Thieliste's new Reference system

[Argonaut]

Yes I know it can get much worse but since this red plating is moderate I wasn’t sure.
Do I have to change only this tube or the pair ?
Thanks

A defective KT120 is one possibility , The other being that there is nothing wrong with the valve per se , and that there may be a slight problem with the bias circuit for that particular tube causing it to draw more current than is specified .

The quick and dirty way of diagnosing the latter , replace the KT120 with a spare and observe , should the spare overdraw and red plate it would be unlikely to be another defective tube and would indicate a slight problem with the bias circuit .

If you don’t have a proven ‘good’ spare KT120 then by merely swapping the recalcitrant tube around with one of the other KT’s would achieve the same end , caviat , don't run the amp for any longer than to prove the experiment , a couple of mins should be long enough.

 

[Thieliste]

Ok I swapped the pair of KT120s and it’s not red plating anymore.
Peharps bias was not settled during the first day yesterday because I was using KT88 before that.

 

[Argonaut]

Ok I swapped the pair of KT120s and it’s not red plating anymore.
Peharps bias was not settled during the first day yesterday because I was using KT88 before that.

Doesn’t quite work like that , so neither KT’s are now red plating including the one that you swapped into the previous red plate socket correct ? How long did you run the amp ?

 

[Thieliste]

Doesn’t quite work like that , so neither KT’s are now red plating including the one that you swapped into the previous red plate socket correct ? How long did you run the amp ?

That's right none are red plating anymore, i ran the amp a couple of hours.

 

[Thieliste]

Ok guys very strange situation here, when I put back this tube in it’s place it does red plate but when I swap it doesn’t do it.
I have no explainations.

 

[Thieliste]

Should I ask Jadis to change both tubes ?

 

[Argonaut]

Should I ask Jadis to change both tubes ?

I think that would be a start If availible to you ? Are you still under warrenty ? If so all good , if not , a word with Jadis regarding your issue would be progress . Do you have a circuit diagram for this model .

 

[Thieliste]

I think that would be a start If availible to you ? Are you still under warrenty ? If so all good , if not , a word with Jadis regarding your issue would be progress . Do you have a circuit diagram for this model .

Obviously they are still under warranty, they are not even a week old.

 

[Argonaut]

Obviously they are still under warranty, they are not even a week old.

Thank you , I wasn’t aware of that , good luck.

 

[Thieliste]

Thank you , I wasn’t aware of that , good luck.

Yes they replaced a full set of Psvane KT88C also from Jadis that went bad.
Looks like a i have no luck with tubes selected by Jadis lol
I have a set of Psvane Acme KT88 that i purchased in Germany and they work just fine.

 

[Thieliste]

Ok guys my problem is solved, I moved the back pair to the front and vice serva and that did the trick no more red plating.
Been burning them for about 100h they sound fantastic, much better than KT88s not even close.

 

[Thieliste]

For the preamp part I tried NOS Mullard, Tungsram, Brimar, Radio Technique and RCA.
Here again RCA smokes them all by a wide margin paired with the KT120s.