Bias Vh4

[animusofabbas]

Hey guy i play detuned metal tuned to drop b. Looking for a proper bias setting for a set of

JJel34ls ANy suggestions? Im not to worried about clean more dirty sound of chan 3 and 4?

thanks

 

[Duolos]

Using bias to get tone is nonsense. That is what the various channels are for in that amp

65mA is where I bias my amps. That range is safe and makes sense .

 

[MARK2C]

In my experience, 60mA may allow for a bit more focused tone. Bias is like the accelerator on a car. The higher you bias,
the less pedal you will have for full speed. Under load, the bias goes up anyway so it's best to leave some head room. Down tuning may put some extra pressure on your power amp to respond. I find 65mA a bit to squishy with 8 strings and D tuning. Although biasing an amp for tone may be a misnomer, biasing for proper operation and allowing the power amp to produce pleasing harmonics is not. 65mA for the VH4 to my ears produces a warmer tone across the board, but there is an audible difference with different bias settings. You just have to set it, wait for the bias to stabilize and listen. I let my amps sit for at least an hour after the first test then recheck the bias and listen again. In my opinion, VH4's get a bit warmer and smoother after they heat up for 30 minutes or so. The real issue is finding tubes that don't have such a high variance in natural plate current.
Some are born cool, even tempered and hot. Each having an effect on how much negative voltage is needed to get them at 60-70% Max Plate Dissipation. Some may not hit 50mA with the bias pot maxed and some may hit 75mA with the pot set to zero. It's best to always ask for a tube with a natural plate current in the mid range of the spectrum. Many tube dealers will sell you anything they want to rid themselves of unusable tubes that are too hot and will not work. Once they explode, it usually your problem. Whether people think there is a tonal or headroom difference between tubes with high, medium and low natural plate currents is up to them. It's a highly subjective topic.

 

[Peter Diezel]

In the VH4 You are measuring single tubes.

I would adjust 25 to 30 mA for the JJ´s.

The Herbert and Einstein have adjustment for
pairs, therefore it´s about 65 mA for common use.

For the KT88 or 6550 I adjust 50mA (100mA a pair).

For class AB power amps please multiplicate the maximum
power of the tube by 0,6 to 0,7 and devide it by
the anode voltage.

For example a EL34 is rated to 25 watts:

25 x 0,7 = 17,5 / 470 volt = 37 mA

6550 SED (42 watts

42 x 0,7 = 29,4 / 470 volt = 62 mA

A lot of manufactures like 0,5 to 0,6 multiplication
to save the tubes for longer life.

Class A amps are running with a minimum of 90%
of maximum tube wattage.

 

[Wizard of Ozz]

In the VH4 You are measuring single tubes.

I would adjust 25 to 30 mA for the JJ´s.

The Herbert and Einstein have adjustment for
pairs, therefore it´s about 65 mA for common use.

For the KT88 or 6550 I adjust 50mA (100mA a pair).

For class AB power amps please multiplicate the maximum
power of the tube by 0,6 to 0,7 and devide it by
the anode voltage.

For example a EL34 is rated to 25 watts:

25 x 0,7 = 17,5 / 470 volt = 37 mA

6550 SED (42 watts

42 x 0,7 = 29,4 / 470 volt = 62 mA

A lot of manufactures like 0,5 to 0,6 multiplication
to save the tubes for longer life.

Class A amps are running with a minimum of 90%
of maximum tube wattage.

I also bias all of my amps to 70% of max plate dissapation (depending on the tubes in question).

 

[ajharris1215]

In the VH4 You are measuring single tubes.

I would adjust 25 to 30 mA for the JJ´s.

The Herbert and Einstein have adjustment for
pairs, therefore it´s about 65 mA for common use.

For the KT88 or 6550 I adjust 50mA (100mA a pair).

For class AB power amps please multiplicate the maximum
power of the tube by 0,6 to 0,7 and devide it by
the anode voltage.

For example a EL34 is rated to 25 watts:

25 x 0,7 = 17,5 / 470 volt = 37 mA

6550 SED (42 watts

42 x 0,7 = 29,4 / 470 volt = 62 mA

A lot of manufactures like 0,5 to 0,6 multiplication
to save the tubes for longer life.

Class A amps are running with a minimum of 90%
of maximum tube wattage.

i thought that when using the shunt method with the vh4 you're measuring pairs. so for el34s, we would bias between 60 and 70ma. this was described in the biasing tutorial on the diezel site - http://diezel.typo3.inpublica.de/tech-corner.3.0.html

am i correct?

 

[MARK2C]

Yes. With a bias probe it would be half of the pair or 30/35mA per tube.

 

[Peter Diezel]

The shunt method is different. You will miss
the screen grid current.

But no concerns, it´s good enough.

 

[duesentrieb]

The shunt method is different. You will miss
the screen grid current.

But no concerns, it´s good enough.

. . . and you're measuring a pair.

 

[Peter Diezel]

............... Amen ................

 

[duesentrieb]

Ich wollte Dich gestern schon "korrigieren", hab mich aber nicht getraut, da Donnerstag war.
Heute, so kurz vorm Wochenende, dachte ich es ist ok

 

[Peter Diezel]

Wenn ich schon mal einen geistigen Erguss habe ...........

 

[Dexter Jackson]

LOL das?