[2359glenn]

 

 

As someone who once blew up an amp, a long time ago, in a failed tube rolling experiment, I have to caution...

If you are not totally sure what you are doing, do NOT go trying whacked out tube substitutions. VERY rare is the amp where a 12SN7 can be safely subbed for a 6SN7. There are a few, but they are few and far between.

gibosi's amp has a 6.3-12.6-25.2 volt switch for the SN7 socket. And if it gets left on 12.6 or 25.2 and a 6.3 volt tube
gets put in it will current limit and not burn out the tube.

Great feature, Glenn....you think of everything  

Your amp will be the same but with 42EC4 rectifiers and Lundahl transformer

 

[3083joe]

and the 12SN7 sounds the same  

How would that work in wa6? !

 

[3083joe]

To change things up a bit, in the picture below is a pair of Mullard ECC31, also known as NR73. The etched production code is "1029.1 1MV". Mullard didn't start using the standard Philips codes until after 1955, or so, and I have not been able to find any reliable information on deciphering these old Mullard codes. As a result, I am reasonably certain these were manufactured sometime before 1955. but can't be more specific than that.

In another forum, someone asked about using these in a 6SN7 socket, but as the ECC31 has a common cathode, that is, both sections share one cathode, I had my doubts. However, 2359Glenn, who made my amp, suggested that if an adapter is used to tie the common cathode to both of the 6SN7 cathodes in the socket, the tube would work, but he couldn't say how good it might sound... 

Well, my curiosity got the best of me, so I began to search Google for information about the ECC31, and I found two very interesting items.

First, the 1949 Mullard Valve Reference manual states:
 

"The ECC32 and ECC31 are identical except that the ECC32 has separate cathodes"

And of course, given the current prices for ECC32, this really got my attention!

And second, the correct cathode resistance for the ECC32 should be 1/2 to 2/3 that of a 6SN7. Well, it just so happens that tying the common cathode in an ECC31 to both 6SN7 cathodes in the socket reduces the cathode resistance by 1/2. As a result, it would appear that using such an adapter provides the ECC31 with the correct bias. On the other hand, simply sticking an ECC32 into a 6SN7 socket results in the cathode resistance being twice as high as it should be. But does this mean that the ECC31, with adapter, will sound better than a ECC32 in the same amp? Unfortunately, I do not have an ECC32, so I won't be able to answer that question....

Oh, I should point out that the heaters draw about 1.0A, so if anyone else wants to try the ECC31 and/or ECC32, make sure your amp can handle it.

Anyway, I found this nice pair of NR73, picked up an ECC31 to ECC33 adapter, and I am very pleased to report that the ECC31 lights up and plays. Of course, it is way too soon to say much more than that, but I am not hearing anything that sounds unpleasant, that is for sure.  

Interesting.
Did you use this type adapter?

 

[gibosi]

Yes, my adapter looks identical to those. I purchased mine from happydiy998 after asking for and receiving a wiring diagram. I wanted to be sure that the common cathode of the ECC31 was in fact connected to both 6SN7/ECC33 cathodes in the socket.
 

 

 

[whirlwind]

 

and the 12SN7 sounds the same  

How would that work in wa6? !

I am not sure if the WA6 takes 12SN7 tubes or not.....maybe someone who owns a WA6 can chime in.

 

[Skylab]

I am not sure if the WA6 takes 12SN7 tubes or not.....maybe someone who owns a WA6 can chime in.

NO. It most definitely does NOT.

Again, while a VERY few designs from people like Glenn have voltage switches that allow for this, the VAST majority of amps that use a 6SN7 cannot use a 12SN7, or 25SN7. I know that you tube veterans know this, but it worries me that some tube noob is going to halfway read this thread, think it's OK to sub a 12SN7 for a 6SN7 just because they both say SN7, and POOF.

For those who do not know/realize, the first digit of the U.S. Tube naming convention is the voltage. So a 6SN7 is 6 volts, the 12SN7 is 12 volts. Unless there is a specific design allowance for it, meaning a voltage switch, one cannot substitute tubes like this.

 

[Mechans1]

NO. It most definitely does NOT.

Again, while a VERY few designs from people like Glenn have voltage switches that allow for this, the VAST majority of amps that use a 6SN7 cannot use a 12SN7, or 25SN7. I know that you tube veterans know this, but it worries me that some tube noob is going to halfway read this thread, think it's OK to sub a 12SN7 for a 6SN7 just because they both say SN7, and POOF.

For those who do not know/realize, the first digit of the U.S. Tube naming convention is the voltage. So a 6SN7 is 6 volts, the 12SN7 is 12 volts. Unless there is a specific design allowance for it, meaning a voltage switch, one cannot substitute tubes like this.

I am new to HeadFi  but not to tubes.  I wanted to agree with this post and add some emphasis, saying it is crucial ,  correct and  important!

 

[bigtube]

How about half a 6sn7.Do any Head amps use 6j5's

 

[gibosi]

  How about half a 6sn7.Do any Head amps use 6j5's

 
With suitable adapters, I would suspect that the 6J5 and the 7193 can be used in many headphone amps using the 6SN7 as a driver.

 

[jamato8]

  How about half a 6sn7.Do any Head amps use 6j5's

They make nice adapters for everything now or you can even request it. I have some very, very fine 6J5 tubes but ended up liking the 27 mesh plate better and the 76 more than the 6J5. 

 

[300b]

hmmmm...good luck!

 

[SonicTrance]

Does anyone know how to test ECC33's in a tube tester that doesn't have settings for that tube in the chart? Is there an American equivalent I should be looking for? Tube tester I'm using is a Heathkit TT-1A.
Thanks. 

 

[jamato8]

  Does anyone know how to test ECC33's in a tube tester that doesn't have settings for that tube in the chart? Is there an American equivalent I should be looking for? Tube tester I'm using is a Heathkit TT-1A.
Thanks. 

What are the electrical properties? What tube does it match closest to? Then get an adapter, if the pin out is different, and use those settings. That is how they did it back in the 1920's and early 30's before they started having more and more tubes and before there was much available. I used to correspond with a user of a 1920's Hickok tester (one of which I own) and he sent me diagrams of tubes that were new back then and how they would make adapters and then test the tubes. Sadly, like all will, he has died so that information and experience that he had, mostly went with him. Anyway, that is one way to do it. Match the electrical properties and then get the pin out. 

 

[SonicTrance]

 
What are the electrical properties? What tube does it match closest to? Then get an adapter, if the pin out is different, and use those settings. That is how they did it back in the 1920's and early 30's before they started having more and more tubes and before there was much available. I used to correspond with a user of a 1920's Hickok tester (one of which I own) and he sent me diagrams of tubes that were new back then and how they would make adapters and then test the tubes. Sadly, like all will, he has died so that information and experience that he had, mostly went with him. Anyway, that is one way to do it. Match the electrical properties and then get the pin out. 

Which properties should I look for? There's so many variables in a tube. If I look at tube gain the 6C8G is very close, as gibosi suggested to me, with a mu 36 vs mu 35 for the ECC33. Heater current is almost the same, 0,4A for ECC33 and 0,3A for 6C8G. But all other specifications are very different I'm afraid.

 

[bigtube]

Let me look at my hickok settings . A ecc33 compared to a 6sn7. I will get back. I know the bises is much lower.