Weston crystal rectifier meter - UK Vintage Radio Repair and Restoration Discussion Forum

Jez1234 · 6th Sep 2023, 7:40 pm

I'm working on a Solartron OS101 signal generator (the phrase boat anchor could have derived from this very unit! OMG is it huge and heavy!) which has
a meter as in the title. Does anyone have any info on these? I presume if I open it up I'll find a (faulty) ancient OA71 or similar inside? Or is it some sort of miniature selenium one? Anyway it needs looking at as a true 11.5V RMS is displayed as 7V...

Jez1234 · 8th Sep 2023, 3:14 pm

I guess these must be rare as hens teeth! I guess I'll just have to go in and see what I find. I don't know if this will be in the next few days or a few weeks away but I'll report back on what I find.

For the sake of clarity, it looks like any other 1950's Sangamo Weston panel meter but is obviously an AC reading instrument and says "Crystal Rectifier" in small lettering at the bottom left of the dial and "2000 Ohms per Volt" at bottom right.

Jez1234 · 13th Sep 2023, 10:33 pm

OK well FWIW it contains a bridge rectifier made up of 4 x GEX34 germanium diodes made by GEC. They varied in forward drop between a "correct" 350mV and a pretty suspicious for a germanium diode 580mV. Just to be sure then I made a new bridge from 4 x Schottky diodes (HP small glass ones) and fitted these. Upon reassembling the instrument and refitting it to the sig gen I can report... it reads exactly the same as before!

There's a rabbit away here.. as an old boss of mine used to say... I've pretty much ruled out any faults but nothing adds up here. I'll start a new thread on the matter that's not specific to the Weston meter movement.

6th Sep 2023, 7:40 pm	#1
Jez1234 Banned Join Date: Mar 2021 Location: Morpeth, Northumberland, UK. Posts: 936	Weston crystal rectifier meter I'm working on a Solartron OS101 signal generator (the phrase boat anchor could have derived from this very unit! OMG is it huge and heavy!) which has a meter as in the title. Does anyone have any info on these? I presume if I open it up I'll find a (faulty) ancient OA71 or similar inside? Or is it some sort of miniature selenium one? Anyway it needs looking at as a true 11.5V RMS is displayed as 7V...

8th Sep 2023, 3:14 pm	#2
Jez1234 Banned Join Date: Mar 2021 Location: Morpeth, Northumberland, UK. Posts: 936	Re: Weston crystal rectifier meter I guess these must be rare as hens teeth! I guess I'll just have to go in and see what I find. I don't know if this will be in the next few days or a few weeks away but I'll report back on what I find. For the sake of clarity, it looks like any other 1950's Sangamo Weston panel meter but is obviously an AC reading instrument and says "Crystal Rectifier" in small lettering at the bottom left of the dial and "2000 Ohms per Volt" at bottom right.

13th Sep 2023, 10:33 pm	#3
Jez1234 Banned Join Date: Mar 2021 Location: Morpeth, Northumberland, UK. Posts: 936	Re: Weston crystal rectifier meter OK well FWIW it contains a bridge rectifier made up of 4 x GEX34 germanium diodes made by GEC. They varied in forward drop between a "correct" 350mV and a pretty suspicious for a germanium diode 580mV. Just to be sure then I made a new bridge from 4 x Schottky diodes (HP small glass ones) and fitted these. Upon reassembling the instrument and refitting it to the sig gen I can report... it reads exactly the same as before! There's a rabbit away here.. as an old boss of mine used to say... I've pretty much ruled out any faults but nothing adds up here. I'll start a new thread on the matter that's not specific to the Weston meter movement.