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| [#4224] ESL It seems quite some improvement made after readjusting the bias of GM20 OTL from 25ma to 30ma. _________________________________________________________________________ dkyyu, Is it more sensitive with passive preamp? Patrick has tried different biases from 22 to 30ma with his Audible Illusion preamp and found not much difference. May be Patrick can share. I always bias at 30ma so I'm not sure what the difference is. Will try. |
cpsjj 正式會員219.xxx.xxx.246 |
2007-08-21 20:00 | |
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| [#4225] ESL I always bias at 30ma so I'm not sure what the difference is. Will try. ---------------------------------------------- can patrick post the schematic? i don't really know what 30ma means. if it is the plate current, it is awfully low for 6c33c. |
drwkng 正式會員 218.xxx.xxx.5 |
2007-08-21 20:03 |
| [#4226] ESL Thanks you for your sharing and handmade cable last Saturday -------------------------------------------------- are you ready for another round cable? i've another pair of slightly different topology. |
drwkng 正式會員 218.xxx.xxx.5 |
2007-08-21 20:04 |
| [#4227] ESL Everything being equal, a lower bias could prolong the life of a tube to “cosmic” proportions without appreciable degradation of sound. Say 10% down on bias current in return for 3 times the life span. A pretty good deal I cannot resist. |
limage 正式會員 219.xxx.xxx.162 |
2007-08-21 20:16 |
| [#4228] ESL Say 10% down on bias current in return for 3 times the life span. ------------------------------------------------ if the 30ma means the plate current of the 6c33c, it is not just 10% down, it is about 10% of the rated current. 6c33c is normally rated for 200+ma. so biasing it at 30ma is way way down. |
drwkng 正式會員 218.xxx.xxx.5 |
2007-08-21 20:54 |
| [#4229] ESL drwkng, Sorry to mislead you. It is actually 30mV across the resistor. I might have the schematic somewhere but have to dig out from the archive. Now just can't find anything of the schematic in the internet. |
cpsjj 正式會員 219.xxx.xxx.246 |
2007-08-21 20:59 |
| [#4230] ESL Anybody have any idea about this so called 'high grade version' of 6C33c-B made by Svetlana; the 6C18C.  |
cpsjj 正式會員 219.xxx.xxx.246 |
2007-08-21 21:15 |
| [#4231] ESL Here's the spec.  |
cpsjj 正式會員 219.xxx.xxx.246 |
2007-08-21 21:16 |
| [#4232] ESL this is what i find through google. take it with a pinch of salt "6C18C is a first generation of the regulators that was introduced before the 6C33C. Then, after the 6C18C the more rigid tubes were made: 6C33C and 6C41C and then the 3-paltes 6C45C. The 6C18C is fine tube but it has very high amount to faulty tubes." |
drwkng 正式會員 218.xxx.xxx.5 |
2007-08-21 21:38 |
| [#4233] ESL "The picture shows 3 tubes, from left to right. First tube is 6C18C production of 1963, 1964 and 1965 (they all look identical). The second tube is 6C18C production of 1968, 1969. The third is 6C33C production of 70s and 80s. 6C18C is a first generation of the regulators that was introduced before the 6C33C. Then, after the 6C18C the more rigid tubes were made: 6C33C and 6C41C and then the 3-paltes 6C45C. The 6C18C is a fine tube but it has very high amount of faulty tubes." No mentioning of whether they are interchangeable. Can't read the spec neither.  |
cpsjj 正式會員 219.xxx.xxx.246 |
2007-08-21 21:38 |
| [#4234] ESL Quotes from the diyaudio forum : -- My understanding is that the 6C33B has wandering bias; correct me if I'm wrong. -- Not exactly. Normal 6C33C ('till late 70s they were 100% tested by manufacturer to fit 5% tolerance after burn-in) is OK. But nowadays 90% of 33's present on market are spoilage. -- IMHO, that's often the case when you buy locally in the USSR. Workers seem to take home rejected tubes and sell them for a $ on the local marketplaces.. -- As is all too often the case, quality depends very much on where and from whom you buy the tubes from, cheap often backfires. -- As for bias drift, yes, I've heard similar cowboy stories from guys that don't understand that beasts like the 6C33-C require hours and hours to settle and stabilize. This tube was often used in OTLs by folk who just wanted to jump on the bandwagon and had little experience with biasing those tubes (and even less about the Futterman topology), hence the drift stories. |
cpsjj 正式會員 219.xxx.xxx.246 |
2007-08-21 21:55 |
| [#4235] ESL they look close enough. but what is the point if they are even more fragile than 6c33c. but then again they might not be. |
drwkng 正式會員 218.xxx.xxx.5 |
2007-08-21 22:06 |
| [#4236] ESL those i sold to patrick are from US importer. i can guarantee that since i hand carried them back from N.Y. so you can ask patrick whether they are spoilage or not^-^ i take it with a big pinch of salt about the comment of cowboy etc. these are not isolated stories. they are almost the norm. but i think what is worthwhile is to let patrick experiment on the graudal ramp up of those tubes. if it does produce more stable and reliable tubes, it might be a worthwhile exercise. |
drwkng 正式會員 218.xxx.xxx.5 |
2007-08-21 22:12 |
| [#4237] ESL i can guarantee that since i hand carried them back from N.Y. ____________________________________________________________ No doubt about that, drwkng. Do your tubes bear the CCCP military logo? I find my tubes which bear this logo much more stable than the others. |
cpsjj 正式會員 219.xxx.xxx.246 |
2007-08-21 22:19 |
| [#4238] ESL Like this.  |
cpsjj 正式會員 219.xxx.xxx.246 |
2007-08-21 22:23 |
| [#4239] ESL Do your tubes bear the CCCP military logo? ------------------------------------------- i don't think so. |
drwkng 正式會員 218.xxx.xxx.5 |
2007-08-21 22:36 |
| [#4240] Hand made cable Dear King, are you ready for another round cable? i've another pair of slightly different topology. ______________________________________________ The two cables sound slightly different. Please allow me two weeks before telling the difference between. With limited listening time, I tend to favour using your first made cable as reference. I really love to try your new cable. Can you tell me the convenient place and time to pick them up, or shall we try together at my place? I am available Saturday afternoon again. To facilitate try out on your cables, I have disconnected the BBA from my system with the single passive pre system connected because I think a passive pre system is more sensitive to cable change or bias readjustment. After adjusting my Graaf's bias from 25ma to 29 ma, I can hear with a more full bodied sound from the Graaf and I guess it's almost half way like adding Tim's BBA without trade-off. I guess I need a bit more time to switch between the 30ma and 25 ma to confirm my initial experience. However, I am afriad I still cannot speed up the pacing (rather slow as described by CP which I share) of Graaf OTL solely by bias adjustment. Perhaps, I shall leave this to some tube rolling exercises on 6922 and EF184 later on. (PS: I need to consult Tim in this respect) See, I am having fun with my TVC and Graaf. |
dkyyu 正式會員 210.xxx.xxx.23 |
2007-08-22 09:50 |
| [#4241] Hand made cable CP, does cccp means check and certified by CP. :) |
dkyyu 正式會員 210.xxx.xxx.23 |
2007-08-22 09:51 |
| [#4242] Hand made cable I really love to try your new cable. Can you tell me the convenient place and time to pick them up, or shall we try together at my place? I am available Saturday afternoon again. ------------------------------------------------- i'm tied up these 2 weekends. let's say first week of sept. |
drwkng 正式會員 210.xxx.xxx.111 |
2007-08-22 11:02 |
| [#4243] ESL Here goes the GM20 schematic.  |
cpsjj 正式會員 219.xxx.xxx.124 |
2007-08-22 15:13 |
