Tube upgrade recommendations

[dhherring]

Still digging the Eros, but I'm getting the itch to try some different tubes.

While I've seen the threads on what tubes will work, I'm looking for recommendations on different brands/type others with the Eros have used in place of the stock tubes.

While I have no complaints whatsoever, I do like to tinker around and swapping tubes seems to be easiest thing to do at the moment.

TIA

Don

[Paully]

I was stunned at how good the Russian EF86 equivalent tubes sounded.  Sounded as good as any of the other European variants I tried though those were not of proven NOS vintage so I wouldn't want to expound too deeply there.  I was told to buy the pre 1970 tubes (I think it was pre 1970) and that they sounded better than later Russian production.  Can't say if that is true with any certainty as I bought the older ones but what I can say is that the early Russian EF86s were truly were great tubes and at that time extremely cheap.  Think you can still find them on ebay.

I ended up going to 6BR7 in the pre.  Probably not worth it for most, but something to consider if you don't mind doing a pin-out change or having an adapter made and are feeling particularly adventurous.

[Doc B.]

Agreed, the winged C 6J32P is very good, and we are transitioning over to them when we can get them.

[debk]

I have tried some of the russian equivalents and they do sound very good.
The best sounding tube I have used in my Eros is a pair of NOS Genalex Z729's

Deb

[Grainger49]

There is a topic of Eros Tube Equivalents that I started several years ago.  It is under the Eros folder, on the second page as of this post.  It lists a number of tube numbers that will drop in.  It also has a few that will work with only changes of the tube pin assignments.

It isn't what is your favorite thread, just a list of all the equivalent tubes.  I'm filled with USSR Military Surplus tubes right now.  Have been since about the first hour of use.

Here is a link:

http://bottlehead.com/smf/index.php?topic=1028.msg21298#msg21298

[Atom Shop]

I've got a suggestion for those who wish to experience what the Eros is truly capable of sonically. After much tube rolling the local tube diehards have reached a unanimous conclusion regarding the better tube compliment for the Eros.

The signal trio is made up of original-factory Czechoslovakian Tesla's (not the JJ crap). Two yello-paint, #32 EF806S's and a yellow-paint, #32 PCC88. (The standard Tesla for the latter would be an ECC88 but the PCC88 is much sweeter.) The yellow paint is the color of the silkscreen and designates the tube to be of late 60's to early 70's vintage. The '32' is the factory ID. White silkscreen would be mid-seventies onward. An often-found '37' (or other) number indicates a later-date factory location. Still good, but not the cr

[4krow]

This seems to be a good place to ask if any of you have heard of 'Vintage Tube Services' on the web. If the website is correct, there is a lot more than simply sticking a tube into tester and reading the results. This guy seems to know a great deal about tubes, and before buying another set, regardless of brand, I would want to know as much as I can before I buy. Your thoughts...

[Paul Joppa]

Just pointing out that the PCC88 has a nominal 7.6v heater. Running it in starvation mode, 18% low, risks early demise through cathode poisoning.

Most tubes specify +/-10%; the premium types usually specify +/-5%. Fortunately, in Eros the plate current around 4mA, much less than the maximum rated current, so it would be less impacted by a cool-running heater. Nevertheless, I would not myself use less than 90% of the rated voltage.

[4krow]

So, this stuff is less plug and play than I thought. Time to make some measurements on my equipment.

[Atom Shop]

Running it in starvation mode, 18% low, risks early demise through cathode poisoning.

Now that's something I sure wasn't aware of, Paul! Under the Eros operating parameters, how detrimental is the low volatge to the PCC88?

[Paul Joppa]

...
Now that's something I sure wasn't aware of, Paul! Under the Eros operating parameters, how detrimental is the low voltage to the PCC88?

I don't think there's any consensus on quantitative measures. Lifetime statistics  must come from large studies, and nobody has had the time or money to test 1000 tubes to death, for many decades. The only literature out there is from the fifties and sixties, and it's all over the place. The best information would come from the manufacturer. I have never seen a Tesla data sheet, though.

The mechanism of cathode poisoning by ion bombardment is well known, though the term has been widely mis-applied in recent decades - look for an old, respected textbook if interested in the gory details.

The only quantitative thing I have was determined for pure tungsten directly heated cathodes, and I don't know how well it applies to thoriated tungsten, much less indirectly heated oxide cathodes such as we use. That rule is that the electron emissivity is proportional to the 13th power of the applied voltage. That would say that at 82% rated voltage, you can take about 8% of the maximum rated cathode current.

I think the best analogy is putting the wrong size tires on a car. If they're only a little different in diameter, you're probably OK but if they differ on the same axle the differential gears will get extra wear. With a bigger difference, such as the mini-spare that cars have these days, handling deteriorates to the point that you want to stay off the freeway and get it fixed in the next few days. And 8" tires on an SUV means you're parked and up on blocks...

[Grainger49]

My car has different tires front and back.  If I get a flat on the rear the manual says to take a front tire and put it on the rear with the tiny spare on the front.   The positraction differential will self destruct if the space saver spare is put on the rear.

[Atom Shop]

...VintageTube Services...

I was completely unaware of this site! With all the time I've spent over the years researching tube vendors I'm just amazed that this one went undiscovered.

Uh, Andy certainly knows something about the original tube manufacturers. He's very opinionated with regard to the current state of tube-ology. And, rightly so! It'd be an understatement to say that he's well-equipped to properly evaluate a tube. His lab and library are phenomenal! How I'd love to see this place firsthand.

His tube selection seems to be limited to only the originals of the tube-manufacturing yesteryear's. This is great for those who will settle for nothing than the real deal. His prices are quite reasonable as well. There're a couple or three other brands I'd have like to have seen included in his roster. Early Sylvania, Raytheon, Tesla, Gold Lion (Genelex), e.g., made some well-respected tubes many years ago and still rate highly on the lists of many tube-aholics. (Me and Raytheon are pretty tight)

Yeah, definitely a good tube reference.   

[4krow]

I ordered a set of GE 6SN7's and a GE 12ax7 from him. After testing, matching, cleaning pins, he will send them out. I talked to him on the phone, and he was quite unassuming in nature. I was comfortable with the conversation, and learned a little bit as well. He says that he has a way of determing the amount of hours a tube has been used, if I understood correctly. There seems to be a lot of good knowledge there without gloat. Just like here.

[Paully]

A way to measure the amount of hours a tube has been used?  That would be interesting.  Everything I have ever read on tube asylum and elsewhere makes it sound like it is impossible to truly know how long a tube has left, some tubes like certain rectifiers can test close to 100% right before they go poof.  If there is a way to really determine, not just generally how long a tube has been used but to get a close estimate of the hours, I would be curious.  I don't have enough knowledge one way or the other to argue, but since this is new I was just curious to find out a little more if you can remember.