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NOS Tubes - Ecstasy or Agony

I have been running tube amps for many years and have built a number of SETs and other tube amps, kit's mostly.  My main power tubes have been 2A3's and 300bs and I have used mostly new manufacture tubes including JJ's and EML 300b's (great tube btw).  I did use NOS driver tubes and headphone amp tubes.  Never really had a problem.

I just transitioned to a Don Sach's 6sn7 based preamp and McCormack SS power amp.  The preamp is very nice and sounds great with Shugang tubes. Of course, I wanted to try some NOS tubes, went online and did my research.  Now the DS2 is a great preamp, the drawback is it uses 4 6sn7s and so I need to get pairs.  Would  have love to get my hands on the Dehavilland, uses one tube!

First Pair - I ordered some Sylvania's from TC Tubes. Advertised as 50's vintage, ,when I received  them they were marked 60's. Hmmm.  So I tried them and they sounded pretty darn good except after a couple hours one of them developed a high pitched hum, like a florescent bulb. So I sent them back.  

Second Pair - ordered from Brent Jesse - has a good rep online and a really informative website.  Received them and one was dead on arrival, they were also clearly of different construction. So they are going back.

Next will try Andy at Vintage Tubes Services, he also has a solid  reputation so hopefully I can get something that works.

I am curious what experiences others have had. Maybe its COVID, or are these dealers just unreliable, or is just 6sn7's?  Really thought I could just buy some NOS tubes and experiment, I can't even get two to work.

I don't really want to disparage these dealers but I do think all the claims of testing are maybe overblown.
drewh1
drewh1 OP
115 posts
 
Thanks for your comments Atmasphere! your products look awesome.

RCA's had a nice sound but were terribly microphonic. So they are going back.  I am having such bad luck, I wonder if something about the circuit in my preamp is especially sensitive to microphonic tubes.

Now awaiting the Ken Rad's from Andy. If I get some decent tubes from him, i'll buy another pair of the RCAs to try as I really did like everything about them (except the noise).
atmasphere's avatar
atmasphere
11,632 posts
 
I wonder if something about the circuit in my preamp is especially sensitive to microphonic tubes.
@drewh1 
It probably is. If that is the case, you have to handpick the tubes for low microphonics. Its a good idea to specify that to the supplier; if they can't do it than you'll have to- by buying tubes, trying them out and sending them back if the microphonics are unacceptable. Keep in mind that all tubes have microphonics so its not a matter of getting rid of them as it is getting them low enough that they are not noticed. If operating the front panel controls of a preamp can be heard then I would consider that unacceptable.
drewh1 OP
115 posts
 
I no longer  think there is an issue with the preamp. I started a new thread but wanted to reply. here to atmasphere.

I just recieved a pair of '56 RCAs and '53 Sylvania's.  None of the tubes are microphonic. even quieter than the new Shuquangs.
audition__audio
1,338 posts
 
If you buy from a reputable and experienced seller, true NOS isnt so difficult to spot. Test results do not indicate NOS and it is not uncommon to see used tubes test near or even above typical NOS levels. Not heard to comprehend when you see variations from new factory tube of up 25%. Same type, same manufacturer and even similar production dates. Beware "NOS in white boxes". Just because a tube tests as new doesnt make this tube NOS. A very good indicator, perhaps the best, is to check the tube pins out under a loupe if one thinks the tube may be NOS. 
audition__audio
1,338 posts
 
Another thing, there are no 2 hole plate Sylvania Bad Boys. A true Bad Boy has 3 hole plates with a bottom getter with dates ranging from 1951 to 1954 (base may have been printed at a later date). They are unique and they sound different.
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