Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers T' started by rreiser, Nov 6, 2009.
What ma per tube would you recommend for an amp that uses 4 6V6 tubes ?
Hi Jade , Would that be for cathode bias ? thanks
Its a Bluefire custom amp built in Milwaukee . I can run it fixed or cathode and I just wanted to see what people have found working with 6V6s. I put in a 5AS4 rectifier tube so the voltages are lower than what Dave worked with when he set up the amp. Love the amp and I will check the plate so I can change the bias resistors if needed to run right below 9 watts. Thanks
9 watts? What crap.I run 6V6's in Deluxe Reverbs up to 30ma at 420v.
A cathode biased amp can easily handle 90% or more plate dissipation.
You have to realize that cathode biased amps run the same current at full tilt as they do at idle,and a fixed bias amp varies the current according to what the preamp sends it for signal.
Now the vast majority of people won't run a Deluxe reverb at '10' so biasing too cold can suck tone at lower volumes.For those who do run the amps at 10,then bias colder.
I use jj 6V6's and have never had one go down when biased hot.I'm talking about gigging amps.
There are many,many amps running 6v6's out there at 14 watts plate dissipation and they live.(cathode biased)
And lots of amps running 6V6's at 70 % plate dissipation with fixed bias.
I bias for tone and that doesn't necessarily mean 'hot' bias is best,it just means you can do it if it sounds better and not worry so much.
Quote:"That's YOUR amp. I'm not comfortable advising people to bias their amps OVER 100% disipation like you just did, and pull that much current through a transformer that I'm not familliar with. While it might be fine with an old fender, we have no way of knowing what kind of transformer is in said amp, and how much abuse it will take. And IMO biasing a class AB amp up over 100% disipation is complete abuse."
Ok,I'm talking about performing amplifiers here,not MY amp.The vast majority of players do not crank a Deluxe Reverb amp,so biasing hot does not automatically kill tubes biased that hot.
And cathode biased amps DO NOT immediately become incendiary bombs when they are biased at 90% plus.And they also are NOT biased class A at 90%.
Case in pointr Z MaZ 18/Maz 38 amps are running happily at 14 watts plate dissipation.(EL84's which are almost the same as 6V6)
And furthermore,tube charts are DESIGN CENTER,not absolute gospel.How many guitar amps ever ran the tubes to be SAFE?
If I build an amp for a customer I bias it at no more than 70% with class AB fixed bias and cathode biased is never at 100%.
Now,when I get requests from customers who WANT hotter bias I do it with a warning.I have done several Deluxe Reverb amps for gigging players at 30ma and they have yet to hurt anything after four years of gigging,not bedroom playing and they never use above 5 on the volume dial.
You wanna play safe all the time?Go for it!
All I'm saying is biasing hot does not always reduce a set of tubes or an amp into a pile of rubish.And at the same time it doesn't always sound the best biased hot.
And NOS tubes,depending on what brand,can take LOTS of current.
Case in point:Original mullard EL34's biased at 46ma/550v in a Hiwatt came accross my bench.The owner wanted to try new production tubes and I had to build a new bias supply so they wouldn't burn down.The Mullards had been there for 35 years like that.
NOTHING is written in stone when it comes to tubes.
Yeah,lets have some beers and not debate it any more!
Jade don't start talking about Canada because then we will have to change the thread to "Hockey"
If you are "not" using JJ's then Jade is dead on, I run my 6v6's at 386v @ 27ma but I am using JJ's.