Hi everyone,
I am asking here because I think it's appropriate but also because Wavebourn might have some knowledge ...
I heard that Soviet tube production decreased in quality after 1981 (some say 1985). I would like to know if there's anything true in this statement.
Among other tubes, I have some beautiful NIB 6P14P-ER from 1990. I didn't test them, but I would like to know your opinion about them (given the year of production).
Thanks!!
I am asking here because I think it's appropriate but also because Wavebourn might have some knowledge ...
I heard that Soviet tube production decreased in quality after 1981 (some say 1985). I would like to know if there's anything true in this statement.
Among other tubes, I have some beautiful NIB 6P14P-ER from 1990. I didn't test them, but I would like to know your opinion about them (given the year of production).
Thanks!!
I use 6P14P-ER in my EL84 amps they have a different tone than for example Mullard but is better than Philips but I think they are close to Tfk but that is my personal opinion. Mine are also from 1990 and I like them a lot.
I can speculate only. I heard that quality went down, but did not experience that. However, sellers always tend to value oldest, rarest items higher.
I come back with something new (at least for me).
Last night I turned on my tube tester and I tested almost all my EL84/6P14P. The tester provides adjustable plate, G2 and bias voltage which you have to set according to the tube datasheet. With a short press on a momentary switch you can read the drawn current.
Now, I am not an engineer and I don't really know if this kind of testing is or it is not relevant enough, but let me tell you what I found out.
I set the plate and G2 voltage at 250V and the bias at -7.3V. Among the used tubes I found values from 30 mA to 52 mA. I found 49, 50 and 52 mA for three long time used Matsushita EL84 (perhaps they had a greater drawn current when they were new).
The Russian used 6P14P have very different values, from 30 mA to 50 mA. As it seemed strange to me to find these very different values, I also checked the new/NIB tubes. 4 Tungsram absolutely new tubes have 45, 45, 48 and 50 mA and 4 6P14P have 32, 39, 43 and 48 mA. Also 4 Sovtek (2010 year) have the same dispersion in this field, despite they only have at most 200h of using: 32, 41, 46 and 57 (!!)
What conclusion should I draw?? Are these Russian tubes already selected for some amp producers or resellers and we find online mostly tubes that did not meet tighter requirements? Or is it normal to have this dispersion? Of course with a slight change in bias voltage I can obtain nominal current draw, but is this the way I should solve the problem?
Also, I want point out that in my humble opinion, a grounded comparison between the sonic features of two kind of EL84 have to be made between two new tubes having similar drawn currents. I read online that Siemens E88CC/Cca had an emission of up to 200% when they were new, so any comparison between such a tube and a "test NOS" tube of other kind (i.e. Tesla, or Amperex or any other tube) is not relevant. I am quite sure the higher emission has a sonic impact. Maybe this is why Siemens E88CC have such a good reputation, maybe it's all about their e- emission.
Last night I turned on my tube tester and I tested almost all my EL84/6P14P. The tester provides adjustable plate, G2 and bias voltage which you have to set according to the tube datasheet. With a short press on a momentary switch you can read the drawn current.
Now, I am not an engineer and I don't really know if this kind of testing is or it is not relevant enough, but let me tell you what I found out.
I set the plate and G2 voltage at 250V and the bias at -7.3V. Among the used tubes I found values from 30 mA to 52 mA. I found 49, 50 and 52 mA for three long time used Matsushita EL84 (perhaps they had a greater drawn current when they were new).
The Russian used 6P14P have very different values, from 30 mA to 50 mA. As it seemed strange to me to find these very different values, I also checked the new/NIB tubes. 4 Tungsram absolutely new tubes have 45, 45, 48 and 50 mA and 4 6P14P have 32, 39, 43 and 48 mA. Also 4 Sovtek (2010 year) have the same dispersion in this field, despite they only have at most 200h of using: 32, 41, 46 and 57 (!!)
What conclusion should I draw?? Are these Russian tubes already selected for some amp producers or resellers and we find online mostly tubes that did not meet tighter requirements? Or is it normal to have this dispersion? Of course with a slight change in bias voltage I can obtain nominal current draw, but is this the way I should solve the problem?
Also, I want point out that in my humble opinion, a grounded comparison between the sonic features of two kind of EL84 have to be made between two new tubes having similar drawn currents. I read online that Siemens E88CC/Cca had an emission of up to 200% when they were new, so any comparison between such a tube and a "test NOS" tube of other kind (i.e. Tesla, or Amperex or any other tube) is not relevant. I am quite sure the higher emission has a sonic impact. Maybe this is why Siemens E88CC have such a good reputation, maybe it's all about their e- emission.
No, OTK is like an usual QC, belongs to the factory. And the OTK number means a personal number of the worker responsible for the quality. Military acceptance stamp is a diamond. "5" in it means it satisfies some very strict military criteria. "9" means it satisfies criteria for nuclear and space programs. There were many different "special conditions". Here is an example, "acceptance number zero". Earlier tubes had "star" military acceptance sign, later it become "diamond".
Yes, change bias voltage and get needed current.
Yes, change bias voltage and get needed current.
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US tubes, we assumed +/-20% variation. (Which is real similar to 30-52.) I do not know how many Lada that is.
Even "Premium" tubes! Look at 6AU6 data below: +/-31% variation in initial current, and even greater variation of Gm from hot-new to 500 hours.
It was not always that great. Some amplifiers are known to be very consistent, in fixed-bias, using tubes Fender or Bogen bought by the crate from RCA or GE.
The job of the *amp designer* is to make it work with "any" tube. Selecting tubes (any part) to narrow range is usually more expensive than a tolerant design.
Nearly all "conservative" uses of EL84 are SELF-bias. Cathode resistor cuts variation to about half. (Yes, yes, I know of several fixed-bias EL84 amps, also amps with 2 or 4 EL84 on one resistor, amps which melt the tolex off the case...)
You may have a point that (in this boutique market) there are buyers for selected tubes, and odd-lot tubes may be "all other" values. I remember a time when a 10% resistor was not within 4% of its marked value: they pulled those to sell as 5%.
Even "Premium" tubes! Look at 6AU6 data below: +/-31% variation in initial current, and even greater variation of Gm from hot-new to 500 hours.
It was not always that great. Some amplifiers are known to be very consistent, in fixed-bias, using tubes Fender or Bogen bought by the crate from RCA or GE.
The job of the *amp designer* is to make it work with "any" tube. Selecting tubes (any part) to narrow range is usually more expensive than a tolerant design.
Nearly all "conservative" uses of EL84 are SELF-bias. Cathode resistor cuts variation to about half. (Yes, yes, I know of several fixed-bias EL84 amps, also amps with 2 or 4 EL84 on one resistor, amps which melt the tolex off the case...)
You may have a point that (in this boutique market) there are buyers for selected tubes, and odd-lot tubes may be "all other" values. I remember a time when a 10% resistor was not within 4% of its marked value: they pulled those to sell as 5%.
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