I bought my first tube amp from Germany a couple of weeks ago. The V70SE to go with my C1s.
It came with 1 Sovtek 12AX7 and 2x RCA 12AT7 + 4x Sovtek 6550WE
I thought I'd pass on some info from my correspondence from Koray Kural at the www.nostubestore.com:
"Sonically, most important tubes in the tube amp topologies are those used in input/preamp stages which is a single 12AX7 tube for your Octave V70SE. This tube gives its sonic character and tones to the system overall. Swapping only this tube with another one would make a serious difference soundwise. Therefore, any upgrade or improvement must start with this stage. Other stages, drivers and output which are RCA 12AT7 and Sovtek 6550 in the amp could be (or must be) just follow ups according to the result of the first upgrade, if necessary.
Here are my suggestions below :
1) Tungsram 12AX7 preferably military stock with balanced sections. Why? Because this tube has an open, warm sound with a large body. The balanced sections property is another "must" since each section of this tube gives the gain for each channel. Here is a link to our web site for this tube >>>http://www.nostubestore.com/2010/04/...v8156b339.html
2) Optionally and with less importance, the RCA 12AT7 driver tubes (only if the stock ones are gray plate types) can be replaced by the black plate Raytheons or Siemens ECC81
3) It is too early to suggest any upgrade for the power tubes. After all or a part of the above done, it might be even unnecessary to do any.
The tubes will come to you tested for anode current draw, GM, gas, heater to cathode insulation, noise and microphonics and matched on the Amplitrex AT1000 computer tester with test scores labeled on boxes.
P.S. As electrons flaw between electrodes inside the tube improve and get stabilized slowly in time, tubes tend to sound better after use for sometime. However, this does not that much apply to the NOS tubes since they were hard tested up to their spec limits being operated 100 hours minimum during quality control process. This was especially important for military and industrial/telecom spec tubes which were intended for war or communication etc. The current production tubes are not subject to such quality control process and strict industrial standard liabilities. So, the end-user (costumer) practically makes the quality control."
After a few hours of listening all I can say is replacing the Sovtek 12AX7 has taken this baby up a whole new level. Much tighter punchy bass and natural sounding instruments.