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In Reply to: RE: Defective 300B Tubes? posted by SETdude on August 16, 2015 at 07:41:25
I contacted the dealer and they indicated that they will replace tubes under warranty.
The dealer wrote the following in their email "I have serious concern about your amp" and also stated "there is a very big chance that your amp is out of specification, as a result, caused the tubes to failure prematurely" and went on further to say "I would like to request you to have you amp check to see if there is any issue".
I understand the dealer's position as these tubes are expensive to replace, a 6SN7 tube ($100 per tube) failed about a month ago and now the 300B tubes ($1,200 matched pair) just a couple of days ago. If I were in their shoes I might also have a concern there may be something going on with the amp but... their tubes are the only ones that failed. I've had JJ, RCA, Sylvania, Ken-Rad and not had a single issue with any of them. That's not to say I never will as anything is possible but as far as I can tell the amp is working just fine with bias rock steady @ 120mA as per their recommendation (Cary advises 160mA), there are no strange noises, smells, etc... just wonderful music.
So my question is this... should I heed the tube dealer's request and ship the amp back to Cary to have them check it out, or are the failures nothing more than tubes behaving like tubes?
Follow Ups:
snip: I understand the dealer's position as these tubes are expensive to replace, a 6SN7 tube ($100 per tube)
You could buy a bunch for that $....and be happier.
"I can't compete with the dead". (Buck W. 2010)
Some of the new 6SN7 tubes are quite good. Have you used them? I have a buddy with boxes of old production and he prefers the Treasure CV-181.
I have well over 500 6SN7s and variants. I don't have any need for modern production tubes. They don't interest me at all.
"I can't compete with the dead". (Buck W. 2010)
Edits: 08/19/15
Good for you.
You're right. It is. Excellent in fact.
"I can't compete with the dead". (Buck W. 2010)
I've seen that exact same response twice before from Sophia. In both cases I checked out the customer's amps (one of them was a Sophia amp) and there was nothing wrong.
This is a common response from them trying to cover their butts.
With that said I highly doubt there is anything wrong with the amp, but if you're not sure have it checked out.
In both previous cases Sophia replaced the tubes, and there have been no problems. One replacement had a piece of glass rattling around inside but the tube worked perfectly well otherwise. I'm inclined to think it's a quality control issue more than anything. But they do stand behind the product.
Dan Santoni
How long have you had the amp? Did you buy it used? If so, how old is it?
Edits: 08/16/15
purchased on Agon, 1994 vintage.
I believe I remember your posts when you bought it. The Cary does run tubes a bit hard but what you described is odd. I'd call Cary and talk to them before using the replacement tubes. There are some upgrades that you may be interested in. No sense in frying more tubes.
It's a nice piece. I had the 300SE monoblocks in 1994.
I plan on contacting Cary tomorrow to discuss having the unit checked out and possible upgrades. Apparently replacing the coupling caps with either Jensen or Clarity caps and hexfred rectifiers are popular upgrades so maybe I'll get that done as well.
Do you know what caps are in there now? The Hexfred upgrade will relieve your rectifiers of some work, the bass will be tighter, but the rectifiers will still be there. That info came from someone on another forum who is having Hexfreds installed on an SLI-80.
I took the bottom plate off to take a peek, mostly out of curiosity of the design/build, and also to check for leaking caps & burnt resistors (considering age of the amp). Everything looked good, and I was impressed with the layout & build quality, even to my untrained eye you could tell Cary did a good job building these amps. And to answer your question, the unit is stock with no modifications.
One thing I want to bring up when talking with Cary's tech is possibly having a power supply delay board installed, I'm not a tech but perhaps the tubes would fare better if they were slowly exposed to voltage during the warm-up process (see 'Power Supply Delay Action Board' under 'Transformers/ Chokes/Parts'). Not sure if it would help but maybe worth discussing.
That may already be in the circuit but you would have to ask Cary to be sure. Do you recall if the coupling caps were a dull silver tone?
It was a couple of months ago when I looked under the hood so can't be sure, but I vaguely remember them as you described but again not 100%.
Then they may be Cary's Audio 1 caps which I believe are Vitamin Q's.
Vitamin Q?
Vitamin Q's are a paper in oil capacitor. They can be very nice in the right application.
SETdude brings up a good point, is it safe to run the tubes @ 160mA, and what's the benefit of running them at the higher amperage?
I would ask Cary about the bias point. That may be an issue with the particular 300B tube you are using.
I just looked at the manual for your amp. It's not tube rectified..no big deal. A bias setting of 160ma is what the manual says but that may exceed the limits of your particular tube. Look up the data sheet. The Hexfreds would be an upgrade. Capacitors? What you would prefer would likely hinge on your speakers.
Tube dealer recommends 120mA so that's what I've been using. Speakers are Merlin TSM.
That is 20ma more than the data sheet for the tube recommends.
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