Philips 650A Low Volume - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

Voxophone · 2nd Sep 2016, 4:45 pm

I've tried a 2-22pF trimmer in parallel with the existing trimmer on MW. The circuit peaks effectively with the added trimmer and the MW volume is now much better on most stations - although the improvement is not uniform across the band. There is also no longer any improvement by touching wire to the V1 grid. I realise this is a bit of a bodged solution but given the fragility of the existing trimmers I think I'm more or less happy to trial it for now.

A more immediate problem is a snapped bowden cable inner. Does anyone know a good source of suitable wire to make a replacement?

Cheers

Liam

ms660 · 2nd Sep 2016, 6:12 pm

If it were mine I would check the IF and RF/Osc alignment with a signal generator.

Adjusting one of the RF trimmers might improve the signal but it doesn't mean to say that the other RF trimmer is set correctly.

Beehive trimmers can be adjusted easy enough, even without the correct tool, always mark some reference points first on the can and the trimmer, the RF trimmers should be adjusted with the receiver set to the correct frequency as per the manual for best performance.

Lawrence.

Voxophone · 6th Sep 2016, 12:21 pm

In the alignment instructions for this set, what are the 'Philips 15 degree jig' and 'aperiodic amplifier'?

ms660 · 6th Sep 2016, 1:03 pm

From what I can gather the 15 degree jig stops the rotor plates at 15 degrees from the minimum capacitance position.

The aperiodic amplifier in the context of the alignment is just a fancy name for a wide band indicator.

You could possibly guess the 15 degree position.

Can't quite see the need for the aperiodic amplifier unless I've missed something.

Lawrence.

2nd Sep 2016, 4:45 pm	#41
Voxophone Hexode Join Date: Oct 2015 Location: Sunderland, Tyne and Wear, UK. Posts: 340	Re: Philips 650A Low Volume I've tried a 2-22pF trimmer in parallel with the existing trimmer on MW. The circuit peaks effectively with the added trimmer and the MW volume is now much better on most stations - although the improvement is not uniform across the band. There is also no longer any improvement by touching wire to the V1 grid. I realise this is a bit of a bodged solution but given the fragility of the existing trimmers I think I'm more or less happy to trial it for now. A more immediate problem is a snapped bowden cable inner. Does anyone know a good source of suitable wire to make a replacement? Cheers Liam Last edited by Voxophone; 2nd Sep 2016 at 4:55 pm.

2nd Sep 2016, 6:12 pm	#42
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Philips 650A Low Volume If it were mine I would check the IF and RF/Osc alignment with a signal generator. Adjusting one of the RF trimmers might improve the signal but it doesn't mean to say that the other RF trimmer is set correctly. Beehive trimmers can be adjusted easy enough, even without the correct tool, always mark some reference points first on the can and the trimmer, the RF trimmers should be adjusted with the receiver set to the correct frequency as per the manual for best performance. Lawrence.

6th Sep 2016, 12:21 pm	#43
Voxophone Hexode Join Date: Oct 2015 Location: Sunderland, Tyne and Wear, UK. Posts: 340	Re: Philips 650A Low Volume In the alignment instructions for this set, what are the 'Philips 15 degree jig' and 'aperiodic amplifier'?

6th Sep 2016, 1:03 pm	#44
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Philips 650A Low Volume From what I can gather the 15 degree jig stops the rotor plates at 15 degrees from the minimum capacitance position. The aperiodic amplifier in the context of the alignment is just a fancy name for a wide band indicator. You could possibly guess the 15 degree position. Can't quite see the need for the aperiodic amplifier unless I've missed something. Lawrence.