Nombrex 31 - question about AF - UK Vintage Radio Repair and Restoration Discussion Forum

6SN7WGTB · 17th Apr 2021, 5:26 pm

Just acquired one of the above in pretty good condition.

Testing the RF on my 'scope proves the RF calibration to be astonishingly good. My re-capped SONY ICF-SW7600 also seems to suggest the Nombrex dial is pretty much spot on.

All I can 'fault' with the RF is a slight defect in one half of the sine wave, but it's minimal and it works.

The one question I do have is around the AF modulator - I see that the schematic (which I spotted on this site and in fact catalysed me to buy the 'non-working' item) reports an AF tone of 400Hz.

Mine is more like 990Hz, and stable. It works fine and modulates correctly.

Given the RF end and the MOD appears to work spot on, I'm not terribly inclined to tinker with the AF end, but am curious if this is a known issue?

It just seems odd that nothing aside this seems to have drifted.

Thanks in advance.

17th Apr 2021, 5:26 pm	#1
6SN7WGTB Hexode Join Date: Apr 2021 Location: Crawley, West Sussex, UK. Posts: 442	Nombrex 31 - question about AF Just acquired one of the above in pretty good condition. Testing the RF on my 'scope proves the RF calibration to be astonishingly good. My re-capped SONY ICF-SW7600 also seems to suggest the Nombrex dial is pretty much spot on. All I can 'fault' with the RF is a slight defect in one half of the sine wave, but it's minimal and it works. The one question I do have is around the AF modulator - I see that the schematic (which I spotted on this site and in fact catalysed me to buy the 'non-working' item) reports an AF tone of 400Hz. Mine is more like 990Hz, and stable. It works fine and modulates correctly. Given the RF end and the MOD appears to work spot on, I'm not terribly inclined to tinker with the AF end, but am curious if this is a known issue? It just seems odd that nothing aside this seems to have drifted. Thanks in advance.