eTracer Build and Review

Tracing valves: an obsession

Since my early days of valves and DIY audio, I developed an obsession around testing and tracing valves. This led me to design and build my analogue curve tracer which I used for many years successfully until I build my uTracer, which was a great innovation in curve tracing. I do have many valve testers (some which I made myself) so why building another one?

Well, Chris Chang from Essues Technologies developed a fantastic new digital curve tracer for valves, the eTracer.  There are a few things which will grab anyone’s attention on this curve tracer. Firstly, the power supplies can accommodate a large range of valves which the uTracer can’t. HT can go as high as 750V @ 300mA and the grid supply down to -170V! This is exactly what you need to test your transmitting valves or even a 300B.  Secondly, the tracing speed is surprisingly fast. This is a nice feature, specially when you want to trace pentodes at various screen voltages to develop a Spice model  for example. 

Build process

Continue reading “eTracer Build and Review”

Flexible CCS board prototype

I’ve been prototyping a flexible CCS PCB. The intent is to provide a cascoded FET pair with some interesting features:

  1. The lower FET can be multiple devices depending on the choice of reverse capacitance and transconductance. These include jFETs and depletion MOSFETs like the 2SK170, J310, BF862 and of course DN2540. For this purpose several pads are provided for SMD devices as well as TO-92 ones, just like the gyrator PCB. A protection Zener diode between drain and source can be soldered when using low VDSS devices.
  2. There is either a string of trimpot plus a resistor to set the CCS current manually during test given the variance in the FET parameters.  There is also an option to put a fixed resistor.
  3. There is a mu-output connection provided.

The board is very flexible and can be used for multiple purposes:

  1. shunt regulators (including VR valves)
  2. Anode load for phono preamps, drivers, LTPs, etc.
  3. LTP tail CCSs

I’ve been running some tests with excellent results.

If there is interest, I will run a batch of PCB to offer to the DIY community. 



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”

Gyrator PCB Update – Rev07

The gyrator PCB has been updated to fit now a wider variety of lower enhancement MOSFETs with low capacitance and high transconductance. The best examples are the BSH111BK and BSN20BK which are great options for currents above 25mA:


The board offers now all the flexibility needed in terms of different TO-92 and SOT-23 package pin-outs to use whatever FET you want.


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!

01a Preamp Build: UV-201a version – step 1

This is what I managed to do with a couple of hours at the workshop. Time is gold for me these days. Quick drilling and fitting the main components. You can’t get a smaller preamp than this one. It’s quite packed:

Next, soldering. Yay, just looking forward to my favourite part of the build process