F1-x Suddenly started distorting.

[jazzyvee]

I took my larger rack system rehearsal on Sunday afternoon. It consists of DS-5, F1-x and SF-2 in the send/return loop and Crown Power amp to drive my Barefaced Big Baby II cab. Everything was fine nice clean powerful with superb definition.
This evening I plugged the same rig together and same bass as I have a gig Friday. Now the rig is distorting at all volumes.
Process of elimination. I plugged the DS-5 mono out directly into the power amp and that was nice loud and clean.
DS-5 into SF-2 in mono then the output into the power amp and again nice clean and loud.
DS-5 into the F1-x, full range out into the power amp and distorting at all levels and lack of volume.


I tried exercising all the jack sockets on the alembic units and tried the above checks again and all options were fine except when the F1-x is in the signal line.
Could it be something else like the valve? It has never been changed since I have had the F1-x and if so what is a good clean valve to look for. I doubt if the local music shops have anything other than standard stuff for bass and guitar amps.. 


I have another F1-x that I am going to try tomorrow after work and see if that is ok.
Any thoughts would be most welcome as it seems odd that it was fine during a 3 hour rehearsal.

[lbpesq]

If the second F-1X works, I’d swap its tube (12AX7) into the first F-1X and try it.  If it works correctly, you’ll know that you need a new tube.  If it still distorts, the problem is something other than the tube.

Bill, tgo

[jwright9]

Yeah, my bet is that it's the tube.

[David Houck]

Bill's suggestion - if the other F-1X is working fine, swap the tubes.

[gtrguy]

Either the F1X or the SF2 (can't remember which) or both have a set of contacts on the jack (output or input,  I don't remember) that can get dirty and cause distortion. A little cleaning with super fine sandpaper will usually cure it.

[jazzyvee]

I tried the second F1-x and that sound is great no problems there. I used it on my gig last night in the rack instead of the noisy one. Hopefully tomorrow I will have some time to swap the tubes and if it's duff then the search for a replacement tube will take place. Any suggestions for a really clean hifi good headroom valve,( if that is the correct terminology), i'd be grateful I don't want it to start breaking up before it's past the 12:00 o'Clock position on the input gain..

[David Houck]

Somewhere around here there's an old thread or two or three on various types of 12AX7s and their differences.

[jon_jackson]

http://club.alembic.com/index.php?topic=22299.msg225055#msg225055

gtrguy's test has one of the better sonic descriptions of tube to tube sound, although of used tubes.

[David Houck]

Thanks Jon!

[gtrguy]

I really do like new JJ 12AX7s and believe that Alembic knows what they are doing when they use them.