6SN7 tubes and variants question.

If the grid of the tube opened up (which can happen due to poor solder joints in the base of the tube, which is a lot more common these days with Russian and Chinese power tubes) the tube can go into runaway. 

@billpete , I am sure that there were some in that massive collection of used pairs that were bestowed upon me, but I will have to go back and check to see which were which. My benefactor mentioned the Sylvanias that he sent me, so those for sure, but I cannot say I remember what sonic impact they had on me when I put them in the preamp.  However, I can absolutely tell you that none of those tubes gave me any problems whatsoever.

But he three pairs of tubes that made the biggest impact on my ears were:

1) a pair of black glass RCA VT231s.  The detail that they brought out in the music I was listening to at the time was incredible (to me).  Imaging was enhanced significantly.

2) in a later batch he sent me, there were a pair of ancient National Union 6F8Gs that I am running right now because although I do not have the vocabulary to describe what it is I am hearing, they have a seductive effect on me.  After expressing my thoughts in an email with Mike, he referred to them as The Velvet Glove.  They do require adapters to use them with.

3) in that same batch as above, he also put in a pair of '52 Sylvania Bad Boys and he actually shipped them in their original packing box that the Navy had them in.  They made me think of the RCA VT231s I alluded to above, but on steroids.  I was infatuated for quite some time with them before I tried out the National Unions.  I emailed Mike to express my thoughts on those, and he called them The Iron Fist.

Getting back to that first batch I was talking about, there were also a pair of TungSol VT231s that I also liked (more than most of the others), but the RCA VT231s captured my heart and ears (at the time) with the incredible detail they brought out.  I do not know if those TungSols were the GTBs he was referring to in the email (I am thinking not), but I will have to go back and check.

@immatthewj 

I think VT231's should be the same specs as GT's or W's as they were made for the military in WWII. GTA's came out around 1952 and GTB's in 1954, if I remember right. Anyway, I have a few pairs of VT231's, just haven't tried any yet. My RCA JAN 231's are the smoke glass not the black. I believe they are also labeled 6SN7GT. I also have a pair of RCA GT's in smoke glass that look slightly different than the VT version. I buy cheap singles when I find them, building a collection the hard way. I enjoy the chase though. At my age, I'm easily entertained.

I have a National Union pair of black glass GT's. I plan to try them today if they are a close match. Also bought separately, one came as a pair with a Sylvania GTB, the other I found by itself and it's a Westinghouse label but the exact same black glass tube. 

I'm waiting for a pair of Sylvania VT231's that I found a few days ago. They are also labeled 6SN7GT. Not sure if they are the bad boy or not. I have to study that a little more to understand which is what. I think the BB's are silver bottom if I remember right and I don't remember what this pair looks like. Seems to me they are silver bottom but the seller never called them bad boys so maybe not? I am still kind of anxious to hear them. 

 My RCA JAN 231's are the smoke glass not the black.

@billpete, I think that it is quite possible that we are talking about the same tube, but I am mistakenly calling them "black glass."

I'm waiting for a pair of Sylvania VT231's that I found a few days ago. They are also labeled 6SN7GT. Not sure if they are the bad boy or not. I have to study that a little more to understand which is what. I think the BB's are silver bottom if I remember right and I don't remember what this pair looks like. Seems to me they are silver bottom but the seller never called them bad boys so maybe not? I am still kind of anxious to hear them. 

I know that there have been some threads on identifying the Sylvania "bad boys", I think if you plug that nomenclature in as a search engine in the 'search discussions' box, you should get some hits.  Regardless, you jumped in with both feet on tube rolling with that SLP98--you have my respect!  I am looking forward to your follow-ups.

@immatthewj 

Well, I hope we are talking about the same tube. The RCA JAN VT231 does get a lot of praise. My National Union pair has much darker glass, literally black like the Tung Sols. The RCA VT231's have a dark gray smoke glass which appears thicker in appearance than the RCA GT smoke glass, which is slightly lighter in color and apparently, the amount of smoke color. I have yet to listen to any of these but looking forward to it.

It looks to me that the Sylvania BB's are black plate. Some people like to brag up how many holes, Brent Jessee says they both sound the same. I've also seen both tall and short bottle and even Chrome top as BB but I think some are probably wrong. The credible ones all fetch $200 a pair and up. The Syl VT231 pair that I just picked up is gray plate. Probably not BB but I think I've read that they can sound very nice, Any of the VT231's get high praise so it appears. They would all be early to mid 40's to very early 50s'. One other difference can be the getter, type and placement since we find top, bottom and side getters all offered in 6SN7 variants. Not sure which the BB's should have but it seems like bottom from memory. Will have to check. 

@billpete Sounds like you've got some nice tubes.  I've read many tube rolling threads and don't recall any warnings about 6SN7s being incompatible with any gear.  I think you're good to roll.