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Old 25th January 2013, 03:12 PM   #501
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Originally Posted by andyjevans View Post
Yes - at least make it a DHT headphone amp, otherwise you'll get anything.
DHT headphone amp

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Old 28th January 2013, 09:07 PM   #502
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hi guys

let's say i intend to parallel feed the output stage and ultrapath as well.

we know the capacitor should go to the output tube's cathode but in the case of using filament bias, where should the capacitor go to?

if it's ac filament, i'll have a hum bucking pot and will wire to pot's wiper.

any suggestions?

thx!

bg
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Old 28th January 2013, 09:19 PM   #503
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Here is my suggestion: biased from regulated power supply through cathode follower, no caps.

One more 4P1L SE

You can get up to 5W of clean power from a couple of tubes.

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Old 3rd February 2013, 04:43 AM   #504
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I finally had a chance to get back to my map and now have it running in pentode mode for the input stage, triode for the output. Battery bias on both.

It seems to work well and sounds pretty clean. There is a lot of clean up to do, but it's a nice start so far. The loose layout is causing some oscillations for time to time, and one of the valves is fairly microphonic. All things that can be fixed I think.
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Old 3rd February 2013, 09:54 PM   #505
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Originally Posted by DonJuan View Post
hi guys

let's say i intend to parallel feed the output stage and ultrapath as well.

bg
Hi Juan!
There is no idea in using parallel feed and ultrapath at the same time. Or one could say that in case of parallel feed the ultrapath cap should go from cathode to ground. That would be the same position as a normal bypass cap.
Also; it is not a good idea to combine filament bias with ultrapath, as the hole idea of filament bias is to get rid of the cathode bypass cap. And the ultrapath cap is a special case cathode bypass. With filament bias the cathode resistor becomes so small, that it doesn´t need bypass.
It might be a good idea to combine filament bias and parallel feed.
Good luck!
Thorsten Larsen
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Old 4th February 2013, 05:22 AM   #506
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hi thorsten

thanks for your explanation!

donjuan
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Old 13th February 2013, 03:48 AM   #507
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To bump this back up - I've now gone to a 6sN7GT on the input and am happy with it. It sounds good and has enough gain to fully drive the 4P1L outputs and is quiet. It's a very smooth sound, probably a lot of H2, but not too sweet. Will check tomorrow.

Running the 6SN7 with LED bias (2X red LED) 125V on the plate, about 5mA current.
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Old 13th February 2013, 08:22 AM   #508
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I was wondering about driving PSE 4P1L with 2C22, pretty much half a 6SN7. I'm wondering if it would work in two stages if I had 2v coming out of my DAC, like an ODAC for instance. I have Mark Audio Alpair 10s. It would be marginal. Right now I get about 0.5v from my DAC with 3 stages, 26>4P1L>4P1L.
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Old 13th February 2013, 08:36 AM   #509
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I'm using 7193 with gyrator Mu-follower load and led bias to drive a 45SE. I have an ODAC and also using the 26 preamp. Bear in mind that the 45SE is really remanding and that for the 4P1L PSE you will be fine with 70Vpp - need to check load line when get back home. The 7193 is at full tilt about 8mA but is cap coupled. Why not an 6e5p or 6j11p shunt cascode?
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Old 13th February 2013, 12:07 PM   #510
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Andy I'm not getting a lot of gain out of the 6SN7, but enough. I see about 3.2V RMS from the 4P1L/OPT secondary with 1.5V RMS into the 6SN7. I think I'll have more gain if the 6SN7 is run off a CCS.

The main thing is to have enough negative bias at the 4P1L grid so that it doesn't clip first.
It seems that with my -17.5V battery bias (2 old 9V in series) the output is limited. I may go back to 2x 9V + 2X 1.5V to see what happens. Could be that it's simply hitting the B+ limit.
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