The Reference 6SN7 Thread

[RoundRound]

The worst is they'll die and take nothing with them. Dont puncture the tubes etc or break them. Also, dont keep the headphones plugged in or use it as a preamp to speakers during burn in. Occasionally plug in headphones to check on low volume to not transmit bad sound into them. Best of luck!

Thank you.
 
I did some testing and the hum definitely comes from the tubes (goes away when I switch to passive or JFET), it's also not volume dependant - if I pause the music and turn up the volume dial up or down (all the way) it stay at the same level...
 
I'm a bit concerned because I read online that one shouldn't leave tube amps unattended or working with out being connected to something at the output end (does a turned off power amp count?).

 

[jamato8]

 
Thank you.
 
I did some testing and the hum definitely comes from the tubes (goes away when I switch to passive or JFET), it's also not volume dependant - if I pause the music and turn up the volume dial up or down (all the way) it stay at the same level...
 
I'm a bit concerned because I read online that one shouldn't leave tube amps unattended or working with out being connected to something at the output end (does a turned off power amp count?).

It depends upon the design of the amp. That is more true with some of the older designs. As an example I have a pair of SixPacs, which are mono amplifiers for speakers and they are fine with no load. Are you referring to a preamp or headphone amp or what? I haven't run into either that needed a load. I think in general though because of the working voltages the it is often best when leaving the house, to turn off tube equipment. 

 

[RoundRound]

Thanks, 
I'm using a Schiit Freya. 
 
I wonder if leaving it connected to a powered-off power amp is considered safe?

 

[Jozurr]

Im not entirely sure what could possibly go wrong with leaving it running without a load? Yes when leaving the house you should always turn off tube equipment generally, but these tubes can't really cause massive damage to anything unless they have some major shorts etc.

 

[dminches]

  Hey guys,
I got a pair of NOS Tang Sols V-231s that the seller said were tested and matched. 
 
I used them a bit in my Freya, after about 6 hours they developed a noticeable, loud hum - I swapped their locations and it went away only to come back after a few hours...  
 
Are the tubes faulty? Can I fix it somehow? should I return them they weren't cheap...
 
Thanks!

 
Given that you paid significantly less than what these tubes normally cost this isn't a huge surprise.  They still may be ok but I would contact the seller and let him know that they may be bad.
 
Are you using them in something designed for 6SN7s?

 

[RoundRound]

   
Given that you paid significantly less than what these tubes normally cost this isn't a huge surprise.  They still may be ok but I would contact the seller and let him know that they may be bad.
 
Are you using them in something designed for 6SN7s?

Yes, I was using them in a Schiit Freya - which was designed for 6SN7 - 
Anyway I now returned them to the seller and got a refund so all good.

 

[RoundRound]

I wonder how long it takes these NOS tubes to break in?
 
I understand that most 6SN7 NOS tubes are used to some degree (although 'test new' , but still even if they were broken in and then not used for 30 years (for example) - how many hours of 'new' usage do they need to reach optimal performance?
 
How long for totally new unused tubes?
 
Thank you!

 

[atarione]

when I got tubes for my DV none of teh 6SN7 tubes I bough have any noticeable hum however the GE 6AS7GA tube I bought had a slight amount of hum (undetectable w/ my 250Ohms DT880's but noticeable w/ the M50's or DT770's
 
blah blah blah... i didn't leave the amp on for hours unattended I just continued listening with my DT880's for a day or two  (maybe 8~9 hours) the hum went away in my case..   but from what I have read the time for hum to die down or if the hum ever goes away can vary considerably.
 
 
with as warm as the DV gets I personally am not too keen on leaving it switched on unattended personally.

 

[RoundRound]

Hello people,
I have a question about tube matching, I saw on ebay a pair of RCA 6SN7GT, their measurements are:
 
Tube 1: Section 1:  2870 uMhos   Section 2:  2870 uMhos
Tube 2: Section 1:  2555 uMhos   Section 2:  2310 uMhos
 
Are they matched? Tube 2 is about 20% less powerful than tube 1, no? Am I missing something?
 
Thank you,

 

[Jozurr]

Hello people,
I have a question about tube matching, I saw on ebay a pair of RCA 6SN7GT, their measurements are:

[COLOR=CC0000][COLOR=000000]Tube 1: Section 1:  2870 uMhos   Section 2:  2870 uMhos[/COLOR][/COLOR]
[COLOR=CC0000][COLOR=000000][COLOR=CC0000][COLOR=000000]Tube 2: Section 1:  2555 uMhos   Section 2:  2310 uMhos[/COLOR][/COLOR][/COLOR][/COLOR]
 
Are they matched? Tube 2 is about 20% less powerful than tube 1, no? Am I missing something?
 
Thank you,

No they are not. Generally a matched pair is considered to be under 10% variation AND the tubes have to be similar in construction. For RCA tubes, you should be avoiding the tall lettering tubes (post 1948) and looking for the RCA logo in a circle.

 

[RoundRound]

No they are not. Generally a matched pair is considered to be under 10% variation AND the tubes have to be similar in construction. For RCA tubes, you should be avoiding the tall lettering tubes (post 1948) and looking for the RCA logo in a circle.

Thanks mate!
Much appreciated.
 
Another Noob question, how to decipher the date on these tubes? Are they good? Supposedly made by Tung Sol:
 

 

[Egill23]

Yes those are made by Tung-sol. the different upper and lowe mica are characteristic together with the grey t-plates. Then the code 322 means they are Tung Sol tubes and I guess they were made in 1952. These are the mouse ears tube without the ears described on the first page as:
Tung-Sol White Label 6SN7GT (1940-50s vintage) [PHOTO HERE]
[made between 1948 and 1956. structure is completely different from the abovementioned Round Plate GTs - these have grey 'T'-plates and a bottom getter. rectangular getter holder. tall bottle with black bases and white labels. these resemble GTBs (the next tube below) except for the bottom getter.]
● “Concurrently with the last days of the TS R-P there was a version with regular ribbed plates - that could have been grey OR black, and has the notorious round side mica spacers termed "mouse ears". A very, very good sounding tube. There was a later version that squared ofc those ears - still the same tube, then they dropped the ears all together and the plates were always grey - still a super sounding tube. But it's not commonly found, and unless it has the mouse ears, people often mistake it for Russian - good for me, I love the tube and pick 'em up at dirrt cheap prices and get better performance that most of the big buck stuff.” –Robert H. (in personal correspondence)
 
I haven't heard them myself, so I can't comment on that. I have been eying these two swell as those Tung sol flat plates 6f8g's he sells on ebay, but I need to chill it with the tube purchases until I have evaluated the ones I bought this last month (Ken-Rad vt 231, Rayteon vt-231. National Union vt-99, Sylvania 6sn7wgt & some 49-53's Sylvania 6sn7gt).

 

[dminches]

  Hello people,
I have a question about tube matching, I saw on ebay a pair of RCA 6SN7GT, their measurements are:
 
Tube 1: Section 1:  2870 uMhos   Section 2:  2870 uMhos
Tube 2: Section 1:  2555 uMhos   Section 2:  2310 uMhos
 
Are they matched? Tube 2 is about 20% less powerful than tube 1, no? Am I missing something?
 
Thank you,

 
Just looking at the gm of a triode is only half the equation.  So the answer to your question is, maybe.  Here is an explanation of matching for triodes.
 
Triodes
Triodes have an interesting relationship where two parameters relate to make a third. These parameters are locked into a relationship so that knowing any two will yield the third. Just like ohm's law. In the case of triodes, Mu = Gm x Rp. Gm has the units of mhos, (amps per volt) and Rp has the units of ohms (volts per amp) and when multiplied their units cancel, making MU (a measure of voltage gain) unit-less as it should be. A Mu of 30 means that what goes in comes out 30 times bigger.

Triodes are most widely used for voltage amplification in our preamps. Here, Mu (voltage gain) is the more important parameter to measure and most directly affects what you hear. If you have a tube with a Mu of 30 in one channel and a MU of 33 in the other, you will have a 1-dB imbalance in your preamp. So let’s say you get two triodes matched for Gm. There is no assurance that these tubes will have equal voltage gain. Voltage gain (Mu) is the product of Gm and Rp. So if Gm is matched to, get matched Mu (the important characteristic in this circuit) Rp must be matched also and Rp is almost never measured. So as you can see although the famous Hickock tube testers are sought for their ability to measure Gm, this was more of a marketing ploy and less useful for real-world testing. If the vendor measuring Gm would give you the Rp then you could calculate the Mu by simple multiplication. The reason you don't get the Rp data is that it is hard to measure and no commercial tube tester ever measured it.

Modern audiophiles are more concerned about "matching" than ever before. They want everything to be matched, though they rarely know what it should be matched for. This is a dangerous situation as many of you are buying because the vendor says it is matched, though it may or may not be matched for something unimportant while something important is not matched. Gm and MU are a perfect example.

Rp or plate resistance is the second most important parameter as it directly affects the output impedance of the preamp. Circuit designers are looking at Mu primarily, Rp next and we hardly care about Gm at all. Why then do most vendors measure Gm and Gm alone? Because most testers only measure Gm! No commercial tester ever measured Mu either. And even the Hickock, treasured for measuring Gm, doesn’t measure it meaningfully (due to current dependency), accurately (due to calibration difficulties) or consistently (due to internal circuit drift).

Since Mu is what controls voltage gain, and voltage gain is what we listen to, then lets measure that directly. That is just what we do at RAM TUBE WORKS. Of course we had to build our own tester to do that. A few years ago I heard that one of my competitors tried to duplicate the RAM tester and gave up after spending $100,000. It took me about a year to develop the small tube tester and another 6 months to develop the power tube tester. These were no small efforts.

 

[ericr]

I'm sceptical of vendors claiming to have the secret sauce (that no one else can figure out) that makes the items they sell far superior to the very same items sold by all other vendors.

Does anyone have links or direct knowledge to confirm or refute the claims of RAM TUBE WORKS?

I'm no electonic engineer, so maybe I'm of the mark, but a few things about this pitch bother me:

1) It's a sales pitch.

2) No one seems to be copying him.

3) "Circuit designers are looking at Mu primarily, Rp next and we hardly care about Gm at all."

Well it seems a designer would be working under the assumption that the tubes used in his design are working to factory specification, and if a tube is faltering the owner will replace it with a new one. What is there to care about?

4) "A few years ago I heard that one of my competitors tried to duplicate the RAM tester and gave up after spending $100,000.

OK, millions of tube testers have been made that measure Gm (they used to be found in every hardware, drug and discount store across the USA) - so that can't be too hard. Mu (aka gain) is a measure of amplification - again something common and often done. I'm not familiar with Rp (which he said was plate resistance). Measuring resistance is also something very common, and even if (for some odd reason) it was more difficult to so for a plate inside tube I doubt it is far from an unsolvable problem.

Someone spent $100,000 and couldn't figure out make these three measurements? If so, IMHO it speaks to their incompetence more than the difficulty of the task. Oh wait, I just remembered he said "These parameters are locked into a relationship so that knowing any two will yield the third."

5) He talks about specific of problems (drift, calibration, etc.) common tube testers face, yet he does not claim to have solved these problems. Rather he says let's measure something else instead. Note that no facts are given to show that the end result is better, just that it took a long time for him to build his testers and "he heard" someone failed to copy it.



I'm much more comfortable with vendors who give measured results. Something like "We have the best matched tubes with Mu, Rp, and Gm each matched to within 3%!"

Instead he employs what in marketing speak is known as FUD (fear, uncertainty, and doubt). If the product you are selling doesn't stand out on it's own merits, you spread FUD against your competitors products.

It seems to me he is either really bad at marketing, or *really* good at it.


PS - I find it hilarious that the company name (RAM) in dminches post above actually links to Walmart.com!

 

[dminches]

While what you are saying about RAM may be true, that doesn't mean that the engineering is wrong.
 
Matching is much more important in power tubes than preamp tubes.  6SN7s do not need to be matched to the same precision as a power tube.
 
If you find conflicting information regarding the engineering please post it.  
 
Bob Putnak of tubesound.com has a very good article regarding tube matching.  Worth the read.
 
http://tubesound.com/2010/10/27/tube-matching-with-a-tube-tester/
 
One of his main points is that tube testers were meant to find bad tubes, not match them.  People who think that 2 tubes shown to be within 10% or each other are matched are kidding themselves.
 
 
Quote:

I'm sceptical of vendors claiming to have the secret sauce (that no one else can figure out) that makes the items they sell far superior to the very same items sold by all other vendors.

Does anyone have links or direct knowledge to confirm or refute the claims of RAM TUBE WORKS?

I'm no electonic engineer, so maybe I'm of the mark, but a few things about this pitch bother me: