Tube Bias

[EnGl]

I just checked my amp bias (6534).
In my previous post one of the user told me that mismatched tubes are not a bad thing. My tubes are 36.5 (hottest) , 32.8 , 32.5 , 32.7 , 32.4 (in mA).
Previously I biased my amp according tube hottest tube but now ... I should do this again or change something ? For example biasing my amp according tube coldest tube ?

 

[AndyK]

Do you get the same high 36 reading if that tube is moved into the first spot? If you do, I'd say get a closer matched tube in there from another set.

If you bias using the higher tube, the majority will be cold. If you bias using the other tubes, that one tube could red-plate.

 

[Dale B]

I just checked my amp bias (6534).
In my previous post one of the user told me that mismatched tubes are not a bad thing. My tubes are 36.5 (hottest) , 32.8 , 32.5 , 32.7 , 32.4 (in mA).
Previously I biased my amp according tube hottest tube but now ... I should do this again or change something ? For example biasing my amp according tube coldest tube ?

Technically, your tubes are still matched if they're within 10 mA of one another. Most people are anal about matched tubes and expect everything to be spot on. 36.5 mA is about 73% of the max plate dissipation if your amp has 500 vdc on the plates. The others are about 64% (based on 500 vdc). If you're really worried about it, you could drop the coolest tube down 2 mA which would drop your hottest tube below 70% plate dissipation.

 

[EnGl]

Ok , to answer the questions :
1.Yup , I get the same reading no matter in which spot the hottest tube is.
2. Redplate ? Nope , they are Ruby BHT EL34 so they can stand very high load. I bought bias meter 2 months after I bought the amp and the factory bias was set to ... 46.5 on the hottets tube Zero redplate. So no worries
3. About plate voltage - AFAIK Peavey 6505 series has about 480PV so 36ma is about 70% mA.

And I also want to ask other question:
Prevoiusly my amp has 34mA. I wanted little tighter feel and the top end was a bit fizzy to my taste so few moments ago I biased amp to 36 mA. The low end was a bit loose but I turned down resonance and low knob (about 0.5) and everything is tight now and top end is not fizzy. Very warm , articulate and "hot" feel. But I noticed that amp noise is increased , very little. It's normal than the hotter the bias the more noise amp can produce ? I must add that I use very high output pickups(EMG 81/85) and I set my gain at 6.5.

 

[crwnedblasphemy]

Dale...are you sure it's within 10ma? I was told within 5ma-7ma max...Just wondering if i was told wrong info.

Thanks...

Rian

 

[Dale B]

Ok , to answer the questions :
1.Yup , I get the same reading no matter in which spot the hottest tube is.
2. Redplate ? Nope , they are Ruby BHT EL34 so they can stand very high load. I bought bias meter 2 months after I bought the amp and the factory bias was set to ... 46.5 on the hottets tube Zero redplate. So no worries
3. About plate voltage - AFAIK Peavey 6505 series has about 480PV so 36ma is about 70% mA.

And I also want to ask other question:
Prevoiusly my amp has 34mA. I wanted little tighter feel and the top end was a bit fizzy to my taste so few moments ago I biased amp to 36 mA. The low end was a bit loose but I turned down resonance and low knob (about 0.5) and everything is tight now and top end is not fizzy. Very warm , articulate and "hot" feel. But I noticed that amp noise is increased , very little. It's normal than the hotter the bias the more noise amp can produce ? I must add that I use very high output pickups(EMG 81/85) and I set my gain at 6.5.

Cool information about the 6534. All of the 6505 or 5150 amps I've biased had just a shade over 500 vdc.

If I recall correctly, JerryP used to bias the modded 5150s around 32mA per tube, but my thinking is Peavey changed the OT for the 6534. The main thing is you know the math behind it and what is safe. Just go with what sounds good to your ears. At the end of the day, it's your money, and the cash comes out of your pocket when it comes to how often you want to retube the power section.

 

[Dale B]

Dale...are you sure it's within 10ma? I was told within 5ma-7ma max...Just wondering if i was told wrong info.

Thanks...

Rian

People have different views on it, but you can comb through all of the old stuff on the internet. 10 mA was usually the cutoff point back in "the olden days". Some people actually like how their amps sound with mismatched tubes that are off by that much. I'm not an electrical engineer, so I have no idea what significance that may have in regard to the rest of the amp. I'm just relaying information about what I've read.

Personally, I like them within at least 3 mA of one another, so I belong in the "anal click". haha!

 

[EnGl]

Ok , to answer the questions :
1.Yup , I get the same reading no matter in which spot the hottest tube is.
2. Redplate ? Nope , they are Ruby BHT EL34 so they can stand very high load. I bought bias meter 2 months after I bought the amp and the factory bias was set to ... 46.5 on the hottets tube Zero redplate. So no worries
3. About plate voltage - AFAIK Peavey 6505 series has about 480PV so 36ma is about 70% mA.

And I also want to ask other question:
Prevoiusly my amp has 34mA. I wanted little tighter feel and the top end was a bit fizzy to my taste so few moments ago I biased amp to 36 mA. The low end was a bit loose but I turned down resonance and low knob (about 0.5) and everything is tight now and top end is not fizzy. Very warm , articulate and "hot" feel. But I noticed that amp noise is increased , very little. It's normal than the hotter the bias the more noise amp can produce ? I must add that I use very high output pickups(EMG 81/85) and I set my gain at 6.5.

Cool information about the 6534. All of the 6505 or 5150 amps I've biased had just a shade over 500 vdc.

If I recall correctly, JerryP used to bias the modded 5150s around 32mA per tube, but my thinking is Peavey changed the OT for the 6534. The main thing is you know the math behind it and what is safe. Just go with what sounds good to your ears. At the end of the day, it's your money, and the cash comes out of your pocket when it comes to how often you want to retube the power section.

You know , I never measured the PV of my 6534. I found forum on the net and guy measured PV of 6534 and it was about 480 so mine will be not different ?

 

[crwnedblasphemy]

Dale...are you sure it's within 10ma? I was told within 5ma-7ma max...Just wondering if i was told wrong info.

Thanks...

Rian

People have different views on it, but you can comb through all of the old stuff on the internet. 10 mA was usually the cutoff point back in "the olden days". Some people actually like how their amps sound with mismatched tubes that are off by that much. I'm not an electrical engineer, so I have no idea what significance that may have in regard to the rest of the amp. I'm just relaying information about what I've read.

Personally, I like them within at least 3 mA of one another, so I belong in the "anal click". haha!

Cool...Yeah, I have read interesting stuff that it is a marketing wives' tale...that it doesn't matter if they aren't matched, and that it's a way for companies to get you to buy another quad. That theory makes sense to me, but just don't chance it.

 

[Dale B]

Ok , to answer the questions :
1.Yup , I get the same reading no matter in which spot the hottest tube is.
2. Redplate ? Nope , they are Ruby BHT EL34 so they can stand very high load. I bought bias meter 2 months after I bought the amp and the factory bias was set to ... 46.5 on the hottets tube Zero redplate. So no worries
3. About plate voltage - AFAIK Peavey 6505 series has about 480PV so 36ma is about 70% mA.

And I also want to ask other question:
Prevoiusly my amp has 34mA. I wanted little tighter feel and the top end was a bit fizzy to my taste so few moments ago I biased amp to 36 mA. The low end was a bit loose but I turned down resonance and low knob (about 0.5) and everything is tight now and top end is not fizzy. Very warm , articulate and "hot" feel. But I noticed that amp noise is increased , very little. It's normal than the hotter the bias the more noise amp can produce ? I must add that I use very high output pickups(EMG 81/85) and I set my gain at 6.5.

Cool information about the 6534. All of the 6505 or 5150 amps I've biased had just a shade over 500 vdc.

If I recall correctly, JerryP used to bias the modded 5150s around 32mA per tube, but my thinking is Peavey changed the OT for the 6534. The main thing is you know the math behind it and what is safe. Just go with what sounds good to your ears. At the end of the day, it's your money, and the cash comes out of your pocket when it comes to how often you want to retube the power section.

You know , I never measured the PV of my 6534. I found forum on the net and guy measured PV of 6534 and it was about 480 so mine will be not different ?

It could be completely different depending on what is coming into your house. BUT... it makes a lot of sense for them to drop the plate voltage a tad in order to compensate for the reliability factor of current EL34s vs. 6L6s these days. The Sovtek 6L6s can handle well over 550 vdc without any problems. Some reports on the JJ EL34s were they started getting a little stupid up past 500 vdc. The =C= can handle it. I've never had any problems with JJ in the Bogner XTCs that I've run them in, and those were dishing out between 515 and 535 on the plates. If I remember correctly, the first version of the Uberschall had a plate voltage at roughly 550ish, and JJ's were always used in those amps. That's just my own experience and should only be taken with a grain of salt, as tubes are very finicky beasts. A lot of the reliability stuff comes into play based on the quality of the runs for each tube. Some runs are better than others.

The other thing that can mess with the plate voltage is the natural draw of the power tubes under load. Hotter tubes will cause the plate voltage to drop a little bit, but it isn't anything to write home about. A 20 mA swing isn't that bad. 70% at 500 vdc on a 25 watt tube is 35 mA. 36.4 mA is 70% at 480 for a 25 watt tube. That isn't anything major.

I would probably bias the amp to where those tubes were falling between 30 and 36mA and call it a day. 60% is a good number. 55% is a good number for a lot of amps these days as well. 70% is just an old, general rule that a lot of people go by.

One funny thing is the SLO. Bill Sundt will tell you to bias those amps at 25 mA per tube. The SLO I have now and the one prior to that had a plate voltage of about 505. I run Philips 7581As in it. Those are 35 watt tubes, but I treat them at 30 watters. 41% = a very clean power amp, but that's how the amp was designed. Power tube changes within the same family don't make much of a difference in the SLO.

 

[EnGl]

Ok , to answer the questions :
1.Yup , I get the same reading no matter in which spot the hottest tube is.
2. Redplate ? Nope , they are Ruby BHT EL34 so they can stand very high load. I bought bias meter 2 months after I bought the amp and the factory bias was set to ... 46.5 on the hottets tube Zero redplate. So no worries
3. About plate voltage - AFAIK Peavey 6505 series has about 480PV so 36ma is about 70% mA.

And I also want to ask other question:
Prevoiusly my amp has 34mA. I wanted little tighter feel and the top end was a bit fizzy to my taste so few moments ago I biased amp to 36 mA. The low end was a bit loose but I turned down resonance and low knob (about 0.5) and everything is tight now and top end is not fizzy. Very warm , articulate and "hot" feel. But I noticed that amp noise is increased , very little. It's normal than the hotter the bias the more noise amp can produce ? I must add that I use very high output pickups(EMG 81/85) and I set my gain at 6.5.

Cool information about the 6534. All of the 6505 or 5150 amps I've biased had just a shade over 500 vdc.

If I recall correctly, JerryP used to bias the modded 5150s around 32mA per tube, but my thinking is Peavey changed the OT for the 6534. The main thing is you know the math behind it and what is safe. Just go with what sounds good to your ears. At the end of the day, it's your money, and the cash comes out of your pocket when it comes to how often you want to retube the power section.

You know , I never measured the PV of my 6534. I found forum on the net and guy measured PV of 6534 and it was about 480 so mine will be not different ?

It could be completely different depending on what is coming into your house. BUT... it makes a lot of sense for them to drop the plate voltage a tad in order to compensate for the reliability factor of current EL34s vs. 6L6s these days. The Sovtek 6L6s can handle well over 550 vdc without any problems. Some reports on the JJ EL34s were they started getting a little stupid up past 500 vdc. The =C= can handle it. I've never had any problems with JJ in the Bogner XTCs that I've run them in, and those were dishing out between 515 and 535 on the plates. If I remember correctly, the first version of the Uberschall had a plate voltage at roughly 550ish, and JJ's were always used in those amps. That's just my own experience and should only be taken with a grain of salt, as tubes are very finicky beasts. A lot of the reliability stuff comes into play based on the quality of the runs for each tube. Some runs are better than others.

The other thing that can mess with the plate voltage is the natural draw of the power tubes under load. Hotter tubes will cause the plate voltage to drop a little bit, but it isn't anything to write home about. A 20 mA swing isn't that bad. 70% at 500 vdc on a 25 watt tube is 35 mA. 36.4 mA is 70% at 480 for a 25 watt tube. That isn't anything major.

I would probably bias the amp to where those tubes were falling between 30 and 36mA and call it a day. 60% is a good number. 55% is a good number for a lot of amps these days as well. 70% is just an old, general rule that a lot of people go by.

One funny thing is the SLO. Bill Sundt will tell you to bias those amps at 25 mA per tube. The SLO I have now and the one prior to that had a plate voltage of about 505. I run Philips 7581As in it. Those are 35 watt tubes, but I treat them at 30 watters. 41% = a very clean power amp, but that's how the amp was designed. Power tube changes within the same family don't make much of a difference in the SLO.

About this plate voltage : I'm not sure if Peavey drop a little bit PV. You know why ? Cause my amp came stock with RUBY EL34 BHT - they can handle some crazy voltages , over 600 PV so ... I'm bit afraid which tubes I should buy...
I want try JJ 6ca7 so bad but ... Bad JJ reputation ( reliability issues) really scare me.
EL34 from SEC C are unavailable in most of the shops in EU or USA due to reliability issues. Doug tubes is one of the examples.

 

[Dale B]

Ok , to answer the questions :
1.Yup , I get the same reading no matter in which spot the hottest tube is.
2. Redplate ? Nope , they are Ruby BHT EL34 so they can stand very high load. I bought bias meter 2 months after I bought the amp and the factory bias was set to ... 46.5 on the hottets tube Zero redplate. So no worries
3. About plate voltage - AFAIK Peavey 6505 series has about 480PV so 36ma is about 70% mA.

And I also want to ask other question:
Prevoiusly my amp has 34mA. I wanted little tighter feel and the top end was a bit fizzy to my taste so few moments ago I biased amp to 36 mA. The low end was a bit loose but I turned down resonance and low knob (about 0.5) and everything is tight now and top end is not fizzy. Very warm , articulate and "hot" feel. But I noticed that amp noise is increased , very little. It's normal than the hotter the bias the more noise amp can produce ? I must add that I use very high output pickups(EMG 81/85) and I set my gain at 6.5.

Cool information about the 6534. All of the 6505 or 5150 amps I've biased had just a shade over 500 vdc.

If I recall correctly, JerryP used to bias the modded 5150s around 32mA per tube, but my thinking is Peavey changed the OT for the 6534. The main thing is you know the math behind it and what is safe. Just go with what sounds good to your ears. At the end of the day, it's your money, and the cash comes out of your pocket when it comes to how often you want to retube the power section.

You know , I never measured the PV of my 6534. I found forum on the net and guy measured PV of 6534 and it was about 480 so mine will be not different ?

It could be completely different depending on what is coming into your house. BUT... it makes a lot of sense for them to drop the plate voltage a tad in order to compensate for the reliability factor of current EL34s vs. 6L6s these days. The Sovtek 6L6s can handle well over 550 vdc without any problems. Some reports on the JJ EL34s were they started getting a little stupid up past 500 vdc. The =C= can handle it. I've never had any problems with JJ in the Bogner XTCs that I've run them in, and those were dishing out between 515 and 535 on the plates. If I remember correctly, the first version of the Uberschall had a plate voltage at roughly 550ish, and JJ's were always used in those amps. That's just my own experience and should only be taken with a grain of salt, as tubes are very finicky beasts. A lot of the reliability stuff comes into play based on the quality of the runs for each tube. Some runs are better than others.

The other thing that can mess with the plate voltage is the natural draw of the power tubes under load. Hotter tubes will cause the plate voltage to drop a little bit, but it isn't anything to write home about. A 20 mA swing isn't that bad. 70% at 500 vdc on a 25 watt tube is 35 mA. 36.4 mA is 70% at 480 for a 25 watt tube. That isn't anything major.

I would probably bias the amp to where those tubes were falling between 30 and 36mA and call it a day. 60% is a good number. 55% is a good number for a lot of amps these days as well. 70% is just an old, general rule that a lot of people go by.

One funny thing is the SLO. Bill Sundt will tell you to bias those amps at 25 mA per tube. The SLO I have now and the one prior to that had a plate voltage of about 505. I run Philips 7581As in it. Those are 35 watt tubes, but I treat them at 30 watters. 41% = a very clean power amp, but that's how the amp was designed. Power tube changes within the same family don't make much of a difference in the SLO.

About this plate voltage : I'm not sure if Peavey drop a little bit PV. You know why ? Cause my amp came stock with RUBY EL34 BHT - they can handle some crazy voltages , over 600 PV so ... I'm bit afraid which tubes I should buy...
I want try JJ 6ca7 so bad but ... Bad JJ reputation ( reliability issues) really scare me.
EL34 from SEC C are unavailable in most of the shops in EU or USA due to reliability issues. Doug tubes is one of the examples.

Yeah, but they very well could have done it in the event that people want try different ones. Personally, I would stick with those Ruby EL34s. They sound great, are built well and even sound great with lower bias settings. They start getting fat sounding around 55% of the plate dissipation.

One thing to keep in mind is Peavey could have chosen any of the other tubes, like EH or Sovtek. If they went with the Ruby EL34s from the beginning, which those were around at that time, they probably voiced the power section around that power tube. I would stick with those if they're easy for you get your hands on.

Have you tried Watford Valves?

 

[EnGl]

Ok , to answer the questions :
1.Yup , I get the same reading no matter in which spot the hottest tube is.
2. Redplate ? Nope , they are Ruby BHT EL34 so they can stand very high load. I bought bias meter 2 months after I bought the amp and the factory bias was set to ... 46.5 on the hottets tube Zero redplate. So no worries
3. About plate voltage - AFAIK Peavey 6505 series has about 480PV so 36ma is about 70% mA.

And I also want to ask other question:
Prevoiusly my amp has 34mA. I wanted little tighter feel and the top end was a bit fizzy to my taste so few moments ago I biased amp to 36 mA. The low end was a bit loose but I turned down resonance and low knob (about 0.5) and everything is tight now and top end is not fizzy. Very warm , articulate and "hot" feel. But I noticed that amp noise is increased , very little. It's normal than the hotter the bias the more noise amp can produce ? I must add that I use very high output pickups(EMG 81/85) and I set my gain at 6.5.

Cool information about the 6534. All of the 6505 or 5150 amps I've biased had just a shade over 500 vdc.

If I recall correctly, JerryP used to bias the modded 5150s around 32mA per tube, but my thinking is Peavey changed the OT for the 6534. The main thing is you know the math behind it and what is safe. Just go with what sounds good to your ears. At the end of the day, it's your money, and the cash comes out of your pocket when it comes to how often you want to retube the power section.

You know , I never measured the PV of my 6534. I found forum on the net and guy measured PV of 6534 and it was about 480 so mine will be not different ?

It could be completely different depending on what is coming into your house. BUT... it makes a lot of sense for them to drop the plate voltage a tad in order to compensate for the reliability factor of current EL34s vs. 6L6s these days. The Sovtek 6L6s can handle well over 550 vdc without any problems. Some reports on the JJ EL34s were they started getting a little stupid up past 500 vdc. The =C= can handle it. I've never had any problems with JJ in the Bogner XTCs that I've run them in, and those were dishing out between 515 and 535 on the plates. If I remember correctly, the first version of the Uberschall had a plate voltage at roughly 550ish, and JJ's were always used in those amps. That's just my own experience and should only be taken with a grain of salt, as tubes are very finicky beasts. A lot of the reliability stuff comes into play based on the quality of the runs for each tube. Some runs are better than others.

The other thing that can mess with the plate voltage is the natural draw of the power tubes under load. Hotter tubes will cause the plate voltage to drop a little bit, but it isn't anything to write home about. A 20 mA swing isn't that bad. 70% at 500 vdc on a 25 watt tube is 35 mA. 36.4 mA is 70% at 480 for a 25 watt tube. That isn't anything major.

I would probably bias the amp to where those tubes were falling between 30 and 36mA and call it a day. 60% is a good number. 55% is a good number for a lot of amps these days as well. 70% is just an old, general rule that a lot of people go by.

One funny thing is the SLO. Bill Sundt will tell you to bias those amps at 25 mA per tube. The SLO I have now and the one prior to that had a plate voltage of about 505. I run Philips 7581As in it. Those are 35 watt tubes, but I treat them at 30 watters. 41% = a very clean power amp, but that's how the amp was designed. Power tube changes within the same family don't make much of a difference in the SLO.

About this plate voltage : I'm not sure if Peavey drop a little bit PV. You know why ? Cause my amp came stock with RUBY EL34 BHT - they can handle some crazy voltages , over 600 PV so ... I'm bit afraid which tubes I should buy...
I want try JJ 6ca7 so bad but ... Bad JJ reputation ( reliability issues) really scare me.
EL34 from SEC C are unavailable in most of the shops in EU or USA due to reliability issues. Doug tubes is one of the examples.

Yeah, but they very well could have done it in the event that people want try different ones. Personally, I would stick with those Ruby EL34s. They sound great, are built well and even sound great with lower bias settings. They start getting fat sounding around 55% of the plate dissipation.

One thing to keep in mind is Peavey could have chosen any of the other tubes, like EH or Sovtek. If they went with the Ruby EL34s from the beginning, which those were around at that time, they probably voiced the power section around that power tube. I would stick with those if they're easy for you get your hands on.

Have you tried Watford Valves?

Nope , I'm from Europe (currently Poland).
I can get few top tubes like Gold Lions KT77 , SED C etc so no big problem here. In the europe we have TAD Tubes (they are the same thing as Ruby in USA). There is one tube : TAD EL34BST which should be regular shuguang but specially designed for TAD .

 

[Anonymous]

most people wont notice a tube 10ma out of spec with the others.

i'd say run em as is, but run em a tad cooler...maybe down around 30 or 32...just to preserve tube life.

mine are way out of spec..and i could care less....they're on their last leg, and i know it....who cares. they still work!

dont over analyze!

 

[EnGl]

Ok So i set my bias lower. It end like this :

31.7 31.2 30.2 28.6

3ma difference so good result IMO.

Effect ? TIGHT AS HELL feeling , bit more compressed , more clarity . I like it very much


By accident I touched output transformer and it was hot ... Not very hot , I keep my fingers for maybe ten second and this was limit for me. Goddamn I can fry eggs on it
(power transformer was cold as ice)

 

[Anonymous]

you're fine! dale b is giving you good advice here!