• 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.) If you want to use trioded 4P1L at 130V, 15mA operating point, must to use about -10V bias.
-10V bias is about 9V on filament bias resistor + half of filament voltage of 4P1L ... at starved filament current. You must to set R.C. regulator to 580-585mA.

2.) The "load" resistor value is the line stage loading resistor (need for capacitor coupling, usually 220k...470k) paralleled with next stage input impedance. If the next stage is SS amplifier, the 22k is possible ... 6k8 is not ordinary value.

3.) What is the "output voltage"?

sample:
4P1L gyrator loaded line stage.jpg
 
Thank you for your response. I need to apologize for not being specific enough in my question (new years hangover tunnel vision....)
My question is about the gyrator board, I posted the question here in 4P1L thread as I am trying to use the gyrator circuit depicted here. I want to use it with a RE134, Ua 130V Ia 15mA.
In my bench test I connected a 22k across "Anode" and "GND" and set voltage across that resistor to 130V. Then I changed that 22k to 8k6, assuming 8k6 connected to "Anode" and "GND" would simulate an RE134 run with 15mA. I had nothing connected to "Out".
 
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If you want to test only gyrator, resistor as static load (without tube) to ground is perfect.

This layout working, gyrator acts as "constant output voltage device" (setting 130V)... until current absorbed by the load (22k or 8k6 resistor) available.
If you measure such -similar- voltages as in my schematic with 22k load (about 6mA) and different values with 8k6 load (15mA), something in the gyrator is limiting.
 
Hi,

I am planning to build 4P1L Siberian Gen4. From PSUD simulations and reading all this thread from the beginning I have a newbie question. I want to calculate voltage for trafos for heater supplies. I know Rod suggests 14V. But I can simulate correct values only when I put 400 mOhms for capacitors ESR values as showed in Rods manual for connecting RC regulators. ESR for capacitors in datasheet is 24 mOhms - https://www.digikey.lv/en/products/detail/cornell-dubilier-knowles/SLPX223M035H4P3/1882075. If I input ESR values closer to 24 mOhms, 14V for trafos seems a bit high. What am I missing?

Thanks in advance!

Screenshot 2024-02-19 at 16.23.18.png


Screenshot 2024-02-19 at 16.24.29.png
 
24mΩ is a low value, even at 22mF.

But it's OK - there is a lot of variable with Raw DC voltages (transformer losses, diode drops, mains supply line voltages...)

You are close enough to build the Raw DC and measure the voltages, when it is connected to the regulator.

If the voltage is still too high - increase the series R (R1 in PSUD2).

It's worth having some low-value resistors in stck, for adjusting the Raw DC.
 
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I used the double 12V@2A output of a Hammond 266L24 and put a 159ZC on one side for L filtering, using a resistor that matches the resistance of the inductor widing on the other side. Loaded down in filament bias it all fell into place with 4-5V headroom on top of my 7-8V of bias on the 4P1L grid.
 
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First of all, the method of calculating is not quite right, you have to start from the back to the front.

Must be decided the filament bias resistor value (in my sample 12R), the filament current (0.65A) and the tube's filament voltage (2.1V).
The required voltage on R.C regulator is:
U= (If*Rfilbias)+Uf in this case 9.9V.

If the R.C. regulator headroom is 4V, the raw supply output must be 9.9+4=13.9V or greater.
This value and transformer estimated secondary voltage will be the starting point.

If you use single secondary and Graetz rectifier, the one of least voltage loss diode is the schottky. I usually use MBR series.
The first capacitor quality is important, must to tolerate such high ripple current, which is originates from it's value, and the schematic other parameters.
If you choose large first capacitor (the 22000uF is HUGE!), the charging current pulse will be enormous, the diodes and the PT dissipating much more than necessary.

Choosing smoothing is depends of required hum value on output (in this case on filament bias resistor+filament).
If - for example - few-few ten uV is enough (caution filament biased DH tube amplifier stage is VERY sensitive to filament voltage/current quality!), must to appreciates regulator (in this case R.C. regulator) PSRR.

I measured Rod's regulators, each of them outperforms 70dB PSRR, usually are over 80dB.

If you assume 10uVpp noise (hum) on output and 80dB PSRR, the allowable input (on raw supply output) noise is 100mVpp.

This will be the target value of raw supply output: equal or more than 13.9V DC, 100mVpp hum at 0.65A load.

Sample:

12VAC_raw_supply_RC7 (4P1L)_12R heater bias.jpg

As you can see, the moderated constant current and relatively low value first capacitor (which ripple current capacity must be greater than simulated) requires relatively large current tolerance diodes and enough large current on secondary.
Even the consumed power not so large, the transformer must be -at least- double (sometimes greater) power capacity, else will be heating.
 
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