GEC Miniscope model BW 464

[Dazz100]

Hi
I have an opportunity to acquire a GEC Miniscope model BW464.
It appears to be complete and in good condition but I doubt it still works.
Here is the same scope.
GEC Miniscope model BW 464.
GEC Miniscope model BW 464 Advertisement
GEC Miniscope model BW 464 dimensions

If I purchased it, I would aim to get it working again, not just be a shelf queen.
This is likely to require some/all recaps plus silicon rectifiers. It is a very compact design so I anticipate working on it will be a challenge. Finding parts to fit another challenge.

Does anyone have experience with these scopes?

[factory]

I've not got one of those GEC scopes, but have repaired a GEC R/C bridge, after replacing the few paper & electrolytic capacitors below, it works very well and is used regularly.



Also check to see if it has an internal or external mains fuse, I added one to the R/C bridge as it didn't have one.

David

[Dazz100]

Hi
That no one with one of these scopes has responded suggests that they are now relatively rare. I haven't yet made a decision to buy it, but I am definitely leaning in that direction. I have a circuit diagram, but no component values. That won't be a problem as long as the caps have the values printed on them.

I am thinking of trying to keep it looking old, even with new components. That would include things like making fake selenium rectifiers with a silicon diode inside and stuffing the existing caps with new replacements. To keep the old look with new parts.

This won't work for resistors.
Hopefully the wire insulation is OK, but possibly not. Replacing the laced wiring loom would be a major job.

[Radio Wrangler]

I had a play with one a long time ago and took no further interest. Cute but barely useable was my conclusion. At the time I was interested in building oscilloscopes and getting better performance. This thing looked like a big step backwards from what I'd done from reading a few books.

If you got one and got it working, it would likely wind up as an ornament, likely showing a Lissajoux figure. You'd not feel much like using it.

Sorry for the cold water.

David

[Dazz100]

Hi
Its got a bandwidth of around 30kHz. Contemporary screen photos indicate mediocre performance from new. I am looking at restoring it much like people restore vintage cars.

[Cobaltblue]

I have a miniscope last working in the 1990's nice novelty item but not practical today. I have a couple of the accessories such as the wobbulator. I'll see f I can locate it and take some pictures later.
Cheers
Mike T

[Cobaltblue]

Finally managed to find it and take a couple of pictures but I could not find the accessories box.

It's a mess in the loft at the moment due to ongoing building works

Hopefully the missing knob for the wobulator is in the missing box.

Cheers

Mike T

[M0FYA Andy]

Why say this unit is 'not practical today'?
The same can be said for nearly everything discussed on this forum - old radios which cover wavebands where hardly anything is transmitted, old televisions receiving analogue signals at 405 lines, need I go on?
This forum is about Vintage Technology for its own sake, not for practical items!

Good luck to the OP if he gets a Miniscope working!

Andy

[Cobaltblue]

Originally Posted by M0FYA Andy

Why say this unit is 'not practical today'?
The same can be said for nearly everything discussed on this forum - old radios which cover wavebands where hardly anything is transmitted, old televisions receiving analogue signals at 405 lines, need I go on?
This forum is about Vintage Technology for its own sake, not for practical items!

Good luck to the OP if he gets a Miniscope working!

Andy

Two things, I rarely use a scope for working on Radio's.

Secondly I have the more usable Cossor 1039M (several examples) if I want to use a small vintage oscilloscope. The GEC looks cute but its tiny screen big close together knobs make it less than practical. When new the Cossor seems to have heavily outsold the GEC if the number of surviving example is anything to go by.

Perhaps I should have said not practical for use by me today.
When I do use a scope I usually need the 100MHz bandwidth of a more modern ( but still from the 1970's) scope.

I also hope the OP gets his Miniscope working I enjoyed playing with mine almost 30 years ago The most useful thing was the wobulator attachment useful for aligning IF strips.

Cheers

Mike T

[newlite4]

I have one of these and it worked straight out of the box with no restoration. Just as well as it is more or less impossible to remove the outer sleeve for servicing. As Andy has just said, it is old, but was probably a valuable addition to the bench when it came out in the mid 1940s. Perfectly useable for servicing vintage electronics and takes up hardly any bench space.
Neil

[GMB]

Its got a bandwidth of around 30kHz.

The specification says 50Hz to 300kHz ±1.5dB although only 100kHz for highest gain input.

I have to admit that I have one of these but still haven't got it working. They look like "nightmare on capacitor street". Mine has a couple of missing knobs and has been worked on before by someone else. The mains plug is missing too.

It is not my only small scope so maybe this is why it isn't fixed, as it will be a total gut and rebuild job I think. I don't think they are so rare but the add-ons certainly are.

[Dazz100]

Hi
I made the purchase so my newest scope is also the oldest thing I own. To be specific, it is a late 1940's, early 1950's, GEC M861B Miniscope in remarkably good condition for its age. It must have been a marvel of miniaturization at a time when test equipment weighed as much as a sack of coal and used enough power to heat a small orphanage.

My research reveals that this model of scope is the direct descendant of a scope (model M861A?) developed to fault-find clandestine radios in WW2 enemy occupied territory. The post war version was sold to traveling TV repair men (probably not many TV repair ladies at that time).

It's military origins can be seen in the knobs. This style was used on aircraft to allow crew to turn the knobs while wearing thick gloves.

It features an astonishing 70kc/s bandwidth with a 1 1/2 inch CRT and a weight of just 7 1/2 pounds.

The plan is to restore it to working condition. I have not attempted to apply power yet because it has probably been in storage for decades. The electrolytic caps may not be caps anymore.

If anyone has a spare M862B Double Beam Unit, a M863B IF Alignment Unit or other accessories lying around, I could be an interested buyer.

[factory]

The manual that was originally from Jonz valve page, no component values are listed but it should help with the circuits. The rectifier diodes & capacitors should be checked, as failure will probably destroy the transformer.

gec_miniscope_300khz_oscilloscope_1949_sm.pdf

David

[Dazz100]

Originally Posted by factory

The manual that was originally from Jonz valve page, no component values are listed but it should help with the circuits. The rectifier diodes & capacitors should be checked, as failure will probably destroy the transformer.

Attachment 295606

David

Hi
The plan is to apply power with a variac in series with a 10R resistor and a fuse. Not sure what size fuse, but I am guessing it should be using less than 100W, so 0.5A fuse. I can monitor the current across the 10R resistor.

[factory]

Why are you guessing the power consumption, it's listed as approx 25W in the pdf manual.

The variac & 10 ohm resistor will offer no protection against possible shorts on the secondary of the transformer, a lamp limiter & appropriate rated incandescent lamp(s) would.

If the mains is 230V where you are, a 250mA time delay/anti surge fuse would be better.

David

[Dazz100]

I took the Miniscope to the local technical institute where I used a variac to gradually build up the supply voltage to 240VAC to reform the caps, and see if any magic smoke was waiting to escape. I was working in a class with 3rd year apprentices and the instructor asked me to give a mini-presentation on what I was doing. They were all interested. I forgot to take photos.

Over a period of about 20 minutes, the voltage was gently eased up and absolutely nothing happened (good result). At full supply voltage it drew about 130W which is way too high.

The critical part is the transformer. This is sealed in a metal can, probably with transformer oil for cooling. If this blows, the Miniscope would probably be unfixable.

One of the potentiometers is seized solid and two others have high friction. They are 1/4" SS shafts with no flat. I suspect this was done to prevent damage by over turning the knobs. The set screws are BSW 1/8, 40TPI, but one screw was 38TPI and that was enough to strip the thread in the Bakelite knob. I am currently making some replacement set screws (can't buy them here). And I need to repair the damaged thread.

Now that I know it can take 240VAC, I plan to run it with a voltage set to use about 25W to go through and check that individual components. Something is taking a lot of current. Before I do that, I need to reverse engineer a circuit diagram with values. That will take a while because of the way the components are packed in.

[Dazz100]

Originally Posted by factory

Why are you guessing the power consumption, it's listed as approx 25W in the pdf manual.

The variac & 10 ohm resistor will offer no protection against possible shorts on the secondary of the transformer, a lamp limiter & appropriate rated incandescent lamp(s) would.

If the mains is 230V where you are, a 250mA time delay/anti surge fuse would be better.

David

Hi
I used a 18R in series with a 120mA fast blow fuse. If anything went wrong, the resistor would have reduced the peak current and the fuse would still have blown quickly enough. At 240VAC/120mA works out to just 29W.

[jamesinnewcastl]

Hi

I have two of these scopes and I don't believe that they are that rare, they usually come in the smelly box too, however the wobulator and double beam unit really are rare! I'd not even heard of the double beam unit before.

Still I got them because they look like great fun to restore - mine are currently at project 33 in line!


Cheers
James

[factory]

Originally Posted by Dazz100

Hi
I used a 18R in series with a 120mA fast blow fuse. If anything went wrong, the resistor would have reduced the peak current and the fuse would still have blown quickly enough. At 240VAC/120mA works out to just 29W.

Fuses might not do anything, it won't blow immediately after passing 120mA when bringing it up slowly, there are usually detailed specs for time taken to blow, at various overload currents in the datasheets.
Shorted turns in transformer secondary windings don't always result in a dead short, they can run for a while heating the transformer up without immediately blowing fuses, how do I know this? from experience, I have several items with bad transformers, using the lamp limiter & checking voltages found these. I don't know the full history of them, or how they were treated before I acquired them, I do know I cant buy a cheap replacement off the shelf, due to the custom spec for the test gear it's from.

Hence why I recommend using a lamp limiter, starting with low wattage lamps and increasing the wattage over several hours, monitoring the power supply rails and making sure nothing is overheating as you progress, if anything suddenly shorts the lamp will give a visual indicator too.
For scopes with a valve rectifier you would need a temporary solid state rectifier for reforming capacitors and those with an oscillator/step up transformer based EHT supply, you would need to disable this until running at normal voltages, as oscillator based supplies will draw more current at lower voltages.

David

[Dazz100]

Originally Posted by jamesinnewcastl

Hi

I have two of these scopes and I don't believe that they are that rare, they usually come in the smelly box too, however the wobulator and double beam unit really are rare! I'd not even heard of the double beam unit before.

Still I got them because they look like great fun to restore - mine are currently at project 33 in line!


Cheers
James

Rarity is relative. It is entirely possible mine is the only one in my country. It think it is highly unlikely to find a double beam unit that is not already paired with a scope.