Laney IronHeart

[Zorky]

Hi all,

I have a Laney Ironheart 60 and I not sure if I read and done this reading right.

I set my Meter to DCV and took the reading at 423 on one side and 424 on the other side of pin 3.

I ran the Weber bias calculator at the top of the page and it said it should be at 49.6mA When my current Bias is at 27.5 mA

I wanted to find out my exact Current in order to dial in my bias.

This amp also supports the El-34's with a switch.

What am I reading wrong to get the 70% dissipation?

[g1]

How did you come up with the 27.5mA measurement? What kind of power tubes are these, 6L6 ?

[Zorky]

How did you come up with the 27.5mA measurement? What kind of power tubes are these, 6L6 ?

Factory setting at 27.5. IronHeart IRT60H come with Ruby tubes. Ruby 6L6GCMSTR.

I measured the DCV off pin 3 on each side and it said 423 and 424 I then tried the Weber Calculator at the top of there page and it said 49.6mA that I know is not even close to being correct.
Everyone say's to get the correct measurements I need to read pin 3

What am I missing?

[g1]

Did you measure the 27.5mA yourself, or did you read that somewhere?
If you did not measure it yourself, that is what you are missing.
If you did measure it, where did you take the measurement?

[diydidi]

Go for 65% I would say.

[Zorky]

I use that things called a Bias Probe. I already know the factory setting but I am trying to figure out the plate voltage so I can get a solid point. I don't know why this has become a riddle?

[g1]

The plate voltage will change a bit whenever you adjust the bias. So you take your bias probe reading and multiply it by the plate voltage you measure after the bias adjustment.
ex. factory 27.5ma (.027A) multiplied by 423V gives 11.42. That is the idle dissipation in watts. The 6L6 is a 30W max. tube, so 11.42/30 equals .38 or 38%.
Now you will adjust the bias and the plate voltage will change. Then redo the calculation and adjust again if needed until you get the % dissipation you are looking for.

[Zorky]

The plate voltage will change a bit whenever you adjust the bias. So you take your bias probe reading and multiply it by the plate voltage you measure after the bias adjustment.
ex. factory 27.5ma (.027A) multiplied by 423V gives 11.42. That is the idle dissipation in watts. The 6L6 is a 30W max. tube, so 11.42/30 equals .38 or 38%.
Now you will adjust the bias and the plate voltage will change. Then redo the calculation and adjust again if needed until you get the % dissipation you are looking for.

Thank you very much.. This is what I needed to know. I don't know if anyone is familiar with the IronHearts but I'm sure they are along the same line as other tube amps.

[g1]

Sorry about the confusion. Let us know how it works out & sounds.

[DRH1958]

Here's another way to go about it. Decide if you want to bias it hot , middle or cold.. Generally, 50-60%=cold; 60-70%=mid; 70-80%= hot. This is just generally and it isn't the point here anyway. Let's say you want it at 70%. A 6L6GC is rated for 30 watts, so 70% of that is 21 watts. Now divide power by plate voltage, 21w/423v=.0496A, so 49.6mA. This is your idle current. I don"t know if Laney does this, but you can solder a 1 ohm, precision(5% or better) resistor in series with the cathode and just measure the volt drop across the resistor. Since it is 1 ohm, volt drop is the same as current according to Ohm's law. If you want 49.6mA, you should measure 49.6mV. G1 is correct, when you change bias, the plate voltage will change because the tube will be operating at a different level, so you will have to repeat this until it stabilizes, of changes very little. This method will work for all output tubes for fixed bias. %wattage/ plate voltage= bias current. Screen current can be ignored for this procedure.

[Zorky]

Sorry I been away for awhile. It makes sense that the Bias should be at 49.6mA or there about, but I moved my Bias up to 30.7 and sounds pretty good, yet I'm worried about pushing the tubes if I try to move it that far.

IN this pic I took the reading from the #3 pin just as you see this board.


In the Center of the two Power tubes is a small plastic Bias thing I guess for Laneys testing probe or such.

[g1]

Did you change power tubes, or is there some problem with the sound of the amp?
If those are the tubes it came with it, and the factory setting was 27mA, and sounded ok, that's where you should bias it. Laney knows better how these amps should be biased than Weber does. The Weber figures are numbers that "should" work in "most" applications, when you don't know what the factory setting is. The lowest setting you can use without making the amp sound bad will give you the longest tube life.
If it sounds ok at 30mA, and doesn't sound any better at 49, then setting it at 49 will just wear the tubes out faster.

[Zorky]

I guess it is all well, Laney did say 30mA is safe and so far the amp sounds pretty good at that setting so far. I was just looking at once and for all getting the plate voltage and doing the math to know what should be the correct setting.
Being it has that EL-34 option at a flip of the switch it is finding a center point that is good for both.

In short I think I will leave it where is it unless I change tubes.

Kudos.

Thank you,

[danelectro]

Hi,

I also own a Laney IRT60 212.

I recently talked to laney about Biasing this amp.

This might be of help. Here are the screenshots of our convo.

[g1]

Just to note that from this it is clear the factory suggests 42% idle dissipation. This is why I don't like the Weber calculator or the '70% rule' that is so often mentioned.