[simon wagstaff]

Sorry if we have covered this before, maybe there is some new information out there/

Last night my U-70 provided me with some entertainment. I went out to get a beer and when I came back no sound from the system. I notice no glow from the tubes so I checked the fuse. Yep, blown out. Replaced it and when I did lots of electrical nonsense from one of the tubes, sparks and such. Shut it down. Tubes were JJ KT77 and had been in there for a total of maybe a year.

I have tried a few different tubes sets;

1) Mullard re-issue EL 34, not tremendous sound, one tube failed after about 7 months
2) JJ EL34, O.K. sound, one tube failed after about 8 months.
3) Ruby EL34, by far the most reliable and best sounding tubes of the bunch.

When I compared the EL34 to the KT77 it seemed like the bubble of sound stretched outward beyond the speakers much more than the KT77, with the KT77 the soundstage depth was much greater, like the bubble of sound was inverted inwards, very deep.

so, I have a couple of questions. Currently, since I had three tubes from each set that had one blow up I put the JJ's in the rear socket of each channel and the Mullard in the front socket of each channel so I have the same tube set up in each channel. Will any harm come from using mixed tubes of the same type?

I like to have a spare set of tubes on hand so I am looking at a new set of tubes. I have read a lot about the Gold Lion KT77 but they are quite expensive, around $150 for a matched quad. Are they worth the money?

Also looking at some Golden Gate Super Tubes from China, with gold pins etc. Does anybody have any experience with them/

Any other tube recommendations for the U-70?

I also just want to throw in that in no means is this behavior in the U-70 troublesome, to me it is just part of the "fun and joy" of tube equipment. Love my U-70, most involving amp I have heard.

[trebejo]

Sorry about the troubles, Simon. Such is life with tubes. I tried both the Genalex KT77 and the EH EL34 and I didn't hear much of a difference. It's hard to to a/b testing on power tubes, you have to wait at least a half hour between tests...

[Wayner]

Usually it's the 5AR4 rectifier tube that likes to spark and and put things in a tizzy. I've run my power tubes for 2 years now with no issues. I asked Frank about the power tubes and he commented one time that he has seen original tubes on some upgrade units, but they are tubes and they certainly can go frizzle at any time.

I have a spare, complete set on a shelf for such occasions. I have lost one 5AR4 within the 2 year period.

Wayner

[simon wagstaff]

I can't remember the type of rectifier tube but I have installed the diodes per Frank's instructions and no troubles there.

Honestly, it is not that big of a deal and worth it for the U-70. The Ruby's probably have been in there for over two years without problems, I just wanted to try the KT-77's, they were nice as well.

[Lefty052347]

I have had a quad of Gold Lion kt-77's in use for a year in my Ultravalve without any problems.  Bias is very stable, .02v drift between channels after 3 months.  The amp sounds great.  I have no plans to replace it. 

I felt the same way about the sound with 6ca7's but was annoyed by the drifting bias setting on the right channel.

Regards,
Dean

[Brett Buck]

Any other tube recommendations for the U-70?

   The obvious solution, and the one I am using, is the EH 6ca7. One tube failed in the first set after about 2 years of about 8 hours a day, due to erroneous bias setting cu The second set has been going for about 18 months about 8 hours a day on average and nothing has budged. That's one blown power tube for a very obvious bias setting mistake in 4 years of very extensive use.



    I would also note that when it was still a dead stock ST-70, it ran all but one of the original power tubes for ~35 years with almost daily use.

  If your power tubes are blowing after less than a year, there's something else going on, or they are unreliable tubes.

  I have blown a lot of rectifier tubes (Sovtek and JJ), most from fast-cycling by accident. None since the series diode change but also no accidental fast-cycling, either.

   Brett

 p.s. anything I have gotten from JJ has been very unreliable. The rectifier tubes were a joke, several of them blew on the very first power-up. Even the 12ax7s were terribly unreliable, but once I found some that got past infant mortality (24 or so hours) they have been bulletproof since. Soundwise I think they are better than Telefunkens (of which I have many) which is which I kept trying.

p.p.s. If you are blowing tubes at this rate, might want to check that your bias grounds are solid:

topic=84622.0 

I would not trust the socket mount screws (or rivets if it was originally a factory job) to make this connection any more. I hard-wired it over to the central ground point, no issues.

[Wayner]

Good point, Brett. I had a stock Dynaco Stereo 70 for years and it always had the same original tubes in it. I don't remember ever getting tubes for the beast. I think the stock tubes were re-branded Dynaco, but can't remember.

I average about 2 hours per day with the Ultravalve for serious vinyl listening, otherwise, it's solid state during the day when I listen to FM.

Wayner

[Brett Buck]

...

[Brett Buck]

Any other tube recommendations for the U-70?

   The obvious solution, and the one I am using, is the EH 6ca7. One tube failed in the first set after about 2 years of about 8 hours a day, due to erroneous bias setting cu The second set has been going for about 18 months about 8 hours a day on average and nothing has budged. That's one blown power tube for a very obvious bias setting mistake in 4 years of very extensive use.

p.p.s. If you are blowing tubes at this rate, might want to check that your bias grounds are solid:

http://www.audiocircle.com/index.php?topic=84622.0 

I would not trust the socket mount screws (or rivets if it was originally a factory job) to make this connection any more. I hard-wired it over to the central ground point, no issues.

    I would also note that when it was still a dead stock ST-70, it ran all but one of the original power tubes for ~35 years with almost daily use.

  If your power tubes are blowing after less than a year, there's something else going on, or they are unreliable tubes.

  I have blown a lot of rectifier tubes (Sovtek and JJ), most from fast-cycling by accident. None since the series diode change but also no accidental fast-cycling, either.

   Brett

 p.s. anything I have gotten from JJ has been very unreliable. The rectifier tubes were a joke, several of them blew on the very first power-up. Even the 12ax7s were terribly unreliable, but once I found some that got past infant mortality (24 or so hours) they have been bulletproof since. Soundwise I think they are better than Telefunkens (of which I have many) which is which I kept trying.

[Brett Buck]

Sorry, there is some sort of software problem here, I can't get my post modified... and the original content is gone.

[AVnerdguy]

Good point, Brett. I had a stock Dynaco Stereo 70 for years and it always had the same original tubes in it. I don't remember ever getting tubes for the beast. I think the stock tubes were re-branded Dynaco, but can't remember.

I have a bone stock Dynaco MKIV with the original Mullards (OEM Dynaco branded). Don't use it daily but it still amazes me how strong these tubes still test after all these years. Have a newer SET amp - doesn't have a tube rectifier but I've run through quite a few output tubes (EL34 or 6L6) in the space of a year. Tried various brands and can't say if one is more reliable that the others. The driver tubes (EH) in my AVA gear have been fine though - I attribute to conservative design.

[rlee8394]

Thought I saw I this thread mention the Philips/ECG 6BG6GA. I have used these tubes in my U70 and like them a lot. To my ears, much better than the EL34/6CA7 tubes. So much so that I intend to rewire the sockets so I don't need the adapter. But before I do that, I have wanted to try the Shuguang KT-66. Last night I ordered a matched quad of Valve Art KT-66 from Antique Electronic Supply for $104.00. I'll put them through extensive listening sessions and decide which I like more. I have two U70's, so comparison should be relatively easy. Stay tuned.

Ron

[simon wagstaff]

Adapter? I am not familiar with this. I look forward to hearing more!

[rlee8394]

Simon,

Go here:

http://www.vacuumtubes.com/6BG6.html

Ron

[simon wagstaff]

Sorry, this link is not for EL34? Am I missing something?  thanks for your help!

[rlee8394]

The U70/UltaValve/Dyna ST-70 can run EL34, 6CA7, KT-66, KT-77, 5881, 6L6, 6P3S-E, even KT-88s. As long as you can properly bias the tubes and the plate dissipation are within the power limits of the amp, there should be no problem.

Ron