View Full Version : 6L6 vs. 7581 swap out...
I have a pair of matched Phillips 7581 tubes that I want to try out in a 6L6 50 watt amp. Is there any potential harm that can occur to the amp if it's not biased? I'm not an amp tech by any means, so keep it simple, o.k.? :)
Thanks,
S.
VaughnC
05-11-2003, 09:40 PM
It's unlikely that you will damage the amp but, if the tubes are underbiased, they could overheat and be permanently damaged themselves.
Thanks Vaughn...I think I will have a friend of mine do the biasing tonite with the new tubes.
BTW....any idea on what differences are between the 7581 and 6L6?
S.
j
Mark Kane
05-12-2003, 07:45 AM
Originally posted by TNJ
Thanks Vaughn...I think I will have a friend of mine do the biasing tonite with the new tubes.
BTW....any idea on what differences are between the 7581 and 6L6?
S.
j
They are loud, clear and IMO colder sounding. Probably fine for a preamp distortion amp.
Thanks Mark!
I'll try them out tonite and report back.
S.
j
Jim Collins
05-12-2003, 10:32 AM
Originally posted by Mark Kane
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.
Well,
That tears it...those tubes are going in tonite.
Thanks for the extra input.
S.
j
Just talked to one of the guys at Two Rock...and he said that the 7581's are actually preferred over the 6L6's by some for these amps...although he liked the GE over the Phillips 7581...he did say that it was really personal taste, but to expect the same sweet tones with the Phillips as with the prior 6L6's.
S.
j
VaughnC
05-12-2003, 11:22 AM
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.
I took the TR CR to my amp tech's place of biz last nite, and took along my PRS Custom 24, and my Mesa 112 M/C 90 cab. I also learned how to bias my amp...very simple procedure with the TR, you dont have to pull the chassis or anything of the sort.
We first tried the 7581's at .050 v. Let it sit for about 10 min. , and rechecked the voltage...no drift whatsoever. I plugged in the PRS, and began playing clean...nice and chimey with that mid presence that I really love. The cleans werent quite what I was looking for, a little 'plain jane' is all I can say to describe it...not as much feel or 3D projection as I remembered with the JJ 6L6's. I remembered that one of the guys at TR recommended .055v instead of .050v...so, right befoe shutting down, I had Jeff change it to .055. Let it sit for a minute, remeasured, and plugged in. Wow! What a difference...the punch and warmth/definition all came thundering back. Dumble overdrive city, as well. I definitely had the Larry Carlton 'Last Nite' tones!
Amazing what the bias reading can do to your tone!
The real test will be this friday, when I take the CR (with my 212 G1265 cab) to an outdoor club gig with the rock band.
So far, though, the tone has returned! My friend/tech Jeff was mightily impressed with both the tones and the worksmanship on this amp. He also said that these tube should last for thousand's of hours. I have another pair of JJ 6L6's coming, and am also thinking of getting a couple of RCA Blackplate 6L6's too...now that I know how to bias the amp, it's time to play a bit!
:cool:
S.
j
veldt666
05-14-2003, 04:07 PM
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.
Latif
05-15-2003, 01:02 PM
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
Latif,
Yes, there is an external test point (+) close to the bias pot. The ground is usually one of the 1/4" jacks on the back of the amp. Biasing can be done without dropping the chassis on my Custom w/ Reverb.
Very nice feature...
S.
j
Blue Strat
05-27-2003, 06:41 AM
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.
guitarpedaladdict
03-22-2011, 02:32 PM
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.
scottl
03-22-2011, 02:39 PM
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.
Blue Strat
03-22-2011, 03:25 PM
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.
scottl
03-22-2011, 03:42 PM
Yep. They often recommend 55ma for the pair. I always preferred more like 65-75 a pair. Especially with 7581 tubes!
They're measuring both at the same time? If so, definitely try .060 or even .070.
Blue Strat
03-22-2011, 03:50 PM
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! :D
scottl
03-22-2011, 03:53 PM
Here Mike. In the manual too.
I remembered that one of the guys at TR recommended .055v instead of .050v...so, right befoe shutting down, I had Jeff change it to .055. Let it sit for a minute, remeasured, and plugged in. Wow! What a difference...the punch and warmth/definition all came thundering back. Dumble overdrive city, as well. I definitely had the Larry Carlton 'Last Nite' tones!
Amazing what the bias reading can do to your tone!
S.
j
guitarpedaladdict
03-22-2011, 11:01 PM
I was thinking the bias would go up a bit w the 7581 being 35 vs 30 watts - had a really nice pair of these a while back but stupidly sold them with an amp.
Blue Strat
03-23-2011, 06:30 AM
I was thinking the bias would go up a bit w the 7581 being 35 vs 30 watts - had a really nice pair of these a while back but stupidly sold them with an amp.
They have the same range as 6L6GCs...it's about 25mA wide like all other power tubes.
guitarpedaladdict
03-23-2011, 10:24 AM
Thanks mike!
I have a feeling that people who find these 'cold' or sterile are not biasing them to anywhere close to their potential. I use the Philips in every 6L6 amp I have, and I have quite a number of pairs of these. I bias them w/ the generic '70%' rule but at a full 35 watts, and believe me, it makes a BIG difference vs. biasing them colder. In fact, I notice much more of a difference in bias adjustments w/ these than with regular GC's. Biased warmer, to my ear they sound more like a great KT66 than a 6L6, jmho.
guitarpedaladdict
03-23-2011, 10:12 PM
I'm wondering if anyone might be able to help me with a bias question - I have one of the meters with the plug adaptor that Eurotubes sells - when I use that to bias on my Two Rock Jet Sig it reads the individual tubes right about 28 ma - when I use the bias point on the chasis - I get 20 ma? I thought the chasis point should give me 2x the single tube reading - any thoughts?
I'm wondering if anyone might be able to help me with a bias question - I have one of the meters with the plug adaptor that Eurotubes sells - when I use that to bias on my Two Rock Jet Sig it reads the individual tubes right about 28 ma - when I use the bias point on the chasis - I get 20 ma? I thought the chasis point should give me 2x the single tube reading - any thoughts?
Well I have the eurotubes bias probe and it reads in MILLIAMPS. I would bet the Two Rock you should be reading in MILLIVOLTS not miilamps. I may be wrong though since I don't own a Two Rock. I'm betting your reading across a 1 ohm resistor so you should have your meter set to read volts, not amps.
guitarpedaladdict
03-23-2011, 11:58 PM
Good call - looked it up volts indeed
guitarpedaladdict
03-24-2011, 09:13 PM
Sure enough - DCV gave me 2x the DCA reading on one tube. As suggested, I also raised the bias from 55'ish to 61'ish (was cooking my fingers on the tubes trying to get to the bias point) and really felt it made the amp open up a bit.
I have done tube swaps and biasing on a lot of amps I have owned and none of them were as responsive to changes as the TR has been. NOS tubes make an already good sounding amp sound outstanding, they also reveal the shortcoming of poorly made tubes. Cool stuff, can't wait to put the 7581a's in, should be here some time next week.
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