software

an EL34 or a 6L6? IIRC the EL34 does, meaning a 6L6 running in an amp biased for EL34 will burn up faster, and an EL34 running in a 6L6 amp will be running quot;coldquot;, right?

Or am I exactly the other way around?

*bump*

Im pretty sure your first statement was right. LOL if im wrong!

You are correct my German Jackson wielding devil music counterpart.

That's correct. 6L6's are usually around 32-33mA and EL-34's are anywhere between 36mA-40mA I think you need to change a resistor that effects the plate voltage to be able to swap between them, otherwise your bias pot won't have enough range.

That's what the switch in a Mesa Rec does......changes the resistance around the tube sockets to accomodate either tube type.

What about 6CA7? There is a number of 46 on the tube from the guy who biased the amp. Is this the ma?

Also you need to account for heater current when swapping between the two. EL34's draw more heater current (I believe 1.5A, but I'm not sure) than 6L6GC's, which draw .9A.

But yeah, EL34's bias hotter.

Don't know jack about EL34's but I have a couple of Fender Hotrods that take 6L6's and their overall functional range is about 60 to 75 millivolts, 67-68 being the sweet spot for my tastes.

yeah, since EL34's can handle more current they would run cold in a 6L6 amp. 6L6's would burn up in an el34 type amp if you dont throw the bias way down.


Originally Posted by ZhangliqunDon't know jack about EL34's but I have a couple of Fender Hotrods that take 6L6's and their overall functional range is about 60 to 75 millivolts, 67-68 being the sweet spot for my tastes.

That's the range for the two tubes combined. For one tube that'd be incredibly hot.


Originally Posted by Quencho092yeah, since EL34's can handle more current they would run cold in a 6L6 amp. 6L6's would burn up in an el34 type amp if you dont throw the bias way down.

It's not that they can handle more current; it's that they draw more current. EL34's would actually burn up a 6L6GC amp (the tubes themselves wouldn't) because they draw so much more heater current. Unless the 6L6GC amp has a very strong transformer, the added Ih would fry the OT. In most cases, the difference in Ih's between the tubes would mean an immediate burn, so the bias supply would need to be modded to get more where it's needed.

Bias, schmias. Idle bias current by itself means exactly jack.

The rule of thumb is that you don't want to bias power tubes at gt;70% of max plate dissipation. This isn't just a function of current but voltage as well. Thus, an amp with a 400V plate voltage can have much higher bias current than a 500V amp while adhering to the 70% rule.

What a lot of folks either don't know or ignore is that a lot of amps sound great at 60 or even 50% of max dissipation. Power tubes would last a lot longer if folks didn't run 'em so much hotter than tone would dictate. IMO, biasing an amp without listening is like setting up a guitar without fretting a string.


Originally Posted by alecleeWhat a lot of folks either don't know or ignore is that a lot of amps sound great at 60 or even 50% of max dissipation.

I have my amp set at the bottom side of the recommendation for biasing. I set it one ideal, but the tone was breaking up earlier than I wanted... So, I turned it down a bit while monitoring with the multi-meter until I got an ideal tone... This actually helped with the pedals I ran in front.. The tubes were running so quot;hotquot; they were distorting the distortion from my pedals.. giving them a quot;muddyquot; sound.... Of course, I had to learn this the hard way... The whole reason I was re-biasing, is because I had to install a new pair of tubes where one burned out! Keep in mind, the bias rating never exceeded the suggested range, they just burned quicker because it was in that 75% range!