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Old 4th Jun 2020, 5:41 pm   #41
TonyDuell
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Default Re: AVT - Avo Two Panel Valve Tester?

You can still get 'Engravers wax', both hard (which needs to be melted into the engraving) and soft (which doesn't) from clockmaking suppliers. I don't know if that would do.
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Old 5th Jun 2020, 12:33 pm   #42
Stevie342000
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Default Re: AVT - Avo Two Panel Valve Tester?

Quote:
Originally Posted by Ed_Dinning View Post
Hi Steve, the proprietary stuff for filling engravings (available in several colours) was "Kwikfil", a small ingot shaped stick of a waxy material.
Not sure if it is still available.
Thanks Ed

You are correct Kwikfil is no longer available.

It looks for now that I will be using Greygate paste for polishing No5 which was developed for the GPO for Cleaning Metal Contacts and restoring bakelite products.

I can get some dental picks to clean out the old filler for engraved legends then using Chinagraph pencil to fill and restore the legends.
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Old 5th Jun 2020, 12:46 pm   #43
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Default Re: AVT - Avo Two Panel Valve Tester?

Quote:
Originally Posted by TonyDuell View Post
You can still get 'Engravers wax', both hard (which needs to be melted into the engraving) and soft (which doesn't) from clockmaking suppliers. I don't know if that would do.
I looked at that as well I could purchase a set of Blue, Yellow, Red, white soft engraving wax for the princely some of £18. I thought against it when I only needed the white or the red, I may however change my mind.

In no hurry I want to get it right and that may not be the first time when it comes to filler for the engraved legends.

As for the rest of the machine, there are few things I need to do:
1. visual inspection/comparison to schematic - to establish if there has been any modifications.
2. Replace any resistors (carbon composition only) and capacitors in the main panel and the socket panel/pin selector panel.
3. check continuity for wiring, transformers etc

There are a couple of schematics one seems to have had the cutout or protection circuit added this I assume would be post the 1943 patent for the cutout? The below is my pondering - writing it down helps me to sort it in my head.

4. Is there any benefit to added some kind of protection ?

5. What should it be fuse - where should they be? Research shows in zero HT return and mains.

6. Could or should a protection circuit be added? Where would you find the protection circuit relay and coil? One has double the turns to balance out and cause equal triggering for protection?

7.Is it the same as the one in an AVO 7? If added where would you place the reset button? Is it too much trouble? Yes probably. One option is to remove the 1.4 heater supply again too much trouble? It would however mean I would gain the two spare sockets back and the extra hole needed for cutoff but I do think it is more trouble - too much potential for error and for a fatal error to be made rendering the whole tester unusable.
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Old 5th Jun 2020, 5:48 pm   #44
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Default Re: AVT - Avo Two Panel Valve Tester?

A white chinagraph pencil would serve to restore the panel markings. I have a 2 panel tester amongst others, and find it simple, useful and versatile. Mine does not have the cutout relay and I have had no significant overloads or "near misses" in the many years I've had it. I'm always careful with valve testers though - double check before applying power.

As an aside, some people feel that the utility of a valve tester is exaggerated. My findings are that 1. The condition of the valves from an unknown piece of equipment often gives a clue to the presence of other faults. 2. There's no point in spending time aligning a set with marginal valves in it. In particular, I would not align an FM set with marginal high perveance diodes in the EABC80. The diodes need to be good and matched to give good long term operation.

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Old 5th Jun 2020, 8:52 pm   #45
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Default Re: AVT - Avo Two Panel Valve Tester?

I agree on both points, I am mostly focused on repairing or restoring my many reel to reel tape recorders, FM tuners, etc. All of which are in various states of working or not. The restoration of the valve tester is the start of my journey in restoring the other non or part working equipment. I do have some other test equipment which of course will of course benefit from having their valves tester.

Many of the pieces will aid me in restoring each and every one, including building some new equipment.

A lamp limiter is another project I will be working on shortly after completing this one.

From what you have said I think I will put in some protection fuses in the HT zero line return and one in the mains possibly an RCB.
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Old 15th Jun 2020, 4:28 pm   #46
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Default Re: AVT - Avo Two Panel Valve Tester?

Can I use toothpick to remove the old paint in the engraving? Got loads of them and it may be gentler than using a metal dental toothpick?
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Old 15th Jun 2020, 7:23 pm   #47
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Default Re: AVT - Avo Two Panel Valve Tester?

Should be fine, metal ones are better until you slip and scratch the panel.......

Peter
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Old 15th Jun 2020, 10:09 pm   #48
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Default Re: AVT - Avo Two Panel Valve Tester?

I use a fine tipped paint pen to fill in the engravings on equipment I restore, especially the indicator on chicken head knobs.

Scratch or wipe off the excess paint from the side once dried and done.
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Old 16th Jun 2020, 4:07 pm   #49
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Default Re: AVT - Avo Two Panel Valve Tester?

Scratching the panel was what I was trying to avoid but was not sure if the cocktail stick was a method that would work.

Paint pen is what I think is was looking for are they common? Is there a specific brand? I will try to do some research as well. Been a bit sidetracked with unifying my new Smart TV with my stereo and my computer. That was in another thread on here. Not resolved the issue with getting sound and picture i.e. playing DVDs on computer and linking it to TV, too lazy to look at instruction manual. But that is whole other subject.
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Old 16th Jun 2020, 5:43 pm   #50
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Default Re: AVT - Avo Two Panel Valve Tester?

I have just re-filled the engraving on my Atkins valve tester, I tried a paint pen but the paint was a bit thin and the tip too large. I ended up using Humbrol enamel applied with the finest brush I could find. Then wiping off the surlus after 30-40 mins with a rag damped with white spirit.

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Old 17th Jun 2020, 11:15 pm   #51
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Default Re: AVT - Avo Two Panel Valve Tester?

That was what I thought when I went to take a look, at least I got options and whichever works best is what I will use.

I purchased this Zig Acrylista 6mm Chisel Nib Permanent Paint Chalk Marker Pen, Glass Metal Wood.
More chance of getting the paint into the crevice/engraving with a chisel point is what I thought.

We will see.
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Old 17th Jun 2020, 11:28 pm   #52
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Default Re: AVT - Avo Two Panel Valve Tester?

Fat crayons used for filling in game dice used for boardgames and Dungeons & Dragons work very well I was told. I had forgotten about those now that I needed to fix a turns counting dial on my high voltage power supply. I played D&D a very long time ago and still have my dice and they still look like new, even the filled in numbers looks very nice. You might have to order from a D&D / Sci-Fi shop though to get hold of these crayons or ask in a well stocked painters shop.

Look here: https://www.google.com/search?client...crayon+fill+in
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Old 19th Jun 2020, 3:55 am   #53
Matthew kane
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Default Re: AVT - Avo Two Panel Valve Tester?

Quote:
Originally Posted by Stevie342000 View Post
Scratching the panel was what I was trying to avoid but was not sure if the cocktail stick was a method that would work.

Paint pen is what I think is was looking for are they common? Is there a specific brand? I will try to do some research as well. Been a bit sidetracked with unifying my new Smart TV with my stereo and my computer. That was in another thread on here. Not resolved the issue with getting sound and picture i.e. playing DVDs on computer and linking it to TV, too lazy to look at instruction manual. But that is whole other subject.

Not sure if you have these brands but I have a BIC, Uni-T and Sharpie paint markers in my disposal for jobs like this. You may need to outline over it a few times (each time a layer of paint has dried up) for the white paint to really be pronounced. Try not to push the tip too hard because it will scrape some of the previous layer of paint off.
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Old 5th Jul 2020, 11:11 am   #54
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Default Re: AVT - Avo Two Panel Valve Tester?

Will keep my eye out for uniball but I think I should have enough options now. Will get to work on it shortly.

Is there anything I need to be wary of when restoring the Two Panel Tester?
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Old 8th Aug 2020, 11:03 pm   #55
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Default Re: AVT - Avo Two Panel Valve Tester?

I finally managed to get the tester out of the base unit earlier this evening.

My notes which I took on the socket panel show that there are 3 waxy paper capacitors all 0.001uF 1000V (will double check as I had not been awake long this morning and do not get my new glasses until Monday).

The main tester panel from what I could see only had 1 waxy paper capacitor in it with a value of 0.05uF at 350V could not see it very well again will check.

There are about 3 dog & bone resistors which look like they were put in yesterday. The other two resistors are by Dubilier and look like fuses one is near the meter & and the capacitor with a value of 0.1M. Are they high tolerance never come across that type before.

It is my intention to replace all the capacitors - which I assume is the correct option.

There are no signs of burning with only a slight small amount of a white mildew mould which wipes off easily.

Not checked to see if there is any date there at all but there may be where should I look.

The dog and bone resistors I assume are likely to be on target - do I need to desolder one end to make sure that I measure only the resistance?

I have some Servisol Super 10 switch cleaning lubricant is this OK to use?

Will try to take some pictures later.....all help appreciated.....
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Old 9th Aug 2020, 6:15 am   #56
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Default Re: AVT - Avo Two Panel Valve Tester?

You could consider removing the metal rod for the "0"-position from the roller switcher unit. This rod connects the pins with "0" in the code to eachother and to earth. This is fine for pins which are truly "not connected". But some later valve types have pins which are internally connected. In some of them, you do not want these pins to be connected to eachother.

In the later types of valve testers, AVO used the roller switcher unit without the metal rod for the "0"-position.
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Old 9th Aug 2020, 11:59 am   #57
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Default Re: AVT - Avo Two Panel Valve Tester?

1. Having studied the schematics and the socket panel it appears I do not have the 500R resistor - I am assuming because that socket is not on the panel? British 7 Pin I think not present?

2. Have added taking out 0 rod on selector - which I assumes gives a true NC? Is it not covered in the notes about IC?

3. Is there a chance of shock from the shorts test?

4. All the dog & bone resistors all look brand new - do they need to be replaced? The shorts test resistors are under the transformer - do not fancy replacing those at all.

5. I am aiming to use 630V Orange drops to replace all the capacitors - lower voltage rating than the 1000V waxy paper capacitors in the socket panel - is that OK?

5. Can any one identify all the sockets on the socket panel? I know I have B9A on top right with I.O. position 3 & 4 - are they both IO? Why are there 2? Different heaters is the only thing I can think of or is one of them British Octal - what's the difference? I see no point in two with roller selector for heaters?

No colour coded wiring does not help with tracing wiring on sockets or in the main tester. I do not intend to replace any wiring - 9 pin socket and wiring is fine - for some reason there is an orange cable at the roller switch end that is not connected to anything or at the British 9 Pin socket either I just checked - which is good.

The only modification that I can see is the addition of the B9A. I have some socket savers on the way for B9A and IO. I got a couple of the B9A with the intention of removing one and putting in B7G - connecting pin1 to pin 1 and leaving 8 & 9 not connected - is that OK?
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Old 9th Aug 2020, 1:05 pm   #58
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Default Re: AVT - Avo Two Panel Valve Tester?

No experience of working on the AVO, but the majority of dogbones I see in early Mullard HSVTs have gone high OOT, regardless of how good they look.

Have a look at the schematic. If, for instance, the resistor connects to a valve base or to a switch, you'll probably be able to check it in circuit, since it will be OC at that end. If not, then you need to desolder one end to check it. This can be a bit fraught if the lead has been wrapped several times around the tag and/or poked through the hole in the tag. Tags are bad enough, but valve base pins can be worse - they're very fragile and won't take a lot of tugging about before they break, leaving you with the hassle of replacing the valve base. DAMHIKT.

One of the Octal sockets may be Mazda Octal as opposed to IO. The centre spigot hole will be a larger diameter than the IO; hard to tell from the photo.
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Old 9th Aug 2020, 1:37 pm   #59
Stevie342000
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Default Re: AVT - Avo Two Panel Valve Tester?

Will double check to see where the resistors are in the circuit and check off the reading against circuit value.

What about the ones that look like fuses - see picture

I have zoomed in on the IO sockets they both look the same to me but there is a slight angle which may not give a true view. Was more concerned about shadows obstructing view.
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Old 9th Aug 2020, 1:49 pm   #60
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Default Re: AVT - Avo Two Panel Valve Tester?

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Originally Posted by Stevie342000 View Post
2. Have added taking out 0 rod on selector - which I assumes gives a true NC? Is it not covered in the notes about IC?
Removing the rod will give true NC. In all later types of AVO valve testers this rod is lacking.

Yes, this topic is covered in the (older) Valve Data Manuals, but leaving the rod in would mean you have to measure the unknown electrode against all other electrodes to be sure what the right code is. On top of that: There are examples of valve types in which the way the internal connection(s) is/are made differs per valve manufacturer.
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