Over 7 years ago I made a run of a great circuit with a bit of a twist. The “Super-linear Cathode Follower” or SLCF is a great way of optimising the cathode follower stage and make it more linear by bootstrapping the anode and forcing the valve to operate in a vertical load line hence reducing the distortion significantly. And it does sound pretty good I have to say. If you aren’t familiar with this topology and want to learn a bit more, of course read Allen Wright’s amazing textbook or have a look at the following posts here.
Read more: SLCF to the rescue? Continue reading “SLCF to the rescue?”Tag: bartola
Hybrid mu-follower boards in SMD
I’ve been using these boards for many years now. Haven’t offered them as is required for anyone to be experienced well enough in SMD soldering to get these done effectively. I have a reflow oven so work at scale is easier this way. I’ve been doing a lot of SMD board design and building over the past few years though.
On a busy time regardless, I found the space to build these four commissioned boards for D3a drivers like the ones I used on my 300B amplifier. There seems to be a lot of interest and build work done around this design, so happy to see this happening.
EML300B Mesh – initial test
My friend Mirek sent me from Czech Republic a few valves for testing, including a pair of precious EML300B Mesh valves. I managed to slot them into my system before departing for holidays. I only listened to them for a few hours, so these are only initial impressions.
I like the sound and was expecting the additional level of detail and sound of the mesh plate. Worth addition clearly. I wouldn’t say it’s a significant step improvement, just minor, subtle details are clearer. You won’t go wrong with the standard EML300B. The Mesh is a nice upgrade but you will need to think (as always) where it best to put the money on. I’d invest in the iron and overall circuit before you get to throw more money on the output valves. That’s my view.
Anyhow, great job Emission Labs for this superb valve.
300B SE Amp: 47 Driver
Going DHT end to end
As previously mentioned, I played around with the 46 driver. I love it sound and is a great valve. However, there were 2 reasons that pushed me to switch to the 47. Firstly, I wanted an extra tad of gain. Secondly, I have a nice stash of RCA 247 globe which measure extremely well. I’ve been reserving it for a 47 PP amp with local feedback (a la Pimm) and hopefully will get to in the future. Anyhow, the 47 in triode mode has a mu of about 8 which in combination with the SUT, gives me good gain to drive my 300B. After tweaking on the bench the stage for optimal swing and distortion performance, I ended up with the following circuit:
The return of the Mule (RE084)
It’s been a while since I experimented with preamps again. I settled as a permanent setup with my 01a/ER801a which I love. However, I wanted to continue with my experiments so I built a new Mule, let’s call it “Mule 2” for now. It’s based out of multiple PCBs which simplifies the construction process and reduces build time:
HP experiments – part 1
Experimenting on headphone amplifiers, not always turn out the way you expected. Well, that’s the nature of experimentation and some smoke may come along the way.
Here is my new take on the headphone amp. Modified the 2P29L to fit the 6e6p-dr valve. I love this IHT one, so wanted to experiment more.
Instead of the classic HT, I used some Chinese 300-450V SMPS modules. I used the 70W version with success before, not these tiny ones.
Individually tested all parts and worked fine. Fired up the SMPS with the hot filaments and the 6e6p-dr running at 20mA each and the SMPS oscillated. They went to 450V instead of the 250V dialled and one of my cap multiplier PCB boards got damaged. Damn!
Back to the drawing board. I will probably stick to the simple HT supply 🙂
Tail CCS PCB test
A belated test of this simple, yet effective PCB. I made it as small as possible, however in order to provide flexible connections, it’s actually double the size. Still at 4 x 4 cm is small enough.
Pentode Differential Pair (Hybrid Mu-follower)
Pentode drivers are very interesting. You can get excellent results out of them. Here is my version of a differential pair using pentodes. I want to try them out in the 45 PP design I wrote previously Continue reading “Pentode Differential Pair (Hybrid Mu-follower)”
4P1L PSE Class A2 Amplifier
It was mentioned here, so I decided to chip in with my previous experience from back in 2013. Here is what I tried myself:
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.
