1. Home
  2. analog
  3. 165509-89448

Blown tube issue

So one of my Tung Sol EL34s blew last weekend after 6 months and I’m not running them constantly. Manley is replacing for me.

My question is : is it ok to pop in a random EL34 in the interim and how does that affect sound ? Same brand better ? These tubes I bought from Manley are all bias numbered . Not sure if there is an exact slot order to the numeration . 
Another thing that concerns me is I bought the snappers used from some Agon user who replaced/upgraded the caps . I’ve been told depending on his work this could be the reason I’ve already blown 2 power tubes in 1.5 years ? Anything I can be aware of appreciated !

my setup :
manley snappers
Manley jumbo shrimp pre
VPI super prime scout
allnic h1202 phonostage

tommypenngotti
millercarbon's avatar
millercarbon
12,531 posts
 
What lewm said. Tubes are just plain unpredictable. New or used, biased or not, they can just blow, or last forever, and I have seen it all. I've had three brand new Preferred Series tubes from thetubestore.com blow within weeks, and I've had the most inexpensive JJ tubes run so many years they very gradually became dull just like lewm said. Only the change was so gradual over so long I didn't even notice until the new tubes went in and then WOW! (Sorry for the hyperbole, wow!) 
tommypenngotti's avatar
tommypenngotti OP
226 posts
 
Yes...I know how to set bias and have done it periodically like Manley suggests ...I just completely re-tubed in October 2020 so one blew from previous owner set (expected) and one blew from the new set (unexpected) 
millercarbon's avatar
millercarbon
12,531 posts
 
To blow a tube in six months is unexpected, and unfortunate, but unfortunately not unusual.
russ69's avatar
russ69
3,579 posts
 
"...Set Bias for 300mVDC measured across 10 ohm cathode resistor..."

That is not driven too hard for an EL-34. Some amps drive them way harder than that.
oldhvymec
5,101 posts
 
OP here is the real question, was the tube failure in the same position? If not, move on and understand, valves fail. If it was in the same position check the bias per position that ONE is to hot.. 300ma is not plus anything, that is MAX. That is every valve? or per bank.. 300 sound HIGH per valve to me.. Anyway LOWER is better for now and accurate is even more important..

Make sure your using a DMM, not an analog meter, they are not close enough.. Every year they are suppose to be calibrated if they are being used as a TOOL, for looks that’s different. Who cares.. Blowing tubes.. MAKE SURE... the meter is good and you're at least bias 300 or LOWER not higher..

Surging ON is a problem too.. Make sure you have a 120 volt maintainer for start up, no voltage dips. Soft start or pre start really helps too..(stand by switch)

I have the older Macs that are 117 vac MAX they don’t like 120vac. They will actually run too hot.. but on a Variac at 110vac.. perfect... Those Manley aren’t that old... are they?

I have VTL 300 deluxe (Manley design) they like 110-115. Above that they run HOT. 110 I can almost tolerate them in the summer.. but I can adjust the bias, the Macs I can’t.. ALL fixed..

Fruit for thought OP..

Regards
More to discover