Allow me to disagree. The plate voltage is always measured between the Plate and the cathode; for an EL84, the red probe on the plate (pin 7) and the black probe on the cathode (pin 3) The test points are connected to Resistor R62 which has a value of 1 ohm With the multimeter set to 200mv, you can read the voltage drop across R62 A reading of 24MV (millivolt) gives a current of 24ma (milliamp) according to the ohm law: I (current) = E (voltage)/R(resistance) Schematic is available here: music-electronics-forum.com/...1&d=1551673832

i still remember doing this last year, the factory bias was 29.5ma. i change the power tubes to groove tubes and keep the stock ruby as spare. then i bias it to 33.1ma. the amp becomes a bit louder with more low mids and low end. it start to hv power amp distortion when volume @ 6.5. but for recording metal stuff i just keep it around 5-6, coz if not there will be too much compression on the transient. tq for your very good video :) i hope you guys ironheart users will find this very useful. cheers

William, thank you so much, your video was exactly the help I needed. Well done!

Thanks very much for the video and info!

Hi William. Thanks for the video! Looking at the dial on your multimeter it seems the setting when you are measuring the bias on pins 1 & 4 is actually set to 2000mV and not 200mA (looking at the small arrow on the left end of the dial at 4:03). Can you confirm the setting for us? I'm seeing the same type of results that Jarod Merle is seeing. Also, even though we're not talking about a lot of voltage or current across pins 1 & 4 at HD4 having the meter configured for an Amps measurement if we are actually talking about measuring voltage is creating a direct short across pins 1 & 4 in order to measure the current between the two pins. So I'd like to be sure of the actual configuration for the meter. Thanks again for posting this video.

@WilliamTanaka Which terminals from the bias test point are you using? There appears to be 4 pins and it looks like you used the outer ones (left and right) but can't tell because the camera gets blurry. Also, when using the online bias calculator under the EL84 chart, how did you know how did you know which line to use which is dependent on volts. You don't mention what you chose. I appreciate your advice. Thanks bro!

Hi William, would you mind measuring the mains transformer voltages?

Is it necessary to do any adjustments if I am changing 1 preamp tube? I am changing an old Ruby 12ax7 for a new Sovtek 12ax7

Hello, can you help me, I have the same amplifier, the problem is that only the 1W input works when I connect it to the 15W input there is no sound, I have disassembled it and where the cable enters everything looks normal.

Hi , thanks for the video ,on the beginning I was getting a 0,3 mA, then I realize that I had to plug the instrument cable to 15watt.

Hi great tutorial. I was wondering which pins in the bias test point are you touching with the probes? The video goes out of focus and it's hard to tell. Looks like the first and fourth pins?

@WilliamTanaka

8 жыл бұрын

+Antony Hills Thanks, and yes it is the first and the fourth pin (counted left to right).

@tonyhills2112

8 жыл бұрын

+WilliamTanaka Awesome, thanks!

@MBSGAMES_

7 жыл бұрын

WilliamTanaka. there are only four pins right?

@WilliamTanaka

7 жыл бұрын

Only four, the piece has some open on the lateral. If I'm not mistaken the piece for the ironheart 6l6 version is only two, maybe they used same in some irt studio since I already saw two versions of the irt studio.

@madbaker76

6 жыл бұрын

Great video! When measuring the bias, what setting on multimeter you set up? it is A - measuring the current is it correct?

Very Nice video, thank you very much! I had a couple of questions, changing the bias from Cool to Hot what will be the ending sound effect ? My IRT i think has too much mids, and lacks highs, it has stock tubes.. What change would be more preferable ? Also, i have a spare tung-sol ecc803s gold pin and i am thinking of trying it in V1 or in another position. Will a re-biasing be needed ? how do you think it will affect the overall sound ? Thank you!

@WilliamTanaka

6 жыл бұрын

From Cool to hot it will tight the bottom end and it will have a more defined sound. But if you gig or play loud , like noon volume above, it will just fuzz the sound on hot when you reach around 7 and the will be way less headroom on the clean channel; in this case stick with the average. The amp has a lot of highs for a medium / high gain amp; it will not reach the level of brightness of a bassman or something. I think It's worth research some speakers / cabinet that better mix with the amp and the sound that you are looking for.

Do the bias pins show the bis value for one valve or for both? I’m not sure. If it’s one valve only being measured it should be 33mV, if the test points show the value for both it should be 66mV. What is right guys? Would be great to know!

@matele901

4 жыл бұрын

It's only for one valve. I have posted a link above for the schematic

Hi, I have a question. Does the valve versioning matters? For example in Laney irt 60 212 manual recommended V1 12ax7 and V10-11 6L6. I have check in tubestore site but it does not indicate V1 or V10-12 on their tubes. Does it matter? Can you explain what the versioning means? Thanks

@WilliamTanaka

8 жыл бұрын

These V's are just tube positions and they are numbered relative to the particular amp circuit; so the tube itself cannot have indicatives for the v's cause amps have different circuits. Each one of these positions perform a different task, you may want a specific kind of tube for each task even if all they are under 12ax7 for example. I advise you to research about the circuit to know what does any v's do in the amp, the kind of tube you may want put in these slots,... it's not only affect how the amp works but you can fine tune it to your own taste; It's a lot of things to read and to choose but it will worth in the end.

@danelectr

8 жыл бұрын

but any V should work right?

@WilliamTanaka

8 жыл бұрын

+danelectr if you mean following the manual, yes it will work ,just respect the kind of tube described there.

@wadehickam2458

7 жыл бұрын

After checking the plate value, do I unplug the alligator clip and just use two leads on the bias check point? And did you check the two points with one hand? I also want to switch from Ruby's to JJs

@WilliamTanaka

7 жыл бұрын

Yes, if you are using one multimeter you had to check plate separately of the bias. I suggest you to use the a small hook test lead to check the bias; I could perform with the regular lead cause I trust on my chopstick skills lol The difference between shuguang and JJ are not that huge, in any context they sound pretty good actually. Ruby just take the tubes test and match and then re brand.

CAn you plz give us the link to the bias calkulator

@WilliamTanaka

7 жыл бұрын

The one I used www.tedweber.com/webervst/tubes1/calcbias.htm there others on google that will do the same

@konradcholewa5317

7 жыл бұрын

thx man

First off, thanks for the great video. Second, I recently purchased a secondhand IRT Studio and decided to check the bias per your direction. Upon first testing, I found the plate voltage to be around 283 V, and the bias current at only around 9.2 mA. Even turning the bias adjustment pot to the max only got the current to around 24 mA, and dropped the plate voltage to about 225 V. Do you have any recommendations or thoughts on why this might be or what I could do to change it? At 225 V, the 60% bias point should be 32 mA.

@WilliamTanaka

6 жыл бұрын

Check the range of the multimeter and if it's really in mA, or even use other multimeter. Otherwise looks for a tech cause it could be a simple bad tube to something even worse; it's odd that you need to turn it to max and seems something is not right.

@jarodmerle

6 жыл бұрын

Thanks for the reply. Maybe it is the meter. I will have to pick up another to try and make sure. The amp works and sounds great as far as I can tell, but this is strange.

@jarodmerle

6 жыл бұрын

For what it is worth, I reached out to Laney customer service about this, and they recommend the following method for biasing the power tubes: "The method we use it to set the bias to achieve 25mV across the test point HD4. Adjust TR1 so you achieve 25mV across pins 1+3 and 1+4 This works out to about 25mA which is around 60%. On D21 the voltage should be around -11V." I followed these guidelines and reached a much more reasonable setting on the bias pot. Thanks for your help nonetheless.

On 4.02 you are saying u should set your meter on 200mA. Is your knob not showing the right setting (sorry new to using multimeter)

@WilliamTanaka

7 жыл бұрын

You have to select a tolerable range. It will fit 200ma, I used 2000ma on the video.

@MBSGAMES_

7 жыл бұрын

Thanx

@panicoguitars4614

7 жыл бұрын

On 4.02 you are saying u should set your meter on 2000mV not mA ? mV is the right fit?

@WilliamTanaka

7 жыл бұрын

Reading across 1ohm resistor 1ma becomes 1mv. Which one is more precise for bias, well, the answer goes beyond me.

When would you need to do this? I wanted to replace the tubes in my IRT-Studio. Would this mean I have to BIAS it as well or just replace the tubes?

@matele901

4 жыл бұрын

Install the new tubes, it's better to buy a matched pair. - Set the bias trim pot to its minimum and switch the amp on and wait 20 minutes before making any measurements/adjustments. - Follow the instructions

Cara você é brasileiro?

@bastianmaoro8278

6 жыл бұрын

O sotaque é típico... Hehe.

With a too hot bias, you can get a very muddy amp. To me 33 mA is too hot for EL84 power tubes. Your amp won't sound better because you're going crazy!