For 6BL7 tube users

[leftside]

Damn you guys. I haven't tube rolled for a few weeks, but now I have something else to try...

 

[mordy]

Hi leftside,
 
Hey, look at the positive - these tubes ain't going to break the bank LOL. And maybe you already have some or all of them...
 
 

 

[leftside]

Got loads lol. Do I risk some of the ECC32 - ECC35 tubes... ?

 

[Badas]

  Hi Badas,
 
Thank you for your suggestion for a speed test. Played the intro a number of times, and I get similar results to yours. My Elise tube amp is used as a preamp for speakers and used together with a 110W Sony ss amp.
 
With my EL3N + 2x 6BL7/6SN7 combination the impact is there, but the very quick drum strokes are a bit slurred. On the back of my ss amp is a switch I use to take the tube amp out of the circuit. In ss mode the quick drum strokes are better separated, but overall the sound is much less vivid.
 
The treble is excellent with the Elise, and the amp keeps up very well with the cymbals.
 
As you mention, the slight slowness in bass response is not a deal breaker. I am sure that some other tubes will respond quicker, but at the expense of the mid range sweetness of this combination.

 
My thoughts exactly.

  Damn you guys. I haven't tube rolled for a few weeks, but now I have something else to try...

 

[Badas]

Hi Badas,

Glad you like this combination.

Here are the numbers for the amplification factors (gain):

6BL7   15

6SN7   20

6SL7   70

Based on my very limited knowledge, I would say that the 6BL7 and the 6SN7 are interchangeable, but the 6SL7 may not work well in some applications.

The 6BX7 has an amplification factor of 10, so it should give less volume in certain applications compared to the 6BL7/6SN7.

It is not clear to me what happens with the gain when you mix tubes.

Hey,

A light bulb went off in my head (doesn't happen often). If the 6SN7 is pinned the same and similar voltage then couldn't you run two 6SN7's per 6080 circuit?

I have a bunch of 6C8G's. From the 6SL7 family just with the heater pin at the top. 6SL7 is pinned the same as 6SN7.
If the voltage is right I'm thinking of being crazy and running 4 6C8G's in the 6BL7 twin adapters in the two 6080 circuits.

Can anyone see faults in doing this?

 

[2359glenn]

 

Hi Badas,

Glad you like this combination.

Here are the numbers for the amplification factors (gain):

6BL7   15

6SN7   20

6SL7   70

Based on my very limited knowledge, I would say that the 6BL7 and the 6SN7 are interchangeable, but the 6SL7 may not work well in some applications.

The 6BX7 has an amplification factor of 10, so it should give less volume in certain applications compared to the 6BL7/6SN7.

It is not clear to me what happens with the gain when you mix tubes.

Hey,

A light bulb went off in my head (doesn't happen often). If the 6SN7 is pinned the same and similar voltage then couldn't you run two 6SN7's per 6080 circuit?

I have a bunch of 6C8G's. From the 6SL7 family just with the heater pin at the top. 6SL7 is pinned the same as 6SN7.
If the voltage is right I'm thinking of being crazy and running 4 6C8G's in the 6BL7 twin adapters in the two 6080 circuits.

Can anyone see faults in doing this?

You can try it but they cant handle the current probably severely shorten there life.

 

[mordy]

Hi 2359glenn,
 
Just to clarify the question - if the 6C8G tube draws 0.3A, four of them would draw 1.2A or 0.6A/channel. If the Woo22 can handle 3A/channel for power tubes, wouldn't it be possible to run 4 x 6C8G as power tubes?
 
Even  dual tubes at 0.6A/channel would seem very feasible as drivers as well since the Woo22 is rated at 1A/channel for driver tubes.
 
Likewise, since the 6SN7 draws 0.6A, four of them should be fine as powers (but not as drivers, since 1.2A exceeds the 1A rating).
 
Please let me know if my assumptions are incorrect - thanks.

 

[gibosi]

  Hi 2359glenn,
 
Just to clarify the question - if the 6C8G tube draws 0.3A, four of them would draw 1.2A or 0.6A/channel. If the Woo22 can handle 3A/channel for power tubes, wouldn't it be possible to run 4 x 6C8G as power tubes?
 
Even  dual tubes at 0.6A/channel would seem very feasible as drivers as well since the Woo22 is rated at 1A/channel for driver tubes.
 
Likewise, since the 6SN7 draws 0.6A, four of them should be fine as powers (but not as drivers, since 1.2A exceeds the 1A rating).
 
Please let me know if my assumptions are incorrect - thanks.

 
In tube amps, there are two different circuits involved. The circuit you are referencing is the heater circuit. But I believe that Glenn's concern is with the circuit that actually runs the amp, in which current flows through the tube itself, from the cathode to the plate. In 6AS7-based amps, that circuit is designed to push something around 100ma through the tube. So if I understand Glenn correctly, if you put 6C8Gs into this circuit, there may well be too much current flowing through the tube which might cause it to fail sooner rather than later. (But of course, I may well be wrong, and if so, I expect that Glenn will correct me.

 

[2359glenn]

  Hi 2359glenn,
 
Just to clarify the question - if the 6C8G tube draws 0.3A, four of them would draw 1.2A or 0.6A/channel. If the Woo22 can handle 3A/channel for power tubes, wouldn't it be possible to run 4 x 6C8G as power tubes?
 
Even  dual tubes at 0.6A/channel would seem very feasible as drivers as well since the Woo22 is rated at 1A/channel for driver tubes.
 
Likewise, since the 6SN7 draws 0.6A, four of them should be fine as powers (but not as drivers, since 1.2A exceeds the 1A rating).
 
Please let me know if my assumptions are incorrect - thanks.

Hi Mordy
I wasn't talking about filament current drawn from the amp. It is the current through the tube cathode to plate will be to high. A 6C8G is only good for 3.1ma
A 6AS7 is 125ma you can replace a 125ma tube with two 3.1ma tubes that would add up to 6.2ma.
I wouldn't even use 6SN7s in this position.
There is more to it then this but I am not getting into it here.

 

[attmci]

 
Hi Mordy
I wasn't talking about filament current drawn from the amp. It is the current through the tube cathode to plate will be to high. A 6C8G is only good for 3.1ma
A 6AS7 is 125ma you can replace a 125ma tube with two 3.1ma tubes that would add up to 6.2ma.
I wouldn't even use 6SN7s in this position.
There is more to it then this but I am not getting into it here.

Attached data for a 6C8G.
 
The thing that paralleling two or more triodes does is double (or multiple) the transconductance (which cuts the source impedance feeding the phones in half or more).
 
The 6AS7 has the same transconductance per triode as the 6BL7, but the 5998 has nearly twice the 6080 transconductance. So two paralleled 6BL7 is roughly equivalent to a 5998 in that parameter. I suspect that is the main reason for the audible difference (not sure about this). But multiple 6BL7/6BX7 had been proved to work in multiple amps. and can beat many 6080/6AS7 tubes.

 

[mordy]

Hi 2359glenn,
 
I am trying to get a better understanding of the plate voltage vs amplifier internal current rating. In the instances that the tubes used are within the rated tube current capacity of the amp, can you add up the plate voltages for different tubes, if adding or mixing tubes?
 
If I use an amp built for a pair of 6AS7 family power tubes, the plate voltage is 125mA/tube.
 
Here are plate voltages for a couple of different tubes that I use:
 
6N7, 6N7G                   6
6SN7                           10
6BL7                            65
7236                           100
6AS7, 6080                 125
 
 
How close should the combined plate voltages be to be a good match for the amp? How many % is going beyond what is safe? From the comments I read a tube using a plate voltage of say 10 may be overtaxed and burn out prematurely, if I understand it correctly.
 
2 x 6BL7 = 130mA which seems close to the 125mA of a 6AS7 tube.
 
In my amp I can use 6N7, 6BL7 and 6SN7 together with a combined plate voltage of 6+10+65 = 81mA (and current rating of 0.8 + 1.5 +0.6 = 2.9A) with external power. Would this be within the operating range of the 125mA of a 6AS7 tube?
 
I apologize in advance if i am asking silly questions - I don't have a background in electronics. It seems to me that there may be many other parameters that are important as well.

 

[attmci]

 
If you make your own adapters besides grid stoppers on every grid put a equalizing resistor on each cathode to balance 
the current in the tubes.    Or modify the adapters you have with these resistors.
This is what I do in OTLs that have six 6BL7s and the current is close to the same in all the tubes.

 

[gibosi]

  Hi 2359glenn,
 
I am trying to get a better understanding of the plate voltage vs amplifier internal current rating. In the instances that the tubes used are within the rated tube current capacity of the amp, can you add up the plate voltages for different tubes, if adding or mixing tubes?
 
If I use an amp built for a pair of 6AS7 family power tubes, the plate voltage is 125mA/tube.
 
Here are plate voltages for a couple of different tubes that I use:
 
6N7, 6N7G                   6
6SN7                           10
6BL7                            65
7236                           100
6AS7, 6080                 125
 
 
How close should the combined plate voltages be to be a good match for the amp? How many % is going beyond what is safe? From the comments I read a tube using a plate voltage of say 10 may be overtaxed and burn out prematurely, if I understand it correctly.
 
2 x 6BL7 = 130mA which seems close to the 125mA of a 6AS7 tube.
 
In my amp I can use 6N7, 6BL7 and 6SN7 together with a combined plate voltage of 6+10+65 = 81mA (and current rating of 0.8 + 1.5 +0.6 = 2.9A) with external power. Would this be within the operating range of the 125mA of a 6AS7 tube?
 
I apologize in advance if i am asking silly questions - I don't have a background in electronics. It seems to me that there may be many other parameters that are important as well.

 
Mordy,
 
While you seem to be talking about plate voltages, the numbers you have posted represent plate current in milliamps. (Although, I should point out that the RCA datasheet for the 6BL7 indicates 40ma, not 65). Moreover, in this case,I am not sure how useful it is to look at plate voltage. Plate current is in fact the characteristic we should be looking at. 
 
In my experience, two 6BL7s, 80ma (again, with a plate current of 40ma per tube, not 65) works very well. And three, with a combined plate current of 120ma is optimal. Your suggested combination, 6N7, 6BL7 and 6SN7 with a combined plate current of 6+10+40 = 56ma, is apparently working well for you. But as Glenn posted, he would not encourage you to use two 6SN7's totaling only 20ma.
 
In an attempt to extrapolate, my best guess, and this is only a guess, is that one-half of 125ma, around 60ma, is probably OK, with more being better. But combinations amounting to substantially less than 60ma are probably best avoided.
 
But as Glenn mentioned, apparently there is more to it than just adding up the total plate current so it may not be quite this simple....

 

[mordy]

Hi Gibosi,
 
You are right, I meant plate current - did this late at night...
 
Take a look at this GE data sheet for the 6BL7GTA:
 
http://www.nj7p.info/Tubes/PDFs/Frank/093-GE/6BL7GTA.pdf
 
The plate current has several values - which one to go by? (page 2) It lists 65 at 150V and 40 at 250V if I understand correctly.

 

[gibosi]

  Hi Gibosi,
 
You are right, I meant plate current - did this late at night...
 
Take a look at this GE data sheet for the 6BL7GTA:
 
http://www.nj7p.info/Tubes/PDFs/Frank/093-GE/6BL7GTA.pdf
 
The plate current has several values - which one to go by? (page 2) It lists 65 at 150V and 40 at 250V if I understand correctly.

 
The RCA datasheet lists only 40ma at 250 volts.
 
http://www.mif.pg.gda.pl/homepages/frank/sheets/049/6/6BL7GT.pdf
 
I notice that the GE datasheet lists both values, but this is for a 6BL7GTA and not a 6BL7GT. According to the GE datasheet, the two sections of a 6BL7GTA are not identical. Section 1 has been "improved" to provide a longer lifetime when used as an oscillator. So perhaps when used as an oscillator, section 1 is operated at a lower voltage allowing for a higher current? But again, I am speculating as I certainly do not know...
 
In talking about my OTL, Glenn has used the 40ma value for the 6BL7, so that is the value I use in my calculations.