upgrade tube for SF line 2

I am new in tube amp, I just pickup a used SF line 2 a month ago. They use soviet 6922, manufacture @ 03/2000. I heard changing the tube will make a big different. Can anyone recommend some brand and model? I do some research and find siemens CCa is a of the best. however, it is hard to find and the price is high. Some body told me I can just change the two tubes in the back and leave the front four as is. that can save some money. Should I change all six to some good NOS tube (but not the best) or should I put all the money in the two that is in the back? If I change just two in the back. In the further will I get benefic by changing another four? One last question, how about bias? Do I need to re-bias them?
Kevin at Upscaleaudio.com is an excellent source of info and NOS tubes.
I tried several different NOS tubes in my Line 2SE including Siemens, Brimars, Valvos, Mullard and some others, but I prefer NOS Sovteks. At about $25. ea. they are not expensive so I put them in all 6 positions. The NOS Sovteks are micro-phonic and I used Herbie's Hal-O tube dampers to cure that. Otherwise, the NOS Sovteks are pretty neutral but dynamic, liquid, detailed, and with lush "body". I got them from Kevin at www.upscaleaudio.com Cheers. Craig
I also have the SF Line 2 preamp (SE version). My understanding with repect to tube replacement is that as LV2 and V2 are the two tubes that provide the most gain by far, it is most beneficial to replace those with the better (read more expensive) tubes. Some others (a minority in my research) have stated that the tubes to replace with better ones are in the LV1 and V1 position. No one has mentioned that LV3 and V3 need to have great tubes.
Personally, what I'm going to do is replace my Valvos when they expire with good Siemens (E88CC - 10000 hr)in the LV2 and V2 positions and have Jan Philips 6922 USA in the other 4 positions. I think this would give great sound at a reasonable replacement cost.


Are those NOS Sovteks from his "Special Stash" - I think that's what he calls it!

David; I don't know if my NOS Sovteks came from Kevin's "private stash", but he was surprised when I ordered 3 full sets and that I preferred them to some of the much more expensive "premium" tubes such as Amperex and Seimens. I guess the NOS Sovteks are just synergistic in my system, or fit my listening biases better than others. Cheers. Craig
the best matching tube for Sonic Frontiers is Sovtek. I have tried the upgraded tubes before.......good improvement in analytics, but lost in bass control......sound too bright.

you may check with the SF website for upgrade kit. SF provide Valvo 6922 for upgrade. Otherwise, Telefunken gold pin will be another alternative for you. I mean reasonably be found.

No need to adjust bias.
As Lafish points out, if you are using single eneded RCA outputs the bias trimpot position doesn't matter, but for XLR balanced outputs you should adjust the bias after replacing any of the tubes. The easiest way is as follows:

1. Disconnect cable from preamp to power amp.

2. With the preamp warmed up for 20 minutes, play a 1 kHz sine wave from a test CD or signal generator.

3. Use a voltmeter set to AC, and measure voltage from pin 1 to pin 2 on left channel XLR output.

4. Adjust volume on preamp so voltage output is approximately 1V.

5. Measure voltage from pin 1 to pin 3.

6. Adjust left phase balance pot until pin 1-2 voltage equals pin 1-3 voltage - check 1-2 after adjusting 1-3 and adjust again as necessary.

7. Repeat for right channel.

The bias tool that comes with SF Power series amps
is perfect for adjusting the pots, otherwise you'll need a long shank small blade screwdriver.
I just put new J-J 6922s in my SF Line2 preamp except one tube is an EH 6922, and now I get some low hz thump sounds in one channel. It is very low HZ - like a bass drum beat and only starts after i play for a few songs. Also, one channel plays allot louder than the other Any ideas?
Anyone still using a SF Line 2 preamp, or are they mostly dead now and thrown away?
The Line 2 tubes have to be matched sets. I believe that your symptoms point to unmatched tubes.
Sounds like your tubes are NOT matched properly or MPs in the wrong position. I had a Line 3SE+ and it only requires MPs.

FWIW, I found Philip Holland e88cc SQ worked best ... EH and Sovtek very hard sounding.
Thanks. Do all 6 tubes need to match or just match at each stage?
Okay, so now i took out the odd ball EH6922 and one of the JJs and put back in two of the stock tubes. Most of the problems went away. The channels play at the same volume and no more drum beats. But ,now its back to making wrestling sound in one channel's tweater, which i thought was due to a week tube. I know the speaker is okay, because I switched speaker cables from side to side. I put the stock tubes in the V3 posistion. Do you know if that is the least important stage? (I am only using the RCA input and outputs too).
What is an MP?
I think the Line 3 has more tubes than the Line 2.
The line 2 has 6 tubes total.
On the Line 3, the MPs are:

LV1 V2
LV2 V1 (6U8A)
LV3 V4
LV4 V3
LV5 V6
LV6 V5

The most important 6922 position is next to the 6U8As, LV1 V2 where most use their best MP. From my experience, the more you use, the better it sounds.

I'm not familiar with the Line 2 but my GUESS is
LV1 V1
LV2 V2
LV3 V3

You could always beam Chris Johnson an email to confirm.
There's been a lot discussed in these forums regarding the critical matched pair locations in the Line 2, if I remember correctly, the LV2-V2 set are the most critical followed by LV1-V1 and LV3-V3 being the least critical. Each pair of sockets (LV-V) must use matched tubes but all (6) pairs don't have to be matched or use the same brand of tubes, so you can experiment with different brands for each socket pair. I hope this helps.