Sunday, 17 January 2016

Bench PSU for Tube Projects

Just back from the West Manchester Club's Winter "Red Rose" Rally, which is held at a leisure centre only a few miles from my home. Unusually, today's Rally lived up to its "Winter" billing, as there was a sprinkling of snow on the ground to greet visitors.

I bumped into some friends from Warrington and found a nice old Farnell E350 power supply - just right for tube projects...


It gives metered, variable HT up to 350V (in seven switched ranges) and a range of filament supplies. This is a useful addition to the m0xpd range of HT supplies - particularly as it is both metered and variable.

The only issue obvious at time of purchase was the ding on the corner of the case...


A little gentle attention in the 'body shop' soon made the case look a little more presentable...


Just needs a lick of paint (don't hold your breath).

I hadn't noticed at the time of purchase a more serious problem - the voltage selector on the rear panel is broken, exposing the internal conductor, which carries mains line voltage...


This is currently addressed using what Roger used to call "insulting tape" - until somebody can come up with a replacement for the nice plug-in, insulated link (not that I will ever wish to change the voltage setting).

Now for a test...

Fortunately, I hadn't got round to yesterday's threat / promise to dismantle the single-tube regenerative receiver. So - there on the bench was a convenient tube project just waiting to be powered.

When I used it before, I had a Farnell L30B on the filament and a Farnell L30BT with its outputs running in series for the HT. Now, the new purchase could power the whole shebang...


It even prompted me to experiment a little more - I can get better performance with higher HT levels than the 40V previously reported. This afternoon I was running around 70V.

This is a nice new (that's to say, old) toy. All for £20. Bargain.

...-.- de m0xpd

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