Ok so who the heck makes a good 6L6 anymore?

[JoeM]

What do you consider "cold bias"

[Steve Conner]

For me, normal bias for a EL34 or 6L6 guitar amp is about 30 to 40mA per tube. Those correspond to about 65% of the rated plate dissipation.

Anything much less than that, like 20 or 15, is "cold". 25% dissipation is about 15mA.

Some cathode biased designs with low B+ voltage can run a lot hotter than 40mA.

[Enzo]

I don't have a specific number, but a stock PV 5150 I expect to show something between maybe 11ma and 20ma. With a B+ in the area of 485v. I think that is pretty cool bias.

[bob p]

I agree in the case of a Mesa, the cold bias is intentional and part of the sound. The whole amp was tuned as a package to sound the way they wanted. If the tone stays consistent between bedroom level and gig level, that's because it's a well-designed package of a master volume amp, not simply because it's biased cold.

agreed. in this case cold-biasing is part of the solution that allows the master volume to work the way you'd want it to work. my point was to say that cold-biasing isn't as stupid as people like to make it out to be. in some cases, cold-biasing can be used to make an amp sound consistent when played loud or played soft.

you do realize, Steve, that saying on this forum that Mesa makes a "well-designed package" puts you in the minority. In fact, when you say that you're climbing out onto a tree limb to join me.

As an effort to bring us back in, I'm going to point out that Fender did the same thing in their high powered amps like the 6x6L6 Super Twin Reverb. It's biased cold enough that the amp doesn't sound like a hot guitar amp when it's putting out well over 100W. It maintains it's character at ear-crushing volume levels. That's precisely why pedal-steelers love the amp and guitarists tend to hate it.

[bob p]

Catching up on the thread, it looks like we might be able to coax Enzo out onto the limb as well, considering his comment on PV amps. If the PV amps are biased on the cool side, we know that PV is doing that to make the amps sound more consistent, and to decrease maintenance headaches that go with hot biasing.

[Enzo]

Peavey's stated philosophy is that adjustable bias in an amp tends to cause more trouble than it cures. That is why for years they made amps not adjustable, it cuts way down on amp failures due to misadjusted bias. They want the reputation for reliable roadable amps.

A guy adjusts his amp to the obligatory edge of meltdown, and when the amp burns up, he will think "Damn Peavey Crap" rather than "Gee, maybe I should have biased it more wisely." SO they don't give him that chance.

Consumers think bias is some sort of hyper-critical thing and feel lost without an adjustable bias, so in recent years, Peavey caved and added a bias adjustment. But they purposely limited its range, so that people could largely not be able to set it whacko. That is also why the factory recommended bias setting on their amps is -55 volts, not a current spec. And the test point shows bias voltage.


Peavey tube power amps have always been designed to be strong and clean, with the amp tone coming from the preamp. They have not designed them with bending the power amp in mind. That is another way of saying cool bias. You can take almost any set of 6L6 from the store, plug them in the sockets, and play. And whether that set of tubes winds up at 12ma or 22ma, it is still well within the safe range of operation. Contrast that with some Marshall or something where a set of tubes might bias out to 40ma, but the next set might bias out to 80ma if left unadjusted. It is that scenario Peavey wants to avoid.

[wizard333]

Peavey does bias the Classic 30 far colder than most other companies 4xEL84 amps. I personally like that. Although:

They want the reputation for reliable roadable amps.

Makes me laugh given how the Classic 30 board is constructed. They were asking for multiple, repetitive failures with that.

Edit: And RE Mesa amps and cold bias, it may or may not make them sound more consistent at bedroom to gig volumes, but that sound is highly compromised. I have not heard one that didn't benefit significantly on the clean channel from bringing that up, without hurting the gain channel. The clean channels are generally decently designed, but have a tendency to sound lifeless and sterile, in large part due to that bias issue. YMMV, I'm not a fan of stock Mesa tone in general, but I am a fan of their feature set and what the right mods can do for them. I've always thought Smith designed a great feature set into his amps, just that good tone wasn't one of those features. That said, it is much easier to mod a Mesa for Tone than it is to mod a 50W 2204 JMP head for 2 channels, footswitchable solo boost, a 5 band eq, etc. Also, I'm not a fan of the recent trend towards 3 different "class" configurations. More complicated that it's worth for the end user when it breaks, in terms of expense vs. tonal impact.

[bob p]

... That is also why the factory recommended bias setting on their amps is -55 volts, not a current spec. And the test point shows bias voltage.

On my Super Twin Reverb, the test point is for -60 volts. Great minds think alike?

[Enzo]

Makes me laugh given how the Classic 30 board is constructed. They were asking for multiple, repetitive failures with that.

Sure, but that is one design out of 40 years worth. Their stuff over the long run has been very roadable.

The C30 is very inconvenient to service, but the reliability issues of the design mainly revolve around those little jumpers snapping from flex.

The 5150 Combo is made the same way, and I can't think of any problems with them being unreliable. The issue with the C30 is that it flexes more than they thought it would, I am convinced. That allowed the notorious tube rattle, and causes the snapping jumpers.

[Bruce / Mission Amps]

WOW!! Snapping Jumpers is going to be the name of my new "old geezers" rock band!

[Enzo]

There y'go, glad we could help.



And now, here they are.... THE ALZHEIMERS!!!!!


Thank you ladies and gentlemen, we'd like to play a song for you that... Well, we'd like to, but we forgot it.



Geezer-rock, CATCH IT!!!

[Gtr_tech]

PV doesn't always fall into the cool bias camp. I've worked on several different models that had a poorly designed bias supply...as in not enough neg voltage available. That to me is a no-no. So if you don't want to add a doubler circuit, yer limited to what tubes you can use that will be happy given the available bias. Seems to me if they wanted to insure the amp would run any *currently available* output tubes, they would design the bias supply accordingly. Keep in mind, these are 90s and newer amps...they were not designed around old US tubes. Given the fact that new production tubes are all over the map as far as bias requirement, you'd think they'd take that into consideration and make some range available.