My next regen receiver - The power supply

I'm just starting to collect components and utility modules for my next homebrewing project, which will be another small tube regenerative receiver.
As a starting point, it is always quite important to decide what the power supply for the receiver will be. In my case, I already had a nice vintage Ameco PS-1 tube power supply that seemed almost perfect for this purpose. However, its internal circuit needed some improvements to be made more efficient; and the existing components (in particular, the old selenium rectifier and the electrolytic filter capacitor) needed to be replaced with something newer and safer.

The original schematic diagram of the Ameco PS-1

So I put toghether a rectifier bridge on a small piece of stripboard, made by four 1N4004 diodes (each in parallel with a 10 nF ceramic bypass capacitor) and I mounted it inside the power supply box, using the same screw that held the old selenium rectifier in place. Then I replaced the existing 2 x 22 uF, 150 V electrolytic capacitor with a new 100 uF, 400 V device. I removed the RC filter, as my intention is to add proper filtering where needed in the receiver.

The final schematic diagram of the power supply is the following:

The schematic diagram of my modified Ameco PS-1

Here below a photograph showing the new internal wiring:

After having taken the image above, I added a 47 kohms, 1W bleeder resistor in parallel with the DC output.

For increased safety, I have also detached the so-called (in the Ameco PS-1 manual) "internal tie point" from pin 4 of the output connector (refer to figure below).

The modified output connector

In fact, pin 4 of the output connector was simply used as a solder lug to connect one wire from the AC mains to one end of the primary winding of transformer. You can see it in the top right area of picture above.

To have the AC main voltage present on a pin of the output connector - labeled as a very generic "internal tie point" - was a bit dangerous in my opinion!

So I detached the AC mains wire and the transponder wire from the connector and I took the oppurtunity for inserting a fuse holder between them, with a 200 mA fuse.

I finally measured the output voltages (with no load) and found about 160 V DC on B+ and about 6.5 V AC for heaters. When connected to the receiver, I suppose the B+ voltage could drop to around 140 V DC, which should be good for my project.

A tiny vintage tube radio power supply

Sometimes I get attracted by small pieces of vintage electronics and - when the cost of the item is affordable for me - often I can't resist and buy these objects with a collector spirit, even if probably I will never find a practical use for them.
The above is the case of this small vintage tube radio power supply, the Ameco PS-1, that I bought last summer from US on a well known site for on-line auctions.
I put hereafter a small collection of images of the Ameco PS-1, together with its very simple schematic diagram. It can provide 6.3 VAC, 2A for tube heaters and a rectified 125VDC, 25 mA for plates (often named as the B+ voltage).

As you can see from images above, an octal socket is available for connecting the Ameco PS-1 to the user circuit. The socket is wired so that it was possible to plug the Ameco CN line of frequency converters (CN-50, CN-144, CN-220) directly into the PS-1 power supply.

I would like very much to use the Ameco as (a part of) the power supply section of a future homebrewed tube radio, most likely another simple regenerative receiver. I could also add in the receiver some better filtering on B+ and a rectifier - followed by a three terminal voltage regulator (LM7806 or similar) - for the heaters voltage and leave the Ameco PS-1 as it is. Of course, here in Italy it will require a step down transformer from 230 V of AC mains to the required 117 VAC that are used in the US, but this would not be a big problem, given the limited power to be delivered.
That's all for now, with my best wishes to all for a great year 2015.