UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - 6-gang FM stereo tuner heads

G0HZU_JMR · 3rd Dec 2022, 1:21 pm

The crystal RBW circuits in the HP 8566/8 are very similar to your third image, except a BJT is used in place of the phase inverting transformer. The compensation trimmer should help with filter symmetry, and I think that section is what needs tweaking in some places in my HP 8568B. The cal procedure is quite detailed and lengthy. I've got the gear here to do it all, but it might take me a long time...

3rd Dec 2022, 1:21 pm	#328
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: 6-gang FM stereo tuner heads The crystal RBW circuits in the HP 8566/8 are very similar to your third image, except a BJT is used in place of the phase inverting transformer. The compensation trimmer should help with filter symmetry, and I think that section is what needs tweaking in some places in my HP 8568B. The cal procedure is quite detailed and lengthy. I've got the gear here to do it all, but it might take me a long time... __________________ Regards, Jeremy G0HZU