Post by cooksferry on Jun 26, 2017 7:50:03 GMT 12
After a little help re some 6SN7 tubes in my amp.
I've noticed over the last few sessions that the sound quality appeared to deteriorate a little , a bit of distortion on vocals sometimes, nothing major but not quite as it should be.
Checking over the tubes on my amp I noticed that out of the 4 RCA 6SN7s one appeared different. While all 4 tubes were lit up at the base there was one tube that didn't have a glow at the top of the support rods. I switched them out for a set of GEC items and all 4 of these had the double glow at the rod top. Is the no light at the top on the RCA a sign of problems with that particular tube?
The set was purchased when I got the amp, so that's some years ago now and I can't remember how much actual working time they've had.
|
Post by Owen Y on Jun 26, 2017 9:42:50 GMT 12
cooksferry - yes there are 2 small round cathode tubes, in the RCA 6SN7 that protruding through the mica flat top, in the middle, ea side - & you should see a red glow inside both. I presume that you are talking about your Melody amp? And that the problem went away with the GEC 6SN7s swapped in?
|
Post by cooksferry on Jun 26, 2017 10:08:01 GMT 12
Hi Owen, yes seemed much better once i swapped the tubes and the GE tubes all had the top glow.
I'm starting to wondering if the Gold Lion KT88s might be getting a little tired as well, they've been in for quite a few years now, probably done something approaching 2000 hours. Dont know what sort of life I should expect from them but hopefully the replacement Psvane won't be too far away.
I really should also look at another 5AR4 rectifier tube, been running my T.A.D version for almost as long as the GL KT88s. Unfortunately NOS versions are pretty expensive but I may yet have a punt in that direction.
|
Post by Owen Y on Jun 26, 2017 10:35:39 GMT 12
Yes the rectifier does a lot of work. I've found that Chinese & Russian rectifs do not last as long as NOS British/US - but that could be due to cct design. Tube life dependsa lot on the cct design, how hard the tubes are set up to run in the amp. 2,000hrs might be 2-4years depending on how many hrs/wk in use - which should still be OK, I'd expect 4+yrs in hifi use, before noticeable sonic deterioration, sometimes much longer (partly due the ears not noticing gradual change). (Tubes have been shown to last over 5,000hrs & if operating ambient temperature is kept low 10,000hrs average life can be expected. Tubes were used in undersea trans-continental telephone cable repeaters, running continuously for years, decades! IIRC)
|
Post by colinf on Jun 26, 2017 11:46:11 GMT 12
Tube rectifiers are usually given a hard time in today's circuits. The capacitance in the power supply has gone up dramatically since when the 5ar4 was designed. Back in the 50s and 60s it could be expected to drive 32uf of capacitance. Nowadays that can be over 300uf! That means the peak current in the rectifier will be high. So they are more liable to wear quickly in a modern amp. In your RCA 6sn7s you should see the glow in the bottom of the internal tube structure in the two separate cathodes. Sometimes seeing a glow at the top of a tube might be less visible because of its construction, and the mirror-like finish of the getter deposit on top.
AMR-iFi R&D
|
Post by colinf on Jun 26, 2017 11:48:30 GMT 12
I've had good experience with Ruby 5ar4c tubes. They are rugged and sound good.
AMR-iFi R&D
|
Post by cooksferry on Jun 26, 2017 15:50:37 GMT 12
I've had good experience with Ruby 5ar4c tubes. They are rugged and sound good. They're cheap enough, so certainly nothing to lose with a trial, thanks for the heads up.
|
