• 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.

4P1L DHT Line Stage

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#1,602
andyjevans said:
Try the 26 with 10 diodes and a 120R resistor. I don't find it masks the sound - on the contrary, it's super detailed. You can decrease the number of diodes as shown. This is normal bias - not filament bias - and I'm sure that also comes into it. The resistors have tiny current through them, so you can use any kind of boutique ones you fancy. I've only used 120R so far, but intend to try different combinations of resistor/diode. This is now my daily preamp.
Click to expand...

merlin el mago said:
Thanks to share Andy. What's the power required for the resistor?
Click to expand...

???
 
#1,606
I need to ask how to correctly calculate the load for Rods filament regulators used in filiment bias.
Do I calculate the heater load plus the the operating point of the tube, as in say for a 2P29L 2 volts at 15 Miliamps to come up with a dummy load to test the regs before firing up the tubes?

Thanks
Ed
 
#1,607
Hi Ed,

The cathode current is mostly negligible. Calculate dummy load with Ohm's law: Rdummy= filament voltage / filament current.

Sample: 4P1L filament

If you use filament bias, the filament current will flow trough filament (DC resistance) + bias resistor. The cathode is negative (compared to grid) about Rbias*Iheater + (Vheater/2), so this determines the op. point (grid voltage) curve.
 

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#1,613
Well, I got the 4P1L line stage built with SIC diode bias. Listening tests are very positive - the sound is smooth, detailed, clean and solid. I broke out in a smile when I put it in my system - good sign! So I recommend this. As a plate choke design it has a lower output impedance than 01A or 26 designs, which could be useful. I recommend this. The plate choke I'm using is a no-name of Asian origin. Sounds fine to me. I haven't tried my NP Acoustics amorphous plate choke yet, but I intend to do so.
 

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#1,614
I finally got the last bits done on my 2p29l preamp. Coleman regs, choke loaded. Thank you Rod, Ale, and all the contributors to this long thread. I do have a question for the experts. I am using Rod's regs in filament bias. When I was setting the voltage I have the rectifier removed. With no B+ on the plate I had a steady 2V. With 154 volt at the plate I now have 2.75v filament. Any recommendation?

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#1,617
andyjevans said:
Well, I got the 4P1L line stage built with SIC diode bias. Listening tests are very positive - the sound is smooth, detailed, clean and solid. I broke out in a smile when I put it in my system - good sign! So I recommend this. As a plate choke design it has a lower output impedance than 01A or 26 designs, which could be useful. I recommend this. The plate choke I'm using is a no-name of Asian origin. Sounds fine to me. I haven't tried my NP Acoustics amorphous plate choke yet, but I intend to do so.
Click to expand...

Nice experiments Andy. It'd be worth trying the SiC array as filament bias as well. I'm sure they will sound as good or even better.
Cheers
Ale
 
#1,619
andyjevans said:
One of the next things to do is put SIC diodes in the PSE 4P1L output stage.
Click to expand...

The challenge is the number of SiC diodes needed, I thought about it. I think you'd add too much output impedance as 75R reflected in the anodes will be close to 750R on top of the 4P1L output impedance (which is halved due to the parallel arrangement. In the end it would be worse than one single valve. Worth trying as probably with the OPT you have it will still have good bass.
Ale
 
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