6SN7 tubes and variants question.

Here's what AI has to say about it:

Nope — using a 6SN7GTA or GTB in a component designed for 6SN7GT is actually safe and often beneficial. Here's why:

🔧 Compatibility Breakdown

• 6SN7GT: The original version, typically rated for up to 300V plate voltage and 2.5W plate dissipation.

• 6SN7GTA: An upgraded version with higher ratings — up to 450V and 5W plate dissipation.

• 6SN7GTB: Same electrical specs as GTA, but with a controlled heater warm-up for better reliability in series heater circuits (like in TVs).

✅ Why It's Safe

• GTA and GTB are backward-compatible with GT. They’re essentially more robust versions.

• If your component is designed for GT, it will not stress a GTA or GTB — in fact, those tubes will likely run cooler and last longer.

• The reverse is not true: using a GT in a circuit designed for GTA/GTB could over-stress the tube and cause failure.

So go ahead and roll those GTA or GTB tubes into your GT-designed gear — your amp will thank you. Want help picking a great-sounding pair?

@billpete , I don’t know if any of this will be helpful or not, but just in case I will paste some text from some emails that a tube guru from another forum sent me as he took me under his wing and blessed me with several pairs of vintage 6sn7s. 

The W in WGTA is the designation for "ruggedized" construction. Thicker mica supports, extra support rods, smaller bottle ... all supposed to reduce the effect of physical shock/vibrations.  The GT is the designation for the bottle shape, and the A (and B for that matter) designates uprated plate voltage capability.  The B further designates the serial heater/filament connection capability.

and

Enjoy the ride, we’ll sort out the money.  The RCA’s are an interesting tube.  No highs, no lows, but boy do they do midrange and 3D.  Absolutely not the tube for rock ’n roll.  Small ensemble acoustic jazz, or acoustic vocal, or chamber music is their forte, IMO.  The TungSol GTB’s (one of those is marked A and one is B, but they are the exact same) and the Sylvania GTA’s are okay tubes.  The TS are kind of bass heavy for my taste, and I could probably live with them or the Syl GTAs if I didn’t know there was better out there.  I found out that the only difference between the GTA and GTB is that the GTB is capable of having the filaments connected in serial in the case of using multiple 6SN7s in a circuit. Furthermore, TungSol built all their 6SN7s at that point in time (late 1950’s) to the GTB spec, and then labeled them as A or B depending on what spec the client order called for.  The GTB always works in a circuit needing GTB, and it will also work perfectly in a circuit where there’s no requirement for the filaments to be connected in serial.  Why make two kinds when one will do both duties?

And, for what it may be worth, I have rolled pairs of both the GTAs and the GTBs in the balanced input sockets of my SLP05 with no ill effects.

@tomcy6 

Thanks. This is essentially what I read. This seems to agree with what I read on Head Fi, that using a GT or early tube in something that was designed for the later GTA/GTB types, could cause problems. What I read made it sound like you could damage your component, where this says that you may just ruin a tube. Some of these early tubes bring some pretty silly money and the gear is certainly not cheap. I'd hate to ruin either one. 

Using a GTA or GTB tube in an older design piece of gear that was designed around the GT types is safe but this is not my situation. Still, tons of people have talked about putting the older GT's, W's etc. in modern components and they end up being their favorites. Most notable is probably the Tung Sol BG RP, seems to me the 40's or maybe early 50's. Can't remember but I'm guessing these are the older GT type. I have not taken that plunge yet, if you find them they generally run $200 each or more. So far, I'm getting plenty of enjoyment from tubes that have been $50 each or less.

There are several tube rolling threads several years back about the very preamp that i use, as well as it's other iterations. The tube compliments are the same in all of them, simply saying 6sn7 but always supplied new with modern versions, which I can only assume match directly with GTA and GTB types with 4.5 to 5w output. Nearly everyone agrees that the best tubes were the oldest, the ones made in the 40's that would have the lower output of 2.5w. None stated that their gear or the tube failed. I have seen a number of reported failures of the old Russian versions with metal base Melz 1578 and 6N8S, which are highly coveted but not without controversy. Many complain about noise which seems mostly attributed to bad solder (sometimes able to be repaired) and some have complained about early failures. Most of these tubes are 70's and 80's but there are versions back to the 50's as well. All speak of great SQ, if all in working order. I have interest in them but am hesitant as well. I have plenty of US made tubes to fool around with for now.

I have several of the older types but have not used any yet. I am enjoying several different varieties of GTA/GTB's but am looking forward to hearing the older ones that everyone raves about. I'd hate to think that they could be unsafe to use (for the gear) or that I would ruin the tubes themselves. Has anyone experienced any of these problems?