Bad NOS tubes...

To be fair: Two months ago, I also purchased a matched pair of NOS Mullard’s 12au7/CV4003/M8136 - from the same vendor Albert Kayser. They sound great! In my preamp, they are extremely quiet - and have no issues at all. They sound just like Albert described them. He was 100% professional. I’m a very satisfied customer.

OTOH: For tube-rolling experimenting, I also purchase a matched pair of La RadioTechnique 12au7/6189 from Watford Valves in England. Noisy as hell. After a several weeks, they’ve calmed down a little bit - but nowhere near as quiet as the Mullard’s from Albert.

It’s very easy to discern the different sonic signatures of the two brands. Each has its advantages and disadvantages. It’s been a great learning curve for tuning my system. Curiously, one of the tube-sellers recommend earlier in this thread, gave me very poor advice. He was simply trying to sell what he had in stock. It’s a crap shoot!

Being an owner of a tube preamp and tube mono-blocks, I’ve resigned myself to this relationship which requires attention and expense. But, it can be so good when all is working.

steakster said... "To be fair: Two months ago, I also purchased a matched pair of NOS Mullard’s 12au7/CV4003/M8136 - from the same vendor Albert Kayser. They sound great! In my preamp, they are extremely quiet - and have no issues at all."

The two good mullards that I am using now in my preamp drive stage are just as you say...very quiet and sound great. My problem are with the remaining four... that do not make the grade with their noise issues. Believe me,I wish they did make the grade.

Jea48, First, I apologize for sounding so pedantic.  Your post actually prompted me to do some research on the metals used in tube pins.  In the URL you provided, are you referring to this passage?: "The 6DJ8 family was originally developed by Amperex. The first tube in the family was the steel pinned 6DJ8 followed by the gold pinned 6922 and 7308. These latter two were premium versions rated as 10,000 hour life tubes. The 6922 was a premium industrial version and the 7308 was the top of the line guaranteed low noise version. Frankly, I’ve measured & listened to a lot of these and there is no correlation between model # and sound quality."

Based on the brief bit of researching I did do, my first thought is that this guy is incorrect as regards the composition of the pins and that he used the word "steel" without really thinking about it.  Moreover, I think any one of us would say that no tube ever made has "gold" pins (as he describes them, carelessly); at best sometimes pins are gold-plated.  Pure gold would be a terrible choice for a tube pin, because it is so soft. You cannot easily plate steel in the first place.  So the notion of gold-plated steel does not make sense, either.  And finally, this is a piece about the 6922 and its many related tube types.  These are frame grid tubes that were only developed at the very end of the "vacuum tube era", mostly for use in instruments and TVs.  So generalizing from the 6922 back to the tubes from the golden era of audio tube technology is dangerous, even if some 6922s do have "steel" pins.  But it's a good question, and there is not much solid info on the internet.  I do believe that older octal based tube types, like 6SN7s probably have brass pins that were plated, maybe with nickel. My NOS 12AX7s and 12AU7s seem to have some copper containing alloy that is tinned.  If I polish a pin with my Dremel tool, it eventually reveals a copper-y color.