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Old 6th May 2020, 3:41 pm   #61
Chris55000
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Default Re: Hunts CRB3

Hi!

If I've not covered all the permutations by now, honestly I give up!

Chris Williams
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File Type: pdf Hunts CRB3 Rev 4.pdf (277.1 KB, 90 views)
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Old 6th May 2020, 3:51 pm   #62
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Default Re: Hunts CRB3

I would show R4a and R4b as I have shown them in my schematic snip, I purposely didn't include any written values because no one actually knows what the maximum value would be....

Lawrence.
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Old 6th May 2020, 4:10 pm   #63
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Default Re: Hunts CRB3

Hi!
In the case of very old gear like this, where it's impossible to second–guess what Hunt's (and that lot from Acton who offered those very cheap signal generators in P.W., etc!) might have intended, only a very generalized note can be appended to a home–produced diagram – unless there is known knowledge from an original designer still living!

However, it's reasonable to assume that the values of the trimming resistors aren't going to be a very large maximum, since the panel scale has already been finalized and put into quantity production, so I suspect much over 150R for both resistors will impair the accuracy and scale linearity adversely!

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Old 6th May 2020, 4:41 pm   #64
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Default Re: Hunts CRB3

Warning, the following does not contain exclamation marks.

Yes but, they are an unknown value so far as the circuit diagram goes and no specification is given so why bother trying to assign a value to them unless you have access to every CRB3 that's ever survived.

Just saying.

Lawrence.
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Old 6th May 2020, 5:17 pm   #65
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Default Re: Hunts CRB3

Hi Al, I have been watching this and thought there was a book with it. Like the rest the circuit is there but no component values. I could post the book to you if you like, please let me know. Norman
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Old 6th May 2020, 5:22 pm   #66
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Default Re: Hunts CRB3

Hi!

Quote:
But, they are an unknown value so far as the circuit diagram goes and no specification is given so why bother trying to assign a value to them unless you have access to every CRB3 that's ever survived.
From long years experience of industrials and gear that's been got at, etc., Murphy's Law is going to state any component in something that gets botched in some way is going to be the one whose value isn't stated, (or even marked on the diagram at all) but a little perspective helps here – you've provided example values from your unit and other Members from theirs, and Wheatstone Bridge theory states the balance point at each end of the scale marked on the panel will be more affected by the lowest resistance in the ratio–arm, so that implies the trimming/equalising resistors aren't going to be large.

As to determining their values, that's done easily – a close tolerance resistor of a value near to each end of the scale is chosen as a trial value, the pointer set to exactly that mark and a decade–resistance box used as an equalising component until the eye opens fully – this is why Hunt's specified a dual–sensitivity EM34 in the design as it's easier to see when it starts to close from a fully open position – (it can be done far more accurately with a centre zero meter rather than an eye).

Taking the above into account I feel it's better to have something indicated on the diagram with a general note rather than not!

Have any other Members anything to suggest in the light of Lawrence's comments?

Chris Williams
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Old 6th May 2020, 5:58 pm   #67
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Default Re: Hunts CRB3

OK....Factoid time, I haven't got one of these units like you've just stated I have, neither have I said that I have one so far as I'm aware.

All the information I've provided was gleaned from info/photo's provided to this forum by members and from other non forum sources.

For me I wouldn't call them R4a and R4b as clearly they're not part of the component R4 as such.

Lawrence.
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Old 6th May 2020, 5:59 pm   #68
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Default Re: Hunts CRB3

If it were me I would label the two resistors "SOT" and "see note a" / "see note b". The notes would then state "known examples include..." for each resistor.
Given that this is a retrospective effort on a long-obsolete product, I think that's probably the most helpful way to describe them.
As mentioned previously, I have 150 (R4b) and zero ohms (R4a). I think it is now clear that every one is different.

edit:
oh, I see that's not much different from what you have done on version 4...
On a point of style, I would omit the exclamation marks from the annotations.

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Old 6th May 2020, 7:49 pm   #69
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Hi!

I can add extra notes on a second sheet if need be!

It might be best to simply add ". . .and any replacements should be the same value as originally fitted to maintain scale accuracy".

S.O.T. is probably the better annotation, in all fairness – I'll do a final Revision 5 but I don't want to be amending it "ad infinitum" to suit everyone's different ideas – my leisure time isn't unlimited and I will be wanting to move onto other topics – I've done the job I set out to do, which was to make a diagram that's clear, has all the important information on it and it's reasonably easy to pick out the principles of operation from it!

Chris Williams
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Old 8th May 2020, 8:41 pm   #70
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Default Re: Hunts CRB3

This is my latest attempt at producing a schematic for the CRB3. Hopefully I have got it right this time.

I have also attached a provisional parts list.

Comments and suggestions welcome.

Al
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File Type: pdf CRB3V2.pdf (19.6 KB, 89 views)
File Type: xlsx Parts List.xlsx (11.1 KB, 72 views)
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Old 13th Jun 2020, 12:20 pm   #71
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The attached file is an improved(OCR) and extended version of the CRB3 manual. I certainly find it much more readable than the original but then I'm biased I compiled it.

The 2 files from my previous post are included but have been amended so please ignore them.

Al
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File Type: pdf NewCRB3manual.pdf (343.3 KB, 98 views)
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Old 13th Jun 2020, 12:51 pm   #72
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Default Re: Hunts CRB3

Thanks for the information Alistair. I have one of these testers and have used it quite frequently over the last 50 years.
Who would have thought at the time I was presented with it by a retiring TV guy that I would soon be using it 50 years later. Life appears short. A really useful bit of kit that has served me well and still does! Regards, John.
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Old 14th Jun 2020, 12:25 pm   #73
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Default Re: Hunts CRB3

I may have made a mistake in the parts list with my description of the neon. Looking at the pictures in this post https://www.vintage-radio.net/forum/...80&postcount=3 it may be a 120-130V device. In that case it will have a series resistor.

Can anyone confirm what the full markings are?

Looking at page 16 of this 1952 Ediswan catalogue http://www.lamptech.co.uk/Documents/...01952%20UK.pdf all of the indicator lamps seem to have built in resistors

Note there is also a suggestion that a Philips device may have been used in later production.

Al
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Old 14th Jun 2020, 12:55 pm   #74
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Hi Alistair,
just whipped mine out to copy the inscriptions, as below:-

100 - 130V
Royal "Ediswan"
36 GASFILLED
Made in England

Hope this helps.
Cheers
Chris
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Old 14th Jun 2020, 1:14 pm   #75
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Hi Al,
managed to get a couple of photos and check the catalogue you linked to, and wondered if it is actually a "type 36", which is not shown in that edition of the catalogue?

The dimensions are close to the 18mm, 54mm size shown for the 230/240V SBC indicator (4th down) but it does say 100 - 130V.

Cheers
Chris
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Old 14th Jun 2020, 2:45 pm   #76
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Default Re: Hunts CRB3

Mine is labelled as follows:

Holland
Mullard Whyteleafe factory code
E5
Philips
110-130V
AC sign
GL42W

The "E5" must be a batch or date code, and the Whyteleafe symbol doesn't make sense if the lamp was made in Holland!

--------

Many thanks to Alistair for the cleaned-up manual, and to Chris for the re-drawn (and easier to follow) circuit diagram.
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Old 14th Jun 2020, 3:32 pm   #77
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Default Re: Hunts CRB3

Chris,
thanks for all the info. I could not find any more info on an Ediswan 36 Gasfilled. From the dimensions you provided. I am going to assume that the neon in the CRB3 is 0.5W like the one in the catalogue.

Dave,
Thank you as well. I will add that to the parts list as well as the Ediswan.

One thing I did find while searching the Internet. https://www.lampco.co.uk/collections...-t16x52mm-neon these look like they could be used as replacements with very little change.

Seeing these neons closer up I now realise that there will be right and wrong way to plug them in. The right way being when the larger electrode illuminates.


Al
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Old 14th Jun 2020, 5:00 pm   #78
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Hi Al,
what a fascinating little device! Now that I've put mine back together, and tested the Neon using a short circuit on the Insulation test, I discover that the applied voltage from the selector switch determines how much of the circumference of the neon circle is illuminated. I've tried to illustrate this in the attached photos, labelled as per min. voltage annotation on the switch position.

I wasn't expecting that from reading the manual!

Rewiring the EM34 to supply pin 5 from the higher voltage on the reservoir capacitor (420V) has made a very worthwhile improvement to the brightness by the way, in case yours is dim when it arrives.

Cheers
Chris
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Old 28th Jun 2020, 5:01 pm   #79
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Default Re: Hunts CRB3

This is a very timely thread.
I had retrieved my CRB3 (November 1953 going by the date on the big Colvern pot).

I had already had a peek inside and checked the components. I had replaced the power supply cap and the 0.5uF cap but the others (simple capacitance and resistance measurements) looked ok.

I fired her up (not literally) and the magic eye glowed a gentle green and nothing went pop.

I dropped in a newly reformed 22uF 450v electrolytic to the leak terminals and switched on again.
Once more the magic eye iris changed colour to a gentle green (with central bluish pupil and a grey internal ring (arcus).
The neon did not develop a ring but more intermittently demonstrated a reddish/orange glow inside on the mesh. Not flashing etc. It did this once more as I switched off before discharging the cap.

I read and reread the instructions but having never used one of these before I am struggling, probably because the device is not 100% (which I am happy to accept and will have to strip it fully with a view to full restoration, but before I do I guess I would like someone sensible to point out what I should be looking for (the photographs above were very helpful - mine does not do this.
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Old 28th Jun 2020, 8:49 pm   #80
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Hi,
I'd say you are struggling a bit not necessarily just because your tester is not 100%, but also because the operator's manual is not 100% either! I read through it at first, but found myself learning by the "suck it and see" method.

This is the key bit, copied from Page2 of my PDF manual:-

"Connect the capacitor to the test terminals and then choose the appropriate range. Rotate control knob slowly until the shadow appears at a maximum on the cathode ray indicator. This is the balance position and the capacitance of the capacitor under test corresponds to that on the dial, either directly or multiplied or divided by the constant depending upon the selected range."

So, the "cathode ray indicator" is the Magic Eye, and the section that's not lit up is the "shadow". The bottom right hand switch should be set to "C&R" and the bottom left switch set to "Cx100". With your 22uF capacitor connected to the "Capacity" terminals (middle is +ve) and the big dial in a random position the eye is probably all lit up. This means it is not set for 22uF.

If you rotate the dial from min to max position you should see the shadow begin to appear, widen to a maximim opening then close again, leaving the eye all lit up. Takes a bit of getting used to, but it should be fairly apparent that the eye is open to its widest at one point, and you can swing the dial slowly and slightly both ways to find the widest opening. Look at the blue scale on the dial at this point, and it should be near ".2" mark, 0.2 x 100 = 22uF.

Rather confusingly, you may find the eye will open somewhat at one end or other of the dial when the selector switch is set to "C" or C/100 as well. The key point here is that it does not open and close again, like it should have done above, but remains partially open as the dial hits the end-stop. So not balancing the capacitance bridge on that range.

Try that and get used to the capacitance bridge side of things first, actually if your test capacitor is a good one after reforming and OK at 450V, then you wouldn't expect much to happen in the neon department, so don't be discouraged!

Hope this helps.
Cheers
Chris
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