[simon wagstaff]

I don't usually like to post negative stuff about a product (Your uniformed opinion is another matter) but I have had some bad experiences with Mullard tubes in my U70. About a year ago I had one that flared up and got really  hot up at the top of the tube and some crackly noises came out of the speakers and I figured I better shut things down, so I did. Stupid enough to let it cool down and then fire the amp up again and all was well. Six months later the same tube did the same thing randomly again, so I pitched it and got a replacement.  I should mention I guess that I check the bias every six months or so and certainly when I put in a new set of tubes.

All is good for a while.

Then, just last night one of the Mullards that I have in the U70, left rear one, for no reason starts to freakin' throw some pretty major sparks from the TUBE SOCKET!

WTF!

It looked like a little sparkler from the 4th of July was burning up at the base of the tube....

So, I wisely shut it down and removed all of the Mullard tubes and figured the best thing was to dump them all in the trash.

I had a spare set of J J Tesla's and still have my set of KT77 so I won't miss those Mullard's at all, no sireee...

I have seen in another section that some big bottle whatever tubes are the way to go. I checked and found them at an attractive price at Parts Express and will look to pick up a set of those.

Kind of thing that could turn a feller against a tube type amp, but still really enjoying the post upgrade U70, minus the Mullard tubes...
 

[hotroady]

You should also check for an overheating capacitor on the bias circuit.

[ltr317]

Are you talking about the reissued Mullard EL34 made in Russia?  I've had EH EL34 do similiar things to my amp.

[boycephoto]

Simon
Tubes and be finickey, for no aparent reason.  I have had simular experience with RCA 6550's in a Dynaco Mark III. Mullard re-issue's did not last very long in my U70.  SED Winged C's work and sound great, I have a NOS quad of Mullard EL34's in my U70 right now and they are surpurb.

If you had sparks comming from the tube socket you might need tighten the connection at the socket.   Don't give up on the the U70, just mark this up to experience. 

Happy listening
Dave

[simon wagstaff]

Oh no, I am certainly not giving up on the U70, since the update it is even more magical than ever.  This sort of thing only seems to happen once every 6 months or so, and only with the Mullard tubes, which are the re-issues.

One of these days I will send it in to Frank to have him take a look at it but I have looked at the sockets and all the wiring and the guts and nothing seems amiss.

Only thing I am giving up on is Mullard Tubes...

[Wayner]

Another reason not to leave your amp on 24/7. Imagine that happening when you weren't home?

Wayner

[hotroady]

  I've had EH EL34 do similiar things to my amp.

                                                                                                  I've had 2 of 4 EH's fizzle. I run 1 JJ34L and 1 GE fat bottle per channel, now. I get the high end extension and mid range boost that way, works out pretty slick.

[ltr317]

  I've had EH EL34 do similiar things to my amp.

                                                                                                  I've had 2 of 4 EH's fizzle. I run 1 JJ34L and 1 GE fat bottle per channel, now. I get the high end extension and mid range boost that way, works out pretty slick.

You're like the fifth person who have told me the same thing about EH EL34s.  They have serious quality control problems, and I will never use this brand again.   I was wondering if this was common with russian made tubes, that's why I asked if the Mullards are reissues.  I've used chinese EL34s and 1970s Phillips EL34s, and neither has given me problems and always hold the bias settings.

[gjs_cds]

  I've had EH EL34 do similiar things to my amp.

                                                                                                  I've had 2 of 4 EH's fizzle. I run 1 JJ34L and 1 GE fat bottle per channel, now. I get the high end extension and mid range boost that way, works out pretty slick.

You're like the fifth person who have told me the same thing about EH EL34s.  They have serious quality control problems, and I will never use this brand again.   I was wondering if this was common with russian made tubes, that's why I asked if the Mullards are reissues.  I've used chinese EL34s and 1970s Phillips EL34s, and neither has given me problems and always hold the bias settings.

So the better tubes are coming out of China these days?
*smacks forehead*

[ltr317]

  I've had EH EL34 do similiar things to my amp.

                                                                                                  I've had 2 of 4 EH's fizzle. I run 1 JJ34L and 1 GE fat bottle per channel, now. I get the high end extension and mid range boost that way, works out pretty slick.

You're like the fifth person who have told me the same thing about EH EL34s.  They have serious quality control problems, and I will never use this brand again.   I was wondering if this was common with russian made tubes, that's why I asked if the Mullards are reissues.  I've used chinese EL34s and 1970s Phillips EL34s, and neither has given me problems and always hold the bias settings.

So the better tubes are coming out of China these days?
*smacks forehead*

I don't know about better, but certainly more reliable. 

[TjMV3]

I'm using the New Sensor Mullard 12AX7 "Re-issue" in my preamp and they have been very reliable and sound great.

I even use one in one of my tubed CD Players (Vincent CD S6.

I work from home and my office system is on all day,  till 10:30-11:00 PM at night.  Music is typically playing 6-7 hours a day.   And these Mullards have continued sounding great for over 10 months.  Not a single problem.

[Listens2tubes]

  Sparking sockets! Are they the original Dynaco sockets? Old sockets can be the source of many problems and should be replaced. For years I put off replacing the sockets in my Mk IV pair. Wandering bias was the most obvious annoyance. Once replaced the amps hold bias superbly and are very quiet, which I did'nt expect. New sockets are really an upgrade an older tube amp can benefit from.

BTW can you add your fire anf brimstone story to [url]http://www.audiocircle.com/index.php?topic=69481.0[url]?