Crystal radio set.

[Syborg007]

I did indeed use a slider on my last radio and also tried one on this radio.
Just to experiment on different scenarios.
Cheers for the coil link folks.
It's shed some light on an issue that's been bugging me.
I've just found a few scrap transformers laying about at work.
Mk3 coming up!!!

There are always a few 'proper' high impeadance 'phones on ebay if you want to reproduce what it was like in the 20's.

[Neil Purling]

If you want High Impedance 'phones drop us a PM. I have a spare pair.

[Sideband]

Originally Posted by Syborg007

Well folks.. Success!!!
My diode arrived on Saturday morning and I set to work.
My coil had a 10 turn primary and a 60 turn secondary coil.
Hooked everything up and got a station straight away!!
I toyed with a few different wiring methods and could only seem to get Mexican stations or China radio international.
today I housed the entire outfit in and on a bisto tub.
Coil round the diameter and the diode and wiring inside with a 4 gang chocblock bolted through the lid for antenna, ground and audio output.
But this time I used a 25 turn primary coil and 60 turn secondary.
I also added a small PVC variable cap from an old Roberts radio.
I'm still getting china radio intermational but loads of french channels.

You also have to remember that the MW band now is a lot different from the MW band 50 years ago. Many of the powerful London stations are no longer there although there are many 'locals' to be heard if you are close enough to them. R4 is best heard on LW (the old R2 or Light Programme frequency in 198 metres) so you will need many more turns on your coil.

As a general guide, I used 100 turns of 26 gauge enamelled wire around a toilet roll and a 500pF variable cap with a tap at 20 turns or so for connection to the diode. For LW you'll probably need to double the turns to 200.

Most of the fun is playing around and I used to have several coils for different wavebands.


Rich.

[Syborg007]

It is done !!!
Yesterday I had an hour between callouts so I wound a new coil.
Using an old 24v transformer I found I wound a coil with a tap every 10 turns and a primary coil below It with 25 turns on a section of packaging tube made of thick cardboard.
This is about 5pm thick and very sturdy.

Once home I started building the tap selector using brass drawing pins for contacts and a copper wiper bolted through a piece of laminate flooring.
All the pin holes were predrilled and counter bored from the back, then left over lengths of mag wire were soldered to the pin ends and onto the coil taps. Also the small variable capacitor was fixed through the laminate.
Everything was wired up and the coil was fixed to a small piece of scrap timber and the laminate front plate was then fixed to the base. I also put sides of the same laminate
Material on the unit to help support the front plate.

All connected up I was receiving a good 4-5 useable channels except I had an annoying buzzing from the amp. I reversed the wiring for the headphone socket and it cured it!!

All In all I'm very happy, I will try to
Post some pics when I'm next at my pc.

Regards

Syborg

[Syborg007]

Cheers sideband. I'm toying with making another coil that can be linked to the original now.
I'm think that I will need to tap the extra coil too?
But surely "stacking" the new coil ontop will
Physically increase the coil length thus lowering the frequency.


Regards

Syborg

[Syborg007]

thought ipost up afew pics.

enjoy...

Spendid job, next step the 'one valver' I knock one up every few years just to be amazed at what one valve (anything triode or above will do) can do

[jim_jobe]

Doesn't Radio China use the original Radio Luxembourg transmitter on 208m?
Jim

[Herald1360]

I built this crystal set years ago and was very impressed by the performance on a long aerial:

http://vintageradio.me.uk/radconnav/...rc/circuit.jpg

The details are here:
http://vintageradio.me.uk/radconnav/crystals/

It's the sensitive and selective set by P A Dewhurst.

[ITAM805]

Originally Posted by Herald1360

I built this crystal set years ago and was very impressed by the performance on a long aerial:

It's the sensitive and selective set by P A Dewhurst.

I built that one too, but I'm sure it was 1965-ish as I was still at school, and I started work in '67? What joy when I connected my old brown bakelite BBC headphones up to it and it worked!

[Radio_Dave]

Here's another vote for the P A Dewhurst design. I built one a couple of years ago and it really does work well.

Although reception isn't great, I've had a lot of fun messing around with a foxhole radio, as mentioned in your first post, so I do hope you don't give up on that.

David

[Syborg007]

Well, now I know everything works as it should, I can now try using the razorblade again, might have to buy another diode so I can build two radios.
At the mo the only large amount of mag wire I have is either 0.15mm or a load still on a transformer doughnut that's gonna take ages to unwind.

Anyone know of an easier way to unwind doughnuts without taking all night and tangling it all up?

Cheers

oldskooltrader

[Herald1360]

You could try making up a sort of widish end notched stick where a single turn round the notches was the same length as a single turn on the toroid, but it would still be a pain. Unwinding a bobbin style transformer is a lot easier!

[Refugee]

We need to look for a video of one being wound.
I wonder if there is anything on the usual sites.

[wireful3]

I have seen a video of a toroidal coil winder working. It was amazing but not reassuring in terms of unwinding one. I can't remember where I saw it but I would guess that I found the link on here.

My suggestion is to try Heralds suggestion. Make something a bit like a wool winder to store the unwound wire. It must be reasonably long so that the unwound wire can be kept tidy, without making it too fat to thread through the ring. The wire will get fairly rough handling so I doubt whether it would work with fine gauge wire.

[Dylan85]

Try this one http://www.youtube.com/watch?v=6lvm3FGTHSI

Dylan