shimmilou said:
bandit2013,
You sometimes have to look very closely at tubes to spot the differences, but none of the Russian tubes that you mentioned are the same tube relabeled, they are all quite different. Some of the differences are hard to spot, some differences can't even be seen, such as the grids underneath the Plates. Some Genalex are Chinese. As you've noted, the easiest way to tell the difference is by the sound.
Man, it really seems like your amp has some problems, it sure eats tubes like no other amp I've ever heard of.
My amp will eat power tubes, but I have only blown 3 sets so far.
Severely red plated one of the Mesa 6L6gc STR440 original tubes, in V8, V9 was also cherry red but did not get scorched. Happened in 45W mode, Effects loop Active, and Variac power.
Same tube positions but 13 year old and used Mesa 6L6GC STR 420 under same operating conditions. Took out both V8 and V9.
Lost one of the JJ6CA7 but in V10, 90W mode full power, Effects loop active.
The Mark IV toasted two of the remaining JJ6CA7. I believe the loss of the JJ tube in V10 was due to defect in the tube.
All the other tubes I have used in the Mark V are still in operating condition. I just did not care much for the tonal characteristics. May it be harsh, they just sounded terrible. What did not seem sound good (subjective ) in the Mark V sounds great in the Mark IV combo. What I found with the Mark V that is different is that only one tube is driven hard in the 45W mode. With effects loop active, V8 gets abuse, in hard bypass it is V9. The JJ6CA7 tubes revealed this due to the super hot glow of the grids and cathode was visible though the mica spacer and a signal applied. Looked like a incandescent light bulb on a dimmer control. 90W mode allows for parallel currents for V8 and V9 so the burden gets spread across all 4 tubes more evenly. So far only the SED tubes appear to be balanced but no proof since I do not have bias meter yet. The TAD6L6gc STR also do not seem to reveal hot spots at the plate seem. The SED tubes will glow slightly but not as much as the Svetlana or Tung Sol tubes (almost complete plate will get a slight orange glow but remains its natural color grey). This is of course with signal and moderate volume levels. They seem to cool down quickly as soon as the signal stops. I have also notices the hot spots with the same tubes in the Mark IV. I am assuming it is normal. Also it is not visible unless viewed in complete darkness.
Yes I would agree that all tubes that look similar are not identical. Case with the Reflektor (new sensor) preamp tubes. Sovtek LPS is identical in appearance to the Mullard re-issue, but they are not the same tube. Internals more than likely are different even if the plates appear to be the same design. TS 12ax7 also shares identical plates to the EH 12ax7 but are notably different in spacer design, and probably screen and cathode as well. Visual inspection cannot identify alloys used, plating, cathode thickness, etc.... Just based on visual cues, it is difficult to tell if it is the same tube. The Tung Sol 7581 looks identical to the Svetlana tube on plate design, they even sound similar but are not the same tube internals. I would expect to see similarities of different tubes made by the same manufacturer. However, if the Gold lion B759 tube is the same as the Mullard re-issue, I would be greatly disappointed. I may get one just for kicks. I do like the Sovtek LPS tube. I am considering getting a few to try out in the AC heated positions to hear if the Hum returns. I could always tube roll the one I have to hear if anything changes.
