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Old 20th May 2022, 9:46 pm   #6
Leon Crampin
Octode
 
Join Date: Nov 2005
Location: Surrey, UK.
Posts: 1,675
Default Re: Kolster-Brandes FB-10 - seems pretty deaf

I have one of the last made FB10 receivers fitted with the long thin ferrite rod and 6BJ6 IF stage. It was a basket case with damaged IF transformer cores.

Restoring this set revealed a few weaknesses - the slotted tufnol plate locating the brass
IF core adjusters is not strong enough to prevent accidental movement. This was fixed by aralditing a paxolin piece over it, carrying a decent 6 BA threaded hole. Two cores were broken from the adjusting screws, probably by a previous attempt at a repair. The IF tuning fixed capacitors were all OK.

The worst fault was broken socket forks in the valve holders caused by dezincification of the brass which makes them brittle. Several in the first two stages of the set had to be changed - it's not difficult to fit replacement socket forks from a spare valve holder.

Following careful realignment, this set performs very well and is sensitive for a 4 valve superhet with a pentagrid mixer. I think the IF gain is considerable with the 6BJ6 and I'm surprised it's stable - but it is. The long ferrite rod also helps and the separate coupling coil for an external aerial connection is effective - unlike the stupid bottom-coupled arrangement used on most sets of this vintage.

I suspect when fully restored, your set will work well.

Leon.
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