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Old 22nd Aug 2017, 11:34 am   #1
andski1
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Default Cleaning VCM 163

Hello,
I just discover this great forum, it is amazing to see so many sharing love for beautiful AVO gear
I have just purchase VCM 163 which is in some what neglected state and bit dirty, but apparently working well (waiting for delivery of the unit due next week)
1.I wonder how hard it is to remove the clear panel meter covers, white meter scale looks like have some spots which I would love to remove if it is possible, question is is it safe to play around with them? I notice from conversation on this here that 163 meters are some what delicate and fragile so wouldn't want to do any damage.
2.Is it safe to use Deoxit D5 on contacts and tube sockets?,
3.Grey knobs will have to be clean as well and I'm hoping that I can remove them safely.
4. Clear plastic around flaying lead socket is gone all dark wonder if that can be rectify?
Apparently this unit was calibrated 5 years ago and supposed still work well, any idea how often this tester should be calibrated?
What would be best way to do some simple test to verify if it is within the range.
Thank you in advance for your help.I have included few photos of the unit below.
Kind Regards,
Andrew
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Old 22nd Aug 2017, 12:11 pm   #2
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Default Re: Cleaning VCM 163

Suggestions below..
All the best
Jeremy

Quote:
Originally Posted by andski1 View Post
1.I wonder how hard it is to remove the clear panel meter covers, white meter scale looks like have some spots which I would love to remove if it is possible, question is is it safe to play around with them? I notice from conversation on this here that 163 meters are some what delicate and fragile so wouldn't want to do any damage.
These meters are basically unobtainable so I would leave them as they are, unless you have a professional meter repairer locally. The meter pointers can so easily be damaged by a sudden touch if they are exposed.
2.Is it safe to use Deoxit D5 on contacts and tube sockets?,
Yes, DeOxit is excellent but try squirting a little into the plastic cap and use a cotton bud to apply the liquid, don't just squirt loads into the sockets. Small quantities of DeOxit can be sprayed directly onto switch contacts.
3.Grey knobs will have to be clean as well and I'm hoping that I can remove them safely.
The knobs should come off easily enough. Clean with scrubbing brush in soapy water
4. Clear plastic around flaying lead socket is gone all dark wonder if that can be rectify?
Could you do a photo to show what you mean?

Apparently this unit was calibrated 5 years ago and supposed still work well, any idea how often this tester should be calibrated?
Professional calibration once done should be good for many years. The manual shows how to do a "standardised" valve to calibrate it yourself. Otherwise, just re-check tested NOS valves every so often and compare results.

What would be best way to do some simple test to verify if it is within the range.
Put something like a new EL84 in and see if the results are close (+/- 10-20%) to the book values. Ditto for a low-current valve like an ECC81/2/3. The only way to double-check calibration is to make up a test-jig using DC supplies. But note that the results in the Avo valve data manuals relate to Avo testers, not necessarily DC results. For DC testing data use manufacturer's data sheets
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Old 22nd Aug 2017, 1:10 pm   #3
andski1
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Default Re: Cleaning VCM 163

Pamphonica.

Thanks so much, quick response I will follow your recommendations .
Attached photo of the effected area around flaying lead socket.
Do you know if anyone still makes dust cover for VCM's like the one in the photo?
Thanks again.

Andrew
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Old 22nd Aug 2017, 1:41 pm   #4
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Default Re: Cleaning VCM 163

Not only are the pointers easily destroyed but the paint on the scales come off even with water after all the years they have been exposed to air and moisture (sometimes you can also smell the cigarette smell from smoke on them). The paint on the scales is very easily smeared if touched with your fingers. Ask for help from Herts Meters if the meters need servicing.

The grey knobs on the front easily break if you apply too much torque on them when removing them as the inner plastic sleeve has usually become quite brittle over the years. So if you decide to remove them do it carefully. I wrote something here at the forum on how to repair them many years ago but I can't find it right now, it is possible but requires some time to do it right.

You shouldn't spray deoxit stright down into the sockets as it will drip down into the tester and carry any loose particles down onto the wiring and components below. It is not that hard to remove the top panel as a unit and placing it away from the tester for cleaining. Also protect the roller selector on top from deoxit. Use a cotton swap or use thin brush like toothpicks like Pamphonica said.

You should be able to have a new protective sheet laser cut for the flying lead socket. It is not that hard to replace it, just a few screws and some soldering if you can't wiggle it loose from the flying lead sockets once the screws are loosened. As long as it isn't cracked and falling apart you can leave it in place even if it looks poor.

As far as I know those dust covers aren't made any longer.
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Old 23rd Aug 2017, 8:47 am   #5
andski1
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Default Re: Cleaning VCM 163

Thank you Martin, your advice is much appreciated.

Regards, Andrew.
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Old 23rd Aug 2017, 10:23 pm   #6
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Default Re: Cleaning VCM 163

A good way to check on your AVO VCM163 would be to participate in testing the standardised valves (see thread on here). Post in that thread and ask if anyone has one they are ready to pass on.

Edit. Oops, just seen where you are. But if you are willing to pay postage I'm sure someone would send one to you.

Also, be brave and get stuck into checking out the voltages etc on yours if you have a variac it's not too difficult.

Nick
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Old 24th Aug 2017, 6:55 am   #7
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Default Re: Cleaning VCM 163

Andrew,

Just a couple more thoughts. Your meter scales don't look too bad. It is possible take off the front cover, undo the two small brass bolts holding in the scale and then slide out the scale vertically. But as others have said, accidents are easy and the meters are delicate, even to the point of making sure the screwdriver used is not magnetised. I would leave well alone.

Your grey knobs don't look too dirty to me. The white line is well defined and you might decide that a bit of insitu cleaning is sufficient. Beware of brittle plastic on something this old.

My perspex on the flying lead terminal is equally faded. I view it as patina and have no intentions of changing it.

Someone has clearly done work on yours inside judging from the cable joins.

Here are a couple of photos of mine of similar views for comparison.

Nick
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Old 24th Aug 2017, 2:03 pm   #8
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Default Re: Cleaning VCM 163

Fourlegsgood,
thank you for your input, and pointing out that there was work done on the unit, seller only mention to me that he replaced the 9 pin socket as it was intermittent in one of the contacts, but by looking at your unit its obvious that other work was done, all that extra cables with joins look very untidy and by compering it to yours solder joints look very messy
I'm hoping that all that can be rectify and this unit will work ok.
Service manual actually states while repairing or replacing cables its recommended that all cables should be laid as per original, as this may effect test results !
Im getting worry now
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Old 24th Aug 2017, 3:23 pm   #9
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Default Re: Cleaning VCM 163

Someone has replaced some of the electrlytic capacitors on your unit, you can compare with the photos from Nick.

The wiring that connects the two circuit boards can quite easily be made like the original design but you will have to provide some more photos of the internals. As long as most of the larger wiring trunks haven't been unravelled there is no problem. The wiring to, from and between the two circuit boards are not bundled but kept quite short.
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Old 24th Aug 2017, 4:20 pm   #10
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Default Re: Cleaning VCM 163

It was just lucky that I still had the side of my unit off after checking the calibration before I participated in the Standardised Valve sharing activities.

Here are a couple more shots for andski1 to compare with his when it arrives.

I will keep the side off mine for the moment in case more photos would help to reconstruct the wiring.

regards, Nick
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Old 25th Aug 2017, 11:33 am   #11
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Default Re: Cleaning VCM 163

Nick.

Many thanks for photos, very handy, Once I get my unit here on Tuesday I will go through it with fine-tooth comb!

Regards, Andrew.
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Old 27th Aug 2017, 1:56 am   #12
andski1
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Default Re: Cleaning VCM 163

Nick,
I was wondering if your VCM is still open if you could make few more photos of area where cable connecting two board are located, it will give me better idea how they should be correctly routed.
Thank you in advance,
Andrew
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Old 27th Aug 2017, 4:01 am   #13
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Default

Is there any conensus about the current condition of the LV electrolytics on the oscillator and amplifier boards? Mine are all the original components, and as it's working well, so there's been no reason to change them. However, it may be that they could need chaning at some time, and clearly, someone has already done that (perhaps un-necessarily?) on Andrews.

Regarding the meters, I had an episode a while ago where the Gm meter was sticking. Looking in through the cover, I could see a good number of tiny white particles around the movement. With great care I removed the movement from the case and was completely shocked to see that there were copious quantities of some white crystaline product growing on the surface of the terminals which pass through the rear of the meter case. Some of this had fallen in to the bottom of the case and clearly some had got in to the movement.

It was very easy to remove and I managed to do that and blow out the stuff that had got on to the movement, which then worked fine, though I felt lucky that it went so well. I smeared a layer of Vaseline over the terminals to try and discourage a re-occurrence. I can only assume it was some abnormality with the plating (zinc or cadmium?) on those parts.

B

Picture of meter internals attached (Mods - please merge posts).
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Old 27th Aug 2017, 6:47 am   #14
andski1
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Default Re: Cleaning VCM 163

This is probably good time for me to purchase Variac, is there particular type/brand you guys recommend? I'm in Australia so we have 240V 50Hz
Also what is the best way and place to start checking voltages on my VCM 163
Thank you in advance
Regards,
Andrew
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Old 27th Aug 2017, 8:19 am   #15
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Default Re: Cleaning VCM 163

I bought my 8A variac on ebay. Although the seller did not mention it the variac had a broken brush but rather than send it back I mended it.

As regards checking voltage etc, just follow the service instructions in the AVO sheets. If you do not have this I can email it to you if you PM your email address to me. (the file size exceeds the upload limit for this site)

regards, Nick
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Old 27th Aug 2017, 9:06 am   #16
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Default Re: Cleaning VCM 163

Buying an isolated variac is always a good idea but more expensive compared to a normal variac. Otherwise I always recommend an isolating transformer as an extra precaution protecting you from electrical shocks (you can still get them but working with isolated mains voltage minimizes it somewhat). Working with one hand in the pocket is also better since it makes it harder to get a shock through both hands then.

You also need instruments that handles half wave rectified voltages correctly, old AVO 8's does this fine as well as modern DMMs but some older DMMs doesn't show correct values (Mean DC and RMS DC in half wave rectified sinusoidal waveforms doesn't give the correct result on some old DMMs). I use Fluke 87Vs and also HP 34401a when doing these measurements, before I was using AVO 8's and a Kikusui 1631B.
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Old 27th Aug 2017, 9:36 am   #17
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Quote:
Originally Posted by Bazz4CQJ View Post
Is there any conensus about the current condition of the LV electrolytics on the oscillator and amplifier boards?
I am not aware of any consensus on the LV electrolytics but I replace them if the owner wants to have them replaced or if they are poor - you can always hide new electrolytic capacitors on the back of the PCBs, just put a few small ones in parallel. Most people I have helped have not bothered to keep the original capacitors, they mostly wanted a working VCM163 that would stay working for a long time.

I test and replace those electrolytic capacitors that are way out of tolerance or have very high ESR and always if the rubber seals have cracked. If the expansion valve has bulged and cracked on the large electrolytics on the high voltage capacitors for the grid voltage and rectifier test - those large ones behind the oscillator board on top of the transformer, 60uF/250V and 8uF/450V, I replace those too. I also check the ripple voltage on the power line for the amplifier and oscillator to see how well the electrolytics perform.

The VCM163 can work quite well even with poor capacitors but it is more prone to picking up external hum and noise from external noise sources like switched power supplies or solar converters if the electrolytics are poor. You can see this on the pointer on the gm-meter as it moves to the right when the amplifier picks up noise when no measurement is performed. In some circumstances using an isolating transformer improves this somewhat and using a mains filter improves other situations, it depends on what the switching frequency is from the switching power supply (or whatever the noise source is). Some of my cheap LED work lamps have drive electronics that affect the gm-meter so I have to switch those off.

If you move the mA switch to the black dot, while not performing any measurements, it shorts the gm-meter. Then you can see how much the pointer moves from the noise that the amplifier picks up. With my LED work lamps switched on it moves some five lines.
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Old 27th Aug 2017, 11:39 am   #18
andski1
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Default Re: Cleaning VCM 163

Thanks Nick, I think instructions and service manual is included with the unit , I should know it once arrives here on Tue
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