Eds bias on amps vs Standard "hot" biased amp

[erupturchops]

Quick question guys,

From what I've read, Ed had his internal bias knob maxed out. Without getting into too much detail regarding that matter, what are your bias setting that get in the ballpark of the VH 1 sound?

I know he biased the tubes hot, but using the standard percentages for biasing 50% - cold, 60% - avg., 70% - hot. If that sucker was dimed, he (from what I understand) was obviously way over that 70% marker. So if you guys are running "hot", how high are you going without having any issues with the rest of the amp? I know you are shortening tube life the hotter you go, I'm just looking for that line where I can bias the tubes hot but not damage the amp while getting close to that tone. I'm not looking to replace the tubes every 10 hours but if the tone is there I won't mind replacing tubes every so many months than try to extend their life a couple years. Let me know what you guys think... Thanks.

[dnatronic]

Here's a question that I have been thinking about that your post reminded me of. If Ed was biasing his tubes to the maximum idle current at 100%, that means the bias voltage is at a minimum (absolute value) for the bias voltage range. That would mean that when Ed cranked the volume on his plexi, he would possibly be driving the grid net positive for the peaks of the voltage swing (when the guitar signal's amplitude at the output of the phase inverter exceeded the magnitude of the bias voltage).

For example, say the bias voltage was set to - 45 V, and the peak output of the phase inverter is + 50 V or so, that means the grid would be driven positive by 5 V. I need to research this some more, but I think at that point the tube is acting like a diode for that positive swing and clipping the peaks of the output waveform like giant power-tube based distortion pedal. If what Dave Friedman says is correct about how Ed biased his amp (and I totally believe he is), this may be another key piece of the brown sound that I haven't heard anyone talk about on this forum. There may be other effects going on under these conditions as well that I'm going to look into when I get more time. If this is indeed what is happening, this would also explain why Ed was using 6CA7 tubes instead of EL34s because 6CA7s were more robustly constructed and could better handle the 100% bias current operation and also driving the grid positive with the volume set to max.

Can we confirm that this is how Ed was running his amp i.e., so the the grid would be driven positive by the guitar signal?

[Robocop101985]

Here's a question that I have been thinking about that your post reminded me of. If Ed was biasing his tubes to the maximum idle current at 100%, that means the bias voltage is at a minimum (absolute value) for the bias voltage range. That would mean that when Ed cranked the volume on his plexi, he would possibly be driving the grid net positive for the peaks of the voltage swing (when the guitar signal's amplitude at the output of the phase inverter exceeded the magnitude of the bias voltage).

For example, say the bias voltage was set to - 45 V, and the peak output of the phase inverter is + 50 V or so, that means the grid would be driven positive by 5 V. I need to research this some more, but I think at that point the tube is acting like a diode for that positive swing and clipping the peaks of the output waveform like giant power-tube based distortion pedal. If what Dave Friedman says is correct about how Ed biased his amp (and I totally believe he is), this may be another key piece of the brown sound that I haven't heard anyone talk about on this forum. There may be other effects going on under these conditions as well that I'm going to look into when I get more time. If this is indeed what is happening, this would also explain why Ed was using 6CA7 tubes instead of EL34s because 6CA7s were more robustly constructed and could better handle the 100% bias current operation and also driving the grid positive with the volume set to max.

Can we confirm that this is how Ed was running his amp i.e., so the the grid would be driven positive by the guitar signal?

I appreciate the response and grasp somewhat of what you are saying... But when it comes to the technical aspect of the amp world I need the dummies version... Anyway you might be able to dumb that down for me

[Carbia]

Don't pay so much attention to the fact that the bias pot is dimed.

Different tubes works different, and 6CA7 change a lot the bias adjust.

Every time I wanted to try 6CA7's in my amp I had to change some resistors to setup the bias in the proper range.

Even with EL34's ... Yesterday I was with a friend and we tried 2 sets of tubes. One Shughuang quad and a JJ quad.
Changing nothing on the amp, the chinese ones measured 28mA and JJ's 35mA...

In my amp, a 71 Super Lead, I have the bias trimmer around 90% to make an average bias setting.

[guitar007]

I agree. I've never had to do anything unorthodox to my bias to get into the EVH ball park. Ed may have simply misunderstood a tech explaining bias adjustments and a new myth was born. If your not in the ballpark to begin with...bias adjustments won't get you there.

[dnatronic]

I think folks are missing the point.

Conventional wisdom says to bias your tubes to 70% based on the idle current, or lower, maybe 50-60%. The original question posted by erupturchops was what happens when you bias your amp to 100% like Ed did.

My post stated that when you bias your amp to 100% like Ed did, you will more easily drive the grid of the power tubes positive when you crank your volume up to 10 than if your bias is only at 70%. This is because when the bias is set at 100%, the bias voltage is at its minimum value. When that happens, if your tubes can handle it, then the power tubes will clip the signal just like a distortion pedal does. The difference is, you're using two (or four) power tubes in your amp to clip the signal rather than using two diodes in a distortion pedal. This effect won't happen in your amp at lower volumes because at lower volumes, the grid of the power tube is at a negative voltage (because tubes are biased by putting a negative voltage on the grid), and the signal in the preamp won't be big enough to overcome this negative voltage at lower volumes.

In other words, think of your power amp as a big distortion pedal. If you crank the bias in your power amp to 100%, then you get more distortion out of your distortion pedal. Nobody ever talks about clipping of the power tubes as a component to Ed's sound. Most discussion has been around the fat cap or the variac, or Ed's hands.

[guitar007]

I didn't miss the point. I just feel the theory is wrong. You don't need to go to extremes with biasing too hot or cold to get that tone.

[dnatronic]

I didn't miss the point. I just feel the theory is wrong. You don't need to go to extremes with biasing too hot or cold to get that tone.

The whole point of this post is "Ed's bias on amps vs Standard "hot" biased amp" - that's the name of this thread. Dave Friedman said Ed maxed out the bias on his amp to 100%. Are you saying Dave Friedman is wrong?

[TWANGGG]

Here are some quotes with what Dave has said regarding how Ed's amp was biased:

RACKSYSTEMS wrote:
...Very important you also have to bias the amp to like around 80ma at normal wall voltage and then drop the amp to 90volts with a variac.

RACKSYSTEMS wrote:
...Variac at 90 biased at 50 to 52ma.

RACKSYSTEMS wrote:
Biased to 50 ma while the variac was at 90 volt I believe it was around 354 v on the screens. Now I am not looking at the paper with the specs so this is not exact but close.. The heaters were around 5 volts with the variac at 90.

RACKSYSTEMS wrote:
...also variac down and turn the bias pot all the way up with no thought about bias. Dave Friedman

[erupturchops]

Guys,

Some great information is coming in here and I appreciate it all. Thanks TWANG for giving me some quotes from Friendman, I've seen some of them but not all the ones you've posted.

So basically, here's what I'm gathering. Ed has his tubes biased to 100%, so if my plate voltage is 418 (I've biased my tubes with a variac on 110v... didn't feel like switching out the resistor) I would take that 100% rating for the formula....

100% x 25 watts(JJ 6CA7s) = 25(obviously) then...
25/418(plate voltage) = 59.8....60ma (rounded)

Replacing the 100% for 70% with the standard hot biasing....

Essentially here's what I'm getting at...Ed was replacing tubes left and right according to rumor. So if that rumor is true, I don't want to be replacing every 10 hours. So has anyone experienced a higher "max safe" hot biasing rating, that typically wouldn't destroy tubes so quickly. Thinking like an 80% even maybe a 90% rating that delivers that tone.... Again thanks for all the input guys....

[Tazin]

If you do the math based on the data Friedman posted you'd see that Ed's amp is only biased at 72% which isn't really different from the 'typical' 70% a lot of people use.

[dnatronic]

If you do the math based on the data Friedman posted you'd see that Ed's amp is only biased at 72% which isn't really different from the 'typical' 70% a lot of people use.

You're right on there. I just did a quick calculation and came up with 73.5% power dissipation at idle when the variac is dropped to 90 volts vs full wall voltage (say 120 volts) when the bias is maxed out (using Dave Friedman's 50 ma). The "cool" thing about using a variac to drop the voltages in the amp is that you can crank the bias to the maximum of the bias range, and the amp will only be running at about 70-75% power dissipation in the tubes. This means the tubes are running cooler at a maxed out bias than if you ran at full wall voltage. As a result, Ed could max out the bias on the tubes, and crank the volume to max, while not being so hard on the tubes thanks to the variac.

Now the next question is, when Ed ran his amp at a maxed out bias voltage with the variac at 90 volts, what was going on in the amp from a voltage standpoint, i.e., guitar signal voltages and bias voltages? Was there anything curious happening?

[guitar007]

I appreciate your passion dnatronic. I trust Dave at his word. Feel free to quote me as well.

I didn't miss the point. I just feel the theory is wrong. You don't need to go to extremes with biasing too hot or cold to get that tone.

The whole point of this post is "Ed's bias on amps vs Standard "hot" biased amp" - that's the name of this thread. Dave Friedman said Ed maxed out the bias on his amp to 100%. Are you saying Dave Friedman is wrong?

[dnatronic]

I appreciate your passion dnatronic. I trust Dave at his word. Feel free to quote me as well.

I didn't miss the point. I just feel the theory is wrong. You don't need to go to extremes with biasing too hot or cold to get that tone.

The whole point of this post is "Ed's bias on amps vs Standard "hot" biased amp" - that's the name of this thread. Dave Friedman said Ed maxed out the bias on his amp to 100%. Are you saying Dave Friedman is wrong?

I sure will. Okay, so if Dave F. said Ed's bias was maxed out and the line voltage was dropped to 90 V with the variac, do you have any thoughts on what was going on in Ed's amp from a signal/voltage perspective with the variac at 90 volts and the bias maxed out? Were the grids of Ed's power tubes being driven positive at maximum signal levels when Ed was using the variac under these conditions? This is what I'm passionate about.

[guitar007]

Try it out and let us know if it works. I hope it does.