AVO valve tester meter servicing

[HBWOODY]

I remember seeing information in this forum about a servicing facility for Avo valve tester meters. I have been unable to find it. Would someone be kind enough to let me have this information.

[Station X]

http://www.hertsmeter.com/

[HBWOODY]

Thanks Graham

[Station X]

I'd be interested to know whether they still service moving coil meters. They fixed a meter for me about 20 years ago. Apparently an "old boy" came in one day a week to do such work. He must be very old by now.

[Dekatron]

I'm also interested to know if they have picked this up again as I've had quite a few people asking me for help as they have been turned down by Robert Longcroft at Herts Meters, some have been forwarded to me by him - but unfortnately I've never done any repairs for AVO meter movements, I've had some repaired by herts Meters but that must have been 10 years ago or so.

I know that Sven_swe here at the forum had a CT160 meter partially fixed not so long ago, but I think that his Mk III meter came back with comments about worn pivots that they couldn't fix - feel free to correct me on this Sven_swe.

[sven_swe]

Hi!
I had two meters serviced by Herts last year, for the CT160 and MK3 testers. I don't know what it looks like right now in this moment for them, since I had them serviced last summer/autumn(2019).
I would give them a call and ask for Robert which was mentioned in the previous post by Martin(Dekatron).

Yes my meter for my MK3 was not fixable. It was described as "pits/dents" in the pivots and at a mounting angle of 60 degrees(in MK3) it tends to get stuck a few millimeters from zero and needs a slight tap to zero(pivoty meter). It works fine except for that and is still accurate, but I decided to go for the replacement meters I have from Martins design which are very robust and have nice "swing" and a great upgrade from the original meters in my opinion. The CT160 meter is working fine and no issues.

To summarize I would call Herts and ask if it is still possible for them to do service of the meters.

[HBWOODY]

Sven. Do you still have the Mk3 meter that needs a slight tap to zero?

[HBWOODY]

Sven. You also mentioned "replacement meter from Martins design", is this available in this forum?

[Station X]

That's a reference to this thread:-

https://www.vintage-radio.net/forum/...ad.php?t=68395

[Dekatron]

I'm sorry but the replacement meters are unfortunately not available from me. Sven_swe is the first person to use them except for myself and they are still in a prototype stage.

There will be an article on how to build these meters yourself, but Corona has delayed all my plans with all hobby projects, as well as a lot of other things like renovating my apartment that I had just started before the pandemic, which in turn means that 95% of my hobby stuff is packed into boxes and stored elsewhere, and I can't say when that article will be published.

[Station X]

The article in the attached copy of Radiobygones may be of interest. I did this conversion and have made a jig for drilling the AVO cases to accept Simpson movements.

[sven_swe]

Originally Posted by HBWOODY

Sven. Do you still have the Mk3 meter that needs a slight tap to zero?

Sorry for late reply, I didn't see your post. Yes I still have it in a box but I'm gonna keep it for future projects, you never know when you might need it or some parts from it. The replacement meter is excellent though, can highly recommend it.

[Craig Sawyers]

Originally Posted by Station X

The article in the attached copy of Radiobygones may be of interest. I did this conversion and have made a jig for drilling the AVO cases to accept Simpson movements.

The Simpson is part number 03851 (not 03951 in the article) is still in their catalogue, page 4 here https://www.simpsonelectric.com/imag..._datasheet.pdf

Difficult to get hold of, although https://www.tequipment.net/Simpson/03851/ might have them. And from the US too. About £120 - £140.

Craig

[Dekatron]

The ones I bought for the article that Euan and I cooperated on in Radio Bygones was the 03951, I got them from a surplus sale and they were the ones that Euan used and also the type that I made the scales for. I guess that you could use the 03851 too but it probably has a slightly shorter pointer so it might not fit for the scales (unless you resize the scales). The 03951 is a 4-1/2" size meter whereas the 03851 is a 3-1/2" size meter. New Simpson Taut Band meters are expensive but in my opinion they are a lot better than the original ones and sometimes the only way to restore an AVO VCM to fully working order.

If you buy any meters in a surplus sale as I did you will have to check if the meters are "standard" Simpson meters or if they are from a special order as they might have slightly different specifications, one such being a 100 degree swing as Euan mentioned in the article whereas most sold through regular distributors have a 90 degree swing, they could also have slightly different internal resistances even if they have the same FSD current.

From my experience the Simpson Taut Band types found in surplus sales have been a lot better when it comes to all parameters compared to the normal moving coil types, the normal ones seems to age worse than the Taut Band types for some reson, they loose more magnetism over the years it seems.

The Taut band types also have a better damped swing which in my opinion is better as the needle doesn't bang as hard on the stops if you make an incorrect measurement or if the tube that you test shorts or have other internal failures. And of course you get rid of the needles and bearings in the Taut Band movement as it is just a flat piece of metal that makes up the pivot points, so nothing that can seize up or wear down compared to the normal types.

The new article that I am writing will contain new scales for the 90 degree movements as well as a circuit board with the compensation and protection components fitted at the back of the meter and also components and parts for LED backlighting of the meter without having to put components inside the meter and also a circuit board that activates this backlight when the cutout relay activates. What I haven't written about in this article is how to fit the Simpson movement inside an AVO housing, but the article in Radio Bygones shows this - except for the necessity to adjust the zero set screw so that it fits with the Simpson movement (it might have been shown in a later article by Euan as I have some photos somewhere of it but I don't remember if Euan ever wrote an article on that piece, I can't find the photos right now though). The article will also contain how to use these Simpson movements to replace meters in the VCM163 series of testers.

As I wrote above I can't say when this article will be finished but hopefully this year. Swen_swe is helping me a lot with tests and measurements in his AVO testers.

[Station X]

Checking my paper work I used an 03591 supplied by Mouser.

[Craig Sawyers]

Apologies - the 03591 is in the same table I linked! Duur.

Mouser have one on order (yes - one) due for delivery on 18th June for £160.85

https://www.tequipment.net/Simpson/03951/Panel-Meters/ have them listed at £118.52, but shipping is £53.02 (!)

Craig

[HBWOODY]

Wow. Plenty food for thought there.
Will take the Simpson road if my meter can not be repaired.
And again thank you all for your input.

[HBWOODY]

I opened up the failed meter to see if there was an obvious fault. The meter did not have the hand wound resistor installed. Would this mean the meter has been tampered with or did Avo not always fit one?. I am going to look for obvious shorts only as all looks so delicate to risk further investigations.

[HBWOODY]

I talked to Herts and the sad news is that the gentleman who used to work on the valve tester meters passed away after a 7 week battle with cancer at the age of 72.
They are hoping to find someone else who is capable of filling the gap left by this gentleman.
Now I need to find someone else to service the meter.

[Dekatron]

I'm sorry to hear that he passed away.

If your meter is from an AVO Mk III and it is missing the swamp resistor it has probably been re-used from an AVO Transistor Tester.