Tube score

[schenr]

Gday all, today I've scored myself 22 tubes, mix of 12ax7 12at7 6v6s 5881s an el84, a 6l6 and a few which have the same pin setup as the 6l6 etc but have a shorter black base thingo (obviously I know what I'm talking about).
Anyway, I'm trying them out on my fender hrd and for now am only messing with the preamp tubes as Im not sure how to bias an amp properly yet.
So far I replaced the v1 and v2 groovetubes with jj 12ax7 and it really makes the clean sound richer and adds more bite. For me this is a step forward and am really digging the tone I'm getting from it.
 
I am wondering though, can I use the 5881s instead of the stock 6l6s? Obviously there would be a different voltage for it and I'd need to bias accordingly, but what sort of tonal differences would this make?
Also, these unknown tubes that look like a 6l6, they have a diamond with "otk 2, v 80" around it and "6n3c-e, 0580" on the other side of the tube. Can anyone hazard a guess as to what type of tubes they are?
Lastly, as you may be able to tell I'm not the most well informed about tubes, and I have a single ruby 6l6, and was wondering what I could use it for, because I'm pretty sure I have to use a matched pair for the power tubes, otherwise you can't bias it properly?

Any input would be awesome!
Cheers

[PhilKing]

They are 6N3C-E's and they are a 6L6 substitute, but should be biased like 5881's.  They are supposed to sound great, though I've never heard a set.

[HTH AMPS]

They are 6N3C-E's and they are a 6L6 substitute, but should be biased like 5881's.  They are supposed to sound great, though I've never heard a set.

These are the same valve as the old Sovtek 5881WGC that was used in just about every '90s-era amp.  They are amazingly robust, but sound like shite (imo) when overdriven - biasing them HOT is the best way forward.

[schenr]

I'll probably give them a miss then.. But I'm pretty keen to try out the jj6v6s in the hot rod.
I also gave a 12au7 a shot in v2 to try reduce the gain in the gain channel, thinking it would give me more control over the sound and give more versatility with using pedals (the clean channel only has one volume/drive control while the gain channel has drive and master), but it was just a bit noisy really.. Maybe a dodgy tube.