Sparton Radio set.

[Geordie McBoyne]

This set has been upstairs and is getting bashed up so it's about time it was removed from that awful storeroom and restored to working condition.
As the first picture shows all the control knobs are missing as well as some push buttons.
Valve lineup is:  6K8G frequency changer. 6K7G IF amplifier. 6Q7G detector, AVC and amplifier. 6V6G output.  5Z4G rectifier, a well known series of valves.  
About Sparton Radio. I'm sure this is the American brand that was introduced in the UK by Michael Sobell.  Might consult the Setmakers book later today.

Geordie McBoyne.

[kalee99]

Hi,
I had one of these sets a while ago and it restored very well. The mechanical push button system on it worked very well once cleaned, lubricated and set up.
They were indeed an American based firm with some sort of manufacturing here in the UK.
It was all very well made and played very nicley.
I moved it on when my collection tipped the 200 mark.
Paul.

[radioman]

That's a nice looking 30's set you've got there David.
I hope you've got a good selection of spare knobs - those push-button ones could be problematic.
I wonder why the loudspeaker isn't in the middle of the baffle ?
EDIT - I've just had a closer look and it would appear that there's a dial lamp right in the centre which would foul with the 'speaker if it was in the middle...


Andy

[Murphyv310]

Always a great valve line up. These old octals just seem to go on forever.

[Geordie McBoyne]

Can't find any service information for this set. One thing for sure, the alignment is way out. Here in Geordieland BBC Radio 4 can be received on 603Khz, close to 500metres. On this set R4 was coming in nearer 450metres, clearly something is wrong. There dosen't appear to be any adjustable oscillator padders in this set, perhaps the intermediate frequency amplifier is wrong. The signal generator tuned in to an IF of <500Khz, is that the correct figure, who knows? Anyway, I've retuned the IFs to 465Khz and now R4 is in the correct position on the tuning scale. As this is a radio of American origin could the IF be 455Khz?
The tuning capacitor is a three gang unit and the medium and long wavebands have two stage bandpass aerial tuning circuits, these are usually associated with receivers having low IFs, rare with sets with the standard radio IF of 450 to 500Kcs. This part of the set is proving difficult to adjust at the HF end of the medium waveband. Long wave coverage is way out, signals are coming in between 300 to 400Khz, faulty oscillator padding capacitor perhaps?
No bandpass tuning on short waves, just a single aerial coil and oscillator coil.

Geordie McBoyne.

[Geordie McBoyne]

The attached picture shows the off-set heater-cathode in the 6K8G valve.  This valve has an interesting triode-hexode assembly , quite different from it's European counterpart the ECH35 which has separate triode and hexode electrode assemblies sharing a common cathode.
Info about the 6K8:  http://www.r-type.org/exhib/aaa0058.htm

To the right of the valve can be seen the rather rubbishy short wave coils.  

Geordie McBoyne.

[Murphyv310]

The interesting thing is fitting an ECH35 to a set with a 6K8 there is no noticeable performance change.

[Geordie McBoyne]

That's a nice looking 30's set you've got there David.
I hope you've got a good selection of spare knobs - those push-button ones could be problematic.
I wonder why the loudspeaker isn't in the middle of the baffle ?
EDIT - I've just had a closer look and it would appear that there's a dial lamp right in the centre which would foul with the 'speaker if it was in the middle...


Andy

Hi Andy,
             I've confirmed that it is a late thirties set and also the Michael Sobell connection.

In page  297 of the Setmakers book we learn that Sobell Industries evolved from a company that employed only about a dozen people at one point before the war to reach a workforce of a thousand in 1950.
His had first established his first British company, Solectric in 1934, and from 1937 had made "Sparton" radio receivers at a small factory in Wembley. The factory was damaged by enemy action in 1940.

The knobs for the set are somewhere in the shop but only three push buttons are in existence.

Meanwhile, I've the long waveband to sort out.

Geordie McBoyne.

[Geordie McBoyne]

"Long wave coverage is way out, signals are coming in between 300 to 400Khz, faulty oscillator padding capacitor perhaps?"

In fact the long wave padding capacitor is missing.  Connecting a 200pF capacitor across the LW padding trimmer restores long waveband coverage.  The precise value will be determined by trial and error, it is likely to be between 120 to 150pF.  
The first attachment shows the position of the trimmers.  The second picture shows the position of the tuning coils. Bottom left the medium wave bandpass coilset, to the right the long wave bandpass coilset. The local oscillator coils are at the top of the picture, MW on the left side of the coil former.

Geordie McBoyne.

[Murphyv310]

Hi David.
Not the nicest of layouts or construction, looks though can be deceiving and no doubt once you have sorted it all out the set will most likely perform very well.