One more 4P1L SE

[Deco-Doctor]

Originally Posted by andyjevans

Deco-doctor

Have a look at the 126B and 126C at Bluebell Audio - look at Transformers > Interstages. They are exactly the same price as Danbury and probably at least twice as good. Also they are bifilar wound and have a known and stated inductance. Philip at Bluebell is very helpful and knows his tubes.

Hi Andy

Thanks for your thoughts. I am already using Hammond 126A interstage in my 45 SE amplifier. I use a triode strapped D3a input/driver running at 160V 12mA. And yes the 126 series are super value. The square wave response is astonishingly good.

I could try the 126A as a load for the 4P1L at up to 15mA if it sounds as good as you say at low current.

Martin

[Wavebourn]

Originally Posted by Deco-Doctor

OK I take your point, but my question is what is the plate resistance of a single 4P1L at the chosen operating point?

There are some curves posted in this thread. You can take a ruler, measure and divide dV/dI

[mogliaa]

Originally Posted by Wavebourn

There are some curves posted in this thread. You can take a ruler, measure and divide dV/dI

About 1100-1200 subject to filament starvation:

4?1?/4P1L triode curves | Bartola Valves

[mogliaa]

Originally Posted by revintage

Hey Ale,
At what load did you get the sweet spot?

Hi Lars,
I run the preamp at 90V, 20mA and about -4V in filament bias with slight filament starvation at about 500-530mA. I did play around quite a lot. Recently found that is more linear at bias greater than -10V providing you don't exceed anode voltage limits. But haven;t tested how it sounds in this region.

Definitely likes it working about 15mA where possible.

You can read some of the learning experience here:

4P1L DHT Line Stage

Cheers
ale

[Deco-Doctor]

Originally Posted by Wavebourn

There are some curves posted in this thread. You can take a ruler, measure and divide dV/dI

Some good curve traces here:-

Tube Tester Files - 4P1L

[Wavebourn]

Originally Posted by Deco-Doctor

Some good curve traces here:-

Tube Tester Files - 4P1L

Yes, they are good. But his curve tracer can't be trusted on positive g1 voltages, though to answer your question it is not required.

[andyjevans]

Originally Posted by mogliaa

Hi Lars,
I run the preamp at 90V, 20mA and about -4V in filament bias with slight filament starvation at about 500-530mA.
Cheers
ale

Hi Ale - what was the value of your cathode resistor in filament bias?

I'm playing around with cathode resistors and trying to find the right value right now. I won't know what different currents sound like until I get my setup working properly. It may sound better at higher currents like everyone says. The 4P1L drivers are running at more like 17mA in my PP 6C4C amp (26 inputs), and that sounds the best of all. Filament bias in SE is a different story.

Andy

[Wavebourn]

Try 12 Ohm if your filaments are paralleled (about 1A current through them)

[mogliaa]

Andy,
I used two ww 15 ohm resistors in parallel that I had at hand

[revintage]

Hey Ale,
You still didn´t answer into what load you found the sweet spot. Unloaded?