4P1L / 4П1Л Siberian Gen4 in Screen mode

Some time ago, I did some initial experiments with the 4P1L (4П1Л) with the screen performing as anode instead. Some DIYers claim the improved sound of the mesh type anodes. Kees Brakenhoff kindly sent me some PL519 to test in screen mode. He has done multiple builds with this mode of operation with great results. Unfortunately I’ve not had the chance yet to build such an amp.

What I could do instead though, was to mod very quickly my 4П1Л preamp to screen mode. It was a very easy and fast modification. I kept the same heating wiring and just adjusted the screen (anode) current down to 10mA: Continue reading “4P1L / 4П1Л Siberian Gen4 in Screen mode”

4P1L (4П1Л) Siberian Gen4 – DHT Preamplifier

The return of the Siberian

After trying out so many DHTs and pre-amplifiers, I decided to wire up my 4P1L preamplifier Gen3 and fit the gyrator board to drive my 4P1L PSE Amplifier.

I have a pair of 4P1L/4П1Л dated 1968 which are properly burnt in. I’ve used them lately in my previous preamp incarnation with great results.

The circuit doesn’t need explanation, I think I’ve covered this repeatedly for a long time. I will only point out the differences:

The main change was fitting a pair of Russian wirewound 27Ω resistors in parallel to get closer to the 15Ω used in this position. I found these Russian wirewound resistors to sound extremely well as filament bias resistors. I tend to be skeptical about the “sound” of some components in circuits, however, they do make a big impact in the cathode of a filament bias arrangement.

The gyrator has my preferred combination: IXTP08N100D and BSH111BK. I have now an upgraded PCB Rev07 which fits the BSH111BK and similar FET and I will offer them shortly.

The latter benefits from the 30mA idle current. The result is lower output impedance whilst providing a great frequency response overall.

M3 needs a proper heatsink, it does get hot with about 2W of dissipation.

How does it perform?

Well, this valve has the reputation of amazing performance and low distortion. The gyrator setup provides the best out of this valve in my view. You can get a flat response as well as great bandwidht from 10Hz up to 3MHz loaded with 100kΩ:

The distortion is very low and is lower than 0.05% below 10Vrms. Dominant H2 with a lovely harmonic profile characteristic of this valve.

How does it sounds?

i’ve been listening and using this valve extensively since 2011. I have to say that it sounds amazing. I never get tired of its sounds. Before I listened to a 4P1L-4P1L system and found a slight edge on the sound (probably due to its H3 component) which I don’t hear on my system. The drive, clarity and tone is amazing. It can drive the 4P1L PSE perfectly well and you get a strong and clear bass. Very powerful. My +600 hours 4P1L are very quiet in this setup, no microphonic noise. I don’t have even dampers in the 4P1L sockets!

Anyway, if you need 19dB (x9) gain in your system or you need a driver for your SE amp, then this is the valve to go. I Still can be found cheaply and is a great contender to the thoriated tungsten filament DHTs like 01a and VT-25.

Build this one and enjoy!

4P1L with screen as anode

A friend in DIYAudio came up with a great idea of using the 4P1L in a different way for a pre-amp/line stage. Given availability of IT and its gapped current, he suggested connecting the 4P1L differently. Instead of using the anode as the anode element, the screen is used as anode. The 4P1L screen has a maximum current of 10mA and dissipation should be within the 1.5W.

The 4P1L curves in this mode

Let’s look at an initial transfer curve with Uak=100V:

I wired the 4P1L in the following way to allow tracing with the uTracer:

The connection is slightly different as the one suggested by Indra. If you are looking to implement filament bias, you will have to rearrange the anode and suppressor grid connection and expect a slight shift on the curves given the change in bias. Filaments are in series here, however is preferred to wire them in parallel when using this valve in filament bias as a smaller filament resistor will be required given there is twice the filament current when filaments are connected in parallel. This will help to keep the output resistance lower as the size of this resistor is smaller (remember it is reflected multiplied by μ+1 times.

Continue reading “4P1L with screen as anode”

4P1L DHT Preamp Siberian (Gen3) finished!

Introduction

Building a new version of the venerable 4P1L “Siberian” was very encouraging. This belated project finally came to life after some recent work on a new set of power supplies. So why 4P1L again? I always found the 4P1L sound to be unique. Great detail, overall tone and fantastic treble. What it makes it well suited for pre-amplifiers is not just its linearity (probably being the most linear valve out there) but the fact that it has a low anode resistance and current capability to ensure any challenging load can be handled effectively without any sound degradation. This can be heard particularly on the treble where the input capacitance of the amplifier is more evident and it is translated into treble loss. Other DHTs like 26, 01A, 30sp can only handle a few milliamperes of anode current and is not enough to charge and discharge the parasitic capacitance at high frequencies. More importantly, the 4P1L has filaments which aren’t demanding. This is a unique feature amongst DHTs that is rare and very useful. Having low-current filaments that can be either configured at 325mA or 650mA, low grid voltages and high transconductance in a valve is very useful. This mean that filament bias can be easily implemented without burning unnecessary power by swinging many volts to perform the desired level of amplification.

Continue reading “4P1L DHT Preamp Siberian (Gen3) finished!”

4P1L Siberian DHT Preamp (Gen3)

Recently I finished the filament supply for the latest incarnation of my 4P1L pre-amplifier. Here is the next instalment of this project. The HT power supply was refined after builiding more than 7 stacked HT supplies for the 814 SE Amplifier.

The supply design is very simple. Perhaps the selection of components and the refinement of some aspects of it is what makes the difference to me: Continue reading “4P1L Siberian DHT Preamp (Gen3)”