Hunts CRB capacitor tester

[Yorkie]

Hi David,
Its the lack of rectifier I'm concerned with

Thanks

Rob

The original rectifier will - as Alan has said - have consisted of a series of small discs in a paxolin tube. I've attached some pics of a disembowelled 'Sentercel' rectifier that I recently stuffed with a silicon rectifier diode in a Heathkit C3-U as it was duff. (Most such rectifiers will be well past it after more than sixty years, even if they still work at all). Because a silicon diode will give a much higher voltage than a metal rectifier, I added a series resistor, the value of which I work out on test to drop the voltage to that required by the C3-U.

However, in your case Rob, the 'phantom dabbler' was who tampered with your CRB before it fell into your hands, may have cared nothing for originality of appearance, and rather than go to the trouble of stuffing the paxolin tube, may simply have binned it, and fitted a silicon diode such as a 1N4007, which is of course very small - just as small as a .5W resistor for example, so may be lurking where you have yet to find it.

If you've got a copy of the annotated CRB circuit with hand-written notes on it, which has been doing the rounds, you'll see that there are three secondary windings on the mains transformer. One is the AC heater winding for the Y63 magc eye filament, another is the AC to the bridge, and lastly, you'll see that one end of the the middle winding in the circuit layout goes to a rectifier, where someone has annotated the circuit 'metal rectifier'. Maybe if you identify that winding, you'll see a diode lurking somewhere? (The other end of that winding goes to a 1 uF cap, and to the wiper of the rear switch wafer).

Another option would be to check that the HT voltage at the magic eye is indeed DC - not AC, in which case, somehow, somewhere, it is being rectified.

I appreciate that comparing a circuit with a rat's nest of wiring and 'switchery' is no easy task, especially when it's been subjected to undocumented bodgery by an unknown miscreant, but that there's only one way to bottom it in my view: Namely, by checking each part of the circuit against the circuit diagram, using a highlighter pen to mark the circuit as you go, noting any ommisions or discrepancies, checking the continuity of switches, transformer windings, and the value of resistors and caps as compared to the circuit.

What we'll never know, due to the poor documentation on the CRB, is whther or not during the production period, it was subjected to any factory mods along the way.

(If you don't have manual and the circuit to which I'm referring Rob, do let me know and I can e-mail it to you, but I don't think I can add it as an attachment as it's a 615K PDF).

Hope this helps a bit, rather than adding to the confusion.