2. amps-preamps
  3. 1260631761

Tube biasing problem

Hi guys, i'm not a newbie in the world of audio, but somewhat a newbie
with tubes. A few months back I took delivery of a beautiful CJ tube amp. It
is rated a t 100 watts per channel, and has 2 sets of quad el34's. Being this is an older amp, the tubes that I received with it are also at the end of there life span. They are not matching quads neither. One set is Svetlana, and the other setare JJ's

My question, just recently I am not able to bias 3 of the tubes. CJ has the biasing pots with the leds which works beautifully. At first I thought there was a problem with the pots, but when I rotate the tubes, the 3 tubes that I was not able to bias before still cannot be biased in different pots. The properly working tubes can be biased in any of the pots so I ruled out the amp itself, and figure it has to be the tubes. Is this normal for a tube to resist biasing at the end of it's life span? As far as the amp performance, I am still playing music, and everything seems to be working properly, and there is no noise coming through the speakers. Any help from experienced users would be greatly appreciated. Thank you
tag1993
5 responses Add your response
recordho
49 posts
 
Get a set of EH EL34's from Jim McShane. Matched Quad or Octet. Search for him on Google. He gives a pretty descent warrant too. You most likely under $140 or close for all 8.
I would contact CJ to see what they offer as well. You may get a great deal from them.
I always retube any amp or preamp I buy even if they tell me the tubes are new. The funny thing is that the tubes you have could have different sonic signatures in each of the different channels with different tubes. I agree with Weiserb. You will have an altogether new experience when you
retube your amp. Good Luck
tag1993 OP
4 posts
 
Thanks TP & Apache, I appreciate the feedback. It was just kind of weird that 3 of them went at the same time within 2 days. I am also a little worried that it may damage my amp, but the sound seems to be fine so far. I plan on changing
both quads with matching tubes.
weiserb's avatar
Ag insider logo xs@2x
weiserb
476 posts
 
I also agree.

Retubing the input and power tubes will give you a new amp for 2010.

Congrats on purchasing one of the best amps from the best companies around. Enjoy
apachef1
164 posts
 
You answered your own question. the tubes in question are at the end of their usable life. Continuing to run the amp with your current tubes puts a harder demand on the one tube that has some good operating life. This will cause that tubes useable life to be used up much faster.

Purchase a matched quad new or NOS and get all four tubes biased and you will have no worries and keep your current one good tube as a spare for future use

Ed
tpreaves's avatar
tpreaves
2,686 posts
 
Tag,I have read that when tubes are on their last leg they will become hard,even refuse,to be biased.Also,biasing too frequently,shortens the life of tubes.Again,this is what I have read,not my ideas.I'd get a new octet of matched tubes and not have to worry about when the next one is going to go bad.I'm sure you're going to get several different opinions,if you want the best answer,call CJ.Good luck.
Log in to respond
More to discover
80x80
Vinnie Rossi Brama Pre-amplifier
80x80
Pass Labs XP-17
80x80
AudioControl The Director 4600