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Old 2nd May 2020, 10:30 pm   #1
kestrelmusic
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Default Portadyne U56

This is a really nice set. There's no printed service data for it, though a helpful amateur did draw a circuit diagram, albeit without the tuned circuits. There are no manufacturer's markings on the chassis and it looks and feels very like a Plessey job - solid steel chassis, nicely laid out for servicing etc. with good access to IFTs and coils to alignment.

It was in a poor state; the whole of the power supply with the exception of the dropper had to be replaced. The valve line-up is 6A8, 8K7, 6Q7, 25L6 and 25Z6 - 300mA series heaters, so the dropper is dissipating nearly 50 watts of heat! There's a metal shield over the top of the dropper, presumably to stop it setting fire to the case! The card back showed signs of burning just under the shield, so I replaced that bit with perforated aluminium for safety. It has a wire soldered to the shield and terminating with a 3mm plug which connects to the aerial socket - it's labelled "capacity aerial" and is better than no aerial!

When I started on this set the first problem was a vicious 50 cycle hum. It turned out that the reservoir cap and both sides of the smoothing cap were completely open circuit. The reservoir cap was rather a nice looking TCC jobbie, so I drilled out the works and inserted a modern electrolytic into it. The cap from V3 anode to V4 grid looked dodgy, so I replaced it, along with a couple more waxies.

Now comes the confession. I never, of course, try to clean glass dials with a damp cloth, but just dust them with a fine brush. Fortunately I had photographed it before removing it, as even the lightest touch of the brush removed all the white paint (the other colours remained intact). In the end I made up a dial and printed it on photo paper, glueing it lightly to the back of the dial compartment. Sooner or later someone will come up with a method of stencilling white paint onto glass, and I will then replace the original!

The case was rather knocked about, so I stripped and French polished it. It's rather nice, with maple and I think walnut inlay. The speaker cone was quite fragile with a lot of tears and cracks - this got my usual treatment of rubber solution and tissue paper.

But the performance of this set is remarkable. With just 16ft of aerial over what I optimistically term the "back garden" it pulls in all sorts of exciting stuff, especially on SW where both sensitivity and selectivity are exceptionally good.
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Old 3rd May 2020, 3:36 pm   #2
Wellington
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Smile Re: Portadyne U56

Good work, kestrelmusic . Glad you were able to recover the dial (potential) disaster!

That set looks like a substantial lump. Could you post anymore photos that show it's size (and the inside, of course)!

It looks as if you're keeping yourself well occupied during the virus restrictions.
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Old 3rd May 2020, 10:07 pm   #3
kestrelmusic
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Default Re: Portadyne U56

Quote:
Originally Posted by Wellington View Post
Good work, kestrelmusic . Glad you were able to recover the dial (potential) disaster!

That set looks like a substantial lump. Could you post anymore photos that show it's size (and the inside, of course)!

It looks as if you're keeping yourself well occupied during the virus restrictions.
Herewith some more pics. "Before and After" of the cabinet; underneath and rear chassis views and one of my "restored" reservoir condenser - I drilled out the original "guts" and inserted a modern one with tinned copper leads soldered on - then a new paper label and a coat of clear varnish rather than wax.
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