Uber Ultra bias question

[glpg80]

They likely aren’t truely independent. Everyone seemingly designs bias circuits wrong in parallel.

When they aren’t truely independent, that means that bias adjustments on one pair will affect the bias of the other pair in the opposite manner. Up on one causes down on the other and vice versa.

You have to adjust them incrementally back and forth together and you have to wait a few seconds for settling. You also should be monitoring B+ as you do it because B+ will change as you bias.

 

[Emerald]

They likely aren’t truely independent. Everyone seemingly designs bias circuits wrong in parallel.

When they aren’t truely independent, that means that bias adjustments on one pair will affect the bias of the other pair in the opposite manner. Up on one causes down on the other and vice versa.

You have to adjust them incrementally back and forth together and you have to wait a few seconds for settling. You also should be monitoring B+ as you do it because B+ will change as you bias.

thanks. thats what i think to about just need adjust bias at other pair to get balance.

interesting part that after my tweak for first v7/v8 pair with 30.5 - 29.0 measures I got a more noticeable growl. like was added real tightness to amp!
very interesting, I dont remember that growl.
I will try it tomorrow with normal volume to hear its really there or I was blinded but I think im not.
this left tube glow became more bright-red. other 3 tubes have a faint glow.
seems I overclock this tube, without even going beyond some high values, and thus I need to do the same for the remaining lamps.

My tubes are from Apexmatching with text - Current 32.
maybe its 32ma/mv maximum for this tubes and I dont even need try boost it to 35-40? or not need look at this and everything is okay?
also we can see it says Kathode resistor. what that mean for me for biasing? other UU el34 has same specs I hope?

btw bro, what is it B+ and where I can check it with multimeter? thanks.

 

[Dale B]

thanks. thats what i think to about just need adjust bias at other pair to get balance.

interesting part that after my tweak for first v7/v8 pair with 30.5 - 29.0 measures I got a more noticeable growl. like was added real tightness to amp!
very interesting, I dont remember that growl.
I will try it tomorrow with normal volume to hear its really there or I was blinded but I think im not.
this left tube glow became more bright-red. other 3 tubes have a faint glow.
seems I overclock this tube, without even going beyond some high values, and thus I need to do the same for the remaining lamps.

My tubes are from Apexmatching with text - Current 32.
maybe its 32ma/mv maximum for this tubes and I dont even need try boost it to 35-40? or not need look at this and everything is okay?
also we can see it says Kathode resistor. what that mean for me for biasing? other UU el34 has same specs I hope?

btw bro, what is it B+ and where I can check it with multimeter? thanks.

They're using their own matching system that gathers readings from several different points, and that is a stable current reading the tubes read at during their process.

You can check the B+ by measuring Pin 3 to Ground on any of the power tube sockets.

 

[Emerald]

They're using their own matching system that gathers readings from several different points, and that is a stable current reading the tubes read at during their process.

You can check the B+ by measuring Pin 3 to Ground on any of the power tube sockets.

Thx. btw as said glpg80 guy, with adjusting bias it also change at B+.
so thats why left tube get more red/bright glow at the top, because it got more voltage from plate?

so I miss this and can damage tube/amp? or not because I return bias almost to same place?

so to check B+ I need power on amp and fast swap tube? or I can swap tube while amp will be fully off and then power on amp?

 

[glpg80]

Thx. btw as said glpg80 guy, with adjusting bias it also change at B+.
so thats why left tube get more red/bright glow at the top, because it got more voltage from plate?

so I miss this and can damage tube/amp? or not because I return bias almost to same place?

so to check B+ I need power on amp and fast swap tube? or I can swap tube while amp will be fully off and then power on amp?

Redplating occurs when the tube bias is running away making the tube shorted to ground at all times which damages the tubes or degrades their lifespan significantly.

You typically bias while also reading B+ at the same time. The external bias points were meant to check bias, not to actively bias which requires pulling the chassis to access B+.

It’s why it says it should be done by a technician - if you don’t know what you’re doing, you run the risk of damaging tubes or killing yourself around live voltage.

I suggest you take the amplifier to get biased from a liability standpoint.

 

[Emerald]

Redplating occurs when the tube bias is running away making the tube shorted to ground at all times which damages the tubes or degrades their lifespan significantly.

You typically bias while also reading B+ at the same time. The external bias points were meant to check bias, not to actively bias which requires pulling the chassis to access B+.

It’s why it says it should be done by a technician - if you don’t know what you’re doing, you run the risk of damaging tubes or killing yourself around live voltage.

I suggest you take the amplifier to get biased from a liability standpoint.

hm, okay but for now I a bit adjust only for first pair and only one tube got red plated.

do you mean that even after the values are returned for this 2 tubes, B+ plate voltage was increased and was not dropped? im understood right?

so how i can reduce it?
need check B+ now, and then continue adjust bias on other pair to get balanced mv/ma measures?

 

[Emerald]

They're using their own matching system that gathers readings from several different points, and that is a stable current reading the tubes read at during their process.

You can check the B+ by measuring Pin 3 to Ground on any of the power tube sockets.

bro, i need full run amp and then quickly remove tube before tubes goes hot?
and amp itself will not be damaged with 3 tubes coz main thing is that it must be connected to cabinet?

and do I really need measure B+? maybe not needed?
i mean I changed bias only at first pair of tubes. when I adjust at other pair it will return balance?

 

[mnemonic]

You need to know b+ in operation with all tubes installed which means you need the amp open to do so.

I would recommend you get a bias probe that can also measure plate voltage (like Weber one or tubeampdoctor, probably some other good ones someone else can recommend) or just take it to a tech.

It really pays to take the time to do some reading and understand the how and why of biasing and how the amp works, how to do the calculations, how to be safe while taking measurements, etc. you don’t really learn anything with a paint-by-numbers approach.

 

[Emerald]

You need to know b+ in operation with all tubes installed which means you need the amp open to do so.

I would recommend you get a bias probe that can also measure plate voltage (like Weber one or tubeampdoctor, probably some other good ones someone else can recommend) or just take it to a tech.

It really pays to take the time to do some reading and understand the how and why of biasing and how the amp works, how to do the calculations, how to be safe while taking measurements, etc. you don’t really learn anything with a paint-by-numbers approach.

thanks, bro. but bad that im not live US to buy nice things fast and have amp tech guys.

Sorry, one thing I was blind and missed...
I adjust 1st and 3rd pin for V7/V8 thinking they are pair but white line shows v7 goes v10... so I need adjust it to see proper results, not 3rd pin of v8.

 

[Emerald]

but I think If i push bias for all tubes to 33ma, which Is safe place as I understood, it will not damage anything and not need check B+ plate voltage?

 

[Emerald]

The center of the 3 holes is ground, left is v7 right is v8. Ground probe into the center and red into the outer 2

can you tell please what measures you have before /after? and did you noticed some difference In sound?

 

[Emerald]

No danger, there should only be millivolts on those connections. Ideally pretty similar measurements for each one

sorry, please help me.
if stock bias was like 29.0 to 29.5 for every tube, so if want adjust all tubes only to 33 it can adjust voltage on B+ plate significally and its dangerous or not?

i just need to know this.
and dont want swap out tube to check plate voltage.

current measures
v7/v10
30, 29.3
v8/v9
28.2, 27 .9

 

[napalmdeath]

You really need to know the plate voltage, but I would say 32-34 would be a good range for EL34's, assuming the PV is roughly 450. I typically find closer to 62-65% to be the sweet spot, vs. 70%.

EL34 = 25 watt tube. 25/450 = .055. .055 X .65 = .035. 34mA is what I'd shoot for, personally, that would be just under 65%, as you want a cleaner power section with a high gain preamp. I like it just warm enough to have some oomph, yet not so hot you're getting power tubes cooking with preamp distortion - sounds like shit.

 

[Emerald]

You really need to know the plate voltage, but I would say 32-34 would be a good range for EL34's, assuming the PV is roughly 450. I typically find closer to 62-65% to be the sweet spot, vs. 70%.

EL34 = 25 watt tube. 25/450 = .055. .055 X .65 = .035. 34mA is what I'd shoot for, personally, that would be just under 65%, as you want a cleaner power section with a high gain preamp. I like it just warm enough to have some oomph, yet not so hot you're getting power tubes cooking with preamp distortion - sounds like shit.

thanks, bro
i found at other forum that EL34 has 490v.
and according to this calculator shows safe 60-70% values (30-35ma)
I push my to 33. hope everything will be okay.

btw one guy I saw says that at colder settings amp can sounds more raw. very good interesting that we have such options

 

[napalmdeath]

thanks, bro
i found at other forum that EL34 has 490v.
and according to this calculator shows safe 60-70% values (30-35ma)
I push my to 33. hope everything will be okay.

btw one guy I saw says that at colder settings amp can sounds more raw. very good interesting that we have such options

33 should be fine. I use probes that read plate voltage and milliamps, (Eurotubes Pro One). I happen to have 2, in case I run into an amp with 2 adjustments. Makes things a breeze, and with them, you can play it, and adjust by ear when you're in range and lock it in where it sounds just right. Couldn't live without the Pro One, great tool. Takes away all guesswork.