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Old 25th Mar 2017, 11:17 pm   #1
John G8MWF
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Default AVO 2 Panel Valve Tester - Help

I recently got hold of this tester and opened it up to see what condition it was in. I haven't a clue what issue it is and I don't know how to determine this.

It looks surprisingly clean except for one resistor which has become unravelled and the marked value does not match the diagram value.

It is connected to REC 30 on the Anode Selector switch.
This resistor is shown on the diagram as 75 ohms but is marked as, and measures, 92 ohm.
Was there a later modification to this equipment or should it be 75 ohms? Also what power and tolerance should it be - for either value as it has to be replaced anyway.

ANY help would be much appreciated.
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Old 26th Mar 2017, 9:10 pm   #2
martiR2R
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Default Re: AVO 2 Panel Valve Tester - Help

R4 is 75R, tolerance 10%, rated at 1W (I do have an army council doc that has it as 82R "preferred value replacement", presumably if you can't get 75R. Either way 92R is too much).
Regards
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Old 26th Mar 2017, 9:48 pm   #3
John G8MWF
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Default Re: AVO 2 Panel Valve Tester - Help

Hello Martin,

Thanks for the information. It did seem a bit of strange value change to the diagram. On a second look at the resistor is could well be Grey and not white but it is a very close call to which one it is - presumably with your information it must be Grey!

I am in the process of making up a 75 ohm ish from a 68 and a 8.2 ohm 3W resistor in series using modern components. Does 3W sound enough?

Then the wax capacitor is being replaced with a 0.47uF 630V Polyester.

The other 'new' technology to me is the Selenium rectifier that looks physically intact but I don't know how to test it as I does not register in the same way as silicon diodes. Any hints?

The unit was briefly powered up with no smoke and I managed to get the meter to go from a slow oscillation to stable - how is this possible on a passive circuit with just a half wave rectifier in it?

Once these have been replaced I hope to find a suitable valve from my collection, read the manual carefully, and try not to break anything.
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Old 26th Mar 2017, 9:48 pm   #4
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Default Re: AVO 2 Panel Valve Tester - Help

That should have been 0.047uF.
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Old 26th Mar 2017, 10:49 pm   #5
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Default Re: AVO 2 Panel Valve Tester - Help

Quote:
Originally Posted by John G8MWF View Post
I am in the process of making up a 75 ohm ish from a 68 and a 8.2 ohm 3W resistor in series using modern components. Does 3W sound enough?
75 Ohm is a standard 'preferred value' but in the less common E24 range, rather than the more commonplace E12 range.

These ceramic ww ones are 7 Watt, but are physically quite small (35mm long - 1.25"). Don't know if that might help:

http://www.ebay.co.uk/itm/10x-CRL7W-...wAAOSwPCVX9mqU

Good luck with the restoration.
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Old 26th Mar 2017, 11:09 pm   #6
John G8MWF
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Default Re: AVO 2 Panel Valve Tester - Help

Hello David,

That is helpful - thank you.

I will get hold of these as I am sure they will be a higher wattage than the one fitted.
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Old 27th Mar 2017, 3:12 pm   #7
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Default Re: AVO 2 Panel Valve Tester - Help

The original rating for C1,2,4 is 1KV.
75R and 82R 1W available from Farnell and others.
If you have'nt already, put avo two panel.......... into the search box at top of page, lots of info on here from members far more knowledgeable than myself.
Good luck.
Martin
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Last edited by martiR2R; 27th Mar 2017 at 3:14 pm. Reason: Grammar
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Old 27th Mar 2017, 3:42 pm   #8
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Default Re: AVO 2 Panel Valve Tester - Help

Hello Martin.

I have looked VERY carefully at my 2 Panel Avo and on the diagram but I can only find ONE capacitor on the main unit. This is rated at 0.05uF 450V DC.
The 75 ohm arrived today and will be fitted shortly.

The searches that I put in came up with some old links and I was trying to talk to someone who has recently worked on one or had not left the group.
It would be nice to find out which version/year my unit comes from as I suspect it is an early release.
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Old 27th Mar 2017, 5:04 pm   #9
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Default Re: AVO 2 Panel Valve Tester - Help

The other caps + resistor are in the valve base panel.
The component values came from an EMER MOD document from 1958.
The Two Panel came out in 1936/7 I think, at a cost of 11gns. The original valve panel did not have the roller switch or transformer (divide by 7) and was available for english or american valves. The second version had a mix of valve bases and the roller switch. The final version had the transformer (divide by 7) as well.
To the best of my knowledge there was only one version of the meter unit although that does'nt mean to say components/ values did'nt change during it's production life.
There should be a serial number bottom left of the meter window - one of mine has 13753-747, wether that means July 1947 or not I can't say with any certainty.
Regards
Martin

PS; There must have been military versions but unlikely to have been fundamentally different.
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Last edited by martiR2R; 27th Mar 2017 at 5:20 pm. Reason: Grammar + PS
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Old 27th Mar 2017, 5:46 pm   #10
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Default Re: AVO 2 Panel Valve Tester - Help

Hello Martin,

My serial number is 9833-546 possibly May 1946? it does have the roller switch M.A/V - C.INS so presumably a MK2?

Sorry but I keep overlooking the valve base components as I have been concentrating on the main unit.
The valve base unit was 'found' separately some years after the main unit was rescued and needs to be checked out as well before plugging it in.

The faulty resistor and wax capacitor were replaced today and I would like to see if I can test it WITHOUT the valve base or a valve in place - do you know if this is possible or not?
I would hate to toast this unit through ignorance!!
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Old 27th Mar 2017, 6:52 pm   #11
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Default Re: AVO 2 Panel Valve Tester - Help

OK I couldn't resist - the unit was powered up, no valves, with no puffs of smoke but the meter needle went far backwards until the end stop.
This was only cured by turning the set zero control fully clockwise. There is evidence of repairs to the low value resistors on a tag card connected to the zero control pot.
The neon light remains on regardless of the roller switch position.

I really am not sure what to do next! I am not convinced that there is a not problem but I don't know what steps to take next.
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Old 27th Mar 2017, 7:10 pm   #12
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Default Re: AVO 2 Panel Valve Tester - Help

I don't know if this is any use, it's a simplified schematic I did a while back for someone else, it shows the general arrangement with a triode valve inserted, hopefully there's no errors in it.

Lawrence.
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Old 27th Mar 2017, 7:52 pm   #13
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Default Re: AVO 2 Panel Valve Tester - Help

The roller switch has nine thumbwheels and is part of the valve socket panel not the meter panel.
I would err on the side of caution before plugging this in, it's 70+ years old, uses raw mains and is not earthed! check the condition of all components, connections, wiring etc.
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Old 27th Mar 2017, 8:44 pm   #14
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Default Re: AVO 2 Panel Valve Tester - Help

Quote:
Originally Posted by ms660 View Post
I don't know if this is any use, it's a simplified schematic I did a while back for someone else
Hello Lawrence - YES that helped - thank you.

Obviously the unit has been worked on in its long life and I do not know what a 'good' one looks like let alone use it!

I have enclosed a picture of the area that both concerns and puzzles me. There appears to be a wire wound shunt on a tag strip with a centre tap. Two of the wires go to the 100 part of the set MA/V and the other, black into roller switch?
There is another brown wire connected to the black wire on the same tag strip going to the Select Anode Switch - this switch position does not connect to anything when rotated! Does this mean that a wiper may be missing?

Could you or anyone else compare my picture to there machine and see if there is anything obviously wrong?
Also, I have the diagram but no parts list which would come in handy.

Phew!!
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Old 27th Mar 2017, 8:59 pm   #15
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Default Re: AVO 2 Panel Valve Tester - Help

That centre tap wire wound could be the 9 ohm and 1 ohm resistors, the wire wound to the left looks as though it might be the 40 ohm resistor...I've used the value refs as per the EMER manual given on manual page 1010 here:

http://www.mif.pg.gda.pl/homepages/f...s/AVO-EMER.pdf

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Old 28th Mar 2017, 12:24 am   #16
martiR2R
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Default Re: AVO 2 Panel Valve Tester - Help

The neon indicates shorts when using the two sockets at the bottom of the panel, the rest of the time it's on permanently to indicate mains.
Re photo - the wiring is fine (identical to mine), the black wire goes to the MA/V - Cins switch, the brown wire does'nt appear to do anything other than provide extra physical support for R1 which is "floating", there is'nt a wiper missing.

Martin
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Old 28th Mar 2017, 12:25 am   #17
John G8MWF
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Default Re: AVO 2 Panel Valve Tester - Help

Quote:
Originally Posted by ms660 View Post
I've used the value refs as per the EMER manual given on manual page 1010 here: http://www.mif.pg.gda.pl/homepages/f...s/AVO-EMER.pdf
Got it - thank you.
It is just taking a bit longer than normal to get my head around this style of documentation!
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Old 28th Mar 2017, 12:28 am   #18
John G8MWF
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Default Re: AVO 2 Panel Valve Tester - Help

Quote:
Originally Posted by martiR2R View Post
Re photo - the wiring is fine (identical to mine), the black wire goes to the MA/V - Cins switch, the brown wire does'nt appear to do anything other than provide extra physical support for R1 which is "floating", there is'nt a wiper missing.
That is really good to hear - I shall press on.

Your help is much appreciated.


John
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Old 28th Mar 2017, 12:45 am   #19
martiR2R
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Default Re: AVO 2 Panel Valve Tester - Help

This might be helpful
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Old 28th Mar 2017, 8:15 am   #20
John G8MWF
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Default Re: AVO 2 Panel Valve Tester - Help

This is VERY helpful - thank you.

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