Creating bias sheets could use help with voltages to include.

[2deaf]

Here is the graph I thought I was looking at.  Along with a chart with bias voltages.

 

[Mike_J]

You were right in that the work has already been done. What my graph and legend shows is consistent with what you posted. Mine is in color and looks a little nicer in its page protector inside the leather binder of honor but yes if those are available for a variety of power tubes it would save a few minutes in calculating the values and preparing the graph. Your graph is based on the same 23 watts maximum dissipation the datasheet shows for the Tungsol 5881.


Thanks
Mike

[Mike_J]

Just to note that the 23W rating of the 5881 is design centre, whereas the 30W of the 6L6GC is design max. A design centre limit for the 6L6GC would probably be about 26W.
Hence the types aren’t really that far apart, certainly the differing rating systems used act to exaggerated it.

That being the case, they would be conservatively biased. Based on a 26 watt max plate dissipation rate, which is a guess based on what you said for the 6L6GC, if you are using a 23 watt graph and chart you would really be biasing at about 60 percent dissipation. I guess customers would blow fewer tubes and your reputation might be better presuming the tubes sounded better biased cold. If the tubes sound better biased hot then the marketing strategy wouldn't be so good. But my guess is Tungsol knew what they were doing.


Thanks
Mike

[Mike_J]

Here is the graph I thought I was looking at.  Along with a chart with bias voltages.

Have given your graph and chart their own page protector sheets in the leather binder of honor. The post asked for help with voltages to include and this goes well below my graph and 100 watts above it and therefore could be quite useful so a place in the binder is befitting of such a product.


Thanks
Mike

[pdf64]

...If the tubes sound better biased hot then the marketing strategy wouldn't be so good. But my guess is Tungsol knew what they were doing.

Within a reasonable range, valves sound pretty much the same per se, however they're biased. At extremes, linearity will deteriorate, eg note that on the anode chart, the spacing between the plots of incremental changes to grid voltages will tend to be closer at one end, further apart at the other. But within that evenly spaced area, the valves themselves have a wide range of operating point options. It's the circuit, not the valves, that causes different designs to sound different. Most especially with push pull class AB designs, which will have a fundamental change in operating conditions according the particular valves, operating point and signal level, eg at low signal levels both valves are working and are effectively in parallel, whereas at high signal levels, each valve flips between working on its own, working in parallel with the other, and being completely shut off. How smoothly the transfer along that cycle things go is dependent on anode current. Not, please note, anode dissipation. I keep repeating this, but anode dissipation is just a limit, it doesn't, per se, affect circuit operation / how an amp sounds.
Moving on to the human factor, transconductance and hence stage gain tends to increase along with anode current. So hotter bias will tend to make an amp a bit louder, all else being equal. And human perception is such that 'a bit louder', eg a 1dB increment in signal level, tends to be perceived as sounding better / fuller / fatter etc, rather than just 'louder'.
So how an amp sounds may be seen as something of a quagmire of unconscious self deception, unless far more effort than most people can be bothered with is taken to normalise signal levels.

[Mike_J]

...If the tubes sound better biased hot then the marketing strategy wouldn't be so good. But my guess is Tungsol knew what they were doing.

Within a reasonable range, valves sound pretty much the same per se, however they're biased. At extremes, linearity will deteriorate, eg note that on the anode chart, the spacing between the plots of incremental changes to grid voltages will tend to be closer at one end, further apart at the other. But within that evenly spaced area, the valves themselves have a wide range of operating point options. It's the circuit, not the valves, that causes different designs to sound different. Most especially with push pull class AB designs, which will have a fundamental change in operating conditions according the particular valves, operating point and signal level, eg at low signal levels both valves are working and are effectively in parallel, whereas at high signal levels, each valve flips between working on its own, working in parallel with the other, and being completely shut off. How smoothly the transfer along that cycle things go is dependent on anode current. Not, please note, anode dissipation. I keep repeating this, but anode dissipation is just a limit, it doesn't, per se, affect circuit operation / how an amp sounds.
Moving on to the human factor, transconductance and hence stage gain tends to increase along with anode current. So hotter bias will tend to make an amp a bit louder, all else being equal. And human perception is such that 'a bit louder', eg a 1dB increment in signal level, tends to be perceived as sounding better / fuller / fatter etc, rather than just 'louder'.
So how an amp sounds may be seen as something of a quagmire of unconscious self deception, unless far more effort than most people can be bothered with is taken to normalise signal levels.

Maybe the last thing on the planet that needs to be louder is the 5f6a Bassman. I was playing with plate current in preamp tubes yesterday and plan to get back to it today. I am willing to expend more effort than most people can be bothered with to normalize signal level. Mainly was interested in plate dissipation because it had been six years since I biased an amp and just wanted to refamiliarize myself with the process. Confidence is now up for that task.


Like I said getting into plate current for the preamp tubes again today. Was surprised the 12AX7 would do better with a 1.1+K something cathode resistor in V1 of a 5f6a build at least under the conditions the schematic shows. The 12AY7 is about 1.64K. Is different depending on what voltage is applied to the plate resistor and the value of the resistor itself. Not ready to understand the plate current in the 5881 or 6L6GC but will be in the near future. Trying to work from the front to the back now.


Thanks
Mike

[2deaf]

...if those are available for a variety of power tubes it would save a few minutes in calculating the values and preparing the graph.

I have graphs and charts for 6V6 and EL34.  I have the graphs and raw numbers for 6L6 and 6550, but I haven't converted the numbers and put them in a chart yet. 

 

[2deaf]

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[2deaf]

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[2deaf]

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[Mike_J]

...if those are available for a variety of power tubes it would save a few minutes in calculating the values and preparing the graph.

I have graphs and charts for 6V6 and EL34.  I have the graphs and raw numbers for 6L6 and 6550, but I haven't converted the numbers and put them in a chart yet.

Thanks for the graphs and charts. They will be of help to me when biasing amps with these power tubes, which is almost any amp I would build.


Thanks
Mike