Well, as for the JJ's the fact is that many companies use them as they can get it fairly cheap in a big amounts. The quality of JJ tubes are controversial. Obviously tubes aren't under warranty so if it fails You got to replace it indyvidually. Manufacturer is happy 'cause You have bought his expensive amp which is filled with quality components, good transformers and tubes... which are available cheap
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It should be also obvious that most of us play with the tubes to shape our own sound and rather rarely stay with stock ones. So it isn't actually essential what tubes we get with our new amp.
Bogner since the beginning was using good quality tubes, when it was available in fair price. First 100B's came out with RFT/Siemens' powertubes. I even have two quads of them labelled Bogner. When the supply dried out they switched to =C='s, which in some time became dramatically pricey. So the choice was in general between JJ's, Shugs and Sovteks. JJ's were chosen for some reason and that's the whole story IMO. They "advantage" is that they simply have ability to SOUND whatsover, so they are good
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From my experience, both preamp and power JJ tubes are muddying XTC insanely. They could sound better in Marshall circuit as it is brighter in nature than the XTC. Despite using exactly the same tooling as for producing old Tesla's JJ's are nothing like them. I have a bunch Tesla's EL34's, ECC83's and ECC803S' and it isn't even generally comparable.
Believe me, I am not NOS lover-at-all-costs. Have simply a bunch of old production tubes, used to use them in my XTC with great tonal results (especially Tesla's in poweramp, Telefunken's in V1 and PI and Philips' or Tungsrams in gain stages) but switched to CP because of the price. XTC is eating tubes quite fast, I mean, the sound indicates rather fast, that the tube isn't fresh. XTC is one of the most sensitive amp when it comes to tubes freshness IMO. But it is worth filling it with fresh sets more often that other amps.
But You can get all JJ's cheap, very cheap... and very likely that is why some of us could advocate them and guard against those who doesn't like them as much
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Cutting long story short - You can always buy JJ's in the end, but before that You might try some other tubes, especially in poweramp. Most likely You won't go back, even if it's a few $$$ more to spend
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Regards, Andy