Bartola® Valves

300B filament supply

In the process of rebuilding my old 300B amplifier, I decided to make a new filament power supply. It all came up around the components I had at hand, so it could’ve been improved but that meant extra cost:

I have a pair of custom-made JMS transformers with multi-taps secondaries. This helps me tweaking the right output voltage. Anyhow, any 15V transformer would do. Perhaps you want 14V to ensure you don’t dissipate too much on the filament regulators (e.g. Rod Coleman regulators)

I used my flexible LT supply PCB which allowed me to build this in less than 1 hour. I also used some existing chokes made in the UK by “Spirit” which are ok for this purpose. The Lundahls are in use, so can’t reuse them:

I used some SOT-128-2 schottky rectifiers but any other should work as well. Resistors are wirewound and the CMR choke is what I had in stock as well. A simple 15mH/3A should do fine.

The output measured well at 9V with a 6R load which dragged 1.5A. A bit more than the 300B but should be a good indication of performance. Also ripple level is good at 2.5mVrms. The rest will be cleaned up by the regulator itself 🙂

Lundahl Transformer PCBs (LL1943 and LL7903)

I made a few additions to the PCBs available. Check these out:

Available until the PCBs run out

Mini Hybrid Mu-follower board test

I had a go first at a mini-gyrator board using SMD. Blimey, it’s hard work to get all these crammed into such a small footprint.

I did a quick test with a D3a and worked fine at 100V/10mA (low voltage of course). It was +35dB flat up until a couple of Mhz. Even the over-current LED works!

Footprint is as small as you can get: 45mm x 25mm 🙂

More to report later!

UX-120 DHT

I’ve got hold of a NOS quartet of UX-120 Radiotron valves made in 1925. These are 95 year old beauties. Unbelievable how well conserved they are and operate.

This valve developed by RCA was the first output valve intended to be used with dry-cells (3 No. 6 cells in series). See the data sheet extract below:

There is no much data available on this valve, if you have some please share and let me know. Here are the curves I traced from a sample which measured 114%:

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Modular approach (Part I)

As time is very limited these days, I’m focused in continuing my modular building approach in LEGO style. I have developed several PCB modules which are flexible to be used in multiple amplifier and pre-amplifier designs. Now, I used the power of PCBs to build some additional supporting modules to speed up my breadboarding over the IKEA boards. Not the most elegant approach, but building becomes a very fast process this way.

You will see what I’m saying when you see a few of the following additions:

Turret and 2mm female connectors in a strip

Continue reading “Modular approach (Part I)”

6BS7 low noise pentode

Here’s an interest pentode to consider for phono stages. It was used extensively in instrumentation up until 1980s. There are a few examples around and you can check the Brimar data sheet to see what I’m taking about.

Cap Multiplier boards (Rev04)

After few tests and revisions (Rev 04) I updated the capacitor multiplier board I developed time ago

Cap Multiplier Rev-04: 0-450V variable regulation

6AG5 pentode

Here is a nice sharp cut-off RF pentode with low capacitance, high gm and nice curves: 6AG5.

E282F HP Amp

First and foremost, Merry Christmas! I hope you’re having a great time with your loved ones and good music.

Without a mood for public introspection this time, I have to say that I will celebrate this holiday the best I can. I will be hosting today with a lot of meat, wine and single malt. What else can I do? When I escape from the little ones, will get back to spin some records and hopefully work on the projects.

Headphone Amp Quest Continues

Obviously, I needed to pursue this project further. I’ve been lately listening a lot to HPs as simply is the best choice for me when the young family is in bed. In addition to this, I find the HP setup to force me to connect a bit more to what I’m listening to as I don’t get easily distracted.

ETF.19 – continued

Whether it was a good idea or not to bring the eTracer to ETF was yet to be seen. Fortunately enough, I escaped smartly to become a prisoner of my own suggestion.

Did quite a few tests with the tracer and contributed to avoid auctioning a worn out 45. Instead, the auctioned pair became a single 45. It felt like a nice contribution.

On the flip side, tracing Pete’s 50 mesh stash was a joy. Handled with care his pension investment when tracing them. However, we found a gassy and a open filament one. Ouch. At the same time, saved the curves of a 50 measuring 100% which was really nice.