choke tail phase inverter

[andrew]

Has anyone here tried a choke tail phase inverter from this site?
http://boozhoundlabs.blogspot.com/
Thanks -

[andrew]

The BHL-15

[roberto]

from that site:

[img:400:215]http://2.bp.blogspot.com/-UodHpZ81cQk/T ... values.gif[/img]

Back to the design - what we need is a device that has relatively low DC resistance so that it won't drop a lot of voltage, but high AC impedance so that it will provide a substantial load for the cathodes of the phase inverter, and give us the linearity we want. One such device is the poor misunderstood choke (inductor). Chokes are the first component eliminated from a design to reduce cost because a resistor is much cheaper than 50 feet of wire wrapped around a hunk of steel. Another Hi Fi truism is that anytime you replace a resistor with a choke, the sound gets better. Ideally, we would replace the cathode resistor and both plate resistors with chokes. Maybe even on all stages of the amp. But that would be a very expensive solution, and have other problems, like picking up hum in the hundreds of feet of wire wrapped around the hundreds of pounds of steel

So this amp simply replaces the cathode resistor with a choke, to allow the use of a high current 6sn7 as a phase inverter/driver for the output pair of 6v6s. This high(er) current driver allows more current to be deliverded to the grids of the output tubes, extending the sweet sopt well into the region where grid current flows. Phase inverters tend to have neat names: cathodyne, long tail pair, concertina. I nominate this phase inverter be the "choke tail" phase inverter.

The phase inverter no longer looks like a long tail pair because the increased AC impedance of the choke makes the "tail" unnnecessary. The bias voltage is generated by the DC drop across the choke, but the large AC impedance typically generated across the cathode bias resistor plus the large tail resistor is generated across the choke as well. A side benefit is that we get to lose the capacitor that grounds the undriven grid in a long tail pair. Removing capacitors is a good thing in Hi Fi, so why not in guitar amps too.

Bob's official report:

"It has an awesome bluesy sound that starts to break up early (volume = 3), and just gets better as you crank it up. It doesn't turn dirty until some point above 9 (these amps go to 12, that's 2 more than 10)... so the sweet spot is really big.

[Masco]

So where do you find a 30H choke w/ low mA rating?

[Zippy]

So where do you find a 30H choke w/ low mA rating?

Knowing Jason (Boozhound), I'm betting that he would encourage you to wind your own.

[roberto]

You can find the Hammond 157G here:
http://www.parts-express.com/pe/showdet ... er=122-320

[img:240:240]http://www.parts-express.com/images/ite ... -320_s.jpg[/img]

[gingertube]

Choke tail is halfway to the real solution - a CCS tail.
Cheers,
Ian

[diagrammatiks]

Choke tail is halfway to the real solution - a CCS tail.
Cheers,
Ian

this is truth.

[Darkbluemurder]

I never tried a CCS tail (nor the choke tail). I only heard that the CCS tail would sound terrible when overdriven.

The choke tail looks interesting. The obvious downside is that you have to get the choke mounted somewhere but in most cases it should be manageable.

Cheers Stephan

[Andy Le Blanc]

thats a simple novel idea, should be fun to noodle with, nothing new with the inverter type, might even try it with self split power side.

[doctorfixit]

Yes, I have built this PI

It works great, although i found it worked better with a small tail resistor on the choke.