6L6 vs. 7581 swap out...

It's unlikely that you will damage the amp but, if the tubes are underbiased, they could overheat and be permanently damaged themselves.

 

They are loud, clear and IMO colder sounding. Probably fine for a preamp distortion amp.

 

I put a pair of these very tubes in my 6L6 Old Flame, replacing a pair of Svetlanas. I biased them properly, and the amp sounded better than ever. This amp is very much in the Fender blackface camp, much like a Vibrolux Reverb. They sounded so good that it depressed me when one of them shorted, and took out the heater element leads to that tube. I repaired the amp, and have been living with the old Svetlanas, since, but I'd really rather have the touch that the Phillips 7581 tubes added.

 

I have a couple of pairs of 7581's mainly for backups for my Komet and I think they sound pretty good. Bold & strong is how I would describe them....but in a marginal amp they might sound sterile. In my Komet they just sound bolder than most 6L6's....but my RCA 6L6 blackplates are sweeter sounding.

 

IMHO, Like it or not, no other 6L6 performs like a 7581. Having used them in my 50 watt combo's for years, I breifly dabbled with other types, (Ruby, GT, Sovtek, other NOS types such as WGB's, GE's, etc), each type having it's own "Signature" sound. Because my ear was accustomed to the 7581's headroom, some of these other tubes even made my amp sound like it was dying.

I took delivery of my first "Fuchs" mod recently, which came with the latest, (I think) "Sovtek" tubes, & I got used to the amp over a two month period, loving every minute of it. I then changed out the "Sovtek's, for a pair of 7581's, biased @ .30ma. Now I have a bolder strident clean sound which I love. Sadly, as you all know 7581's wont last forever, but then, neither will I, So I'll enjoy them while I can.

 

Jato,

Does the CR have external bias check points?. I've had to pull the chassis on my emerald and then it was easy but havn't checked my Custom as it keeps sounding so good as is. Havn't looked for external test points on it yet.

Latif

 

7581As are great tubes and SUPER durable. They're also the cleanest of all 6L6 types.

Most players like these though if you're looking for early power tube distortion, these may not cut it for you.

 

Great thread, I have two pairs of RCA blackplates (one in my amp right now), but really wanted to try out the 7581a to see if I could get a little more headroom out of my Jet Sig. Thanks TNJ for posting your experience. One thing you might want to try, if you haven't, put a 5751 in V1 on your TR - I really love what this did for mine.

 

Now up the bias to .060 and enjoy it even more!!! I never agreed with the super cold bias recommendatiosn of TR. No right or wrong. I'd try 30-35ma and see if you like it. My guess is you dig 32 (.064) or so.... Just a hunch.

 

They're measuring both at the same time? If so, definitely try .060 or even .070.

 

Yep. They often recommend 55ma for the pair. I always preferred more like 65-75 a pair. Especially with 7581 tubes!

 

Damn, THAT'S COLD!

 

Here Mike. In the manual too.