UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Decca Bradford Preset Brightness Modification?

Chris55000 · 18th Apr 2021, 5:22 pm

Hi!

There seem to have been at least four distinct printed Decca Bradford Service Manuals in circulation, and in one of these, the PCB for the sound o/p and PSU had a modified Preset Brightness Control circuit, with R611 (1M8) added from the cathode of the h.t. rectifier diode to the top end of VR601, plus R612 (47k) added between the +25V l.t. line and the top end of VR601.

These resistors were properly designed in the relavent PCB, not simply added on the copper side with track cuts, etc!

Can anybody suggest the reason behind this modification?

(I only found out about it after I'd sent Chris Field's New Telpro panel for production, but I have now made a second revision to incorporate these resistors!)

Chris Williams

18th Apr 2021, 5:22 pm	#1
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,868	Decca Bradford Preset Brightness Modification? Hi! There seem to have been at least four distinct printed Decca Bradford Service Manuals in circulation, and in one of these, the PCB for the sound o/p and PSU had a modified Preset Brightness Control circuit, with R611 (1M8) added from the cathode of the h.t. rectifier diode to the top end of VR601, plus R612 (47k) added between the +25V l.t. line and the top end of VR601. These resistors were properly designed in the relavent PCB, not simply added on the copper side with track cuts, etc! Can anybody suggest the reason behind this modification? (I only found out about it after I'd sent Chris Field's New Telpro panel for production, but I have now made a second revision to incorporate these resistors!) Chris Williams Attached Thumbnails __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed! Last edited by Chris55000; 18th Apr 2021 at 5:30 pm.