The title suggests that this is a restoration thread but it is not. Please read on if you are interested in a little story about a metal box bought at an auction somewhere in UK!
The box in question is a component bridge made by EMI just before the war (there was a later model using later valves). QD-211 is the type number and it uses a U10 4V rectifier valve and a 6.3V DH63 for oscillator and detector. The later version (1960) uses a B7G 6AT6 instead of the octal DH63.
After a quick inspection, the instrument appeared in good condition and so I did a few things to make it comply more easily with today’s safety rules – for example, remove the fuse in the neutral leg of the incoming mains feed. After that, it was Variac time. A slow run-up and before long, the bridge was working, even the tally light. A kind forum member from UKVRRR was able to email me a copy of the service manual which was a great help in finding out what the beast could do. First of all, I cleaned up the 21st generation copy of the manual which actually came up very well (the Photoshop work was well worth the trouble and the result was a very reasonable copy of the manual). Do you want a copy for the library Chris?
The basic tests performed by the instrument are as follows:
- Basic leakage for capacitors. These can be tested at 200V, 400V and 600V with the capacitor being discharged when the switching from Leakage to Bridge.
- Reforming electrolytics can be performed using the leakage facility and using the meter to indicate completion of the process (or not, as the case may be!).
- Resistor measurement from 10Ω to 100M.
- Capacitor measurement from 10pfd to 100µ
- Inductance measurement from 1H to 100H.
- Power Factor Measurement from 0% to 50%.
So it is basically a very useful piece of kit. However, I didn’t want to restore it but to use it in anger in the workshop. So another good look at it revealed about 5 rather large paper/wax capacitors. These, of course, would be leaky. This was one of the reasons for rescuing the bridge - my previous leakage tester (an ancient AVO bridge) had packed up – was to use the leakage facility of the EMI instrument. Sure enough, all the caps failed the test so were replaced.
I said that this was not a restore so the dark brown wax caps were replaced by bright yellow film caps. Does anyone know why all manufacturers (except some audiophool companies) use the same bright colour?
In its original form, the bridge was fitted with 3 pairs of screw terminals. I find these a pest to use and prefer banana plugs so I bought some 4mm sockets from RS and they are splendid:
Anyway, I now have a reasonable looking bit of kit which will perform all the measuring I need to do on basic components with very little outlay and effort and it’s not a bad looking piece of test equipment to boot!
Hi Brian,
That's a very nice and excellent piece of vintage test equipment you have there, isn't it nice to have authentic test equipment to use in conjunction with your period sets.
What I find quite amazing, is from the outside it looks more 60's than 40's, quite a timeless design they adopted. I feel a component bridge is pretty much a must have unit for most workshops and as you rightly point out superb for reforming electrolytics. What's more these old LCR units a far superior at testing those caps by placing them at rated voltage than some of the cheapo imports available these days.
Thanks for an interesting post and a look at unit I hadn't seen before.
A copy of the manual would be most welcome for the library 
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The manual would be a good read, it's piece of test equipment I have never used.
Frank
That's a lovely piece of useful vintage test gear Brian, nice to see it pressed back into action.
Marc.
Marc
BVWS member
RSGB call sign 2E0VTN
Brian Cuff said
Does anyone know why all manufacturers (except some audiophool companies) use the same bright colour?
I'll offer an educated guess. The film material (Mylar) is also used in coil winding (transformers and the like) The principle supplier is 3M, and that yellow is a trademark or at least a branding by 3M. I've used their type 56 transformer tape (also bright yellow)
Brian Cuff said
The title suggests that this is a restoration thread but it is not.
Anyway, I now have a reasonable looking bit of kit which will perform all the measuring I need to do on basic components with very little outlay and effort and it’s not a bad looking piece of test equipment to boot!
Very nice instrument, great restoration to be a practical tool on your workbench, too. Well done!
Agreed, a well worth piece of equipment to have. Great job 
To understand the black art of electronics is to understand witchcraft. Andrew.
