5150 III 6L6 heather voltage change?

[eschertron]

Unfortunately everything I mentioned in post was information from amp designer himself
https://m.youtube.com/watch?v=CrVRW-cS69g

By his own admission the information is passed on to him secondhand. He says "Fender did some research, and...". You'd have to go to the primary source to get real data on that. I'm not qualified to weigh in on whether the 5.95v filaments make a difference in tone, but I do know that 'secondary sources' such as his comments in the interview are met with skepticism in the world of scholarly research. Just my read on that.

[Helmholtz]

And 5.95V is just 5.5% down from 6.3V.
That's not an unusually low heater voltage at all.

[Chuck H]

By his own admission the information is passed on to him secondhand. He says "Fender did some research, and...". You'd have to go to the primary source to get real data on that. I'm not qualified to weigh in on whether the 5.95v filaments make a difference in tone, but I do know that 'secondary sources' such as his comments in the interview are met with skepticism in the world of scholarly research. Just my read on that.

See, now, this can be very telling. If someone with any particular charisma convinced a Fender exec that "filament voltage alters tone" and is responsible for the "brown sound" there may be shenanigan's. Is this within the 10% spec? Is this even something a corporate business mogul can absorb? Or is this just a game of mojo chasing for the sake of having an agenda implemented by the less technically informed and acted on by hired engineers that are getting a monthly paycheck and don't have "no" in their vocabulary? I find it highly suspect as well.

[loudthud]

Ok, here's some photos from my 576 Curve Tracer of a random 12AX7. The heaters were run in series just to make it easier on the DC power supply I used.

Sorry, can't do 6L6 at this time.

[Grrrg]

You could also check which way the PT is hooked up. If it is set for 240V you can hook it up for 220 V and if I am not mistaken when it is plugged into 240 V from the wall the filament voltage will increase. As will the other voltages. But thinking about it: the mains voltage is probably also not always the same.
And first you should probably measure the filament voltage. Otherwise the discussion gets a bit pointless.

[Mick Bailey]

Some Hayden amps (designed by Dave Green) intentionally run the preamp tubes at 5v off 7805 regulators.

[Helmholtz]

Interesting!
Didn't expect to see that much difference.

[J M Fahey]

Ok, here's some photos from my 576 Curve Tracer of a random 12AX7. The heaters were run in series just to make it easier on the DC power supply I used.

Sorry, can't do 6L6 at this time.

Thanks a lot for actually measuring (a rare occurrence these days) and posting real results.

I didnīt (and still donīt) expect any audible result from slightly undervolting preamp triodes, at most some change of operating point.

I would expect less lower idle current at any bias point because of reduced emission (colder cathode) and your graphs show exactly that.

Taking the topmost (0V?) bias curve (the one yielding maximum current), it reaches "7 divisions" at maximum voltage (300V?) with 12.58V filaments; while same curve at 11.8V it only reaches 26.5 divisions",very visible.

So if it passes less current, it will drop less across plate resistor, plate voltage will be somewhat higher.

Will this change stage gain, maximum Vpp, even more "sound"???
Very much doubt so,specially the latter.

And about 6L6?

There we might a very slight sound difference at clipping, at the edge of audibility .... if that much.

[catalin gramada]

Just wound one or two more turns with heater wires around the coil and will restore the voltage. Be careful at the winding sense. If you winding in opposite direction than the wound it will substract.(don.t bother to determine just measure the output).You just need to have a gap between iron and coil to run the isolated output wires through the gap around the coil. Of course you central tap will be compromised if any and need to create one with two 100 ohm resistors

[pdf64]

I’m sure he designs great amps, but in regard of operating heaters slightly under nominal voltage, I get the impression he’s just regurgitating unfounded hypothesis / misinformation, rather than reporting real info.
My ‘mental model’ (from Tomer) is that if the valves are properly made (a big if I acknowledge), heater voltage down to 5.7V should maintain a surplus in the electron cloud around the cathode even at max rated demand. The electron cloud protects the cathode’s high emissivity coating from being damaged by any stray ions, which would otherwise accelerate and crash into it.

I’m also sceptical why he’s instructing 6L6 models to be biased hotter than the later equivalent EL34 models.
Hopefully it’s from real world statistical life info, but I wonder if, like so many internet sites, it’s due to not grasping the difference between the 30W design max rating of 6L6 and the 25W design centre rating of EL34?

Tomer http://tubebooks.org/Books/Atwood/To...um%20Tubes.pdf

Design max system https://www.one-electron.com/Archive...on%20Tubes.pdf