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Old 18th Apr 2018, 1:45 pm   #1
BulletMag
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Default Telequipment D61 110v to 240v conversion?

Hi guys, I’m hoping you can point me in the right direction,

I have obtained three Telequipment D61 scopes, all with various issues however they all appear to be 100v to 120v only.
The manual does show there is actually a 200v to to 240v model.

If I want to use these on 240v uk power would I need a new transformer or could I use a step down transformer?
I would like to convert each one but I have no idea if there’s a modern equivalent of the 200 to 240 transformer.

As you may have guessed I’m a bit of a noob when it comes to vintage electronics (I’m more used to newer gear) but everyone needs to start somewhere.

Any advice would be appreciated
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Old 18th Apr 2018, 5:32 pm   #2
winston_1
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Default Re: Telequipment D61 110v to 240v conversion?

A step down transformer of the correct rating would be OK. Don't use a voltage converter. These are cheap but only suitable for heater type loads.
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Old 18th Apr 2018, 5:48 pm   #3
BulletMag
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Default Re: Telequipment D61 110v to 240v conversion?

Cheers for that, as this is my first time messing with a vintage scope I wasn’t sure if a step down would have introduced issues as I know how fickle scopes can be with input voltages. Hence the voltage selector on the rear of this scope.
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Old 18th Apr 2018, 6:27 pm   #4
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Default Re: Telequipment D61 110v to 240v conversion?

I guess a 110v yellow site transformer would be easy and cheap enough to get hold of. This has the advantage that your scope is then floating - so you can stick your probes across things without worrying where they sit in absolute terms. Often folk use a 1:1 isolating transformer to power gear when they want to wave scope probes over it for this reason - you would be floating the instrument instead (though note: this means you don't get the protection yourself if your device under test has a high voltage on it, and you touch it with your hand).
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Old 18th Apr 2018, 6:43 pm   #5
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Default Re: Telequipment D61 110v to 240v conversion?

Run two of them in series
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Old 18th Apr 2018, 8:01 pm   #6
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Default Re: Telequipment D61 110v to 240v conversion?

Whatever approach you choose please don't use or sevice your oscilloscope without a proper safety earth. There are too many ways to accidentally induce death by electrocution without adding to the risk.

Alan
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Old 18th Apr 2018, 11:57 pm   #7
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Default Re: Telequipment D61 110v to 240v conversion?

If that scope is not isolated from the power line, beware.

I learned the hard way and blacked out the entire wing of the tech school working with a Telequipment scope and a hot chassis TV set. (Not only 1X but 2X in a row). Made one heck of a bang when I hooked the scope probe ground to the TV hot chassis.

Seems the teacher was a theory only man and had no idea of practical experience or isolation transformers.

I am just lucky I didn't fry myself or damage the set. Now everything I work on is isolated and all my test equipment is too.
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Old 19th Apr 2018, 9:44 am   #8
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Default Re: Telequipment D61 110v to 240v conversion?

FrankB has highlighted the possible need to use an isolation transformer without safety earth when working on a live chassis. He is also used to working in a 110/120V mains environment and has many years of practical experience. It also worth noting that the safety earth in his example did its job and nobody was killed or injured.

This issue is all about understanding risk and consequent mitigation. I think Rod Elliott of ESP sums up the situation rather well in this extract from his article about electrocution:

"Do not assume that isolation or stepdown transformers are safe - they are not. Isolation transformers will cheerfully kill you if you become connected across the output - an isolation transformer has no active (live) and neutral. Many stepdown transformers do not provide isolation. Isolation transformers can lead to a complacent attitude, and one lead can connect to chassis if there is an insulation failure - with no effect on the equipment or transformer. The other lead is now a killer! Isolation transformers will prevent an electrical safety switch from operating if a fault develops on the isolated side!

It is commonly believed that using an isolation transformer for service work is a good safety measure, but this is simply untrue. A mains fault in equipment being serviced can go undetected, and people used to using an isolation transformer are at real risk if they have to work without it for any reason. Isolation transformers should only be used when working on equipment with a 'live chassis' (also known as a hot chassis), and provide safety for your test equipment - not for the operator!"

Alan
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Old 19th Apr 2018, 10:40 am   #9
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Default Re: Telequipment D61 110v to 240v conversion?

Quote:
Originally Posted by mark_in_manc View Post
I guess a 110v yellow site transformer would be easy and cheap enough to get hold of. This has the advantage that your scope is then floating - so you can stick your probes across things without worrying where they sit in absolute terms.
Not true, I'm afraid. Apart from the fact that floating test equipment like this can be extremely hazardous if done inexpertly, yellow 'site' transformers are not generally isolated from earth. They're centre-tapped so that the output is 55-0-55V, ensuring that no wiring on the output side is ever more than 55V from earth even under fault conditions. That's where the safety comes from. The earth conductor is continuous from the 240V input to the 110V output.

The scope doesn't care about any of this, though, so a site transformer will work fine, and safely, for running the scope in its normal way.

Chris
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Old 19th Apr 2018, 11:30 am   #10
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Smile Re: Telequipment D61 110v to 240v conversion?

Hi,
Sometimes the mains transformer has two primary windings which can be hard wired in parallel for 115 volt operation, or in series for 230 volts.
I bought two H-P 400H valve voltmeters at the weekend. One was made in Germany and had a voltage selector switch. The other was made in the USA and was marked 115 volts. I connected it to a step down transformer and nothing happened except that the heater voltages were around 3.1 volts.
On closer inspection, the input had been rewired for 230 volts in the manner stated above, but the 115 v label was still in place.
Hope this helps.
Cheers, Pete.
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Old 19th Apr 2018, 12:37 pm   #11
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Default Re: Telequipment D61 110v to 240v conversion?

Unfortunately I don't think the D61 has two primary windings unlike some later Telequipment oscilloscopes. The manual shows only one winding and refers to two different model versions in relation to mains compatibility.

Alan
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Old 19th Apr 2018, 12:54 pm   #12
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Default Re: Telequipment D61 110v to 240v conversion?

Dear Alan,
I belive, its better to check your transformers version as think about how it can be-sorry...
@ Others:
Isolation transformers are originally mostly safty types, what means = have more robust insulating and are tested with higher voltages too. Other case is, that nowadays most people believe in error that isolating is automatically = safty- but IT IS NOT so_ we all must it so memorise, I think!
rgds, Karl
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Old 19th Apr 2018, 4:00 pm   #13
BulletMag
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Default Re: Telequipment D61 110v to 240v conversion?

Ok so I’m a little confused, would I be ok using a yellow site step down with say a RCD connected?
TBH my intention is just to repair the scopes not to use them to repair other stuff, as they looked like they needed some TLC but obviously the fact they are 110v is holding me back.
Thanks for all the great advice so far though.
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Old 19th Apr 2018, 8:57 pm   #14
TrevorG3VLF
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Default Re: Telequipment D61 110v to 240v conversion?

I have an isolation transformer with a centre tapped secondary. There are two output sockets, one the standard 13A on 240v and a USA socket on 120V. Thus US equipment can be energised on 120V but will not plug into 240V.
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Old 19th Apr 2018, 9:55 pm   #15
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Default Re: Telequipment D61 110v to 240v conversion?

Just to dispel any doubt, the D61 was supplied either with a 110/115 transformer, or a 220/230v transformer. The OP appears to have the former. The later D61A DID have a dual primary, so could be connected either way.
A while since I played with one, but if you wanred to "cheat", you could hide the transformer from one of the other two INSIDE, connecting its primary IN SERIES with that of the incumbent one. Fully isolate all secondaries.
Alternatively, get a 230:115vtransformer (auto transformer OK), and hide that inside.
Les
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