Tubes, cheese, wine and cognac

Thanks for your posts (grapes collected long time ago may have better flavour). I have some idea now on old collected grapes and old wine fabrics that do not exist anymore. 😏

Goot point, @petg60 - it might well be the case that new amps are oriented to newly made tubes. Anyway, if the tube amp production will continue, one cannot always count on NOS tubes. Looks like that Russia and China are out of the competition in the current tube production (I personally exclude new JJ tubes which, for my taste sound dull - I even prefer Chinees ones. I also had Yugoslavian EL84 tubes which bowed up too fast, nothing to compare with Soviet EL84s. Does Phillips produce new tubes?). 

It is crucial how a tube gets unfunctional. If it just becomes weaker is not a problem for me. If it blows up damaging the amp, it is a big problem. I would not buy such a tube even if it sounds great. One of the supplied EL34 tubes in my SET amp blowed up after about 500 hours or lee of use (I can see white sand inside the glass of the burned EL34, i don't have an idea where it came from). There was a sharp smell of burned plastic; perhaps, it was a resistor (it could not be the tube I guess). I ordered new tubes, replaced them. The amp woks but the channel with the burned tube sounds weaker. So far, I use balance control to somehow balance the sound. The amp has auto bias, I also thought that the bias went automatically low and did not rise "enough" (but there also was this smell). 

@akg_ca , i think one may well distinguish sound of different tubes in amps or preamps, I guess in DACs this may not be so evident. I am using Soviet NOS military EL84 tubes (6P14P-EV) for already 20 years in my other amp. They sound fine and remain strong. I rarely need to adjust the bias.

Is there some particular reason for not using new Chinees made tubes? I tried Shuguang tubes, but just for a couple of hours - nothing exceptional but they did not sound terrible. New PSvane tubes are also Chinees by the way. 

@noromance , if cannot be detected visually, can one detect a damaged cathode resistor by measuring the outcoming voltage (sorry, if this is a silly question)? 

I think that in that era tube production was crucial as there where no semiconductors and tubes were used not only for home for entertainment but also in military equipment. Nowadays tube production is no more if a primary importance, it is done for some audio fans and perhaps enough  attention  is not given to this matter. This is my personal interpretation. I already tried a number of different new production El34 tubes including Russian Mullards, Tang Sol, Gold Lion and Chinese Shuguang which are twice cheaper. All of them give more or less similar results, no drastic differences. I expected Golden lions would be better, but i think  twice less expensive Tang Sol is a bit better in my 5 watts SET amp. 

I just replaced JJ E88CC input tubes with Soviet 6n23p. These tubes are basically used for phono amplification in this amp. The Soviet tubes give a considerably more power and more airy reproduction. None of the JJ that i tubes i had i liked, i knew I needed to replace them. 

Does anybody know if el34 can be replaced with Russian 6n3c tubes? A correct replacement would be Russian 6p37c but it is difficult to find them. I  just ordered a pair of NOS Millard  El  34s.  Will post on my impressions once I try them.