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Help! A red plating mystery. New Cayin mt 12-n

jbones said:
update: the mystery goes deeper. I found that actually it’s 2 tubes that are issues, and one just red plates faster than the other. So, I put them both on the same side of the unit, to test that they both glow ( as they each do in other positions), and lo and behold - no red plating. I’ve literally had the amp running 30mins and I could not go more than 2min without red plating. Would this be something to do with them being more bias? The amp sounds fine( not amazing as 2 obviously damaged tubes now I’ll bet) but can’t tell.

Does this help? Does this mean it was potentially just two garbage tubes from electro harmonics/cayin?
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There is something wrong with that channel, that causes the tubes to red plate.

The suspect tubes are fine on the other channel. Correct? ---> It isn't the tubes.

Just to be sure, you have never worked on a tube amp, before. Correct? My advice, don't learn on this one.

You prolly should think about having a tech look at the circuitry. :idea:

Really poo-poo that Cayin doesn't back their new units. Truly, a landfill mentality.
 
Mr Boochie said:
There is something wrong with that channel, that causes the tubes to red plate.

The suspect tubes are fine on the other channel. Correct? ---> It isn't the tubes.

Just to be sure, you have never worked on a tube amp, before. Correct? My advice, don't learn on this one.

You prolly should think about having a tech look at the circuitry. :idea:

Really poo-poo that Cayin doesn't back their new units. Truly, a landfill mentality.
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You are very right. I will take it in for sure. Basically this is my system at my cabin which is 5 hours north of Vancouver and 3 hours north of anywhere, so while I’m “stuck” here I’m just spending way too much time trying to figure out the logic.

I emailed cayin again. Shocking how little they want to help or support.

So yea, I’ve narrowed it down. Two bad tubes. When I move them to the same side, one or the other red plates, the other channel is fine. No matter the channel. If I split them up, either one or the other red plates in their position. The red plating follows these tubes around. The weird thing is, when they are on the same side, they don’t seem to red plate as hot or as fast. Anyways, I’ll take it in. But my hopes for this being tubes at least in my mind, is higher.
 
If it follows the tubes, it must be the tubes. I have had brand new tubes or 1 month old tubes do this, but they were JJ, not EH. Lots of problems with JJ in the past year. Just buy a new matched set of tubes and try them.
Also, you said this is a brand new amp? Can't you return it to the place you bought it? Or get your credit card company involved.
 
dr*audio said:
If it follows the tubes, it must be the tubes. I have had brand new tubes or 1 month old tubes do this, but they were JJ, not EH. Lots of problems with JJ in the past year. Just buy a new matched set of tubes and try them.
Also, you said this is a brand new amp? Can't you return it to the place you bought it? Or get your credit card company involved.
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" I found that actually it’s 2 tubes that are issues, and one just red plates faster than the other. So, I put them both on the same side of the unit, to test that they both glow ( as they each do in other positions), and lo and behold - no red plating. "
 
Mr Boochie said:
" I found that actually it’s 2 tubes that are issues, and one just red plates faster than the other. So, I put them both on the same side of the unit, to test that they both glow ( as they each do in other positions), and lo and behold - no red plating. "
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It could still be the tubes. I have seen brand new tubes (these were JJ's) that in a fixed bias amp would redplate because the emission was so high. Here's what I recommend:
1. Try new tubes
2. If it works with the new tubes, you're done. I'd replace the other tubes that work ok because my experience has been that if some of the tubes of a given lot redplate, the others will eventually follow.
3. If the new tubes redplate, return the amp to the place you bought it or get your credit card company involved.
4. If #3 is not feasible, measure the resistance of the grid resistors, and the connection to ground.
 
jbones said:
You are very right. I will take it in for sure. Basically this is my system at my cabin which is 5 hours north of Vancouver and 3 hours north of anywhere, so while I’m “stuck” here I’m just spending way too much time trying to figure out the logic.

I emailed cayin again. Shocking how little they want to help or support.

So yea, I’ve narrowed it down. Two bad tubes. When I move them to the same side, one or the other red plates, the other channel is fine. No matter the channel. If I split them up, either one or the other red plates in their position. The red plating follows these tubes around. The weird thing is, when they are on the same side, they don’t seem to red plate as hot or as fast. Anyways, I’ll take it in. But my hopes for this being tubes at least in my mind, is higher.
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I'm confused here. Didn't you state that the red-plate tubes were okay in other sockets. For like 30-minutes?

All right --- to narrow this puppy down. Wait for the new tubes to arrive. Put one into the socket that caused the initial set to red-plate.

No red-plate with new tube? = bad initial tubes. Toss out bad tubes. Insert new tubes.

Red-plate? = bad amp. Seek technical help.

Don't try swapping your current tubes around anymore. This is confusing the diagnosis.

Good luck! :thumbsup:

​

 
Mr Boochie said:
I'm confused here. Didn't you state that the red-plate tubes were okay in other sockets. For like 30-minutes?

All right --- to narrow this puppy down. Wait for the new tubes to arrive. Put one into the socket that caused the initial set to red-plate.

No red-plate with new tube? = bad initial tubes. Toss out bad tubes. Insert new tubes.

Red-plate? = bad amp. Seek technical help.

Don't try swapping your current tubes around anymore. This is confusing the diagnosis.

Good luck! :thumbsup:

​

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Agreed! They should be in by end of this week, and I’ll post the update! Thanks so much eveyone!
 
jbones said:
Update: I installed new JJ matched tubes. So far no red plating. I’ve run the unit about 5 hours, and with the old tubes it would only take about 1 min before they red plate. So, so far feeling positive.
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Yay!

I like the simple fixes.

thumbsup (1).gif
 
Can someone give me some advice please, I purchased this amp and I really like it, wanted to try new EL84 tubes and bought some NOS RCA, Valvo on eBay , but unfortunately it does not work, it makes a very high pitching sound and the tubes glow more than the originals? Wondering if anyone here has been able to roll some NOS EL84 on the amp?
 
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