Hunts CRB capacitor tester

[Mark R]

Rob
I have no doubt you will fathom it!

An old northern saying, "keep going yed down".

cheers regular Mark

[Paula A]

OR.. and this is always a beaut.. back in days gone by when a resistance was needed to be absolutely precise they used to fit a long carbon composition resistor and then stick it on a bridge and file away at it until it was spot on the required value... In a precision piece of test equipment this is probably what you have, and may have soaked up loads of damp over the years and be the cause of your problems..

Best approach now would be to trace out and draw your own schematic (with values) and see where it lives in the circuit. My guess would be in one leg of the bridge or the oscillator timing circuit..

Another thing to check is the speed the oscillator is running at, either problem could be causing the 40% off reading. Somebody who has a calibrated working example should be able to help with accurate voltage readings for the test points lurking within.

[tiv48]

no oscillator just uses 50-hz mains the bridge resisistors in mine are almost spot on the same can not be said for the wax caps
but were they selected? i am loathed to change them as it is quite accurate
rob t

[tiv48]

[quote='tiv48' pid='14767' dateline='1319064389']
no oscillator just uses 50-hz mains the bridge resisistors in mine are almost spot on the same can not be said for the wax caps
but were they selected? i am loathed to change them as it is quite accurate
rob t


the circuit seams to of vanished so here it is again

[tiv48]

the circuit seams to of vanished so here it is again

[Paula A]

Never seen one in the flesh.. my test for caps was and is to rip them out and replace them.. Only bridge I have ever ownde was a home made one from a 1924 design using a "r-type" (swapped by me for 1/2 ecc83) with an oscillator which ran at 1k (or thereabouts).. also from the same book I built a pretty much untuned rf amplifier using a triode wired ef80..

So how to sort out a bridge which is miles off? .. how about bashing up another on a board using known good bits and bobs and then using that to test the components you have in the faulty one?

Of course don't forget.. it's a Hunts and doubtless uses their caps (aka - random resistances with a bit of capacitance thrown in or infinite spark gaps with no capacitance whatsoever and a bit of leakage depending on the weather/proximity of warm coffee.. I'm dreading recapping my Laney.. it's full of the buggers).. so those all need replacing straight off .. Real glaring suspect has to be the big 1µF cap.. but could be all of them .. the "brown stick" is guaranteed to be one of the odd value 1% resistances..

I remember a long time back somebody saying they had a "russian" analog meter which always read 20% out on all ranges.. running over it with the car squashed it but also fixed the "wrong" reading..

[Yorkie]

The 1uF cap appears just a smoothing cap in the DC line. As the bridge reads 40% out on all ranges it has to be something to do with the three legs of the bridge circuit itself (the fourth leg being the cap/res under test). If you look at the circuit, it's inconceivable that the components in that part of the circuit marked A,B,C, & D are all out by the same amount - 40%. The two which are most suspect in my view are the pot, and its series cap (0.02uF) which are common to all ranges. It's unlikely to be the pot as it isn't open circuit and won't have changed in value over time, as might a carbon resistor. If we assume that the dial position on the shaft hasn't somehow slipped, which I doubt as it will have end stops, I think it more likely that the 0.02 cap is leaky and acting more like a high value resistor than a capacitor. The value of the two 1% resistors 'D & E' (1592K and 1592???) are easily checked, and the other two caps (A & B) in the bridge can be checked and replaced if need be, but wouldn't be high on my list of prime suspects.

The other thing that's puzzling Rob is that he couldn't find a rectifier diode - the original paxolin tube encased metal rectifier having been removed. As I've mentioned before, if the HT on the Y63 is perhaps 150 - 175V DC, then there must be a rectifier lurking somewhere. One end of the top winding (on the circuit) of mains transformer secondary goes to the 1uF cap, and then on to the rear wafer of the switch - the other end of that winding goes to the rectifier, then the output of the rectifier goes to ground, and the middle wafer of the switch. Hence, by tracing the connections from the lower end of the top winding, the elusive rectifier should be found!

Unlike many of us, Rob is not a man of leisure - he still has to work for a living to help to contribute to my winter fuel allowance and free bus pass, so is limited for leisure time. I guess therefore that the CRB won't be too high on his 'to do' list! Maybe when he surfaces, he'll update us on progress, if there has been any!

[Bushbaby]

Hi All,
I'm here, although David is correct, I have been tremendously busy working towards the close out of the 'construction phase' of the Olympic Park. I digress at this point to say that the landscaping looks truly magnificent and if I had my way, when all the work is finished I wouldn't let anyone on the OP just in case they spoil it!

I cannot find a rectifier in any form within this tester! It also appears to have been highly modified to the point that it does not resemble any of the 'loose' schematics. What made me suspicious of this unit is that a paxolin tag strip has been added where the original rectifier would have been situatated. Furthermore, this tag strip extends into the area where the original neon light mounting (which I have as kindly supplied by Kevin Hoyland) should be mounted.
It also has 5 10k restistors in series on the tagboard which is not original.
It also appear that the transformer has been 'played with' as has been mounted upside down from the original and all of the wires from the primary and secondary windings have been cut and had cables added.

All in all its somewhat a Frankensteins monster! I am proposing to revert this to the original layout. In the next month or so know that I have cleared out my garage to free up some workspace (I'm blushing at this point having let David see my 'tip' that i can now call a garage!)

Regards

Rob

[Yorkie]

All in all its somewhat a Frankensteins monster! I am proposing to revert this to the original layout. In the next month or so know that I have cleared out my garage to free up some workspace (I'm blushing at this point having let David see my 'tip' that i can now call a garage!)

Regards

Rob

Crikey Rob, it really has been got at! What puzzles me is the thought process which passes through the minds of people who do such things, then don't document what they've been up to, or the rationale behind it. Surely the older an item is, the least one should radically alter things, and the more one should try to conserve what's there. Metal rectifiers are known to fail - they often still work, but don't attain the required voltage. However, a silcon diode can be placed in the paxolin tube, along with a series limiting resistor to preserve the original appearance.

It sounds like your only hope would be to to do as you intend to Rob - re-work it alongside an original and working CRB.

Your mention of a string of resistors brought to mind an Ekco AC86 which came into a friends hands and had allegedly been 'professionally restored' for a previous non-technical owner who put his trust in the 'restorer'. I've attached some pic showing several strings of resistors and appalling soldering. In one instance there are no less than nine resistors in series! In one instance if you look closely, you'll see two resistors with their wires twisted together, but apparently not even soldered.

As to your garage, I'm glad you hadn't tidied up when we called as I'd have had the hard word - 'why can't you be neat and tidy like Rob?' You should have seen the state of my garage today! I've been turning Perspex on the lathe as mentioned in my post about Fenman knobs. There were fine streamers of Perspex waste from the lathe, all over the bench, the floor, and me. I was just about to clean it up when Jennifer appeared in the garage with a cuppa. After 49 years of marriage she still considers me to be 'work in progress' rather than beyond redemption. She doesn't get cross with me - she just says things like 'look at the state of you - you look like Wurzel Gummage'.

I've got a chum in the village who's a fellow woodturner. His worshop is immaculate and he's such a natty dresser that he's never owned a pair of jeans and when he's mowing his lawn or woodturning he looks as though he's dressed for a wedding, with a sharp suit and fancy tie. He's so fastidious that he has what he calls a 'plug park' in his worskshop. It's one of those six-way extension socket jobbies, except it has no lead, and no power to it. It's screwed to the wall with each socket marked 'Bandsaw, Pillar Drill, Lathe, Dust Extractor' etc. When he's finished in the workshop, he unplugs all his equipment and puts the plugs in each marked socket so the power leads and plugs aren't dangling.

Do what? I bet he drives his wife nuts - he does everyone else!

So don't make the garage too tidy Rob - you might build up false hopes in Angela's mind that you've turned over a new leaf:D

[AlanBeckett]

David,

On the subject of old rectifiers I've got an ancient Battery Eliminator with a 1N4007 and a 100Ohm soldered discretely underneath.
I've also got a little Pye - what else - with a couple of WW resistors hidden behind an O/C Dropper section.
I'm not a stickler for authenticity, but I don't see any reason why it shouldn't be neat.

I'm fascinated by the strings of resistors. Perhaps the 'Professional Restorer' only had a limited range so he made them up as required.

I'm not sure about turning in a jacket and tie. Back in the dim and distant past of my schooldays Woodwork and Metalwork were a couple of the few occasions when we were told to take them off.

I can't claim any great tidyness, and Col's workshop always sets me to shame. I must give him some gear

Alan
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