Heath-Robinson-Style One Valve Receiver

[Sparks]

What on earth is spade tuning, I have never heard of it?     I tried to wade through the Marconi document, but could see nothing referring to the mysterious spade tuning.   (Attention span of a goldfish   ).     I am very curious.   It sounds like something I would be interested in making, if only I knew what it was!
Bob      

[pwdrive]

What on earth is spade tuning, I have never heard of it?     I tried to wade through the Marconi document, but could see nothing referring to the mysterious spade tuning.   (Attention span of a goldfish   ).     I am very curious.   It sounds like something I would be interested in making, if only I knew what it was!
Bob      

It's in that Google Books link I posted....

Basically the tuning coils are flat wound, a metal "spade" (copper) is moved in and out relative to the coil thus altering the coils inductance, the high range coil alignment adjustments in the HRO receiver worked on the same principle except that the coil was a normal circular solenoid and the metal used was a an adjustable brass disc inside the coil.

Lawrence.

[Sparks]

Thanks, that makes things a lot clearer. Sounds just like an adaptation of a tuning slug, or maybe an early version of it. I once came across a short-wave transmitter where the tuning of the final stage was done by pushing a brass rod in or out of the front panel, it moved a great lump of metal in and out of the large coil. Probably easy enough to make, but I wonder how good (or bad) they were?
Bob

[pwdrive]

Yes, metal tuning slugs were used in all sorts of stuff, some TV's used aluminium ones if I remember correctly.

Lawrence.

[valves4amps]

Also known as permeability tuning where brass or copper reduces inductance or ferrite increases. Used to be used in car radios before synthesised tuning became the norm.

Dave.

[Geordie McBoyne]

In fact I introduced the V4 recreation project in the Golborne Forum earlier this year.

http://golbornevintageradio.co.uk/forum/...p?tid=5297

Geordie McBoyne.

[Aerodyne]

Permeability tuning for the VHF band can be found in VHF/FM receivers of the 1950s-early 60s.
Tony

[ppppenguin]

This may be a daft question. Whay use permeability tuning? What advantages are there over a variable capacitor?

[pwdrive]

Constant selectivity across the band.

Lawrence.

[AlanBeckett]

Rigidity. Space. In a Car Radio it's much smaller than a Gang.

Alan