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 Post subject: Russian 1578, 6H8C or 6SN7 tubes...
PostPosted: Mar Mon 08, 2010 8:35 pm 
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Lately, I've been hearing about these tubes. I happen to have a Cary CD Player that uses 2 of the 6SN7's. I'm quite happy with the sound but think the output level is a little low. Using my cheap Onkyo CD player, I only go up to about the 9 o'clock setting on my volume control and the sound fills the room. With this Cary player, I need to go up to about 1 o'clock to get to the same level. Same amp/preamp and source connection. The CD player came with 2 Sovtek's and I upgraded them to a pair of vintage RCA's. All tubes tested about the same on a Hickok.
Does anyone have any experience with the 1578's and is it worth trying it on my Cary? Worth as in would it make an improvement in sound. Also, is there really any difference between the 6H8C MELZ manufactured and the same tubes stamped with "1578"? One told me that the former was the version for the Russian market while the latter was the Western counterpart. I wonder if that in fact was the case or only someone's idea or guess.
Lastly, what's a good source for these tubes?

I appreciate any feedback!

Regards,
Tony


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 Post subject:
PostPosted: Mar Tue 09, 2010 12:27 am 
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Tony, I would approach those Sovtek tubes skeptically, in your place. To begin with, I would want reliable documentation that they are (and are meant to be) mutually interchangeable with 6SN7's, and I would avoid using them unless I could get that documentation.

And that meants PRINT documentation, from a reliable source, i.e., someone whose credentials are established and verifiable, and someone whose work has been editorially reviewed and passed upon by peers with comparable credentials. That's how it works in the reputable sector of the textbook industry (and it is manifestly NOT how things work on the web!).

True high-fidelity circuits come out of the top drawer, and they are tightly designed, with none of the compromises that characterize middle-market players, even the kind that used to house their products in fancy consoles.

True high-fidelity circuits allow for relatively little variation in parameters among tubes. A circuit designed for a 6SN7 will be meant to work, and should work, with the variations of parameters normally found in functional, non-defective 6SN7s, and close equivalents such as the 5692.

The circuit will likely not be appropriate, however, for a tube which is only a rough equivalent at best, and potentially far off base at worst.

You've already described a falling-off in gain with those Sovteks, by comparison with 6SN7s. That alone would be enough to persuade me that I was working with an ill fit.

Best regards :) Larry

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 Post subject:
PostPosted: Mar Tue 09, 2010 1:09 am 
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What part of the circuit uses the 6SN7's? If used as output drivers, there could be an impedance mismatch between that circuit and your preamp.

Dave


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 Post subject:
PostPosted: Mar Tue 09, 2010 1:45 am 
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Thanks, Larry!
I've been trying to find the tube data for these Russian wonder tubes (supposedly) but could not find one. One tube vendor here in the US sells them for $95 a pop and posted the following:

"This is a NOS Russian 6SN7-GT tube, metal base with "T" plates. Another common name for Russian 6SN7 tubes is 6H8C tube.

We brought these tubes in on a whim because of their amazing build quality. The responses we’ve had back from some of our customers have been outstanding with many claiming this is the best 6SN7 they’ve ever heard! Incredible sound stage and presence.

View Russian 6SN7 / 6H8C tube data sheet."


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 Post subject:
PostPosted: Mar Tue 09, 2010 2:08 am 
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Hi Dave,
I'm not sure what part uses the tubes but it might very well be the output. Looking at the CD player, it's actually manufactured by Rotel with Cary modifying it to add the tube circuit and sold by Cary. I don't have the schematic and I tried looking for one unsuccessfully.
Any recommendation if there's any impedance mismatch?

Thanks!


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 Post subject:
PostPosted: Mar Tue 09, 2010 3:21 am 
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Is the output level and impedance of the Cary listed in it's specification sheet? The "line" input impedance of most tube preamps is usually over 100k while most solid state preamps generally have an input impedance in the neighborhood of 10K. If your CD player has an output impedance of 10K or less, you should be fine. How does this compare with the specs of the Onkyo?

Dave


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 Post subject:
PostPosted: Mar Tue 09, 2010 1:46 pm 
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Quote:
"This is a NOS Russian 6SN7-GT tube, metal base with "T" plates. Another common name for Russian 6SN7 tubes is 6H8C tube.

We brought these tubes in on a whim because of their amazing build quality. The responses we’ve had back from some of our customers have been outstanding with many claiming this is the best 6SN7 they’ve ever heard! Incredible sound stage and presence."


Tony, these claims are pure BS, as such claims always are. "Incredible sound stage and presence," indeed! Please don't fall for such hogwash.

Any tube in ANY voltage amplifier stage (which is invariably class A) is supposed to contribute NOTHING to the "sound" of any amplifier except amplification.

Its operation is supposed to be perfectly linear. It is supposed to take an incoming waveform, expand (amplify) it, and discharge it without otherwise altering it in the slightest.

If it does otherwise alter the waveform passing through it, in ANY fashion, guess what? It's called distortion! In a properly designed voltage amplifier stage, that is NEVER supposed to happen.

Very nearly 100% of the "sound" of any amplifier derives from the circuit in which the tubes function. The remaining fraction derives from such inescapable distortion as the power output stage contributes.

In preamps etc. with only voltage amplifier stages and no power output stage, the contribution of the tubes to the "sound," apart from amplification, should be nil.

Best regards :), Larry

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 Post subject:
PostPosted: Mar Tue 09, 2010 9:40 pm 
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Hi Larry,
I see your point and based on the theories, what you wrote is absolutely how things should work.
Now, here's one person's claim who I had a conversation with first hand. He uses a preamp designed by Cary audio that uses 6SN7 drivers. He said that the preamp came with ElectroHarmonics tubes and he was happy with the sound. After reading a lot of audiophile articles about these tubes, he decided to get some vintage RCA's hoping to improve on an already good sound but could not hear any difference. Further research linked him with the 1578 articles so he acquired a pair. When he got the tubes on the preamp, he started hearing instruments he never knew were part of the song. I can't vouch for him but I see no reason why he would make up stories. He wasn't selling me the tubes, in fact, he removed them from the preamp to keep with his favorite collection.
After reading your post, I can only think of a couple of reasons for his experience. (1) It could be that the EH and RCA tubes were the ones distorting the sound that the 1578 reproduced cleanly and (2) the planets lined up the night or day he tested those tubes and he started hearing things.
I guess the only way to prove this is by live auditioning. I went ahead purchased a pair from a seller in Russia. I don't know how long it will take to get here but I can't wait. My only concern is that it may not make any difference on my CD player but I'll look for a preamp that uses these tubes for a good listen. I'll let you know what I found out.

Thanks for the always credible insights.

Tony


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 Post subject:
PostPosted: Mar Wed 10, 2010 12:44 am 
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Hi, Tony:

Quote:
When he got the tubes on the preamp, he started hearing instruments he never knew were part of the song. I can't vouch for him but I see no reason why he would make up stories.


He probably thought he wasn't making up anything. He probably thought he was actually hearing something.

The power of suggestion is incredibly strong, as you probably know. If you've been coached to hear something, you'll very likely believe that you should hear it. That, in turn, can easily lead to an illusion that you do hear it in fact, whether it's there to hear or not.

This is how the hucksters and fly-by-nights gull the audiophool crowd. It's only unscrupulous sales psychology 101.

If you're going to put yourself to such a test as you say, don't coach yourself to believe you will (or won't) hear any particular thing.

In fact, it will be better if you get a friend to help you and make the tube substitutions for you. You should NOT know which tubes are playing in any given test. Run through a dozen tests at the very least, taking notes of what you hear (or think you hear) with each test. Note which tubes you believe to be in the preamp with each test, and have your friend keep track of the tubes that are actually there.

Then, when it's all over, compare your notes with your friend's reports on which tubes were in the preamp, test by test.

If he's any kind of a friend, he'll slyly leave the same pair in for two or three times running. And if your notes don't match his? Well, so much for illusions....:mrgreen:

If the notes DO match, and if there IS a significant difference with those Sovteks operating in a 6SN7 circuit, you should immediately find out why. Either they are incompatible with 6SN7s and therefore don't fit a 6SN7 circuit, or they are defective.

Believe me, it won't be because they are doing a "right" job "righter" than the 6SN7s were doing it.

Best regards as always :wink:

Larry

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 Post subject:
PostPosted: Mar Wed 10, 2010 12:57 am 
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I've really tried to hear the differences in 'rolling' tubes in an amplifier to find the best one but I never could. Thanks for that explanation Larry. I KNEW I wasn't hearing any difference!!!

I've read that SOME of the new tubes being made(usually from China) don't actually meet the specifications of the tubes they say they replace. I've got a pair of 6N1 Chinese tubes that are supposed to replace the 6DJ8 but they not only have 1/4 of the gain but have twice the heater current. Problem is, the only way to get that info is to find it in Chinese so you have to take a seller at his word. I now have 2 of those tubes and nothing they fit.

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 Post subject:
PostPosted: Mar Wed 10, 2010 1:42 am 
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I'm always glad to oblige, Kyle, and many thanks for your endorsement. It's nice to know that I'm doing some good. Heaven knows I try.

I'm sorry you got stuck with those two tubes that don't fit anything you have. It sounds as if they were made as equivalents for some tube other than the 6DJ8, and somebody got a bright idea about marketing.

If you could snap a good close-up photo of those tubes and tack it into this thread, I'd appreciate it, for I'd like to do a little digging.

In the meantime, hang on to the tubes. They sound like they might make good experimental or "project" tubes, somewhere along the line.

Good luck and best regards, :) Larry

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 Post subject:
PostPosted: Mar Wed 10, 2010 1:48 am 
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At the risk of sounding completely stupid, why can't one put NOS USA or Great Britain made 6SN7 tubes in the device? There are literally tons of those tubes of all description available for a very, very reasonable price. Yes, there are! Why would one want to even think of using something that "might" work in the circuit. I do not subscribe at all to the "tube rolling" thing. I think that exactly as Larry has described, you must do the double blind taste test and flip (or not flip) the tubes back and forth in the same circuit at the exact same settings with the exact same source. I would bet that the "difference" is not nearly as different.

Many get very passionate about this very subjective topic. And I know that what is on paper may sound different when the electrons are flowing. But there is a lot of black and white in addition to the gray.

What really kills me is that some out there who start playing around with vacuum tubes think that they are experts after 6 months and know more than the engineers did that designed the circuit. And I am certainly not referring to anyone in this thread. Rather to ones in another site that talks about this constantly with the self-professed pseudo "experts". Yes, many, many know much more than me. I am not an engineer. But I don't fall of a lot of those shenanigans.

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 Post subject:
PostPosted: Mar Wed 10, 2010 2:03 am 
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I understand completely, Don, and I totally agree.

:wink:

Larry

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 Post subject:
PostPosted: Mar Wed 10, 2010 2:25 am 
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Totally understood and I already planned that "Name your tone" game with my wife when the tubes arrived.
Same argument I made with one local guy who claims to be a true audiophile and was bashing the ST70 for being a junk of an amp. I own 2 of those (one active, one shelfed) for my garage sound and told him that between my Marantz 8B and the ST70, I couldn't hear the difference. Both have a good quad of Mullard power tubes. I do enjoy listening to my 8B knowing that its a Marantz I'm listening to though. Of course, I can't make the same claim on preamps. The good ones are way better than my PAS. My nearly fully restored KT600 blows it away. They're like night and day.

My apologies to the Marantz 8B fans. I'm one of you but IMHO, the ST70 holds its own side by side. That's not to say that I would trade my 8B for another ST70 anytime. And BTW, the ST70 I'm referring to has an upgraded PSU based on Van Alstine's super PAS.


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 Post subject:
PostPosted: Mar Wed 10, 2010 3:35 am 
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Keep us posted, Tony. :wink:

It's good to hear that the KT600 is turning out so well. Keep up the good work!

Larry

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 Post subject:
PostPosted: Mar Wed 10, 2010 5:57 am 
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The 6SN7 is readily available. I've probably got 20 of the things that I keep drumming up uses for, just so they're not loafing about. I think my next project may be a headphone amp, for no better reason than I want an excuse to use them for something productive.

The 6SL7 has a fair bit more amplification than the 6SN7 and is a drop-in sub, though the bias and plate resistance are fairly different so it probably won't work optimally without some circuit tweaks.

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 Post subject:
PostPosted: Mar Wed 10, 2010 6:04 am 
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Ask and ye shall receive, the first is alone, the second is next to the ElectroHarmonix 6922EH that ended up being the permanent resident in that particular project.

Image Image

Datasheet. http://www.mif.pg.gda.pl/homepages/fran ... /6/6N1.pdf

I've considered building them into a little push-pull stereo amp to have at work.

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 Post subject:
PostPosted: Mar Wed 10, 2010 7:16 am 
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gadget73 wrote:
The 6SN7 is readily available......

The 6SL7 has a fair bit more amplification than the 6SN7 ...


I believe the 6SL7 is similar to a 12AX7, Hi MU Dual Triode and the 6SN7 is similar to a 12AU7, Medium MU Dual Triode. So if you are more familiar to the small tubes, this may help.

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 Post subject:
PostPosted: Mar Wed 10, 2010 1:26 pm 
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Many thanks, Kyle. I will check this out.

Larry

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 Post subject:
PostPosted: Apr Sat 03, 2010 12:47 pm 
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Location: Russian Federation
Hello members I'm brand new here.

This what i know about 6N8S / 1578 tubes:

Application: LF voltage amplification
Cathode type: oxide,indirect heating
Envelope: glass
Filament voltage,V: 6,3
Filament current,A: 0,55-0,65
Anode voltage,V: 250
Anode current,A: 0,0055-0,0115
Anode power,W: 2,75
Grid1 voltage,V: minus 8
Steepness,mA/V: 2,1-3,1
Reverse grid current,uA: 2
Microphnic noise,mV: 150
Gain: 18,0-23,0
Socket type: rsh5-1

And there are some different kind of tubes on the market:

6N8S in black plastic base.

6N8S in metal base.

6N8S / 1578 in metal base with holes.

Thank you,
Alex


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