Having some issues biasing my PRS Archon 25W combo

[Omega1397]

Hey guys,

I got some new tubes for my PRS Archon 25W combo and I was having some issues biasing them. They originally had Tung sol 5881's set at 30 mA. I was recommended by two tube vendors that Ruby 6L6GCM's would be a good replacement for them. I ran the formula to find my bias range (364V plate voltage, 30W tube rating) and got somewhere in the ballpark of 52-57.5 for a good mA range. My issue is that I cranked my bias control all the way to the max, and my current is topped at 42 mA. I was wondering if there was any way to get to my desired current range, or wether or not I should be using these tubes at all.

If anyone could help me out it would be very appreciated.

 

[napalmdeath]

Tubes are too cold. Need a warmer grade.

 

[GuitarGuyLP]

Even if you calculate the range on the stock tubes it should be up around 45 if I remember right, but the bias range can’t go that high. PRS recommends bias at 30-35 amp whichbis way too cold for an amp with such a low plate voltage. I just put it as high as it goes, and it sounds fine, but when I order new tubes I’ll ask for a warmer grade.

BTW - the Archon is killer with a Creamback H speaker. I just put one in mine, and it really makes that amp shine!!!

 

[Loudness250]

Send them back and let them know that you need tubes within the range that you need.

 

[Omega1397]

Send them back and let them know that you need tubes within the range that you need.

Thank you. By grade you mean I need to change the entire tube type- or the same tube just a different setting (They have an early distortion one). I was under the impression that the plate current (mA) is a quality of the amp itself, not the tube.

 

[napalmdeath]

Send them back and let them know that you need tubes within the range that you need.

Thank you. By grade you mean I need to change the entire tube type- or the same tube just a different setting (They have an early distortion one). I was under the impression that the plate current (mA) is a quality of the amp itself, not the tube.

No. Some amps have a very small adjustment range. If you get a cold rated pair, it's likely the adjustment window wont get you there. Call Eurotubes, and ask what their recommendations are for JJ 6L6s. They'll likely have hands-on experience.

 

[Omega1397]

Thank you. Are you saying I should get a new but hotter set of the same ruby 6l6gcms, or I need a whole new type of tube? Also, Are the JJ 6l6 25w or 30w?

 

[Omega1397]

Even if you calculate the range on the stock tubes it should be up around 45 if I remember right, but the bias range can’t go that high. PRS recommends bias at 30-35 amp whichbis way too cold for an amp with such a low plate voltage. I just put it as high as it goes, and it sounds fine, but when I order new tubes I’ll ask for a warmer grade.

BTW - the Archon is killer with a Creamback H speaker. I just put one in mine, and it really makes that amp shine!!!

Thanks for the input man! I was wondering why it came biased so cold.

Creamback H speaker eh? How would you compare them to the G12-75's that come stock? I would appreciate it if you could give me some input- I don't really have time to google right now because i'm trying to cram in some guitar practice before class

 

[Omega1397]

Hmm..I just heard back from Doug and he tells me that it could be possible to change my value resistor. Thoughts?

 

[Chris6870]

Hmm..I just heard back from Doug and he tells me that it could be possible to change my value resistor. Thoughts?

So he is suggesting modifying the amps circuitry so his tubes will work? Just get a hotter set of tubes. Should not be a big deal.

 

[Omega1397]

Thank you. By a hotter set of tubes do you mean I should get an entire different type of tube, or can I get the same tube, just one that runs hotter ?

 

[mixn4him]

Or better yet get another pair of Tung Sol 5881's and life will be so much easier...The amp and bias range were obviously set up around those tubes and they are good sounding tubes, so use them...

 

[GuitarGuyLP]

The Tung Sol 5881 are great tubes, and you can get the bias high enough to sound good without modification. These amps have not been out for all that long, is there any reason you are replacing power tubes? Did one fail?

The creamback is much fuller sounding, and has much better mids. The high end is more clear, and not as piercing as well. I didn't do a back to back on the T75 to Creamback because I took the T75 out after about 20 minutes, and put in a greenback just after I got the amp. The greenback sounded good, but not full enough. I put the creamback in about a week ago, and now the amp sounds perfect to me.

 

[Omega1397]

The Tung Sol 5881 are great tubes, and you can get the bias high enough to sound good without modification. These amps have not been out for all that long, is there any reason you are replacing power tubes? Did one fail?

The creamback is much fuller sounding, and has much better mids. The high end is more clear, and not as piercing as well. I didn't do a back to back on the T75 to Creamback because I took the T75 out after about 20 minutes, and put in a greenback just after I got the amp. The greenback sounded good, but not full enough. I put the creamback in about a week ago, and now the amp sounds perfect to me.

Thank you very much for the input. I just think that my current tone on the Archon sounds a bit too rolled off on top, and spongy overall. In regards to getting a hotter set of tubes, is that a matter in which I need to change my entire tube type, or simply exchange for the same tube but that has a higher rating.

EDIT: By the way, I just want to make sure. For the creamback- 16 Ohm, 75W right?

 

[GuitarGuyLP]

That's what I put in. That is kind of the voice of the amp, it is a on the darker side. A speaker change can drastically change the sound, but keep the same character. I would recommend if you can plug it into a couple of different cabs with different speakers to see which one sounds best for you. You can unplug the internal speaker, and plug it into whatever cab you want, and the impedance of the speaker you put in doesn't matter too much you can set the amp to 16, 8, or 4.

Changing the power tubes isn't all that drastic unless you go from 6L6 or 5881 to something like EL34s which the Archon 25 might not be able to use, EL34s draw a lot more heater current so they could damage the power transformer if its not rated for them. Other than that different tubes from the 6L6 family including 5881s will make a small difference but it is more fine tuning than changing the character. I'm going to see if I can remember what the plate voltage is, and I will be able to calculate what the bias should be for the 5881s, but I know PRS says 30, but that is way too low.

 

[Omega1397]

That's what I put in. That is kind of the voice of the amp, it is a on the darker side. A speaker change can drastically change the sound, but keep the same character. I would recommend if you can plug it into a couple of different cabs with different speakers to see which one sounds best for you. You can unplug the internal speaker, and plug it into whatever cab you want, and the impedance of the speaker you put in doesn't matter too much you can set the amp to 16, 8, or 4.

Changing the power tubes isn't all that drastic unless you go from 6L6 or 5881 to something like EL34s which the Archon 25 might not be able to use, EL34s draw a lot more heater current so they could damage the power transformer if its not rated for them. Other than that different tubes from the 6L6 family including 5881s will make a small difference but it is more fine tuning than changing the character. I'm going to see if I can remember what the plate voltage is, and I will be able to calculate what the bias should be for the 5881s, but I know PRS says 30, but that is way too low.

Thanks man. My plate voltage read 364V when I had the Rub 6L6GCM's in, and around 344V when I had the Tung sols in. Also, sorry if I keep repeating the same question here, but i'm trying to sort this out quick so I can figure out what to do in regards to my RMA situation. By getting a "hotter" tube as recommended by multiple users here, does that mean I need an entirely different tube type, or simply exchange for the same tube type, but one that just runs at a higher current?

 

[GuitarGuyLP]

A hotter tube will draw a higher plate current at a lower setting of the bias pot.

The 5881s should be around 38ma (read in mV from the test points)

If I were you I would send the details to the place you bought the tubes from including plate voltage, and maximum bias measurement you were able to get, and see if they have a tube that is hot enough for your amp, if not I would stick with the 5881s.

 

[Omega1397]

A hotter tube will draw a higher plate current at a lower setting of the bias pot.

The 5881s should be around 38ma (read in mV from the test points)

If I were you I would send the details to the place you bought the tubes from including plate voltage, and maximum bias measurement you were able to get, and see if they have a tube that is hot enough for your amp, if not I would stick with the 5881s.

Thank you. So there's no way I can get another Ruby 6L6GCM's that will draw more current- so is it a property of the tube which determines how much current it draws? or would I be able to get another set of the same tube but one that draws a higher current?

Also, for the 5881's, I see you say they should be around 38 ma. I'm running calculations (Plate voltage is 344Vish, 25W for the tubes) and i'm getting 42 mA for 60%. I was wondering where you got the 38 mA from- perhaps i'm doing something wrong?

 

[GuitarGuyLP]

5881s are 23 watt tubes

Tubes are not all exactly the same, They are measured, and rated based on current draw, that is how they are matched. They should be able to get you a set of Ruby 6l6gcms that will draw more current.

 

[Omega1397]

Thanks a lot !