• 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.

DHT Headphone amp for HifiMan Edition XS

Joined 2009
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PSU Voltage across 30R (don't have 27R) = 14,96V it's enough?


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Joined 2004
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now two 10R in each +- rails.
It's (if current is 0.65A): 20R*0.65A= 13V wasted voltage.

Set the raw supply loaded output voltage to 18V with 30R as dummy load (0.6A).

Measure C1 voltage if output of raw supply is unloaded.

If it -for example- 21VDC, for loaded (0.6A) output R1 value:
(21V-18V)/0.6A= 5R.
Paralleled 10R resistors.

If you want to use two resistors (only dissipation limits justify this, only one is suitable), use two 2R5.
Joined 2004
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R.C. current setting (with trimmer) due to the CCS section, so if you test it with 18R dummy load, it turns out that it works or not.
If you haven't 18R, even with 15R the 0.65A can be set.

NEVER use parts (in this case R.C. regulator) "in live" without preliminary testing.
Joined 2004
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I wrote (as you cited Rod's recommendation):
"4.7K for 14V of filament bias (Regulator output = 16,1V, Supply input = 21,1V)"
As you can see Rod also recommend 5V headroom for v4.

Is headroom satisfying?
Is control range of R.C. working well?

If raw supply output (R.C. input) is 18V, and setting of current 0.65A, about 11.85V voltage will be on 15R series 4P1L paralleled filaments.
If the trimmer setting not working or results bad value current the output (bias and filament) voltage also bad.

Check again R.C. regulator with 18-20R dummy load.
Check the headroom voltage.
Check the control range of regulator current.
Joined 2009
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Bela, What's the most important bias measurement:

1-Set the filaments to 2.1V?
2-Set the grid to -10V aprox.?
3-Set the current across 15R for 650mA?
4-For B+ I use a 10R between the OPT & the plate so using SSHV2 I set the current to 45mA, I do that because I'm using Edcor GXSE5-15K - 5W, 15K Ohms - 600 Ohms single ended tube output transformer to see if I like the sound of 4P1L with my Sennhs HD600 of 300R before to buy a new OPT and spend money.

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Joined 2009
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I set the bias:

Left channel
B+ 160,01V
Plate 40,66mA
Grid -9,03V
Filaments 2,1V / 597mA
Measured resistor filament 15,13 ohms

Right channel
B+ 158,94V
Plate 44,17mA
Grid -9,78V
Filaments 2,1V / 645mA
Measured resistor filament 15,16 ohms

N.B. As you can see the OPTs don't draws the same volts & the resistors aren't the same value
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Joined 2004
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"resistors aren't the same value"
2% difference ... it's nothing ... even your "measuring instrument" -handheld DVM?- has 2-5% accuracy.

Set the B+ and grid voltages roughly equal, then measure Ia, Uak.

The first tube filament little thinner, than other, so hot resistance is higher, at the same filament current (I prefer it, opposed to equal filament voltage) the filament voltage will be also higher.

Do you have another tubes?
The Russian 4P1L tubes standard deviation may enough large, so even large quantity required to select similar tubes.