Sparton Radio set.

[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.