On 05/02/2022 12:17, Pamela wrote:
> It's new to me and Ian mentioned something about caapcitors. It's probably
> 5 years since I used the radio. What drill should I follow next time I use
> it?

Large electrolytic capacitors can also make a mess if they fail, i.e.
explode!

On 05.02.2022 13:17, Pamela wrote:
> On 10:27 5 Feb 2022, Eddie King said:
>
>> On 05.02.2022 02:32, Pamela wrote:
>>>
>>> I have a 1940s valve radio which needs an external aerial like
>>> yours. I haven't used it in ages but we would use a long wire.
>>> Positioning a loop every time you tune a station would be too
>>> fiddly. Using an earth would be posh.
>>>
>>> The last time I tried it the creaky old thing was working well. It's
>>> almost identical to this one on eBay, although not as glossy and
>>> perfect. Mine has a wooden case and I love it to bits. Visitors
>>> think it's some broken old radio kept as an ornament but actually
>>> it's kept because it works.
>>>
>>> https://www.ebay.co.uk/itm/224819633440
>>
>> Hii Pamela,
>>
>> you are probably aware, but just in case.
>>
>> If the radio hasn't been properly restored there is a danger of
>> serious damage to components which are no longer available (mains and
>> output transformers) if switched on after a long period of storage.
>> Some coupling Capacitors are notorious for becoming leaky, leading to
>> overstressed output valves and high currents causing damage to these
>> components.
>>
>> Sorry if I'm teaching my grandmother to suck eggs but I though it a
>> good idea to mention this to possibly prevent a much loved radio
>> being damaged.
>
> It's new to me and Ian mentioned something about caapcitors. It's probably
> 5 years since I used the radio. What drill should I follow next time I use
> it?

Exploding electrolytic capacitors are a remote possibility but far more
likely is a leaky grid coupling capacitor to the control grid of the
output valve which would cause it to draw a great amount of current
which could eventually destroy the parts mentioned in my previous post.
The danger here is that the radio would still work to a degree, possibly
with audio distortion until something went pop.

If the radio has never been serviced in the last few years I would
advise getting it checked over. The problem with this is that many
electronic shops nowadays have no idea about valved equipment and won't
touch it.

If in doubt it might be a good idea to look on the UK Vintage Radio
Repair and Restoration Discussion Forum under the section Repair and
Restoration Services Wanted. We are are friendly bunch always willing to
help and if you ask you will probably find somebody close to you willing
to give it a quick once over.

https://www.vintage-radio.net/forum/index.php

In message <XnsAE357F6DD7A7A37B93@144.76.35.252>, Pamela
<pamela.private.mailbox@gmail.com> writes
>On 08:48 5 Feb 2022, Ian Jackson said:
>
>> In message <XnsAE35FBC3B84937B93@144.76.35.252>, Pamela
>> <pamela.private.mailbox@gmail.com> writes
>>>On 16:05 2 Feb 2022, David Paste said:
>>>
>>>> Hello all,
>>>>
>>>> I return with yet more aerial related questions.
>>>>
>>>> The radio next to me has an AM radio with reception from 522 kHz to
>>>> 1629 kHz, giving approximate wavelengths of 574 metres to 184
>>>> metres. I understand that AM radio is vertically polarised in the
>>>> UK. A quarter wave dipole would be a bit unwieldy at those
>>>> wavelengths, so loop antennas are used.
>>>>
>>>> 1. How long should the wire that is looped be?
>>>>
>>>> 1(a). Can connecting the AM aerial terminal to the central heating
>>>> copper piping act as an aerial? I am discouraged from just trying
>>>> this in case there's something I am not aware of which results in a
>>>> release of the Magic Smoke.
>>>
>>>I have a 1940s valve radio which needs an external aerial like yours.
>>>I haven't used it in ages but we would use a long wire. Positioning a
>>>loop every time you tune a station would be too fiddly. Using an
>>>earth would be posh.
>>>
>>>The last time I tried it the creaky old thing was working well. It's
>>>almost identical to this one on eBay, although not as glossy and
>>>perfect. Mine has a wooden case and I love it to bits. Visitors
>>>think it's some broken old radio kept as an ornament but actually
>>>it's kept because it works.
>>>
>>>https://www.ebay.co.uk/itm/224819633440
>>
>> Before ferrite rods, some radios did have internal loop aerials
>> inside the wooden case (usually with additional connections for an
>> external aerial and earth). Obviously the loop was directional, but
>> unless the required station was exactly in one of the two broadside
>> nulls, the orientation of the radio was probably not that critical
>> for normal domestic use.
>>
>> Regarding using old radios and record players, I'm rather bemused
>> when someone brings one into The Repair Shop (on TV) for restoration.
>> So far I've never seen any repairer take the precaution of at least
>> doing a slow, controlled wind-up of the mains voltage to give the
>> electrolytic capacitors a chance to reform, and to minimise the
>> chances of other catastrophic failures.
>
>I haven't used the radio for about 5 years, when it worked fine. What
>precautions should I follow to keep it going?
>
>I've never heard of reforming capacitors. How do you do a "slow,
>controlled wind-up of the mains voltage" or anything else that's needed? I
>couldn't find any decent web pages offering advice.

Start here:
https://tinyurl.com/2p8kdad6
>
>I was given the radio second-hand by the local TV shop which was throwing
>it out 50 years ago and it would be nice to keep it going.
>
>All the components are original (I once changed the speaker cloth!) but I
>don't have the stamina or equipment to get into a restoration project
>swapping lots of new components for old. However if doing something pays
>dividends then I would have to do it.

Old electronic components are prone to changing their values over time.
Capacitors generally go leaky. The leaky high-voltage electrolytics can
short out the HT supply (often around 200V or more), and something's
going to go bang or burn out (could be something irreplaceable, like the
mains transformer). Although usually not electrolytic, leaky coupling
capacitors (between anode and grid) will cause a valve to take excessive
current.

Ideally you should check all potentially faulty components before
applying the normal mains, but the minimum work might be at least to
gradually wind up the supply voltage. If you don't have the facilities,
try inserting a filament mains light bulb in series with the mains
(maybe starting with a low wattage one (which will have the highest
resistance), and then progressing to higher wattages.

Of course, if there's a valve rectifier (and not solid-state), leaky HT
electrolytics won't get any voltage across them until there's sufficient
mains voltage to get the rectifier heaters glowing - so it's all a bit
of a compromise.

With any old electronic equipment that's working, it's probably a good
idea to power it up every so often to help stop the capacitors going
leaky.
--
Ian

On Wednesday, 2 February 2022 at 16:24:06 UTC, SH wrote:

> Before I answer the question of MW aerials, I didn't think there were
> that many MW stations left on MW? In any case there would be DAB or FM
> equivalents or even an internet radio station equivalent. The audio
> quality will be better than on MW

There aren't, but i am still captivated by radios!

> Yes they can. You often see this as a horizontal halo to recieve
> stations from all directions but the gain is not as good as a vertical
> dipole (Most FM stations use mixed polarity) Horizontal dipoles have
> better gain than a halo but are obviously rather directional.

Thanks. I should have make the link between those horizontal things and the loops of wire, but...

On Wednesday, 2 February 2022 at 20:15:48 UTC, Dave W wrote:

> How old is that radio? Surely it has an internal ferrite rod aerial
> and you rotate the set to get best reception?

It's a small DVD player / receiver. Doesn't have an internal ferrite, but spring
clips for a loop.

On Wednesday, 2 February 2022 at 21:02:18 UTC, wrightsaerials@aol.com wrote:

> Here's the one I built when I was a kid. Actually I built several.

Thanks Bill.

> Despite such things being earthed they often do work as an AM aerial.
> When I was a teenage stop-go man (boy) I used to connect my tranny (shut
> up)

We all know.

> to the steel rail of the bridge if I happened to be on one. This
> brought in Radio Caroline.

I shall give it a go.

> > 5. Can FM aerials be made into loops?
> Get the aluminium to about 450C and apply gentle pressure around a
> former. Keep the heat away from the plastic junction box.

Will I need special gloves or facewear?

Cheers!

On Wednesday, 2 February 2022 at 22:20:44 UTC, David Woolley wrote:

> > 3. I understand loops are directional, how should they be oriented? To
> > roll towards the transmitter, or to roll at ninety degrees to the
> > transmitter? (I am just curious about this because obviously the practical
> > thing to do is just turn the loop for best reception.)

> To roll away from the transmitter, as the radiation pressure will tend
> to push them in that direction :-).

Ha!

> If you are using it for communicating with aircraft, yes, because there
> is no capture effect, so you can hear if a weaker station is trying to
> use the same frequency and have some ability to work when another
> aircraft has the microphone key stuck down.

Interesting, thank you.

On Thursday, 3 February 2022 at 07:53:55 UTC, Woody wrote:

> A much easier solution: given that almost all VHF/FM transmissions are
> now mixed polarisation, just put up a vertical dipole.

This is what I will do once the weather is better. I was just curious about
the small loop aerial for VHF. Cheers.

On Thursday, 3 February 2022 at 10:39:33 UTC, Jim Lesurf wrote:

> The ferrite rod can be viewed almost like a 'grip' that has taken hold of
> of the radio broadcast's RF magnetic field over a large volume and pulled
> it togther to pass along the rod, though the coil. I looks like this if you
> plot the external field lines.

Wide angle lens in photography terms?

> The higher the mu value, the bigger the effect. Alas, this also tends to go
> with the response being 'slower'. So the effect tends not to work at much
> higher frequencies. Thus although you can use a ferrite rod at, say, 100
> MHz, it's ability to 'pull in' signal power is much less than in the MW/LW
> bands. So not usually used above MW for domestic reception.

Ah right, thanks Jim.

On Saturday, 5 February 2022 at 01:33:13 UTC, Pamela wrote:

> The last time I tried it the creaky old thing was working well. It's
> almost identical to this one on eBay, although not as glossy and
> perfect. Mine has a wooden case and I love it to bits. Visitors think
> it's some broken old radio kept as an ornament but actually it's kept
> because it works.
>
> https://www.ebay.co.uk/itm/224819633440

That is a lovely looking thing! :)

On Saturday, 5 February 2022 at 10:22:30 UTC, Adrian Caspersz wrote:

> Anyway, we had a BT rotary dial-stop telephone back then, and I somehow
> found connecting the aerial wire to the dial-stop made a massive
> improvement to its pickup of broadcasts.

Could you pick up Dial a Disc?

On 05/02/2022 16:07, David Paste wrote:
> Wide angle lens in photography terms?

Not a valid analogy.

On 05/02/2022 01:32, Pamela wrote:
> On 16:05 2 Feb 2022, David Paste said:
>
>> Hello all,
>>
>> I return with yet more aerial related questions.
>>
>> The radio next to me has an AM radio with reception from 522 kHz to
>> 1629 kHz, giving approximate wavelengths of 574 metres to 184 metres.
>> I understand that AM radio is vertically polarised in the UK. A
>> quarter wave dipole would be a bit unwieldy at those wavelengths, so
>> loop antennas are used.
>>
>> 1. How long should the wire that is looped be?
>>
>> 1(a). Can connecting the AM aerial terminal to the central heating
>> copper piping act as an aerial? I am discouraged from just trying
>> this in case there's something I am not aware of which results in a
>> release of the Magic Smoke.
>
> I have a 1940s valve radio which needs an external aerial like yours. I
> haven't used it in ages but we would use a long wire. Positioning a
> loop every time you tune a station would be too fiddly. Using an earth
> would be posh.
>
> The last time I tried it the creaky old thing was working well. It's
> almost identical to this one on eBay, although not as glossy and
> perfect. Mine has a wooden case and I love it to bits. Visitors think
> it's some broken old radio kept as an ornament but actually it's kept
> because it works.
>
> https://www.ebay.co.uk/itm/224819633440

I have an old radiogram which has a 78s only deck so perhaps 1940s or
early 1950s. When I got it the radio motor-boated until I tapped each
valve and found that the rectifier being tapped sometimes brought the
radio into working order, and a replacement rectifier valve was all it
needed.

I ran a wire from the aerial socket out of the window, and connected it
to the washing line that had a steel core and ran down the garden, and
the radio reception was excellent with that arrangement.

Jim

On Saturday, 5 February 2022 at 16:19:10 UTC, David Woolley wrote:

> Not a valid analogy.

Oh well.

On 05/02/2022 08:48, Ian Jackson wrote:

> Regarding using old radios and record players, I'm rather bemused when
> someone brings one into The Repair Shop (on TV) for restoration. So far
> I've never seen any repairer take the precaution of at least doing a
> slow, controlled wind-up of the mains voltage to give the electrolytic
> capacitors a chance to reform, and to minimise the chances of other
> catastrophic failures.

I saw it done once on an old radio, and the man explained it was to not
damage the smoothing circuit which had capacitors of the type that he
couldn't get hold of.

So the repair shop was aware of the advantages of doing that. Perhaps
they didn't make a big point of mentioning it.

Jim

On 05/02/2022 08:48, Ian Jackson wrote:
> Before ferrite rods, some radios did have internal loop aerials inside
> the wooden case (usually with additional connections for an external
> aerial and earth). Obviously the loop was directional, but unless the
> required station was exactly in one of the two broadside nulls, the
> orientation of the radio was probably not that critical for normal
> domestic use.

These little plastic frames wound with about six turns of thin wire are
still supplied with some tuners and audio units.

Bill

On 05/02/2022 16:51, williamwright wrote:
> On 05/02/2022 08:48, Ian Jackson wrote:

>> Before ferrite rods, some radios did have internal loop aerials inside
>> the wooden case (usually with additional connections for an external
>> aerial and earth). Obviously the loop was directional, but unless the
>> required station was exactly in one of the two broadside nulls, the
>> orientation of the radio was probably not that critical for normal
>> domestic use.
>
> These little plastic frames wound with about six turns of thin wire are
> still supplied with some tuners and audio units.

Are they as good as ferrite rod aerials? I've got a couple of radios
like that, but I assumed that it was to facilitate orientation and
portable radios changed from frame to ferrite as they can be turned
fairly easily. (Roberts radios had a swivel base for the purpose.) I
also had a table radio that had an internal ferrite with a lever at the
back to turn it, but that requires space inside. My Armstrong 626 had a
ferrite aerial at the back cased in plastic which could be turned if
there was space.

--
Max Demian

On 05/02/2022 15:55, Roderick Stewart wrote:
> On Sat, 5 Feb 2022 13:07:24 +0000, MB <MB@nospam.net> wrote:
>> On 05/02/2022 12:17, Pamela wrote:

>>> It's new to me and Ian mentioned something about caapcitors. It's probably
>>> 5 years since I used the radio. What drill should I follow next time I use
>>> it?
>>
>>
>> Large electrolytic capacitors can also make a mess if they fail, i.e.
>> explode!
>
> The liquid filled ones are the most fun, but they're pretty rare now,
> and I don't really think you're supposed to connect them directly
> across the mains...

If the smoothing ones in cans dry out you could just wire a (much
smaller) modern one across the terminals under the chassis.

--
Max Demian

In article <cubQ+fFWnj$hFwXu@brattleho.plus.com>, Ian Jackson
<ianREMOVETHISjackson@g3ohx.co.uk> wrote:

> Regarding using old radios and record players, I'm rather bemused when
> someone brings one into The Repair Shop (on TV) for restoration. So far
> I've never seen any repairer take the precaution of at least doing a
> slow, controlled wind-up of the mains voltage to give the electrolytic
> capacitors a chance to reform, and to minimise the chances of other
> catastrophic failures.

I have seen them do this on more occasion. But I assume they don't bother
to show it every time. Alas, they seem more interested in ancient
mass-market items than anything from the more 'hi fi' era. Possibly because
their 'expert' wouldn't be able to correctly repair them.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
biog http://jcgl.orpheusweb.co.uk/history/ups_and_downs.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article <djksvg9e4p6vbi4ub7fi22mnap6j86hpu7@4ax.com>, Martin
<me@address.invalid> wrote:
> >https://www.ebay.co.uk/itm/224819633440

> It's quite modern it has FM :-) In the 1950s, I had a radio that an
> uncle had bought during the war. I was given it when he emigrated to
> Canada. My parents binned it when they emigrated to Australia. Such a
> waste.

My first 'stereo' system was based on one of the record players that only
had a mono amp and speaker, but a socket for the 'other channel'. I
connected this to a line input on my parents ancient radio. IIRC it was
called something like a 'Barker 88'. I used that for a few years until I
could afford a 'proper' stereo system.

I really liked the old radio, so told my parents when I left home that I'd
want it if they ever decided to get rid of it. But, alas, they forgot, and
eventually threw it away without telling me.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
biog http://jcgl.orpheusweb.co.uk/history/ups_and_downs.html
Audio Misc http://www.audiomisc.co.uk/index.html

On 05/02/2022 16:35, Indy Jess John wrote:
> On 05/02/2022 01:32, Pamela wrote:
>> On 16:05  2 Feb 2022, David Paste said:
>>
>>> Hello all,
>>>
>>> I return with yet more aerial related questions.
>>>
>>> The radio next to me has an AM radio with reception from 522 kHz to
>>> 1629 kHz, giving approximate wavelengths of 574 metres to 184 metres.
>>> I understand that AM radio is vertically polarised in the UK. A
>>> quarter wave dipole would be a bit unwieldy at those wavelengths, so
>>> loop antennas are used.
>>>
>>> 1. How long should the wire that is looped be?
>>>
>>> 1(a). Can connecting the AM aerial terminal to the central heating
>>> copper piping act as an aerial? I am discouraged from just trying
>>> this in case there's something I am not aware of which results in a
>>> release of the Magic Smoke.
>>
>> I have a 1940s valve radio which needs an external aerial like yours. I
>> haven't used it in ages but we would use a long wire. Positioning a
>> loop every time you tune a station would be too fiddly. Using an earth
>> would be posh.
>>
>> The last time I tried it the creaky old thing was working well. It's
>> almost identical to this one on eBay, although not as glossy and
>> perfect.  Mine has a wooden case and I love it to bits.  Visitors think
>> it's some broken old radio kept as an ornament but actually it's kept
>> because it works.
>>
>> https://www.ebay.co.uk/itm/224819633440
>
> I have an old radiogram which has a 78s only deck so perhaps 1940s or
> early 1950s. When I got it the radio motor-boated until I tapped each
> valve and found that the rectifier being tapped sometimes brought the
> radio into working order, and a replacement rectifier valve was all it
> needed.

What kind of pickup does it have: magnetic or crystal? I once had a 78
RPM record deck which had a heavy horseshoe magnet with a coil between
the pole pieces and a moving iron holding the (use once) needle. It
produced a big enough signal to feed a normal audio amplifier without a
special pre-amp as modern magnetic pickups require. There was a strong
spring built into the pickup arm hinge to counter the weight of the pickup.

> I ran a wire from the aerial socket out of the window, and connected it
> to the washing line that had a steel core and ran down the garden, and
> the radio reception was excellent with that arrangement.

In my (buying old radios from jumble sales for 2/6) youth I found that a
wire dangling from the aerial socket and no earth was usually adequate.

--
Max Demian

On 05/02/2022 16:19, David Woolley wrote:
> On 05/02/2022 16:07, David Paste wrote:
>> Wide angle lens in photography terms?
>
> Not a valid analogy.

The human brain is like a giant fish. It had gills through which it can
breathe.

In article <WPWdnW7i4qC8J2P8nZ2dnUU7-UHNnZ2d@brightview.co.uk>, Max Demian
<max_demian@bigfoot.com> wrote:
> On 05/02/2022 16:35, Indy Jess John wrote:
> > On 05/02/2022 01:32, Pamela wrote:
> >> On 16:05 2 Feb 2022, David Paste said:
> >>
> >>> Hello all,
> >>>
> >>> I return with yet more aerial related questions.
> >>>
> >>> The radio next to me has an AM radio with reception from 522 kHz to
> >>> 1629 kHz, giving approximate wavelengths of 574 metres to 184 metres.
> >>> I understand that AM radio is vertically polarised in the UK. A
> >>> quarter wave dipole would be a bit unwieldy at those wavelengths, so
> >>> loop antennas are used.
> >>>
> >>> 1. How long should the wire that is looped be?
> >>>
> >>> 1(a). Can connecting the AM aerial terminal to the central heating
> >>> copper piping act as an aerial? I am discouraged from just trying
> >>> this in case there's something I am not aware of which results in a
> >>> release of the Magic Smoke.
> >>
> >> I have a 1940s valve radio which needs an external aerial like yours.
> >> I haven't used it in ages but we would use a long wire. Positioning a
> >> loop every time you tune a station would be too fiddly. Using an earth
> >> would be posh.
> >>
> >> The last time I tried it the creaky old thing was working well. It's
> >> almost identical to this one on eBay, although not as glossy and
> >> perfect. Mine has a wooden case and I love it to bits. Visitors
> >> think it's some broken old radio kept as an ornament but actually it's
> >> kept because it works.
> >>
> >> https://www.ebay.co.uk/itm/224819633440
> >
> > I have an old radiogram which has a 78s only deck so perhaps 1940s or
> > early 1950s. When I got it the radio motor-boated until I tapped each
> > valve and found that the rectifier being tapped sometimes brought the
> > radio into working order, and a replacement rectifier valve was all it
> > needed.

> What kind of pickup does it have: magnetic or crystal? I once had a 78
> RPM record deck which had a heavy horseshoe magnet with a coil between
> the pole pieces and a moving iron holding the (use once) needle. It
> produced a big enough signal to feed a normal audio amplifier without a
> special pre-amp as modern magnetic pickups require. There was a strong
> spring built into the pickup arm hinge to counter the weight of the
> pickup.

> > I ran a wire from the aerial socket out of the window, and connected it
> > to the washing line that had a steel core and ran down the garden, and
> > the radio reception was excellent with that arrangement.

> In my (buying old radios from jumble sales for 2/6) youth I found that a
> wire dangling from the aerial socket and no earth was usually adequate.

Not for getting Radio Lux in Edinburgh.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

On 16:35 5 Feb 2022, Indy Jess John said:

> On 05/02/2022 01:32, Pamela wrote:
>> On 16:05 2 Feb 2022, David Paste said:
>>
>>> Hello all,
>>>
>>> I return with yet more aerial related questions.
>>>
>>> The radio next to me has an AM radio with reception from 522 kHz to
>>> 1629 kHz, giving approximate wavelengths of 574 metres to 184
>>> metres. I understand that AM radio is vertically polarised in the
>>> UK. A quarter wave dipole would be a bit unwieldy at those
>>> wavelengths, so loop antennas are used.
>>>
>>> 1. How long should the wire that is looped be?
>>>
>>> 1(a). Can connecting the AM aerial terminal to the central heating
>>> copper piping act as an aerial? I am discouraged from just trying
>>> this in case there's something I am not aware of which results in a
>>> release of the Magic Smoke.
>>
>> I have a 1940s valve radio which needs an external aerial like
>> yours. I haven't used it in ages but we would use a long wire.
>> Positioning a loop every time you tune a station would be too
>> fiddly. Using an earth would be posh.
>>
>> The last time I tried it the creaky old thing was working well. It's
>> almost identical to this one on eBay, although not as glossy and
>> perfect. Mine has a wooden case and I love it to bits. Visitors
>> think it's some broken old radio kept as an ornament but actually
>> it's kept because it works.
>>
>> https://www.ebay.co.uk/itm/224819633440
>
> I have an old radiogram which has a 78s only deck so perhaps 1940s or
> early 1950s. When I got it the radio motor-boated until I tapped each
> valve and found that the rectifier being tapped sometimes brought the
> radio into working order, and a replacement rectifier valve was all
> it needed.
>
> I ran a wire from the aerial socket out of the window, and connected
> it to the washing line that had a steel core and ran down the garden,
> and the radio reception was excellent with that arrangement.
>
> Jim

A radiogram is a big snazzy step upwards compared to a plain radio. Only
for the well off.

In message <VJCdncRsQYJQKWP8nZ2dnUU7-WHNnZ2d@brightview.co.uk>, Max
Demian <max_demian@bigfoot.com> writes
>On 05/02/2022 15:55, Roderick Stewart wrote:
>> On Sat, 5 Feb 2022 13:07:24 +0000, MB <MB@nospam.net> wrote:
>>> On 05/02/2022 12:17, Pamela wrote:
>
>>>> It's new to me and Ian mentioned something about caapcitors. It's probably
>>>> 5 years since I used the radio. What drill should I follow next time I use
>>>> it?
>>>
>>>
>>> Large electrolytic capacitors can also make a mess if they fail, i.e.
>>> explode!
>> The liquid filled ones are the most fun, but they're pretty rare
>>now,
>> and I don't really think you're supposed to connect them directly
>> across the mains...

I'm glad you don't think that!!!
>
>If the smoothing ones in cans dry out you could just wire a (much
>smaller) modern one across the terminals under the chassis.

They rarely 'dry out'. Normally they go low-impedance.
>
The older type of electrolytics are, if not wet*, damp, and rely on a
thin insulating layer between the +ve and -ve electrodes, and which is
actually initially formed by electrolytic action. If the capacitor is
left for a long time without any voltage applied, this layer dissolves,
leaving a more-or-less a short circuit. However, it can often be
re-formed by the gradual application of the DC voltage (preferably
individually, via a current-limiting resistor, and observing the ingoing
current and the voltage across the capacitor). *Some really old types
really WERE wet, and you could hear the electrolyte sloshing around if
you shook them.

If you are restoring an old (collectible) radio (etc), purists will
remove the innards of faulty electrolytics (and other components), and
fit a modern one inside. Correctly done, the unit will look like new.
--
Ian