Would I need to bias my amp for this tube swap?

Zultan · January 9th, 2008, 07:26 AM

I'm not too much of an expert on tube amps and tubes so please excuse me if this is a stupid question, but I don't like the tubes that came in my amp and I would like to switch from these: http://www.musiciansfriend.com/produ...uet?sku=211201
To these: http://www.musiciansfriend.com/produ...ube?sku=211212

Would I need to get my amp biased? Can I bias it myself with some kind of tool? What would you suggest?

sjhusting · January 9th, 2008, 07:55 AM

Those are both New Sensor-made 5881s; the same tube, so to speak; what are you trying to achieve? Don't ask me why there is such a big difference in price. Maybe because GT isn't taking a slice.

Instead you might consider JJs or the new Tungsol (which is also New Sensor, but not the same as the above, as far as I know). Or SEDs, if you can get them where you are. Shuguang also makes good 6L6s (TAD and others).

But it would be useful to know what kind of amp you have. And what it is you don't like about what's in there now.

steven

Zultan · January 9th, 2008, 07:58 AM

I have a 1969 Super reverb and a 1966 Super reverb. The GT6L6s are in the 1966 and the 6L6WGCs are in the 1969. I just like the sound of the 1966 better so I figured it might be the tubes. It might be the circuitry though, I don't know.

sjhusting · January 9th, 2008, 08:12 AM

So, yes, you have to bias. But have you tried swapping the tubes to see if it's the tubes or (more likely) something else? For the test, you wouldn't necessarily need to bias. They wouldn't be operating optimally, but probably good enough to tell the difference.

steven

Zultan · January 9th, 2008, 08:14 AM

No i haven't tried to do that. It's probably not the tubes, it's probably the amp. I need to get it converted to AB763 circuitry, etc. It sounds great, just not as great as my other one. I dunno. Anyway, is there anyway I could bias my amp myself?

teleamp · January 9th, 2008, 08:18 AM

A good premp tube would be better noticed.

MikeY

Zultan · January 9th, 2008, 08:23 AM

Quote:

Originally Posted by teleamp

A good premp tube would be better noticed.

MikeY

elaborate?

sjhusting · January 9th, 2008, 08:39 AM

Yeah, try some good NOS preamp tubes - a 5751 is my favorite in the input stage.

A '69 Super may be pretty close to a blackface as it is; the early SF were still AB763. If you have a 'hum balance' pot then it is the later circuit (probably AB568). If you have a bias adjust, then it is still AB763. The 763 specifies a GZ34 rectifier, the 568 specifies a 5U4. Check the tube chart.

But even so, between 10-20% tolerances and component drift, the older amp might just sound better.

steven

Zultan · January 9th, 2008, 08:44 AM

My tubechart says AB763, but I thought they only used those charts because they didn't make any new ones? What is a hum balance pot and where can I find it?

sjhusting · January 9th, 2008, 09:49 AM

No, there were SF AB763s.

But it's too hard to guess. You should either check the serial number, or open the amp and look at the circuit. But if you do this, recall that the filter caps might still be charged.

steven

loudguitars · January 9th, 2008, 09:56 AM

Bias your AMP EVERY time you change power tubes, UNLESS you have a other tubes that are matched to the first. Also change your amp driver tube with a balanced 12ax7 every time you change power tubes. I have an amp that uses 2 power tubes and I buy matched JJ quartets so I have matched spares. I have an amp that I can bias myself, and it makes a HUGE difference in the warmth and presence. I would stay away from Chinese tubes. I don't have any good experiences with them. IMHO

Zultan · January 9th, 2008, 12:47 PM

Well after a while of looking around I've decided that I'm going to get two Sovtek 6550WE power tubes and a JAN Philips 5751 tube.

I'm still interested knowing how to bias my amp myself..

sjhusting · January 9th, 2008, 03:53 PM

Woah!! A 6550 is not a good choice in a 6L6 amp.

steven

Darcy Hoover · January 9th, 2008, 04:47 PM

Woops, posted in the wrong spot...

Sorry...

Darcy Hoover · January 9th, 2008, 04:48 PM

Sorry, I meant to post a new thread, clicked the wrong button.....

Just do your best to ignore my inane mistakes!

Big Mike Simpson · January 9th, 2008, 07:02 PM

Quote:

Originally Posted by loudguitars

Also change your amp driver tube with a balanced 12ax7 every time you change power tubes.

What is an "amp driver tube"... Are you referring to a preamp tube?

How is a single 12ax7 "balanced"... or to what is it balanced to... itself?

I have not heard these terms....

nonvintage · January 9th, 2008, 07:04 PM

I have a 65 Super Reverb and the best tubes I've found for my amp are Winged =C= 6L6's. I think balanced 12at7's for the phase inverter position (V6 ) are recommended by some and others think it's hogwash to get them balanced. I've never tried a balanced PI myself but NOS is recommended since 12at7's are relatively cheap compared to new production tubes.

Zultan · January 9th, 2008, 10:31 PM

Are you sure 6550s are not good for a 6L6 amp? I've read that SRV used them in a super reverb modded for 150w and 4 powertubes.. I dunno. I'll just go with the GT6L6s.

By the way, I noticed I have the AB568 circuitry. Can anyone give me some detailed instructions on how to convert it? I don't want to leave my amp with some tech just to get this so called easy job done and have him over charge me.

loudguitars · January 10th, 2008, 02:56 AM

A "driver" tube is a phase inverter. It is used on Most amps (Class AB). Having a balanced PI prevents "phase cancellation" between the power tubes. Having matched power tubes is approaching pointless of you don't have a balanced or near balanced PI "driver tube" All Fenders, Boogies and Marshall come with balanced Driver tubes when new. The quickest way to lose tone is have unmatched cold biased power tubes with an unbalanced PI.
Proper powertube bias and balanced drivers is a HUGE part of a warm full tone with ANY tube amp. There is a site "amplifier blueprinting" search it, it explains the process. Or go to Eurotubes, or Dougs Tubes or KCANOS tubes . com and ask those guys. I have heard the difference and I will probably NEVER own a fixed bias amp again.

Paul G. · January 10th, 2008, 12:12 PM

I don't mean to be neurotic here, but you don't mean "fixed bias"--you're probably referring to "non-adjustable bias".

Fixed bias means the bias is set by the circuitry of the amp, it may be adjustable.

The other scheme is "self-bias" or "cathode" bias in which the current draw of the tube sets the bias.

Carry on.

P.

Zultan · January 10th, 2008, 07:31 PM

well I'm probably going to get the circuitry and bias stuff and whatever changed to AB763 this weekend

loudguitars · January 10th, 2008, 08:01 PM

Quote:

Originally Posted by Paul G.

I don't mean to be neurotic here, but you don't mean "fixed bias"--you're probably referring to "non-adjustable bias".

Fixed bias means the bias is set by the circuitry of the amp, it may be adjustable.

The other scheme is "self-bias" or "cathode" bias in which the current draw of the tube sets the bias.

Carry on.

P.

You are NOT neurotic, and you are correct. MY BAD! Damn Nomenclature.
Thanks for clearing that up that is a big deal!!

loudguitars · January 10th, 2008, 08:05 PM

Quote:

Originally Posted by Big Mike Simpson

What is an "amp driver tube"... Are you referring to a preamp tube?

How is a single 12ax7 "balanced"... or to what is it balanced to... itself?

I have not heard these terms....

A balanced 12ax7 is balanced to itself. Both halves have equal output. Important! The advantage of having balanced output tubes is diminished without a balanced driver (PI) tube.

Rocks · January 10th, 2008, 08:17 PM

Quote:

Originally Posted by Zultan

Are you sure 6550s are not good for a 6L6 amp? I've read that SRV used them in a super reverb modded for 150w and 4 powertubes.. I dunno. I'll just go with the GT6L6s.

SRV also had one heck of an amp tech and very little was stock in his amp. Just changing the tubes to 6550 was only part of what he did to make them work in that amp and to get the SRV sound.

sjhusting · January 11th, 2008, 12:53 AM

Well, to begin with, the 6550 requires 1.6A heater current, compared to 0.9A for a 6L6GC, so you better make sure your 6.3V winding will support an additional 1.4A (for 2 tubes). There are other differences; the pinout is the same, but the operating conditions are different; they are not substitutes.

And I always heard SRV used KT66s, not 6550s.

steven

sector9 · January 11th, 2008, 06:24 PM

Quote:

Originally Posted by Zultan

Are you sure 6550s are not good for a 6L6 amp? I've read that SRV used them in a super reverb modded for 150w and 4 powertubes.. I dunno. I'll just go with the GT6L6s.

By the way, I noticed I have the AB568 circuitry. Can anyone give me some detailed instructions on how to convert it? I don't want to leave my amp with some tech just to get this so called easy job done and have him over charge me.

You don't even know how to bias your amp but your going to change the circuitry of it?? I think you should give "some tech" a call before you fry your brain. As far as tubes go just get a set of 6l6gc's and be done with it, imo thats what sounds the best in a super.

January 9th, 2008, 07:26 AM	#1 (permalink)
Zultan Tele-Meister Join Date: Jun 2007 Location: Louisiana Age: 26 Posts: 141	Would I need to bias my amp for this tube swap? I'm not too much of an expert on tube amps and tubes so please excuse me if this is a stupid question, but I don't like the tubes that came in my amp and I would like to switch from these: http://www.musiciansfriend.com/produ...uet?sku=211201 To these: http://www.musiciansfriend.com/produ...ube?sku=211212 Would I need to get my amp biased? Can I bias it myself with some kind of tool? What would you suggest?

January 9th, 2008, 04:47 PM	#14 (permalink)
Darcy Hoover Tele-Meister Join Date: Sep 2007 Location: Halifax, Nova Scotia Posts: 412	Woops, posted in the wrong spot... Sorry... __________________ http://www.soundclick.com/darcyhoover

January 9th, 2008, 04:48 PM	#15 (permalink)
Darcy Hoover Tele-Meister Join Date: Sep 2007 Location: Halifax, Nova Scotia Posts: 412	Sorry, I meant to post a new thread, clicked the wrong button..... Just do your best to ignore my inane mistakes! __________________ http://www.soundclick.com/darcyhoover

January 10th, 2008, 12:12 PM	#20 (permalink)
Paul G. Tele-Holic Join Date: Mar 2003 Location: Rhode Island Posts: 885	Uh oh. I don't mean to be neurotic here, but you don't mean "fixed bias"--you're probably referring to "non-adjustable bias". Fixed bias means the bias is set by the circuitry of the amp, it may be adjustable. The other scheme is "self-bias" or "cathode" bias in which the current draw of the tube sets the bias. Carry on. P. __________________ Listen to your mother

January 9th, 2008, 07:55 AM	#2 (permalink)
sjhusting Tele-Holic Join Date: Jul 2003 Location: Germany Posts: 613 14 Photos	Those are both New Sensor-made 5881s; the same tube, so to speak; what are you trying to achieve? Don't ask me why there is such a big difference in price. Maybe because GT isn't taking a slice. Instead you might consider JJs or the new Tungsol (which is also New Sensor, but not the same as the above, as far as I know). Or SEDs, if you can get them where you are. Shuguang also makes good 6L6s (TAD and others). But it would be useful to know what kind of amp you have. And what it is you don't like about what's in there now. steven

January 9th, 2008, 07:58 AM	#3 (permalink)
Zultan Tele-Meister Join Date: Jun 2007 Location: Louisiana Age: 26 Posts: 141	I have a 1969 Super reverb and a 1966 Super reverb. The GT6L6s are in the 1966 and the 6L6WGCs are in the 1969. I just like the sound of the 1966 better so I figured it might be the tubes. It might be the circuitry though, I don't know.

January 9th, 2008, 08:12 AM	#4 (permalink)
sjhusting Tele-Holic Join Date: Jul 2003 Location: Germany Posts: 613 14 Photos	So, yes, you have to bias. But have you tried swapping the tubes to see if it's the tubes or (more likely) something else? For the test, you wouldn't necessarily need to bias. They wouldn't be operating optimally, but probably good enough to tell the difference. steven

January 9th, 2008, 08:14 AM	#5 (permalink)
Zultan Tele-Meister Join Date: Jun 2007 Location: Louisiana Age: 26 Posts: 141	No i haven't tried to do that. It's probably not the tubes, it's probably the amp. I need to get it converted to AB763 circuitry, etc. It sounds great, just not as great as my other one. I dunno. Anyway, is there anyway I could bias my amp myself?

January 9th, 2008, 08:18 AM	#6 (permalink)
teleamp Tele-Holic Join Date: Oct 2006 Location: Central TX Age: 49 Posts: 589	A good premp tube would be better noticed. MikeY

January 9th, 2008, 08:39 AM	#8 (permalink)
sjhusting Tele-Holic Join Date: Jul 2003 Location: Germany Posts: 613 14 Photos	Yeah, try some good NOS preamp tubes - a 5751 is my favorite in the input stage. A '69 Super may be pretty close to a blackface as it is; the early SF were still AB763. If you have a 'hum balance' pot then it is the later circuit (probably AB568). If you have a bias adjust, then it is still AB763. The 763 specifies a GZ34 rectifier, the 568 specifies a 5U4. Check the tube chart. But even so, between 10-20% tolerances and component drift, the older amp might just sound better. steven

January 9th, 2008, 08:44 AM	#9 (permalink)
Zultan Tele-Meister Join Date: Jun 2007 Location: Louisiana Age: 26 Posts: 141	My tubechart says AB763, but I thought they only used those charts because they didn't make any new ones? What is a hum balance pot and where can I find it?

January 9th, 2008, 09:49 AM	#10 (permalink)
sjhusting Tele-Holic Join Date: Jul 2003 Location: Germany Posts: 613 14 Photos	No, there were SF AB763s. But it's too hard to guess. You should either check the serial number, or open the amp and look at the circuit. But if you do this, recall that the filter caps might still be charged. steven

January 9th, 2008, 09:56 AM	#11 (permalink)
loudguitars TDPRI Member Join Date: Jan 2008 Location: Boise Age: 47 Posts: 60	Bias your AMP EVERY time you change power tubes, UNLESS you have a other tubes that are matched to the first. Also change your amp driver tube with a balanced 12ax7 every time you change power tubes. I have an amp that uses 2 power tubes and I buy matched JJ quartets so I have matched spares. I have an amp that I can bias myself, and it makes a HUGE difference in the warmth and presence. I would stay away from Chinese tubes. I don't have any good experiences with them. IMHO

January 9th, 2008, 12:47 PM	#12 (permalink)
Zultan Tele-Meister Join Date: Jun 2007 Location: Louisiana Age: 26 Posts: 141	Well after a while of looking around I've decided that I'm going to get two Sovtek 6550WE power tubes and a JAN Philips 5751 tube. I'm still interested knowing how to bias my amp myself..

January 9th, 2008, 03:53 PM	#13 (permalink)
sjhusting Tele-Holic Join Date: Jul 2003 Location: Germany Posts: 613 14 Photos	Woah!! A 6550 is not a good choice in a 6L6 amp. steven

January 9th, 2008, 07:04 PM	#17 (permalink)
nonvintage Tele-Meister Join Date: Mar 2006 Location: San Diego Posts: 465	I have a 65 Super Reverb and the best tubes I've found for my amp are Winged =C= 6L6's. I think balanced 12at7's for the phase inverter position (V6 ) are recommended by some and others think it's hogwash to get them balanced. I've never tried a balanced PI myself but NOS is recommended since 12at7's are relatively cheap compared to new production tubes.

January 9th, 2008, 10:31 PM	#18 (permalink)
Zultan Tele-Meister Join Date: Jun 2007 Location: Louisiana Age: 26 Posts: 141	Are you sure 6550s are not good for a 6L6 amp? I've read that SRV used them in a super reverb modded for 150w and 4 powertubes.. I dunno. I'll just go with the GT6L6s. By the way, I noticed I have the AB568 circuitry. Can anyone give me some detailed instructions on how to convert it? I don't want to leave my amp with some tech just to get this so called easy job done and have him over charge me.

January 10th, 2008, 02:56 AM	#19 (permalink)
loudguitars TDPRI Member Join Date: Jan 2008 Location: Boise Age: 47 Posts: 60	A "driver" tube is a phase inverter. It is used on Most amps (Class AB). Having a balanced PI prevents "phase cancellation" between the power tubes. Having matched power tubes is approaching pointless of you don't have a balanced or near balanced PI "driver tube" All Fenders, Boogies and Marshall come with balanced Driver tubes when new. The quickest way to lose tone is have unmatched cold biased power tubes with an unbalanced PI. Proper powertube bias and balanced drivers is a HUGE part of a warm full tone with ANY tube amp. There is a site "amplifier blueprinting" search it, it explains the process. Or go to Eurotubes, or Dougs Tubes or KCANOS tubes . com and ask those guys. I have heard the difference and I will probably NEVER own a fixed bias amp again.

January 10th, 2008, 07:31 PM	#21 (permalink)
Zultan Tele-Meister Join Date: Jun 2007 Location: Louisiana Age: 26 Posts: 141	well I'm probably going to get the circuitry and bias stuff and whatever changed to AB763 this weekend

January 11th, 2008, 12:53 AM	#25 (permalink)
sjhusting Tele-Holic Join Date: Jul 2003 Location: Germany Posts: 613 14 Photos	Well, to begin with, the 6550 requires 1.6A heater current, compared to 0.9A for a 6L6GC, so you better make sure your 6.3V winding will support an additional 1.4A (for 2 tubes). There are other differences; the pinout is the same, but the operating conditions are different; they are not substitutes. And I always heard SRV used KT66s, not 6550s. steven