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Hi, I bought some JJ 5AR4's a couple of months ago and only just now put them in my amps that I use on a regular basis with 5R4WGB's. When I fired the amps up (an apt expression) I got major arcing along the full length of the plates in both tubes. The amps are a DC design with a choke input filter and have been working without problem for a couple of years. When I tried some 5V4's and replaced the original 5R4WGB's I have no problem, just the slightly different voltage drop across each tube you would expect. Anyone have a similar pyrotechnic display with JJ's?
Follow Ups:
This tube may be more sensitive than a true 5AR4 for the initial current surge.FWIW, I blew up two very nice Dario GZ32 (5V4G) tubes in my 300b amps due to exceeding the rated voltage (not by much). Generally the 5AR4 is much more rugged than the 5V4.
It's a choke input supply ie LCLC which should present an easy load to the rectifier. As I mentioned below this amp works fine with a variety of rectifiers, just not with the JJ's. I would think that they have sold a number of these tubes and I was wondering if I got a bad batch or something. I have another pair (I bought 4) that I may try in a 6L6 PP amp that also uses 5AR4's and see what happens. I have a tube tester but it's very old and non-replaceable so I'm a bit leery of toasting it for curiosity's sake. At any rate, testers don't tell you what's wrong with a rectifier, only if it works or not.
Are you sure that you can substitute a 5AR4 in your amps??? None of the tubes you said worked list a 5AR4 as a substitute or vice versa in my tube data references.I've been using the new Sovtek and JJ 5AR4's in my Dyna's and have had zero problems with either.
Thanks for the reply. The 5v4's and 5R4wgb's are directly heated but all three types have high enough voltage ratings to use in this circuit and I have other 5AR4's that I have used in the past with no problem.
Kyle,FYI. On a tube guitar amp board, several folks found out that the JJ 5AR4 was mis-wired, at the factory. This mis-wiring is visible at the based of the tube.
"Apparently, some have the cathode connected to pin 2 instead of 8, according to info on a Japanese tube vendor site (someone pointed this out on their BB and the vendor confirmed that this was the case with the JJs they had in stock).
According to the poster, this means that all the rectified current travels through the heater and means drastically shortened life (the vendor confirmed/agreed and commented that they were consulting with JJ about the matter)."
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