Marconi RB12 Smokers Cabinet radio 1924.

[Geordie McBoyne]

I'm still having no luck trawling through the net for any infomation about the coil and tuning assemblies employed in the Smokers Cabinet Marconi Model RB12.  Similar models are the V4 and VB4.
These receivers employ a spade type of tuning system
I Have found the pictures of the internals of the later model VB4 showing the circular aerial and detector tuning assemblies.
Evidently the spade tuning system was attributed to Marconi Man C. S. Franklin.
Some cabinet construction details are different, for example, my set has a box for the 40 volt battery. The set shown in the attachment has a retaining bar to hold the battery in position.  Seen at the left rear view of the VB4 internals.
What is known the coils are of the "pancake" type similar to those in the V2.  A sliding copper spade does the tuning in the V2 and it is known there is something similar in the RB12, V4 and VB4.        There must be some type of gearing to move the spades inside the RB12 tuners.

Also the flat coils must be quite compact considering there are two separate assemblies for short and long wavebands.

Geordie McBoyne.

[Murphyv310]

Hi David.
I'm sure you will find the info you need. The lads on here are very helpful and I am sure you will get the info you need.
Good luck.

[pwdrive]

Make sure it's insured, there's a V2 up for auction at the moment, it's already up to £730....

Lawrence.

[Geordie McBoyne]

At the moment the set is just an empty box. The first attempt to do a reconstruction was thirty-five years ago. Slowly but surely I'm gathering construction data. The two stage amplifier is the easy part of the recreation. It's those coils that holding things up.

The V2 is going up in value again.

Geordie McBoyne.

[Yorkie]

When you say 'it's those coils that are holding things up',  I'm not sure if you're intending to home-brew them, but if so, there's an excellent Dutch website which might be of interest. It shows how to make basket, honeycomb and spiders web coils, showing both the construction techniques and how to calculate the inductance. Lots of other interesting stuff, albeit a lot of amateur radio, of no interest to me:

http://www.pa2mrx.nl/UK/coil%20homebrewing_uk.htm

Hope that helps a bit.

[Geordie McBoyne]

That's an useful website.   The insides of the smokers cabinet were discarded sometime in the early 1930s. Judging from the cutouts in the cabinet floor and shelf some other type of radio had been installed for a while.  The cabinet floor was recently replaced and the shelf repaired.                                               In due course the RB12 was replaced by a another Marconi, a model 272.
The early superhet that looks like this one:  http://www.radiomuseum.org/r/marconi_272.html

The coils will resemble the pancake types in the pictured  model 32 although I suspect those coils are recent reproductions.   According to the Brown Brothers advertisement for the VB4 the set covers 300 to 3000 meters in four stages.   "Tuning is by means of the spade system and the spades are of such a shape that straight line tuning is obtained.
The wave-length range is covered without the use of interchangeable coils or range blocks by means of four coils and a four position switch which connects the coils in series and in parallel, so that the set is self contained for the receiving broadcasting as well as the Eiffel Tower time signals and other longwave transmissions."   "For the lowest wavelengths the two smaller coils are used in parallel. The next stage is obtained by these coils in series"
The higher wavelengths are covered by separate coils used in a similar manner, parallel and series.

The tuning assemblies are about six inches diameter and no more than one inch deep.

It's not going to be an easy recreation job.

Geordie McBoyne.

[peter scott]

Hi Geordie,

Does this help?
http://earlywireless.com/marconiphone_v2-picinfo.htm

Peter

[peter scott]

Also: http://dighera.com/marconiphone_v2_early_version.htm

You can see the D shaped copper plates here:

[peter scott]

A V2 on eBay shows the plates with the scale pointers:
http://www.ebay.co.uk/itm/Rare-Vintage-M...1655656987?&_trksid=p2056016.l4276

This one appears to have the vernier tuning rather instead of the simple push and pull knobs.
I guess the rods are just threaded and actually screw out through the holes in the back of the knobs.

Peter

[Geordie McBoyne]

Hi Peter,
Thanks for your input. Yes indeed the V2 receiver employs a simple spade tuning system and a more refined system is employed in the RB12. But what goes on inside those coils assemblies is up to now a mystery. I do know that there are one or two V4 or VB4 receivers in existence but even if one was located I'd imagine the owner would be reluctant to have the set dissected in order one could examine those coils.

Geordie McBoyne.