Nombrex 62. - UK Vintage Radio Repair and Restoration Discussion Forum

mickm3for · 13th Jul 2022, 2:12 pm

Hi the nombrex 62 cr bridge from David now working as it should
I found that the nul of the bridge was ok 0v waveform on tr2 B also on tr3 B
BUT on tr3 C no change, scoping tr3 C i found a huge + spike at around 1khz ,
checked then changed all parts around the metering circuit this making no improvement. transistors gain tr2 hfe 65 tr3 hfe 236 so changed them both no difference. where was the spike coming from if i removed the coupling cap c 9
no spike but it was not on the c of tr2 . While poking around with a decoupling cap .01uf decoupling the supply rails i placed the cap between the b of tr3 to its emitter no spike and the c of tr2 now -9.4v . I wonder if it was going into self osc. some how ? Any how its now working as it should with the .01 added and fairly accurate Mick

David G4EBT · 14th Jul 2022, 11:36 pm

Really pleased you’ve got it working Mick!

it’s a neat little thing, and it’s nice to be able to use vintage test gear when restoring vintage radios. I’ve often wondered whether - in its day - it was aimed at hobbyists, service engineers or both. Not as clear cut as with brands such as AVO, Taylor, Advance, clearly aimed at the trade.

I hope it comes in useful.

13th Jul 2022, 2:12 pm	#1
mickm3for Heptode Join Date: May 2015 Location: Chatham, Kent, UK. Posts: 964	Nombrex 62. Hi the nombrex 62 cr bridge from David now working as it should I found that the nul of the bridge was ok 0v waveform on tr2 B also on tr3 B BUT on tr3 C no change, scoping tr3 C i found a huge + spike at around 1khz , checked then changed all parts around the metering circuit this making no improvement. transistors gain tr2 hfe 65 tr3 hfe 236 so changed them both no difference. where was the spike coming from if i removed the coupling cap c 9 no spike but it was not on the c of tr2 . While poking around with a decoupling cap .01uf decoupling the supply rails i placed the cap between the b of tr3 to its emitter no spike and the c of tr2 now -9.4v . I wonder if it was going into self osc. some how ? Any how its now working as it should with the .01 added and fairly accurate Mick Attached Thumbnails

14th Jul 2022, 11:36 pm	#2
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,763	Re: Nombrex 62. Really pleased you’ve got it working Mick! it’s a neat little thing, and it’s nice to be able to use vintage test gear when restoring vintage radios. I’ve often wondered whether - in its day - it was aimed at hobbyists, service engineers or both. Not as clear cut as with brands such as AVO, Taylor, Advance, clearly aimed at the trade. I hope it comes in useful. __________________ David. BVWS Member. G-QRP Club member 1339.