upgrade tube for SF line 2

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.