using a hunts crb cap+ resistor analyser.

[Paul m3vuv]

Good morning all,i have this hunts crb analyser,ser no 412 any idea of the age of it,the neon and magic eye light up but i dont know how to use it and read the eye etc,i have read the manual but dont understand what the eye should display,can anyone explaine?,thanks in advance Paul m3vuv.

[Mike Watterson]

It's a bridge with the magic eye replacing a meter. The eye changes how much it's open near balance. I forget if actually balanced is the eye as open or as closed as it goes, but you'll easily see which it is.
It's likely from the 1950s.
It will need some of the internal paper dielectric capacitors replaced.

The neon is usually part of a relaxation oscillator. It doesn't light when the terminals are open and will appear on with a low resistance or short. My stand alone neon leakage tester uses about 500V via 2 x 1 M Ohm in series for safety. It will flash quickly with 10 M Ohm and slowly with 100 M Ohm.

A leaky paper cap (or any electrolytic or a too low volatge rated cap) will likely make the neon light. It may flash slow or fast according to leakage, assuming there is internally a 100nF (0.1uF) very low leakage cap across the neon. A polyester or polycarbonate type. Original cap, if fitted, will be too leaky.

The paper dielectric caps had about 10 year life. Some are in waxed card tubes, some in aluminium or steel cans and some in now crumbling plastic. Only the hermetically sealed ones last (Military PIO with hermetic seals, not rubber bungs).

[Paul m3vuv]

i HAVE NOW SORTED OUT HOW TO OPERATE IT,I PLAN ON REPLACING THE CAPS AND SWAP THE DIODE STACK FOR ONE FROM A MICROWAVE OVEN HV TYPE,APPARENTLY I NEED TO ADD A RESISTOR TO IT,ALSO ANY IDEA OF THE WORKING VOLTAGE OF REPLACEMENT CAPS I NEED TO GET,IT ACTUALLY SEEMS TO WORK FINE AND IS QUITE ACCURATE,THE LEAK TEST DOESN'T SEEM TO WORK THO,THE NEON IS EITHER ON FULL TIME OR OFF,IT WONT FLASH,ANY IDEAS?,THIS IS THE SCHEMATIC I FOUND BUT HAS NO VOLTAGE RATINGS FOR THE CAPS!,CHEERS PAUL.,SEEMS I CANT ATTACH THE SCHEMATIC ON HERE( I SEE NO WAY TO DO IT)!.

Mod edit: sorted out faulty shift lock

I have now sorted out how to operate it, I plan on replacing the caps and swap the diode stack for one from a microwave oven HV type, apparently I need to add a resistor to it, also any idea of the working voltage of the replacement caps I need to get, it actually seems to work fine and is quite accurate, the leak test doesn't seem to work tho, the neon is either on full time or off, it won't flash, any ideas? This is the schematic I found but has no voltage ratings for the caps!

Cheers Paul.

Seems I can't attach the schematics on here (I see no way to do it)!.

[Mike Watterson]

Assume 300V rating (minimum).
The neon only flashes if there is a non-leaky capacitor across it and a test capacitor is only a bit leaky. A typical paper dielectric cap has so much leakage the neon seems just lit.

A microwave oven rectifier is a bad idea. A single 1N4007 rectifier.
   

Is this like yours?
   

Schematic revised by someone here.
I checked the PDF downloaded from here and there is a capacitor across the neon. It will need replaced. Any polyester 150V or more. It's listed as C7 0.47 uF, but 0.1uF or more will work. Claimed to need 500V, but the neon strikes at less than 100V and is about 55V to 60V when lit. I suppose needs to be 500V if the neon broke.

Unplug valves and disconnect metal rectifier. Put 30V limited to 5mA on + of C5 to reform the C5 & C6. If the current doesn't fall to zero they may be leaky. If the 30V disappears too quick when PSU removed, then the caps may be dried out.
C1 and C2 are silver mica so likely OK.
C4 is allegedly 1000V 10nF. A ceramic part should do.
C8 is ceramic so should be OK

C5 & C6 are electrolytic, supposedly 500V

[Paul m3vuv]

yes the pic is the same as mine,i have hv diodes from a tek 453a eht psu they have about a 5v drop,i understand i need a resistor in series with a diode replacement for the selenium stack but then was told the resistance of the transformer windings will be enough to omit a resistor,any ideas?,it actualy works fine as is,just off by about 15% on the readings,i assume this is resistors drifted,i will replace the wax caps soon but thought removing the selenium stink bomb a good idea?.

[Mike Watterson]

Don't use EHT diodes unless you know they are silicon and can manage the current.
I suppose it's possible the  PIV might be close  to the limit of a 1N4007, in such case use two in series and across each put a pair of 470K in series (because some  small resistors are only rated about 250V). The 1N4007 are slow so don't need the 470p to 1nF caps sometimes used in parallel with rectifiers. 
Some Hunts CRBs have 1200 Ohm (a 2W approx likely fine) in series with the rectifier anyway.

Don't change any resistors till the caps that are paper types replaced.
   
This revision shows all option caps and resistors.
Once you have enough posts you can download the version of the manual with this and full parts list.