The 3BP1 Anderson monitor

[Harry Dalek]

Harry, you do need to disconnect all loads to see if you have saturating cores. A perfectly normal transformer winding with a bridge rectifier, capacitor and regulator looks like below. this is due to the diodes, capacitors and in-built transformer losses. With no load at all it's a sine-wave, that's why I said no load.

The flat part is where most of power is lost in the transformer and why they get hot, but within design ratings. With saturating cores the same general shape applies but the 'shoulders' will be more rounded, not so square...again with no load.

The best way to check this is with a scope, look at the 330/340V waveform with no load, it should be a nice 50Hz sine. If the peaks and troughs are 'crushed' then the cores are saturating - not good.

Steve A.

Steve due to the ac voltage is 300 volt its way out of range on my scope all i can see is the middle of the waveform .mmmm head scratching time ..could use another transformer and drop it back to something i can read ...but not right i bet ..

[Steve Anderson]

Harry, use a 1M and a 100k resistor to form an 11:1 divider which should then be OK for your scope. If it still can't handle that use a 1M and 10k resistor to form a 101:1 divider. We're not so much interested in the actual voltage, but more the wave shape.

Using this trick is OK at low frequencies (50Hz), but anything above audio will give misleading results.

Steve A.

[Harry Dalek]

Harry, use a 1M and a 100k resistor to form an 11:1 divider which should then be OK for your scope. If it still can't handle that use a 1M and 10k resistor to form a 101:1 divider. We're not so much interested in the actual voltage, but more the wave shape.

Using this trick is OK at low frequencies (50Hz), but anything above audio will give misleading results.

Steve A.

Oh Ok Steve i will make one up and test ,i was just playing around today with different transformers....I forgot to ask do you think i have a magnetic problem with the transformers in the case ...... from the deflection test ...as i am going to have to do something as you did if so .

Thinking of replacing the 2 high voltage transformers with these ...after testing more today i think those need to be matched in every way i am just wondering if its to small...
Specifications
12.6V CT, 150mA 1.9VA Centre Tap - Type 2851 Transformer
Type: 2851
Secondary winding(s): Centre tapped
Primary voltage: 240VAC
Total VA rating: 1.9VA
Secondary voltages: 12.6V, 6.3V(CT)
Secondary current (max): 150mA
Magnetising current:: 150mA
Temp rise above ambient at rated power: 40°C
Regulation: 8%
Weight: 112g
Primary connection 200mm Fly Leads
Secondary connection 200mm Fly Leads
Conforms to AS/NZ 3108 & AS/NZ 61558.2.6 CS06918V
Dimensions(mm) A46 D44 L37 W16 H32

[Steve Anderson]

Well. they do appear a bit on the small side at 1.9VA. You're going to have to have a couple of mA in just the focus resistors which at a kV or more is over 2W alone. I think you need to uprate them to at least 10VA, 20 would be better. The heater for the CRT is 6.3Vx0,6A=3.8W so these aren't suitable for much really.

150mA should be enough for just the low-voltage stuff, unless using really old TTL. You've also got to consider the supply for the deflection amplifiers. But you need to remember that figure is for a resistive load, not a bridge rectifier, capacitor and so on. I would rate these at 75mA under those circumstances.

I wish people would not use (as they have here) 12.6V CT, it's ambiguous, is it 6.3-0-6.3V or 12.6-0-12.6V? That's why I always write it (something)-0-(something) - no ambiguity. Thankfully the photo makes it perfectly clear.

Steve A.

[Harry Dalek]

Well. they do appear a bit on the small side at 1.9VA. You're going to have to have a couple of mA in just the focus resistors which at a kV or more is over 2W alone. I think you need to uprate them to at least 10VA, 20 would be better. The heater for the CRT is 6.3Vx0,6A=3.8W so these aren't suitable for much really.

Whoops to late ~! well sort of i will explain ! What i did is i replaced those for the HV ones i was using to see .

Voltage with out load is 191 volts per transformer nice and even at least thats ok but with load it drops to 175 volts per transformer . i am feeding them 12volts ac these being 12.9

I hooked it all up and tested seems better than with the other transformers ...but i was looking also for a case of sorts today to see if i can make a power supply as you did to feed it via a cable so i am not overly worried about what i did today ...as i will do that as well
So in the photo the larger transformer is the 12 volt one feeding the two smaller ones for the 191 volts per transformer .

150mA should be enough for just the low-voltage stuff, unless using really old TTL. You've also got to consider the supply for the deflection amplifiers. But you need to remember that figure is for a resistive load, not a bridge rectifier, capacitor and so on. I would rate these at 75mA under those circumstances.

Lucky i was feeding the heater via the first transformer i would have no hope

I wish people would not use (as they have here) 12.6V CT, it's ambiguous, is it 6.3-0-6.3V or 12.6-0-12.6V? That's why I always write it (something)-0-(something) - no ambiguity. Thankfully the photo makes it perfectly clear.

Steve A.

That was the Jaycar electronics data for it ...good or bad !
Ok now i will make a AC power supply to feed this away from the CRT ,i have ones that are big enough..found some thing to case them so that is good ...then hopefully i will get a spot when i turn it on !

[Steve Anderson]

Some years ago whilst wandering around the electronics area of Bangkok I noticed a load of transformers which looked useful. Two wires on one side labelled 220V and two wires on the other side labelled 380V. (3-phase to single phase). I intended to use them the other way around. They were marked as being rated at 50VA. So I bought four of them thinking they'll be useful one day and with all the other stuff dragged them home.

They sat on the shelf for over a year until one day I found a use for them. 380Vx1.414 (root two) should give me about 520-540V less a bit due to using them in reverse. Voltage doubled around a kV.

NOPE!! As soon as I plugged them in the RCCB in the house tripped - they were damn auto-transformers! Useless!

I did wonder at the time why they were so cheap yet appeared new and unused - I now know!

If they only had three wires or terminals or been labelled correctly I would have clued on immediately.

Steve A.

I just dug one out, there is no indication at all they're auto-transformers. The price marked on the top is 205 Baht, about four pounds Sterling.

In fact there is a clue if you examine the second photo, where the bobbin is split there's what appears to be a piece if tape covering the join between the two windings. But who would notice that when out shopping at a busy, noisy and crowded market-style environment?

[Harry Dalek]

Those transformers look interesting with those stickers ! I would buy them without knowing.
I really have only been stung once which a usb stick 250 gig it was a scam the thing looked right but didn't hold bugger all ,didn't cost much but i suppose they were going for numbers like catching fish.
Yours is worse as you could of caused a fire or who knows .its bad enough selling rubbish but selling something it is not that is dangerous Yakes !

I will start on the power supply in its own case tomorrow Try number 3 should be it

[Steve Anderson]

Those transformers look interesting with those stickers ! I would buy them without knowing.

Yep, I did, now I have four of them, anyone got a use for them?

Thankfully the ones I purchased some time earlier marked 220V one side and 500V on the other are actually 'proper' transformers. Though from a different seller. It's a shame that I only purchased four that time, I should have gone back and got more before they vanished.

Steve A.

[Harry Dalek]

Harry, you do need to disconnect all loads to see if you have saturating cores. A perfectly normal transformer winding with a bridge rectifier, capacitor and regulator looks like below. this is due to the diodes, capacitors and in-built transformer losses. With no load at all it's a sine-wave, that's why I said no load.

The flat part is where most of the power is lost in the transformer and why they get hot, but within design ratings. With saturating cores the same general shape applies but the 'shoulders' will be more rounded, not so square...again with no load.

Steve A.

Steve i had time to day after starting some construction on the AC scope power supply case .

Heres some results i gather the one on the lower 200 voltage seems a nicer waveform.

These 2 are strange transformers to me but i am giving them a go at the multi AC voltage one using the yellow wires i am getting 200 volts ...the transformer has 3 primary wires not spot one even but saves me using another transformer seems ok at 200 180 volts ...the main transformer is 13 volts which i suppose is for a 12 volt dual power supply ...
I have to put another in just for the heater .

[Steve Anderson]

I guess the acid-test is if you're getting the results required, then leave it on for a while (hours - but turn the CRT brightness down) and see how hot things get. If you can leave your hand or finger on the transformers for a good 30 seconds I guess all is OK. If you have to withdraw it quickly something is amiss.

Steve A.

[Harry Dalek]

I guess the acid-test is if you're getting the results required, then leave it on for a while (hours - but turn the CRT brightness down) and see how hot things get. If you can leave your hand or finger on the transformers for a good 30 seconds I guess all is OK. If you have to withdraw it quickly something is amiss.

Steve A.

Well it seems fine i will do a long test tomorrow ,,,,if i want 6 volts AC i will have to put another transformer which was my intention.
Then i can hook it up to the CRT case ,the AC power supply is a project in its self but i know its a good idea having it .i hope now i will get cleaner results with a spot happening /

I would expect with heating the voltage would slowly drop in the transformer .

Its steady on the short run tests today .

[Steve Anderson]

What I have done, partly due to the magnetic problem, is put a bunch of transformers in one box and arranged the umbilical connector such they can be used or not depending on what the CRT needs. When I plug the supply into one monitor it uses all transformers, e.g. something requiring higher voltages like a 5ADP7 or a 5ADP1. If the monitor is just a DG7-32 then some of the transformers aren't used (no load).

It saves mucking around with building many and various power supplies, after all you're unlikely to be using more than one monitor at a time. You may have two eyes, but there is a limit!

A D-type (25-pin) is rated to quite high voltages, but there are many others to choose from. The 3-plus pin XLR style connectors are worth looking at. Often rated in the kV range, but not cheap if purchased new. Or the old-style octal plugs/sockets.

Steve A.

[Harry Dalek]

What I have done, partly due to the magnetic problem, is put a bunch of transformers in one box and arranged the umbilical connector such they can be used or not depending on what the CRT needs. When I plug the supply into one monitor it uses all transformers, e.g. something requiring higher voltages like a 5ADP7 or a 5ADP1. If the monitor is just a DG7-32 then some of the transformers aren't used (no load).

I was looking at your monitor you posted pictures of a few posts ago so i will do similar see what i have handy cable plug and socket wise .

It saves mucking around with building many and various power supplies, after all you're unlikely to be using more than one monitor at a time. You may have two eyes, but there is a limit!

Yes making power supplies per device that is a pain ! i see your logic ,the magnetic field problem i was not expecting to be as bad any case i see i am walking the same path you have been.

A D-type (25-pin) is rated to quite high voltages, but there are many others to choose from. The 3-plus pin XLR style connectors are worth looking at. Often rated in the kV range, but not cheap if purchased new. Or the old-style octal plugs/sockets.

Steve A.

I will look what i have handy i did look at jaycar but that was a pain what i wanted they either were out of stock or had plugs no sockets ,i gave up and see what i have in my junk box !

[Harry Dalek]

I now have the power supply working connected to the crt case via the cable .

I swapped the Heater to AC supply and looks like the distance has helped with the the magnetic field problem have a spot now .

I have not put in any plugs or sockets yet just cabled the power supply to the monitor .

[Steve Anderson]

...as I suspected it was the transformer magnetic fields. The effect drops off rapidly with increasing distance, usually 500mm or so is enough but it will vary between different transformers and CRT sensitivities. A mu-metal screen around the CRT neck helps a lot but getting one for your CRT isn't easy. Even a supply of just the plain sheet mu-metal here is probably impossible so you could make up your own. I haven't even bothered trying to get some, I would probably have to import it from the UK or the US.

Steve A.