KT-88 People. Anyone try the Ruby KT88V-STR? 50 watts??

[donalddemon]

Supposedly these are a return of the Penta Labs/Shuguang KT88SC (or KT88S?), which were my favorite tubes for my Splawn Pro Mod. A little pricey but I'm recording soon so I splurged because I miss my tone with the Pentas.

http://www.dougstubes.com/power-tubes/6550-kt88/ruby-kt88-v-str.html

I've noticed some modern tubes have a different max anode/plate dissipation rating, especially for KT88's. Looking at the data sheet for the Penta/Shuguang/Ruby KT88V-STR, the max anode dissipation is 50 watts!! Compared to the regular 42 watts or even 35 watts on some more common KT88's that seems pretty high and really makes a big difference (about 10 mA) for the bias calculations. Anyone try using these at these specs? I'd be looking at biasing around 63mA instead of the usual 48-52 mA range for 60% dissipation.

Here is the data sheet in question:http://www.dougstubes.com/Penta-KT88.pdf

 

[Gsxrbusa]

The Pentas were my favorite KT88. I picked up a quad of the Ruby but have yet to load them in anything yet. I have 2 amps that I run these in. Love what they do to my amps!

Don't know about running them hotter.

 

[donalddemon]

The Pentas were my favorite KT88. I picked up a quad of the Ruby but have yet to load them in anything yet. I have 2 amps that I run these in. Love what they do to my amps!

Don't know about running them hotter.

The regular Ruby KT88-STR's are very good and cheaper. The Penta KT88SC's just have a little more in the high end clarity, more chimey. I've been running the cheaper Ruby's for the past few times though because I can't always justify $200 for a quad. Hopefully these new KT88V-STR's hold up to the old Penta's. I'll know soon but I just don't know where the hell I should bias them at. I may just have to find an acceptable range between the 42 and 50 watt rating and bias from ear at that point.

 

[Gsxrbusa]

The Pentas were my favorite KT88. I picked up a quad of the Ruby but have yet to load them in anything yet. I have 2 amps that I run these in. Love what they do to my amps!

Don't know about running them hotter.

The regular Ruby KT88-STR's are very good and cheaper. The Penta KT88SC's just have a little more in the high end clarity, more chimey. I've been running the cheaper Ruby's for the past few times though because I can't always justify $200 for a quad. Hopefully these new KT88V-STR's hold up to the old Penta's. I'll know soon but I just don't know where the hell I should bias them at. I may just have to find an acceptable range between the 42 and 50 watt rating and bias from ear at that point.

My experience as well fine sir. The Pentas are just better.

I meant to say the quad I have sitting here are the V-STR. Just haven't installed them as of yet.

 

[donalddemon]

The Pentas were my favorite KT88. I picked up a quad of the Ruby but have yet to load them in anything yet. I have 2 amps that I run these in. Love what they do to my amps!

Don't know about running them hotter.

The regular Ruby KT88-STR's are very good and cheaper. The Penta KT88SC's just have a little more in the high end clarity, more chimey. I've been running the cheaper Ruby's for the past few times though because I can't always justify $200 for a quad. Hopefully these new KT88V-STR's hold up to the old Penta's. I'll know soon but I just don't know where the hell I should bias them at. I may just have to find an acceptable range between the 42 and 50 watt rating and bias from ear at that point.

My experience as well fine sir. The Pentas are just better.

I meant to say the quad I have sitting here are the V-STR. Just haven't installed them as of yet.

Definitely. Ah well, even better, I'm interested to know your thoughts on the V-STR, report back here if you remember. What amp are you putting them in and what power rating will you use to bias?

 

[Gsxrbusa]

The Pentas were my favorite KT88. I picked up a quad of the Ruby but have yet to load them in anything yet. I have 2 amps that I run these in. Love what they do to my amps!

Don't know about running them hotter.

The regular Ruby KT88-STR's are very good and cheaper. The Penta KT88SC's just have a little more in the high end clarity, more chimey. I've been running the cheaper Ruby's for the past few times though because I can't always justify $200 for a quad. Hopefully these new KT88V-STR's hold up to the old Penta's. I'll know soon but I just don't know where the hell I should bias them at. I may just have to find an acceptable range between the 42 and 50 watt rating and bias from ear at that point.

My experience as well fine sir. The Pentas are just better.

I meant to say the quad I have sitting here are the V-STR. Just haven't installed them as of yet.

Definitely. Ah well, even better, I'm interested to know your thoughts on the V-STR, report back here if you remember. What amp are you putting them in and what power rating will you use to bias?

They will either go in my Framus Cobra or my Bogner Uberschall rev green. Both have plate voltages at 500. I have typically run them at 45mv. I could go higher and see if I hear any tonal advantages. I'll let you know.

 

[Hardvalve]

I want to put some KT-88s in my KSR Ares, these are pretty pricey. Looking for a pair of decent ones.

 

[baron55]

Great tubes! exact same as the Penta Labs

 

[donalddemon]

The Pentas were my favorite KT88. I picked up a quad of the Ruby but have yet to load them in anything yet. I have 2 amps that I run these in. Love what they do to my amps!

Don't know about running them hotter.

The regular Ruby KT88-STR's are very good and cheaper. The Penta KT88SC's just have a little more in the high end clarity, more chimey. I've been running the cheaper Ruby's for the past few times though because I can't always justify $200 for a quad. Hopefully these new KT88V-STR's hold up to the old Penta's. I'll know soon but I just don't know where the hell I should bias them at. I may just have to find an acceptable range between the 42 and 50 watt rating and bias from ear at that point.

My experience as well fine sir. The Pentas are just better.

I meant to say the quad I have sitting here are the V-STR. Just haven't installed them as of yet.

Definitely. Ah well, even better, I'm interested to know your thoughts on the V-STR, report back here if you remember. What amp are you putting them in and what power rating will you use to bias?

They will either go in my Framus Cobra or my Bogner Uberschall rev green. Both have plate voltages at 500. I have typically run them at 45mv. I could go higher and see if I hear any tonal advantages. I'll let you know.

Ok cool. Yeah that's a little low if you go but the data sheet specs, though I don't know how accurate that is.

 

[donalddemon]

Great tubes! exact same as the Penta Labs

Good to hear! I loved those Pentas. Which amp are you using them in and do you remember where you biased?

 

[baron55]

I always biased them up as 35 watt tubes. The datasheet rating is the MAX plate dissipation rating and not an indication of how they should be biased up. The SED KT88's had a max plate dissipation of 42 watts.

I have found the Penta KT88SC are much more tolerant to a high grid to bias (ground) resistance than most others.

 

[donalddemon]

I always biased them up as 35 watt tubes. The datasheet rating is the MAX plate dissipation rating and not an indication of how they should be biased up. The SED KT88's had a max plate dissipation of 42 watts.

I have found the Penta KT88SC are much more tolerant to a high grid to bias (ground) resistance than most others.

Yeah I tend to shoot for 60% of max dissipation but that number changes pretty drastically if the max is 35, 42, or 50!

 

[SpiderWars]

FWIW, I would not exceed the amplifier power rating when deciding what max power to base your 60% on. As long as the amp power rating doesn't exceed the tube power rating, I'd bias it based on the amp power rating.

 

[baron55]

Power tube output power is dependent on Plate Voltage, screen voltage, output transformer specs fixed bias vs cathode bias. The tube dissipation limits have nothing to do with tube power output, they are just heat limitations for the plate. A Pair of EL34's can put out a 100 watts, 60 watts, 50 watts, and 45 watts, its all based on the above variables. So dropping a pair of tubes that have a 50 watt plate dissipation rating does not mean you are going to put out any more power than a pair of tubes at 35 watts dissipation rating. So biasing the amp at 60% of the 50 watt dissipation rating won't hurt the amp because the power supply and voltage isn't high enough. I actually have biased these KT88 very hot and the end result was the power supply wan't design for that much current so the voltage sagged and the output dropped.

What I take away from the high plate dissipation, is the tubes are more robust and will last longer

I just bias KT88's in general as a 35 watt tube because there is a lot of creative marketing that goes on.

Years ago when Groove tubes came out with the EL34LS they said it was a 32 watt tube. Well the fine print told the story, plate 26 watts and screen 6 watts

 

[donalddemon]

FWIW, I would not exceed the amplifier power rating when deciding what max power to base your 60% on. As long as the amp power rating doesn't exceed the tube power rating, I'd bias it based on the amp power rating.

So 120w amp, each tube would be biased at 30w, which is 60% of 50w. But I don't think it works that way because we bias at idle current, not peak. As we play through the amp, the power spikes, as I understand it. I could be wrong though, I'm not tech, just a guitarist.

 

[donalddemon]

Power tube output power is dependent on Plate Voltage, screen voltage, output transformer specs fixed bias vs cathode bias. The tube dissipation limits have nothing to do with tube power output, they are just heat limitations for the plate. A Pair of EL34's can put out a 100 watts, 60 watts, 50 watts, and 45 watts, its all based on the above variables. So dropping a pair of tubes that have a 50 watt plate dissipation rating does not mean you are going to put out any more power than a pair of tubes at 35 watts dissipation rating. So biasing the amp at 60% of the 50 watt dissipation rating won't hurt the amp because the power supply and voltage isn't high enough. I actually have biased these KT88 very hot and the end result was the power supply wan't design for that much current so the voltage sagged and the output dropped.

What I take away from the high plate dissipation, is the tubes are more robust and will last longer

I just bias KT88's in general as a 35 watt tube because there is a lot of creative marketing that goes on.

Years ago when Groove tubes came out with the EL34LS they said it was a 32 watt tube. Well the fine print told the story, plate 26 watts and screen 6 watts

That makes sense that it means they are robust. It still makes it confusing on which numbers to calculate for within a safe range. It seems more common to see modern KT88's rated for 42 watts, rather than 35. I admit I don't fully understand the screen voltage since I just use a bias meter and use the cheater method, only relying on power rating, cathode current, and plate voltage. What I'm really trying to do is avoid biasing the amp hot because for one, they are expensive and would rather get longer life, and this amp really sounds better with a colder bias in the 60% range. When the tube in question can have three different power ratings, how does one come up with what is truly 60% of max dissipation?