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Old 10th Jun 2011, 2:58 pm   #1
davidgem1406
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Default AVO 2 part valve tester

Hello All,

How does one go about making the valve base adapters to be able to test the later type valves such as 9 pin Rimlock, B9A, B7 etc.

I have seen these testers for sale but without the adapters so restricting their ability.

Any help and info would be appreciated.

Thanks
Regards Dave
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Old 11th Jun 2011, 4:47 pm   #2
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Default Re: AVO 2 part valve tester

Dave, as long as you can set the correct voltages for Anode, Screen and Grid for the valves you want to test and you have the datasheet from the manufacturer or the values from the AVO Valve Data manual for these voltages you will just have to connect each pin in sequence.

If you want to measure a valve with nine (9) pins you will have to use the B9A socket and then use a plug that fits and solder each pin on the plug in sequence to the socket you want to use, ie 1-1, 2-2 and so on up to 9-9.

In the manual for the AVO Mk I / Mk II, AVO describes the procedure for setting the roller switch on pages 9-13 for any valve you want to test.

You will of course not be able to measure valves that draw too much current on the heater or on the Anode circuit, but otherwise you can test most newer valves as long as you are within the limits of the AVO Mk I valve tester.
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Old 12th Jun 2011, 1:15 pm   #3
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Default Re: AVO 2 part valve tester

Hi Martin,
Nice and easy to do from the sound of it. Thanks very much for the info all I need now is the tester.

Best regards Dave

Last edited by Brian R Pateman; 12th Jun 2011 at 5:22 pm. Reason: Forum rules section C.
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Old 29th Jun 2011, 8:04 pm   #4
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Default Re: AVO 2 part valve tester

I have now obtained a MKI tester now in quite good condition, also I managed to obtain some base adapters. However still need to add a B9 base to the base unit, no problem there.

Whilst checking this unit out It struck me the number of differences that exist between this model and the circuit diagram I have, for instance, some transformer taps that do not exist, others that do exist but not shown on the circuit. Also additional capacitors and wiring, 2 rectifiers instead of one, a single winding for the 1V supply and not center tapped, and a cut out assembly. These are just what I have found so far.

I have to assume that these are differences between different models although model numbers don't seem to exist.

I did some basic emission tests using rectifier valves but obtained no results, no meter movement at all, although the zero pot worked. So some investigation was done first to check out the meter circuit where this was found not to have continuity. The problem being switch SF contact set A, B, C this was not working and O/C between B & C, thus no meter path. Temporarily I bridged the contact out to carry on with some tests.

Checking the rectifier valves again and we had meter indication. I then tested some others 6K7G, 6L7G & EF35. This is where the next problem arose.
As the valves warmed up the meter indication came up quietly to about half way into the green area then continued of scale and hard onto the end stop where it vibrated hard against the end stop, not good for the meter for sure.

The question is has anybody come across this one and if so what was the cure? or has anybody some idea of what might be the cause?
All input gratefully received.

Also the three top cap sockets on the valve base unit in what order are they? I have assumed as per the circuit that they are from left to right Grid, Screen, Anode. These are all lose as the threads are damaged so need replacing, I think I will replace with colored ones say Green, Orange, Red for instance.

I have searched these pages for info on the vibrating needle problem but it seems nothing is there, apart from it happening at the zero end of the scale because the meter was connected round the wrong way.

Regards Dave.
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Old 29th Jun 2011, 9:11 pm   #5
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Default Re: AVO 2 part valve tester

Ok, a quick update. I just noticed that the three TC sockets are actually marked on each socket in order of Anode, Grid, Screen, left to right. Makes me wonder why I missed that before!!

As for the bouncing of the meter end stop well that still happens but not violently, I had the anode connected to the top caps and it should have been the Grid.

I checked 3 valves EF36, 6K7G and X63 they all act the same. As they warm up the meter rises and passes full scale to the end stop where the needle vibrates gently against the stop. Turning the "Set MA/V" control anti clockwise, increasing the MA/V pulls the needle back on scale.

To me this is then indicating an emission figure of 10 or more, is this correct or is there a problem with the reading or is it meaning that the emission is very high? I somehow doubt the emission could be that good as these are not new valves.

Dave
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Old 2nd Jul 2011, 9:14 am   #6
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Default Re: AVO 2 part valve tester

I have now repaired the MA/V - C.INS switch so that is now OK. One of the insulators that allows the contacts to be moved by the actuator was missing so a replacement was made up from a nylon rivet. It was pretty obvious that somebody had been at the switch at some time.

While I was at it I removed the meter and cleaned the scale and the glass, this needed to be resealed as well.

I now have the problem of the meter needle always going over scale and vibrating against the end stop regardless of the valve type used. The valves used were U10, CY31, X63, 6K7G, 10P13 & 6BE6 all producing of scale travel.

Is there a calibration procedure that needs to be done? so far I can find no reference to such, or is it indeed a fault to be found?

Any help would be most welcome. Thanks.

Dave.
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Old 2nd Jul 2011, 10:53 am   #7
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Default Re: AVO 2 part valve tester

Its possible at the age of the tester that components are out of tolerance.Certainly be checking all resistors.

David GM8JET
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Old 2nd Jul 2011, 12:23 pm   #8
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Default Re: AVO 2 part valve tester

The vital piece of information (which you may not have) relating to the Mk 1 tester is that the "SET M.A./V." (sic.) control is a switch as well as an adjuster.

When fully anticlockwise, the meter sensitivity is reduced by a factor of 10 and this position (100) is used initially when setting the "SET ZERO" control. There is thus little possibility of damage to the movement. This position is also used in conjunction with "REC" when testing rectifiers; the meter then shows anode current in mA with about 25V RMS applied to the device under test.

When turned clockwise incrementally to "M.A./V." the meter sensitivity is set with an FSD of 10 mA/V - adequate for most valves.

High slope valves will oscillate in this tester unless you take some rather devious precautions. I generally test them at lower anode and screen voltages and log the expected result.

If you know its wrinkles, the 2 panel tester is a remarkably useful device.

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Old 2nd Jul 2011, 3:54 pm   #9
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Default Re: AVO 2 part valve tester

Hi David GM8JET.
I will check the resistors but there are not many to check most are wire wound specials. Knowing the correct value could be a problem as the circuit and parts list differ in some respects.

Hi Leon.
You right I did not know that, I did know that the MA/V was the 2 controls quite how they go together i have not worked out as yet.

I just did some tests the way you have said and the picture is quite different.
For the CY31 with MA/V set at 100 the meter zeroed (The zero pot is basically fully clockwise with very little adjustment available before the needle goes to the left hand stop) pop in the valve and all is good. With "Select Anode" set to D1 we get a reading of 6.6 a good one.

With the U10 that is more like what we expected D1 No reading and D2 1.3 a duff one.

I then did the X63 Set MA/V to 100, Av to 250 and Sv to 100. the reading was 0.4 not good.
The valve data states that the MA/V is 1.6 so I have assumed that the MA/V control would be set to this. However moving the control clockwise FSD is reached at an MA/V of 3.5, then moving the switch to the MA/V position sends the needle to the stop where it vibrates.

I'm sure I read only yesterday about the oscillation problem having capacitors added to cure this, I will have to check the document I was working on again. The unit I have does have some capacitors that are not shown on the circuit diagram.

Thanks
Best regards Dave
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Old 2nd Jul 2011, 4:07 pm   #10
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Default Re: AVO 2 part valve tester

Dave, have you read the EMER manuals? If not you can find them here:

http://www.vmarsmanuals.co.uk/archiv...ta_summary.pdf

http://www.vmarsmanuals.co.uk/archiv...structions.pdf

http://www.vmarsmanuals.co.uk/archiv...escription.pdf

http://www.vmarsmanuals.co.uk/archiv...ultfinding.pdf

http://www.vmarsmanuals.co.uk/archiv...aseRepairs.pdf

http://www.vmarsmanuals.co.uk/archiv...iscInstNo1.pdf

http://www.vmarsmanuals.co.uk/archiv...iscInstNo2.pdf

http://www.vmarsmanuals.co.uk/archiv..._Inst_No_3.pdf

They are full of information on how the "AVO Valve tester NO.1" is working, that is the name it is given in these manuals. You will also find repair, calibration and diagrams in those manuals.
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Old 2nd Jul 2011, 5:52 pm   #11
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Default Re: AVO 2 part valve tester

Quote:
Originally Posted by davidgem1406 View Post
I then did the X63 Set MA/V to 100, Av to 250 and Sv to 100. the reading was 0.4 not good.
The valve data states that the MA/V is 1.6 so I have assumed that the MA/V control would be set to this. However moving the control clockwise FSD is reached at an MA/V of 3.5, then moving the switch to the MA/V position sends the needle to the stop where it vibrates.
Hi Dave,

When you turned the mA/V control from 100 to 1.6 did you zero the meter again, before pushing the mA/V switch?

By the way, are we talking about AVO's first valve tester (the two panel one) or the AVO mkI valve tester?

HTH
David
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Old 3rd Jul 2011, 1:27 pm   #12
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Default Re: AVO 2 part valve tester

Hello Martin,
Thanks very much for the links I will take a look at them all with interest.

Best regards

Hi HTH David,
No I did not do that as at the time I did not know about it. However the meter goes full scale at 3.5 well before 1.6 is reached, so don't know quite where that leaves us unless we have to back of the zero control whilst rotating the MA/V control towards the 1.6 mark. I will have to try that.

It is the 2 panel unit, I thought that was the MKI.

Many thanks
Regards Dave.
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Old 4th Jul 2011, 11:39 am   #13
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Default Re: AVO 2 part valve tester

I have now read the user instructions and a couple of the other documents and have gained an understanding as how this works now.

Testing a number of valves now gives sensible results so it looks as though the unit is working all OK. I find the zero control a bit touchy to be able to set zero accurately, it seems rather to coarse for the job!!

I now have some cosmetics to do like the front panel to clean and engraving to clean or redo and a chip out of one edge of the Bakelite panel to fill in and disguise. For the moment I cant release the control knobs, the grub screws are corroded in, so they are soaking up WD40 in the hope they may release. Don't hold to much hope on that as they tend to sooner break up rather than let go.

Will put some pics here when it is finally done.

Thanks to everybody

Regards Dave.
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Old 4th Jul 2011, 11:48 am   #14
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Default Re: AVO 2 part valve tester

That control could be a bit noisy and worth replacement even if only to prove a point.

David GM8JET
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Old 4th Jul 2011, 12:37 pm   #15
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Default Re: AVO 2 part valve tester

Replacing the "set zero" control on a 2 panel tester is impossible (nearly). It's a complex assembly of wire wound elements and is very definitely an "in house" AVO special.

Unless open circuit (rare) these wire wound pots usually respond well to a mild cleaning of the track - alcohol and a toothbrush used lightly seems to work. They will never be noise free - when did you last have an Avometer which could be set to zero easily on Ohms?

Leon.
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Old 4th Jul 2011, 1:31 pm   #16
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Default Re: AVO 2 part valve tester

Quote:
Originally Posted by davidgem1406 View Post
For the moment I cant release the control knobs, the grub screws are corroded in, so they are soaking up WD40 in the hope they may release. Don't hold to much hope on that as they tend to sooner break up rather than let go.
Will put some pics here when it is finally done.
It might be worth giving the grub screws a good squirt of freezer spray to shrink them a little.

Al
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Old 7th Jul 2011, 3:51 pm   #17
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Default Re: AVO 2 part valve tester

Well I have no intention to try and replace the zero pot, as you say it's an AVO special.
I will try a clean though.

As for the grub screws I don't think they are going to move. I feel that freezer spray may well not penetrate deep enough into the grub screw to cause it to shrink within the insert.

I will look at drilling them out and finding / making up a guide of some sort to keep the drill centered in the grub screw.

To be continued, hmmm!!

Dave
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Old 7th Jul 2011, 5:26 pm   #18
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Default Re: AVO 2 part valve tester

Removing frozen grub screws. Sorry if I am telling you about grandmother's eggs. I am sure you are aware of screw extractors. First drill a small hole in the screw, and then the extractor will often move it when a screwdriver in the slot jumps out. The smallest size I have fits in a 1/16th hole. The advantage is that you don't have to centre the hole too strictly and you don't destroy (too badly) the existing thread in the collett. Use a small tap wrench to hold the extractor, and twist left handed. From engineering suppliers. I have found them very helpful in the past.
Alternatively use a penetrating oil and warm the area as much as possible. Freezer spray very limited help, as the threads are blocked with rust/corrosion, so friction is the problem.
The traditional agricultural engineers method is to get the gas and heat it to red hot, but this might destroy the knob and the rest of the instrument!
I have warmed the collett etc with a soldering iron or the screw with a jewellers blowpipe, but very difficult to stop a bakelite knob burning. Plastic will just melt, so heat is useless. Bill
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Old 7th Jul 2011, 7:06 pm   #19
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Default Re: AVO 2 part valve tester

Screw extractors "easy outs" etc are normally very good like Bill says soak for as long as possible first, and heat after drilling if it is practical to do so.

Good luck with it.

Lawrence.
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Old 7th Jul 2011, 11:26 pm   #20
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Default Re: AVO 2 part valve tester

Hi Bill and Lawrence,

Yes I thought of extractors but I think they will just snap as they are going to be rather thin. The amount of turning pressure required with a screw driver is quite large and still they don't move after they have soaked in WD40 for 3 days now. Drilling out and re-tapping is I suspect the only way out.

Dave.
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