The 3BP1 Anderson monitor

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The 3BP1 Anderson monitor

Postby Harry Dalek » Sun Oct 25, 2015 8:23 pm

Had my 3bp1 since the 1980s ,Steve helped me work out i did have one of these a few years back now .
viewtopic.php?f=8&t=1321&hilit=3bp1
I will slowly work on this to get this going in the hope i can make a monitor out of it in time .
The circuit to power the CRT i hope to use is from this site which says it works with my crt .
http://www.electronixandmore.com/projects/simplescope/
Circuit below.......
I got all the parts earlier in the year so just a matter of putting the circuit together .
I spent a bit of time today cutting up an old aluminium back panel from something scrapped years go to make something to house the CRT ,the fan area was fine for the crt display hole ,and the fan with its motor removed was great for holding the front of the crt .
So have something to work on now when i have the hankering :)
Whoops mistake...i forgot to place this in the electronic tv topic if Steve or Andrew would like to swap it over i am happy and a big sorry.
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Last edited by Harry Dalek on Sun Feb 14, 2016 3:39 pm, edited 2 times in total.
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: 3BP1

Postby Klaas Robers » Mon Oct 26, 2015 5:37 pm

Looks good to start with Harry. Be sure to place and keep the transformer away from the picture tube, as the stray field will give a hum deflection on the trace. I made the same mistake years ago, however I had a mu-metal screen for the 3BP1 and hoped that would screen the magnetic fields. It did, but by far not enough.

There is no need to place the high voltage rectification and smoothing also outside the cabinet, this can be placed inside. It will require a multi wire connection to your picture tube unit.

In my Heathkit SB-500-cabinet for my SSTV monitor there was the ability to place the transformer at quite some distance. I will make a few photos soon and place them on this forum. Then you will see that I wound a shorted coil around the transformer to decrease the magnetic stray field. I don't know yet if it was sufficient.
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Re: 3BP1

Postby Harry Dalek » Mon Oct 26, 2015 10:56 pm

Klaas Robers wrote:Looks good to start with Harry. Be sure to place and keep the transformer away from the picture tube, as the stray field will give a hum deflection on the trace. I made the same mistake years ago, however I had a mu-metal screen for the 3BP1 and hoped that would screen the magnetic fields. It did, but by far not enough.

There is no need to place the high voltage rectification and smoothing also outside the cabinet, this can be placed inside. It will require a multi wire connection to your picture tube unit.

In my Heathkit SB-500-cabinet for my SSTV monitor there was the ability to place the transformer at quite some distance. I will make a few photos soon and place them on this forum. Then you will see that I wound a shorted coil around the transformer to decrease the magnetic stray field. I don't know yet if it was sufficient.



Thanks for the advice there Klaas ,i have a old 80s Trio scope and i was sort of going to copy the placement of the transformer or what i end up using around the same area in the back of the case as i made the case to around the same size as that scope ,i had been thinking of the magnetic field problem near the crt and that idea of placement seemed logical .
I didn't think of a screen for the tube i suppose i could make one if needed and come to think of it the trio scope i think has one .
Perhaps also a small metal steel box over the transformer might help ,any case i will find out either way.
Yes i would like to see what you did on the sstv with the coil around the transformer .
I was just looking today what size boards fit in the case but i need to see really first what i can find transformer or transformers for the power supply,every thing will go quick when i have the AC voltages.
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: 3BP1

Postby Steve Anderson » Tue Oct 27, 2015 3:40 pm

There's always toroidal transformers which have far less external magnetic field. But watt-for-watt they are more expensive, not many have tube-friendly secondary windings and they're most unlikely to be found in junked domestic equipment.

The highest secondary voltage that's easy to get is 240V where the windings are isolated. This will probably be a 50VA or greater unit, OK for a tube radio or similar, but then you need to get another transformer for the heaters...also toroidal!...but very easy to get.

There are companies that will make a custom toroidal transformer with tube-friendly windings, those I know of are in the UK but surely in other places too. 250V-0V-250V and 2x6.3V at various currents can be done at a reasonable cost, even one-off. Even so, the project needs to justify the expense.

Hans Summers got a custom toroidal made with a single secondary for a tube project. For the heaters he added an overwinding himself after working out how many turns-per-volt were required. The load on this additional winding needs to be only a small proportion of the transformer's VA rating which should be deducted from the main secondary rating. It worked well.

Steve A.
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Re: 3BP1

Postby Harry Dalek » Tue Oct 27, 2015 5:48 pm

Hi Steve thanks for your advice on the transformer ,i more than likely have something but they are very large looking into it .

I was thinking of a few options

Could use 2 transformers back to back to get the higher voltage but because most on the primary side of things don't have a middle winding connection i am not sure how the circuit would work on floating ground ......i could feed say a 12 volt ac to 2 6 volt transformers then connect 2 of the primary winding's together and get the split 240/240 ac supply or what ever voltage that might give.

I was thinking also perhaps a dc to ac converter might drop the transformer size , i made one to work on 50hz a while back as in the flyback schematic but mines a 50 hz version running around the voltages needed.

i will have a look today what i have...before making up my mind
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Re: 3BP1

Postby Steve Anderson » Wed Oct 28, 2015 12:44 am

I wouldn't consider going down the road of using a 50Hz transformer in flyback mode, keep it simple, keep it linear. Two back-to-back transformers, say 12V-0V-12V will give you potentially +/-18V which can be regulated down to whatever voltages you need and also (perhaps with series resistors to supply the tube heaters, though unlikely the CRT heater itself). This stuff works, inefficient, maybe, but it does work. Efficiency is not a great concern to us. Reliability is.

Switched-mode and flyback supplies also generate a bucket-load of interference which can be difficult to eradicate. With 50Hz you know what you're dealing with.

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Re: 3BP1

Postby Harry Dalek » Wed Oct 28, 2015 5:37 pm

Steve Anderson wrote:I wouldn't consider going down the road of using a 50Hz transformer in flyback mode, keep it simple, keep it linear. Two back-to-back transformers, say 12V-0V-12V will give you potentially +/-18V which can be regulated down to whatever voltages you need and also (perhaps with series resistors to supply the tube heaters, though unlikely the CRT heater itself). This stuff works, inefficient, maybe, but it does work. Efficiency is not a great concern to us. Reliability is.

Switched-mode and flyback supplies also generate a bucket-load of interference which can be difficult to eradicate. With 50Hz you know what you're dealing with.

Steve A.


Thanks Steve i have been looking at what i have transformer wise ...it as always comes down to size as well ...i have a small one that gives 6 and 12 volts out another one a little larger a few voltages up to 18 volts .

I will take your advice on keeping to simple ...before i start the only real problem the 480v center tap so 240 240 ...before i start could i use a capacitive Voltage Divider say 2 1 uf high voltage caps and split the Ac this way ? only other way i can think of is using 2 transformers as in this quick drawing below ,that does mean another transformer.
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Re: 3BP1

Postby Harry Dalek » Thu Oct 29, 2015 2:35 pm

I have hooked up a 2 transformer system ,transformer 1 connected to the mains gives 6.7 volts and 12 and 18 i am using the 18 to feed the second transformers its giving about 360 volts about tops ......even trying different transformers ....

I think i am going to have to play around a bit connecting the 2 transformers as its still a bit low and voltage doubling it after as it is would be a bit high.

1 switch and 2 transformers so far i placed the transformers out of the way at the back not much room for boards other wise ...
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: 3BP1

Postby Steve Anderson » Thu Oct 29, 2015 3:40 pm

Harry, what sort of voltages are you aiming for? For a 3" CRT the 3BP1 is quite a high-voltage CRT.

If you don't have any data I attach two datasheets for the tube.

Steve A.
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3BP1Aa.pdf
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Re: 3BP1

Postby Harry Dalek » Thu Oct 29, 2015 4:43 pm

Steve Anderson wrote:Harry, what sort of voltages are you aiming for? For a 3" CRT the 3BP1 is quite a high-voltage CRT.

If you don't have any data I attach two datasheets for the tube.

Steve A.


I didn't think of the tubes voltage range might be on the lower end with the rectifier circuit as is but i was just trying for 480v ...perhaps i should just try it as is and see with out over thinking it ...

Thanks for the data sheets
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Re: 3BP1

Postby Steve Anderson » Thu Oct 29, 2015 7:19 pm

I know this is of no use to you Harry, but a more modern and lower voltage CRT is the DG7-32. It can work as low as 500V but it is quite dim, at 800V it's far better. These are still to be found in Europe with sockets and are quite short in length compared to just-post-war CRTs like the 3BP1.

I'll have a detailed look at the 3BP1 data and see if I can make any recommendations as to how I would go about it. I assume you wish to use this for NBTV not SSTV. I'll also assume that apart from the CRT itself, you want to use all semiconductor parts.

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Re: 3BP1

Postby Harry Dalek » Thu Oct 29, 2015 7:56 pm

Steve Anderson wrote:I know this is of no use to you Harry, but a more modern and lower voltage CRT is the DG7-32. It can work as low as 500V but it is quite dim, at 800V it's far better. These are still to be found in Europe with sockets and are quite short in length compared to just-post-war CRTs like the 3BP1.

I'll have a detailed look at the 3BP1 data and see if I can make any recommendations as to how I would go about it. I assume you wish to use this for NBTV not SSTV. I'll also assume that apart from the CRT itself, you want to use all semiconductor parts.

Steve A.


Hi Steve Well i have had this tube so long and have started on it now,last time i tried to do any thing with this was around the 1980s i had 2 of them then don't recall what happened to the last i might of left it when i moved to Melbourne along with my P7 crt i now regret.

Any case the circuit in the first post and link shown it can be used as a tv monitor,and yes in time a NBTV monitor would be nice but i know i need a few things to work before i can think of that .

I started on the DC side of it ,it looks to me to be a voltage trippler i think ,the Main transformer 240 volt windings via the 2 rectifiers circuit is a problem as i only have 2 not 3 connections out of that transformer ,so i have done away with the top rectifier as i have nothing to connect it to anyway....
I was going to hook it up and tomorrow and carefully test what crazy high DC i am getting :wink:
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Re: 3BP1

Postby Klaas Robers » Fri Oct 30, 2015 5:24 am

Harry, this circuit will not give you "crazy high" voltages. When I suppose the second output lead to be grounded, then:
- the first (top one) will give you + 300 volt. You need that for the deflection amplifiers.
- the third line gives you nothing, a capacitive voltage divider doesn't work on DC
- the fourth (bottom) output line will give you -900 volt.
In total the voltage then is 1200 volt, which is low for the 3BP1. It could do for an oscilloscope, but for a monitor, that should give some light on the screen, this is too low. You will need between 1500 volt and 2000 volt for some brightness.
However you can extend the circuit to a 5x voltage multiplier and then you get -1500 volt. Together with the +300 volt this is 1800 volt in total, reasonable.

Then I still would use the trick of Steve: one transformer 240V to 12 volt and two smaller transformers of 12 volt back to 240 volt. Of these transformers the 12 volt windings are in parallel and the 240 volt windings in series. Then you are back in the Hammont 270X situation, at least for the high voltage. The 12 volt intermediate voltage can be used for low voltage rectification, the +5 and -5 volts. You will need a separate transformer 240 V to 6,3 volt (6 volt) for the filament of the 3BP1, as the cathode is on -1500 volt.
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Re: 3BP1

Postby Harry Dalek » Fri Oct 30, 2015 12:24 pm

Hi Klass i have taken the advice on the 2nd transformer after hooking them all up ......these are the AC results from the transformers i am now getting 230 and 270 volts so hooking the second transformer up has dropped the ac a ways on the first one which is understandable but close enough.
The main transformer supplying those 2 i am now getting out of its other winding connections 5 volts and 6 volts ac for the circuits and heater ,have not checked what the winding supplying the 2 transformers for the high voltage is now giving .

Checking the DC might be a problem my meters don't measure that high .

The pictures the new transformer shown hooked up and thats my old trio scope for size parts placement comparison.
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Last edited by Harry Dalek on Fri Oct 30, 2015 7:14 pm, edited 1 time in total.
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: 3BP1

Postby Steve Anderson » Fri Oct 30, 2015 6:22 pm

A couple of suggestions, if you find you have modulation from the transformer(s) magnetic field 'borrow' the mu-metal screen from the Trio scope - assuming it will fit. Otherwise do what I often do and place the transformers in a separate box, a hassle yes, but with a 1.5m umbilical cord you can separate the troublesome transformers. All the other PSU components (assuming you're not using an HT choke) can be part of the monitor proper. I tend to put the monitor on the workbench and the transformer box on the floor. More effort, but it works.

My first ever NBTV monitor is in the picture below. There are actually two transformers, the second one is obscured by the rear panel. They were also in the back-to-back arrangement. There was a mild about of magnetic interference, not that bad, but I relocated just the transformers into a second box. Problem fixed.

In the second photo, after a total re-build, the transformers are gone and the umbilical is the feed from them.

Steve A.
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