- Feb 20, 2005
- 27,956
- 20,348
- Disclosures
- Endorsing artist: Dingwall Guitars
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Let's talk about 6SL7 tubes!
- Thread starter BurningSkies
- Start date
Passinwind
I know nothing.
- Dec 3, 2003
- 23,045
- 45,909
- Disclosures
- Designer/Toaster Tech @ Passinwind Electronics
Passinwind
I know nothing.
- Dec 3, 2003
- 23,045
- 45,909
- Disclosures
- Designer/Toaster Tech @ Passinwind Electronics
Heh, they actually belong to a local tech friend of mine who took on a lot of my work load when I "retired." Gotta get up to his place one of these days and snag a few...
Ya, really! As much as you're into 6SL7's, you certainly should.
So question...B-15N...each preamp channel gets a 6SL7 and there's a 6SL7 phase inverter. Does the phase inverter matter for tone or is it all in the preamp tube?
So question...B-15N...each preamp channel gets a 6SL7 and there's a 6SL7 phase inverter. Does the phase inverter matter for tone or is it all in the preamp tube?
Passinwind
I know nothing.
- Dec 3, 2003
- 23,045
- 45,909
- Disclosures
- Designer/Toaster Tech @ Passinwind Electronics
Everything matters, but typically the first stage matters the most, IME. You should ask David though, he knows a lot more about B-15s than I do. I owned one, but it was my first real bass amp and I never got it working as well as it could have.
The first stage is very important. I think that the phase inverter is also an important component of the tone. As Charlie said, everything matters. This includes the tube stages, the tone stage, the phase inverter and power stage, the output transformer, as well as the power supply and how much ripple is present. They all come together to define the performance and tone of the amp.
In the B-15, the first stage is designed to amplify in a very conservative, pure way, minimizing compression and other forms of distortion. It is basically pure 6SL7 tone applied to the instruments signal. They achieve this by the way the tube is biased, with a relatively high plate voltage, and not using a cathode capacitor. Very different than what Fender was doing at the time. This sets the B-15 apart from other amps and is what imparts some of the magic it offers.
The phase inverter in the B-15 is what they call a floating paraphase design. It works very well in the B-15. It was used in some of the early radio circuits. The purpose of the phase inverter is to split the input signal into two out of phase signals that are used to drive the power tubes. The problem with phase inverter designs is that they are not perfect. These imperfections affect the performance of the power amp, and can impart some of the character than an amp has. This is why some people, especially in hi-fi where accuracy is desired, install a phase inverter tube where the two halves of the tube are matched. This helps optimize how consistent the two output signals of the phase inverter are. This isn't as important in musical instrument amps. As I mentioned, an imbalance can add character to the sound of the amp. A big plus of the 6SL7 tube is that the two halves age fairly consistently. This offers stability over time in terms of how the phase inverter performs. It keeps the amp sounding the same.
Here is an explanation of the contribution that the phase inverter makes in an amp. Take what they say with a grain of salt. The contribution of the phase inverter, as far as tone is concerned, will vary from amp to amp. For an amp that offers a lot of distortion, the phase inverter can make a big contribution to the sound. Not as much in the B-15, although don't underestimate its contribution.
In the early 60's, not that long after WWII, designs looked to the future. Everything was radically different, new and improved. Fender moved away from octal tubes in their designs. Ampeg needed to be different to compete with Fender. The B-15 was intended to be a hi-fi sounding bass amp. They took their queues more from the hi-fi world than they did from the musical instrument industry at the time. The octal tubes, the potted transformers, the James tone stage all harked back to the 1950's hi-fi designs which had great tone. It was old school and vintage which was in the opposite direction that contemporary designs were going in. The amp had an artistic, conservative, and vintage look that matched the tone. The design has stood up to the test of time in a way that very few other amps have. It has also proven that new and improved isn't always best. There's definitely something in the sound of those old octal tubes that people love.
In the B-15, the first stage is designed to amplify in a very conservative, pure way, minimizing compression and other forms of distortion. It is basically pure 6SL7 tone applied to the instruments signal. They achieve this by the way the tube is biased, with a relatively high plate voltage, and not using a cathode capacitor. Very different than what Fender was doing at the time. This sets the B-15 apart from other amps and is what imparts some of the magic it offers.
The phase inverter in the B-15 is what they call a floating paraphase design. It works very well in the B-15. It was used in some of the early radio circuits. The purpose of the phase inverter is to split the input signal into two out of phase signals that are used to drive the power tubes. The problem with phase inverter designs is that they are not perfect. These imperfections affect the performance of the power amp, and can impart some of the character than an amp has. This is why some people, especially in hi-fi where accuracy is desired, install a phase inverter tube where the two halves of the tube are matched. This helps optimize how consistent the two output signals of the phase inverter are. This isn't as important in musical instrument amps. As I mentioned, an imbalance can add character to the sound of the amp. A big plus of the 6SL7 tube is that the two halves age fairly consistently. This offers stability over time in terms of how the phase inverter performs. It keeps the amp sounding the same.
Here is an explanation of the contribution that the phase inverter makes in an amp. Take what they say with a grain of salt. The contribution of the phase inverter, as far as tone is concerned, will vary from amp to amp. For an amp that offers a lot of distortion, the phase inverter can make a big contribution to the sound. Not as much in the B-15, although don't underestimate its contribution.
In the early 60's, not that long after WWII, designs looked to the future. Everything was radically different, new and improved. Fender moved away from octal tubes in their designs. Ampeg needed to be different to compete with Fender. The B-15 was intended to be a hi-fi sounding bass amp. They took their queues more from the hi-fi world than they did from the musical instrument industry at the time. The octal tubes, the potted transformers, the James tone stage all harked back to the 1950's hi-fi designs which had great tone. It was old school and vintage which was in the opposite direction that contemporary designs were going in. The amp had an artistic, conservative, and vintage look that matched the tone. The design has stood up to the test of time in a way that very few other amps have. It has also proven that new and improved isn't always best. There's definitely something in the sound of those old octal tubes that people love.
I keep telling people that hamfests are a great source for tubes. Well worth checking if there is one in your area. This is where you can also find very affordable test equipment.
I bought a tub full of NOS RCA 6SN7 tubes for $2 each at one. Now if I can only find a similar deal on Western Electric 300B tubes, I'll be a happy camper.
I bought a tub full of NOS RCA 6SN7 tubes for $2 each at one. Now if I can only find a similar deal on Western Electric 300B tubes, I'll be a happy camper.
Thanks for the kind compliment Jimmy but we all know that you are a sage when it comes to bass and Ampeg that trumps me any time.
Not to paraphrase, but I believe you mean paraphase.
Another interesting thing about paraphase inverters (if you're into this sort of thing) is that they are very inefficient, but introduce very little distortion. As Beans-On-Toast points out, Fender and others were looking "forward" at the time and were abandoning 50s-era paraphase inverters for a type of inverter called a long-tailed pair. It's a much more efficient inverter that can drive the power tubes harder, but it also imparts a much different sound on the amp, further distancing the sound of the B-15 from the other bass amps of the time.
Not to paraphrase, but I believe you mean paraphase.
Yes! The spelling checker on my mac drives me nuts by changing what I type faster than I can type it.
That's because the 6L6s are being run very conservatively in the B-15. The entire design is focussed on avoiding distortion. Having extra drive for the power tubes isn't needed here because they are already able to reach their full swing.
On paper, it shouldn't make any difference. If the cathode resistors were close to the edge of their rating it might be worth splitting them up, but they're not. There's no reason not to tie the cathodes together. Since they are out of phase with each other, there's no issue with any sort of cross-talk; they're recieving the two halves of the same signal... or as close to it as the the PI is balanced and will allow.
- Feb 20, 2005
- 27,956
- 20,348
- Disclosures
- Endorsing artist: Dingwall Guitars
Tease.
I keep telling people that hamfests are a great source for tubes. Well worth checking if there is one in your area. This is where you can also find very affordable test equipment.
I bought a tub full of NOS RCA 6SN7 tubes for $2 each at one. Now if I can only find a similar deal on Western Electric 300B tubes, I'll be a happy camper.
Thanks for the link. I've book marked it for future use. There's one event listed within an hour of me sometime in September. I like these kind of events.
Not that I should...but say that someone wanted to really get into trying out different 6SL7s in a pre-amp. Say....a Jule Amps Monique 
Are there any tubes you guys would recommend staying away from, or any tips for a (tubey)newbie?
Are there any tubes you guys would recommend staying away from, or any tips for a (tubey)newbie?
Wow, David and Lo-E just ramped up this conversation to quite a degree! Thanks for the awesome back and forth you guys are having. And thanks back for the compliment, but I only wish knowing about bass playing pays what being able to repair amps does and was as steady an income
I don't have as much experience with them as Charlie and David, but I'm hoping to use this thread and other people's upcoming Monique tube rolling experiments to narrow it downNot that I should...but say that someone wanted to really get into trying out different 6SL7s in a pre-amp. Say....a Jule Amps Monique
I've been using Sylvanias in my B-15, and I briefly tried RCA's. The RCA's I got sounded great but crackled. Probably a fluke, but I was weirded out that they all crackled and got a few Sylvanias because that's what Ampeg used. They sound great to me. Ampeg's using JAN Philips 6SL7's in the Heritage B-15, but my tube guru who knows every single thing there is to know about every tube made told me they're Sylvanias. Wish I could compare them to the Sovteks it came with when I bought it, but I'll say this for the Sovteks...they lasted for years.
