Rgds, Gio |
#8
Posted to rec.audio.tubes
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favourable triode section
wrote in message
... On a semi-related subject - do you know if the 5751 is equivalent to the ECC82? It is essentially a 12AT7 which is vibration resistant. It's filament current is slightly higher to achieve a more rugged filament. 73, Barry WA4VZQ |
#9
Posted to rec.audio.tubes
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favourable triode section
Am 09.02.2013 23:40, schrieb Barry:
wrote in message ... On a semi-related subject - do you know if the 5751 is equivalent to the ECC82? It is essentially a 12AT7 which is vibration resistant. It's filament current is slightly higher to achieve a more rugged filament. 73, Barry WA4VZQ ??? I always thought is more like a 12AX7 with a little less gain. It has an internal resistance in the 60kohm range - opposed to 10k of a 12AT7. All datasheet values read more "12AX7ish" than 12At7. They do a pretty fine job in the input stage of old Fender Tweed amps. Especially the 5E3 Deluxe. regards Jochen |
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