• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Loftin-White

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You could also change the cathode resistor from 6K to 500R, and use a 33K anode resistor to B+290.

That would put you at 9mA biased around -5.5V and should be more linear still. and closer to the recommended operating point.

There is a lot of room to work with once you reference the anode resistor to the B+290 supply.
 
You could also change the cathode resistor from 6K to 500R, and use a 33K anode resistor to B+290.

That would put you at 9mA biased around -5.5V and should be more linear still. and closer to the recommended operating point.

There is a lot of room to work with once you reference the anode resistor to the B+290 supply.

I think i'll go with the 500 ohm cathode resistor and the 33k anode resistor from a divider on the 290v supply. You just solved a mystery for me on the original LW where the anode resistor is tapped above the cathode of the second tube on the resistive divider from b+ to ground. -Fred
 
Hi Jeff,

Ever tried the 6AN4. High mu, and with current drive to spare ?

No, But I will look it up and see its curves for linearity.

High current is NOT particularly needed and wanted in a L-W to a 2A3.

Asano used 0.43 mA., Shishido 1.0 mA. with two sections ( NG-skews) , Fraker 0.6 mA. I THINK the term is grid admittance, where the input signal has to overcome a wall of current.

Jeff
 
I think i'll go with the 500 ohm cathode resistor and the 33k anode resistor from a divider on the 290v supply. You just solved a mystery for me on the original LW where the anode resistor is tapped above the cathode of the second tube on the resistive divider from b+ to ground. -Fred

Gimp gave you some very good advice.

The first thing to do is to study exising L-W circuits, ( Lipman, Asano, Shushido ) and email me privately for a write up I did on designing such a circuit.

Your minor mistake was to stack supplies, a SINGLE 490 VDC supply actually sounds better to me !!!

Your major mistake was to use a mu of 20 tube in a two stage amp. It will only sound good when PUSHED HARD. Try a 6SL7WGT, mu of 70. Use 225 Ea, -1.85 VDC bias, and about .00215 A. current.

The grid stoppers are useless, a sonic degrade. Eliminate them.

Use HIGH QUALITY wire to the grid of the Driver and to the grid of the Finals. Eg: (1) Siltech is best, (2) two Kimber TCSS, or (3) One Kimber AGSS, one TCSS.

Use only ONE tube in the Finals, no skewing or choir effect. Try a 6AQ5/6005 in place of the 6V6. Use about 210 VDC P-K, .028 A Ia, and ABOUT -12.5 or -13 VDC ( guessing ) bias.


Write to me. drlowmu@gmail.com

Jeff
 
Hi. I appreciate all the help I can get. I'll try thegimp's suggestion first. I'm interested to read your write-up. -Fred

Edit: I am, however, very interested in retaining the stacked power supplies and is a huge part of my inspiration for building any of it. I respect your perspective on this though.
 
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The grid stoppers are useless, a sonic degrade. Eliminate them.

Use HIGH QUALITY wire to the grid of the Driver and to the grid of the Finals. Eg: (1) Siltech is best, (2) two Kimber TCSS, or (3) One Kimber AGSS, one TCSS.

Use only ONE tube in the Finals, no skewing or choir effect. Try a 6AQ5/6005 in place of the 6V6.

Hi Jeff. I removed the grid stoppers and adjusted the layout a bit and I like it better for sure. Thank you. I'll have to look and see if I have a 6AQ5 in my stash. I acquired several hundred tubes recently and I still don't know what I have. I just recently found the 6V6's and I like them a lot.

I like the idea of one power tube and I'll be trying that. I started a new thread on it here since I realize it's not a LW. Thanks for your help and ideas. I'll give you an email. -Fred
 
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