Westminster T5534 poor LW performance

[McMurdo]

This radio was a chance-find at an antique shop and I felt sorry for it. The proprietor helpfully suggested it 'will probably work once the tubes are replaced'.

Apart from the fact it had been damp judging by the rusty chassis and detached cabinet battens, it didn't seem too bad in the daylight. I replaced the mains lead as it had been eaten bare by mice, carefullly released the rimlock valves, and cleaned the pins. The McMurdo valveholders felt taut and a quick prod with a scalpel showed the little forks all looked intact. Then, I put a bit of tape over the speaker wires which had been bared, I assume to add another speaker, replaced the grid coupling capacitor and switched on.

It was dead, one half of the mains switch being open. Cleaning and working it made no difference so I bridged it out for the time being. The result was one of the two dial lamps glowing and soon a loud raw hum from the speaker.

I checked the main smoothing capacitor, a dual 32uF hunts can; it measured open, both sections. I tagged a 22 and 47 across from the drawer and tried again.
This time I got hiss and signals and a faint radio-4 on LW. I replaced the broken dial cord and fashioned a new pointer from an old clock seconds hand and a bit of brass. This showed me that R4 was in about the right place at 1500m or about 60% of the way from left to right.

I then removed, tested and replaced the other wax caps. None of them showed particularly leaky on the multimeter, even the little brown hunts moulded ones that had split open.

With a long wire aerial and the usual sourced of noise in the workshop turned off (cctv monitor, mainly, but also an overhead fluorescent light) I tried again. Radio 4 was much louder now but everything else was swamped with noise, mainly loud buzzing, slightly irregular, not a mains hum, something similar to interference. I've done alot of radios on this bench over time and I'm used to the interference sources, and I eliminated all of them, including the wifi and other fluorescents. But the radio continued to be swamped with noise.

I tried to find a service sheet for the radio, but the nearest I could find was for a Sobell 512W, almost identical except my radio uses an EAF42 IF valve rather than the sobell's EF41. I did a basic alignment, checking the IF first (470khz) which was almost spot on anyway, the RF coil on MW was broken off and chewed up, so I reglued that, everything else was pretty good with minimal adjustments. One of the SW trimmers had a cracked ceramic washer which I replaced. I had a quick scout-around the resistors with the multimeter and found them all about right.

However the poor, noisy performance continues. It's ok on SW, but MW is marginal and LW poor. I've subbed all the valves one by one, tried screens on the FC and IF valve, and experimented with different aerial and earths, lifting or fitting a mains earth, that sort of thing.

I've taken it home to a different 'evnvironment' but the noise is still there, albeit now it also picks up noise from my LCD tv in the lounge when its on. Linking aerial and earth terminals renders the set quiet.

There's evidence of previous repairs but nothing major, other than a good twiddling of the coil cores judging by the state of the slots.

Pasted inside the right side of the cabinet, at the RF end, is a foil sheet, it looks factory fitted, with a black flylead. It was roughly soldered to the aerial tag under the chassis. I wonder if this should be on the earth tag instead? The sobell sheet makes no mention of it.

Here's a youtube video of a chap with a similar chassis (but not quite the same!)

https://youtu.be/slKaOyPjHqs

I'd welcome any ideas!

[cathoderay57]

Originally Posted by McMurdo

This radio had been damp judging by the rusty chassis and detached cabinet battens

Quite likely the coils have been affected by damp leading to reduced Q. You could try the hairdryer/heatgun treatment on the osc and ae coils then see if S/N improves. Cheers, Jerry

[McMurdo]

interesting suggestion. I wonder if its new centrally heated residence will improve it?