Sparton Radio set.

[Geordie McBoyne]

Today the push button tuning assembly was removed for cleaning and to figure out how it works?
I was looking for a button latch bar but in fact there is nothing like that in the unit, so just how are the stations pre-set?
Easy!  Push in the tuning knob to find a station. Chose a button you wish to assign the  station to. Loosen the push button, gently push in the button so that the rocker is pushed up the swinging bars, retighten the button.  Station is preset. Simples.

The attached pictures show the push button mechanism.

Geordie McBoyne.  

[Terry]

Reminds me of the preset tuning setting on Radiomobile and Motorola car radios ...

[Old Sparky]

That type of P.B. mechanism was used on most makes of Car radios in the 50s, 60s, & 70s - usually called 'Prestolock'. A variation called 'Prestotune' used mainly by Philips, Pye & Ekco, in which eac individual button was tuned to the required station, was also produced, but I didn't know that such mechanisms had ever been usefd in domestic radios, nor with variable capacitance tuning. Most car radios emplyed permeability tuning in which the inductance was varied, and the capacitance fixed. Some Philips and Blaupunkt Car radios used a more complex version of the Prestolock tuning mechanism which had Eight pre-sets.

[Geordie McBoyne]

Alternative frequency changer valve. Some UK made Sparton radios were supplied with a Tungsram 6TH8G frequency changer valve in lieu of the 6K8G.

http://www.radiomuseum.org/tubes/tube_6th8.html

Geordie McBoyne.

[Geordie McBoyne]

Performance on long waves is absolutely hopeless, those aerial bandpass coils will need replacing. Actually the frequency changer mixer grid tuned circuit is OK, it can be peaked up at the higher frequency end of the LW band, it's the aerial tuned circuit where the problems are.
On medium waves it is the HF end of the waveband that is not so good, the LF end of the waveband is very lively. The problem is in the bandpass coupling arrangements used in this set, in fact I don't see any advantage of having such circuits in a receiver which has the standard IF of 455Kcs.
So I'm on the lookout for a new set of aerial input coils for the set.
Denco coils would be an excellent solution but these are difficult to find.
Considering the rubbishy short wave coils used in this set, SW performance is not an issue, no bandpass RF tuning circuits employed on SW.

The push-button tuning system is excellent, easy to setup and easy to use.

Geordie McBoyne.

[Geordie McBoyne]

Alternative frequency changer valve.   Some UK made Sparton  radios were supplied with a Tungsram 6TH8G frequency changer valve in lieu of the 6K8G.

http://www.radiomuseum.org/tubes/tube_6th8.html

Geordie McBoyne.

Found the Tungsram 6TH8G, as can be seen from the attachment it's a huge thing.  This example was made in Hungary, it's stamped "importe de Hongrie".
In use it does perform better than the 6K8G. Only adjustment needed was a tweek of the anode trimmer of the first IF transformer.
The only other UK made set to employ this valve was a pre-war Decca. 

Geordie McBoyne.

[pwdrive]

I don't know what the difference is between a 6TH8g and a 6TH8 is, Peto Scott used a 6TH8 in their Trophy 8 apparently.

Lawrence.

[Geordie McBoyne]

According to the Radimuseum 6TH8 and 6TH8G is the same valve.   Seems that the valve was widely used in France.

http://www.radiomuseum.org/tubes/tube_6th8.html

Peto-Scott Trophy 8:   http://www.radiomuseum.org/r/petoscott_trophy_8.html

From the VWRRR:  https://www.vintage-radio.net/forum/show...hp?t=76926                                                                                                                                               The contributor informs us that the 6TH8 is essentially a Continental ACH1 fitted with a 6.3volt heater.    Info on #3

Geordie McBoyne.