Tag: Swenson regulator

Valve test rig with fixed bias

My test rig for DHT/IHT stages (and even Pentodes) has evolved over the years. Lately I settled with some nice modifications to allow testing the majority of valves I have. I use a modular socket system, nothing fancy and can add/remove a source follower stage at the output. There is also a screen regulator in case pentodes are submitted under the mercy of the jig.

Here is the simplified diagram. I added a nice fixed bias supply formed by a SMPS PCB board which delivers up to 400V, however the output is dial to about 100V. Then I use a Swenson Regulator to knock down the noise by about 100dB. A simple pot provides the voltage needed between 0 and -100V. It can be tweaked for whatever range you need. The pot is 20T wirewound so allows a fine adjustment on the bias:

For the curious builders, here is the rig mounted on a piece of floor board:

 

Swenson+ HT regulator test

So the developing is progressing. This time I tested the first PCB prototype of my enhanced “Swenson” regulator which I baptised Swenson+. It’s a great circuit and performs really well. Although component selection and track cree page and clearance is for about 1kV, I think it should safely operate at least to 800V. Not really thinking to use it at those voltage levels, but rather as phono stage supply instead, which requires much lower voltages.

As usual the focus of the PCB is to provide as much flexibility in component selection (SMD and TH) as well as use cases.


Still some layout refining and further testing but so far so good! Here is a taster which shows at least 60dB rejection of the incoming power supply noise which wipes out all rectified-related harmonics (100Hz etc). The 100dB 50Hz and byproducts is likely to come from my workbench:

More to come soon (hopefully)