UK Vintage Radio Repair and Restoration Discussion Forum

UK Vintage Radio Repair and Restoration Discussion Forum (https://www.vintage-radio.net/forum/index.php)
-   Other Vintage Household Electrical or Electromechanical Items (https://www.vintage-radio.net/forum/forumdisplay.php?f=142)
-   -   Ampro New Educational - motor woes, issues and solutions (https://www.vintage-radio.net/forum/showthread.php?t=192486)

EF80TVVALVE 3rd Jul 2022 4:31 pm

Ampro New Educational - motor woes, issues and solutions
 
Hi all

Some may remember we previously discussed the Ampro New Educational amplifier some time ago. At the time I was also having a problem with the motor, on the odd occasion it would drop in speed, almost stalling. A flick of the on/off switch usually had it back working okay. At the time giving a visual inspection I found there was a Hunts Mouldseal capacitor inside the motor itself and thought this to be the likely cause.

Fast forward a long time until today and I decided with a spare afternoon I should tackle this motor and get that capacitor replaced. After much frustration the motor was free, although still wired in to the projector. It's here that you have two options, either conduct what is equal to keyhole surgery on the motor to remove and replace the original capacitor or unsolder all motor wires and completely remove and fully dismantle the motor to gain good access to the motor.

Due to the design of the motor its impossible to lift the back housing clear of the spindle due to the internal wiring. To completely remove this the windings must also be loosened off and removed along with it. This is due to two carbon brushes that sit on the end of the motor body which make contact with a rotary centrifugal contact breaker for the speed regulator.

This speed regulator is where I found my next problem, the points have a lot of pitting so I had to remove and file back as much as I could, this still leaves a fair amount of pitting on the points but after several attempts of cleaning, refitting checking, removing, adjusting etc I now have the motor working relatively well, it still however runs a little uneven at times but no severe speed drop or stalling.

I'm now at the point where I know that any more rough running is due to this speed regulator which is somewhat unfortunate. I have tried scouring the Internet for ampro spares in hopes that spare breaker points are available, but it seems like none can be found.

The next thing is to see if this type of centrifugal breaker regulator can be serviced, ideally if anyone knows the actual name for this sort of speed control then that may lead me to the right path, alternatively I'll have to see what I can do with some breaker points for an old car and see if they can provide spares suitable to repair these.

Aplogies for the lack of photos, when I have the cover off again I'll add some to the post!

Vintage Engr 3rd Jul 2022 5:11 pm

Re: Ampro New Educational - motor woes, issues and solutions
 
Many years ago, I used to have an Ampro, that I assume was similar to yours.
This also had the common problem of this type of centrifugal speed regulator acting directly on the the motor. (Nice smell though!)

Kenwood, on their very early food mixers used exactly the same system, & even with a capacitor / snubber across the contacts, they suffered a similar fate. Some early portable reel-to reel recorders also used the same method, only of course with a with a D.C. motor. Later recorders, used the same contacts, to switch a transistor, thus relieving the contacts of their inductive load.

If you are going to use this projector regularly, then I wonder if it might be possible to use a similar approach, only of course for A.C.
You could isolate the contacts, & use them to switch an electronic solid-state relay which in turn controlled the motor.

Just an idea of course, you may wish to keep it original.
I wish you luck with it.

David.

EF80TVVALVE 3rd Jul 2022 5:58 pm

Re: Ampro New Educational - motor woes, issues and solutions
 
Thanks for your thoughts David, some things to think about. The only problem with any modification on these projectors is the tight space inside it, everything was designed to be as compact as possible and it can make repairs difficult.

I do wonder if I can make some replacement point contacts up and replace those currently fitted, another option is to try and find the Ampro part number for the points so I can see if any old stock exists anywhere. A third option is to file them down more which will probably reduce the thickness of the points by half.

It makes me wonder how many hours this projector has done, from appearance it looks to be relatively low hours but I suppose with proper care these machines can look so even with thousands of hours use.

joebog1 3rd Jul 2022 9:49 pm

Re: Ampro New Educational - motor woes, issues and solutions
 
2 Attachment(s)
If you want to keep origionality, I think you are stuck with a cacky motor. These type speed regulators were also used on early cassette recorders made in Asia.
If you want to use it as a projector, I would be looking for a motor of the same size designed for a "quadcopter ". These motors are three phase, very powerful, and need a speed controller regulator with them. The electric motors start with prices as low as $10 and a speed controller/regulator about the same. To have speed control and regulation you then add a "servo tester " which is just a squarewave oscillator with variable mark/space ratio. Total cost would be less than 20 quid. Oh, I forgot to mention, that under high torque these little motors can suck lots of current and need a decent power supply. The room you would gain by using such a small motor would give you the room for the extra "bits ".
So the pics show a motor and regulator, a full mounting kit ( which is supplied ) and a rule to give you some idea of size. This motor ( its a small one ) is 27.5mm dia. Its also external rotor. Under full power it can take 30 amps !!! at 12 volts. The speed controller is sized to suit. The one in the pic is labelled 30 amps. It will rev to about 8000 RPM,s and can go down to a few revs without cogging.
Its just an idea!.

Joe

Lucien Nunes 3rd Jul 2022 11:19 pm

Re: Ampro New Educational - motor woes, issues and solutions
 
Buried very deeply at Bedford I have a few spare centrifugal governor assemblies. I don't think there are any for Ampro, but if you can post a pic I might be able to recall. I make no guarantee of being able to retrieve them in any particular time frame though.

Last year I had to sort out the governors on a couple of GB 516's both of which had been interfered with. One had a mangled spring, the other had wrong screws etc. I've no idea why this had taken place, as both were capable of correct operation when reassembled properly. IIRC the contacts were in reasonable condition.

EF80TVVALVE 4th Jul 2022 8:38 am

Re: Ampro New Educational - motor woes, issues and solutions
 
Joe, this is something to think about, it would be possible with some well thought modification. The original motor has a spindle through both ends so a similar motor would have to be sought, one end operates the cooling fan drum and the other drives the mechanism. I've never in the past had problems with these contact breakers but there's a first for everything.

Lucien, I'll take some photos of it as soon as I can. This example is a single breaker, I was looking at the 'Stylist' service info which has two breakers and in fact I think most 16mm sound projectors have two breakers, one for silent and one for sound. The motor speed arrangement of the New Educational means that the breaker is only needed for full speed sound films and silent is variable by a rheostat control.

wd40addict 4th Jul 2022 8:49 am

Re: Ampro New Educational - motor woes, issues and solutions
 
I assume it's C23 we're talking about which is the 0.5uf across the governor contacts. The usual failure mode of these is short circuit: I was once watching a film on my Stylist when it suddenly speeded up to probably 48FPS until the film broke! These caps have a very hard life.

My New Educational has been fine so far, but still has the original cap AFAIK...

Stylist has two governors for 16 & 24FPS, Educational is governed at sound speed only.

EF80TVVALVE 5th Jul 2022 7:06 pm

Re: Ampro New Educational - motor woes, issues and solutions
 
wd40addict, it's not C23, I already replaced that when I first bought the projector as it started shorting. The capacitor I am referring to is within the motor casing itself and is wired between the two brushes for the commutator. As far as I'm aware it isn't actually noted on the schematic. It's value is 0.05uf, different to C23 which sits inside the bottom of the projector and has a larger value of 0.5uF

Now I have the points cleaned and adjusted the best I can, I'm going to run it for a while and see if they bed in a little. The motor is now running correctly but there is noticeable drops in speed every now and then. Hopefully with some use a good contact will be made between the points and rid it of any need for more attention.

wd40addict 6th Jul 2022 7:18 pm

Re: Ampro New Educational - motor woes, issues and solutions
 
Ok, so it's for suppression. Can't remember if I changed this on mine or not, but I don't hear any motor interference on my sound.

Regarding your speed dips is it worth temporarily bypassing the rheostat to prove its contacts are ok?

Are you also confident the rubber drive belt isn't slipping? I had real issues with mine.


All times are GMT. The time now is 11:51 am.

Powered by vBulletin®
Copyright ©2000 - 2022, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.