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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?
waip7
garfish
1,840 posts
 
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
david_berry
211 posts
 
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.

Craig,

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

David
garfish
1,840 posts
 
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
lafish
151 posts
 
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.
kana813
956 posts
 
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.
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