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[Sticky] New project: Capacitor reformer

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Boingy
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Hello all,

Hopefully this topic is in the right place. I'm sure Chris will advise if it's not 🙂

I'm just getting started in the process of of making up a capacitor reformer, as I want to repair and restore vintage electronics. I already have plenty of experience as a TV service engineer, so I'm up for a challenge.

I've already got a circuit to work from and have ordered up the parts required. The restorer should be able to deal with electrolytics rated from 500V to below 10V.

Once I get the bits together, I will update with progress, photos etc.

Getting a transformer with a high voltage secondary proved to be quite difficult, but more on that later.

Parts should get to me by Tuesday, so it's twiddle my-thumbs-time right now!

Here goes!

All the best,

Tony

 

Standards are like toothbrushes. Everybody needs them, but nobody want to use yours!

 
Posted : 22/04/2018 3:06 pm
crustytv
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Posts: 11903
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Hi Tony,

really looking forward to this project so will follow it with great interest to see what the circuit consists of and how you tackle the construction. What will you be using for indication, meter? Neon? Both or something else?

I've often thought of building one but never got around to it,  I just use my Hunts CRB-3 bridge which gives me 0-500V with a neon for leakage indication and my Fluke strapped in to monitor voltage. 

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Posted : 22/04/2018 3:20 pm
crustytv
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Rob Titheridge, who was a member of Vrat 1.0 ( don't think he came over to Vrat 2.0) made a very nice reformer. Whilst you're waiting for the parts for yours, you might enjoy watching him demonstrating it, some good shots and description of the circuit towards the end.

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Posted : 22/04/2018 3:31 pm
Boingy
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Posted by: Chris

Hi Tony,

really looking forward to this project so will follow it with great interest to see what the circuit consists of and how you tackle the construction. What will you be using for indication, meter? Neon? Both or something else?

Hi Chris,
I'm all expectant right now! Just found out that some parts will be delayed until mid-may 🙁
Should be able to get things going within the next week or so.
So, I'll be using an 11 step potential divider network to give voltages from 500V down to 63V, with a variable lower voltage of 0V - 50V. There will be a totally unnecessary volt meter to watch for the pretty fluctuations whilst reforming. There will also be a current meter with switchable ranges and bypass for leakage values. Oh, and a neon bulb just in case there's the need for flashing lights. Lastly, there'll be a setting to discharge the cap.
It's one of my "things" that whenever I build something like this, it's just got to be full of switches, meters and lights 🙂
I don't care if I use it only once. It'll be built for a lifetime. That's just me 😉
BTW thanks for the video. Lots of useful info there.
All the best,
Tony

Standards are like toothbrushes. Everybody needs them, but nobody want to use yours!

 
Posted : 22/04/2018 6:24 pm
Marc
 Marc
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This should be good Tony, I like the idea of the wide voltage range. I built a cap reformer a while ago using a design from Paul Stenning's site and used parts from the junk box to house it, It works very well but is fixed to either 275v or 350v.

DSCF4495 (Medium)

Marc
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Posted : 22/04/2018 8:26 pm
Doz
 Doz
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I documented my awful attempt here ... it works...

 

http://andydoz.blogspot.co.uk/2015/03/the-mk87a-dreadnaught-capacitor.html

 
Posted : 22/04/2018 9:04 pm
Boingy
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Posted by: Marc

This should be good Tony, I like the idea of the wide voltage range. I built a cap reformer a while ago using a design from Paul Stenning's site and used parts from the junk box to house it, It works very well but is fixed to either 275v or 350v.

It'll be fun, that's for sure!
I'm glad yours works well. This will be the first time I've designed and built a reformer from scratch, so I'm hopeful that I'm on the right track 🙂
All the best,
Tony

Standards are like toothbrushes. Everybody needs them, but nobody want to use yours!

 
Posted : 22/04/2018 9:43 pm
Boingy
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Posted by: Doz

I documented my awful attempt here ... it works...

 

http://andydoz.blogspot.co.uk/2015/03/the-mk87a-dreadnaught-capacitor.html

Like the blog and the MK87a bit 🙂
I'm sure the saved capacitors would be thankful to you and the MK87a Dreadnought Capacitor Reformer, if they could speak 🙂
All the best,
Tony

Standards are like toothbrushes. Everybody needs them, but nobody want to use yours!

 
Posted : 22/04/2018 9:49 pm
Boingy
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Hello all, 

So today, I got most of the parts delivered. I got busy this evening and started to get the electronics sorted out.

Here's a few of the bits, all neatly laid out 🙂

PSX 20180425 013819

The built voltage selector switch. From left to right, each wafer switch does :-

Autoranges the voltmeter.

Selects voltages from the potential divider.

Selects limiter resistors for the reforming capacitor.

PSX 20180425 013901

The potential divider.

PSX 20180425 013350
PSX 20180425 013505

The voltage doubler, now with an added 30 volts!

PSX 20180425 013425

The voltage selector switch with limiter resistors and wiring.

PSX 20180425 013541

Transformer, doubler and selector switch wired up for basic testing.

PSX 20180425 013650

The voltages are a little out, because I haven't fitted a trimming resistor to the top of the resistor chain. I'll pick up some more bits on my travels tomorrow.

I think that's enough for one evening!

I'll try to do some more tomorrow, when I get back home.

All the best,

Tony 

Standards are like toothbrushes. Everybody needs them, but nobody want to use yours!

 
Posted : 25/04/2018 1:25 am
crustytv
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Burning the midnight+2 oil there Tony, that's what I like to see dedication.  ? 

I quite enjoy the wee hours for tinkering too, its very peaceful and luckily my shop is way out on the extremities of the house with a buffer zone of the conservatory, plenty of noise can be made. 

That's a good start and my appetite is well and truly whetted for more instalments. Can I ask is the circuit your own creation or an adaption of one?

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Posted : 25/04/2018 6:56 am
sideband
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Just a note....if that is Veroboard with the two large caps on, make sure there is plenty of clearance between adjacent strips. Remove the strips completely between the terminals. Of course if it's just plain old perforated board, there's nothing to worry about.

 
Posted : 25/04/2018 8:24 am
Boingy
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Posted by: Chris

Can I ask is the circuit your own creation or an adaption of one?

Hi Chris,

The circuit is an adaption. The original circuit basically relied on the neon to indicate the state of the capacitor, except on the lowest voltage, where an external voltmeter was applied. I can post up the pdf later if you want.

Standards are like toothbrushes. Everybody needs them, but nobody want to use yours!

 
Posted : 25/04/2018 9:06 am
Boingy
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Posted by: sideband

Just a note....if that is Veroboard with the two large caps on, make sure there is plenty of clearance between adjacent strips. Remove the strips completely between the terminals. Of course if it's just plain old perforated board, there's nothing to worry about.

Hello Sideband,

Not to worry, I have already cleared the adjacent strips on the veroboard 🙂

I should have put up a photo of the print side of the board!

Thanks for taking the time to ensure my health and safety 🙂

All the best 

Tony

Standards are like toothbrushes. Everybody needs them, but nobody want to use yours!

 
Posted : 25/04/2018 9:10 am
Marc
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Posted by: Chris

Burning the midnight+2 oil there Tony, that's what I like to see dedication.  ? 

I quite enjoy the wee hours for tinkering too, its very peaceful and luckily my shop is way out on the extremities of the house with a buffer zone of the conservatory, plenty of noise can be made. 

That sounds like heaven Chris, that's my biggest problem being next to two bedrooms I can only work till the early evening especially when my lad has to often be up for work at 5am

Tony, this project is looking good so far  ? 

Marc
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Posted : 25/04/2018 10:14 am
sideband
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Posted by: Boingy
Posted by: sideband

Just a note....if that is Veroboard with the two large caps on, make sure there is plenty of clearance between adjacent strips. Remove the strips completely between the terminals. Of course if it's just plain old perforated board, there's nothing to worry about.

Hello Sideband,

 

Thanks for taking the time to ensure my health and safety 🙂

All the best 

Tony

Well of course your health and safety is important but in this case it was more the safety of the board.....Veroboard as it is not good at voltages much higher than about 100V because the strips are so close together. Add a couple of solder blobs on adjacent tracks and there could be flashover problems. Removing tracks completely where necessary and all is well. 

 
Posted : 25/04/2018 11:11 am
Boingy
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Not so much progress tonight.

I thought that it would be wise to run the divider network at the designed 500v. After grafting on a couple of wirewounds to the output of the doubler, I got 500v, but noticed the resistors in the divider were getting quite hot. After clipping on a thermocouple probe, I got this after 5 minutes running.

PSX 20180425 235049

The resistors are able to withstand 155 Celsius, but I'm not overly enamoured with 100 degrees!

Currently, the divider is drawing about 23mA, for about 12 watts, which is probably more than is required. 

What I'm going to do is up the divider resistors to 3K3, which should draw about 15mA. This should also bring the consumption of the divider down to about 7.5 watts.

Whilst I'm at it, the doubler caps will be reduced to 15uF. Hopefully, the HT can be reduced closer to 520v. I can then regulate with zeners, without too much hassle.

So, another order to RS tonight!

Fingers crossed, might get the basic electronics working over the weekend. We'll see.

The article with the original circuit was found below.

http://www.vmarsmanuals.co.uk/newsletter_articles/big_bang.pdf

There will be a lot of changes to this basic circuit, so I'll draw up a diagram when it's all finalised.

Right, it's bedtime, so night night all 🙂

All the best,

Tony

Standards are like toothbrushes. Everybody needs them, but nobody want to use yours!

 
Posted : 25/04/2018 11:40 pm
Boingy
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Hello all,

Quite a bit of progress made with electronics today. Brought in 5 x 100V zeners to help regulate the divider.

The original divider as made to the original circuit diagram had a flaw in the divider. All voltages above 63V had a 13V offset, so 300V would be 313V. This fact, coupled with the very hot resistors forced me to redesign. Most of the resistors in the divider are now 3K3, instead of 2K2. The 100V, 63V and 0-50V taps in the divider now correct. Things are running much cooler now, as current through the divider is about 15mA.

500V selected

500v

350V selected

350v

50V selected

50v

0-50V selected, pot set to 16V

LowVolts

 

In addition, the switched shunts for the ammeter have now been sorted.

The spec on the meter said it had a resistance of 1K2. It was found out to be more like 1K4. So a few tweaks later.

100uA

100ua

1mA

1mA

10mA

10mA

100mA

100mA

And lastly, ammeter off

AmmeterOff

 

Tomorrow, I'll tidy up things and start to mount components into the box.

Off to bed zzzźzzzz

All the best, 

Tony 

Standards are like toothbrushes. Everybody needs them, but nobody want to use yours!

 
Posted : 29/04/2018 2:33 am
crustytv
(@crustytv)
Posts: 11903
Vrat Founder Admin
 

Excellent progress there Tony and nice to follow how design theory on paper, evolves when practical experiments start at the bench. Really looking forward to see the construction moving into a box.

I've been hunting through my box of bits and found a NOS RS 1mA FSD meter, a project box which has a failed 70's pattern gen project. Its got a TX and filter cap, multi-point wafer switch, toggle switches and a multi-turn pot, I'm starting to  wonder if I can utilise any of this to make myself a cap reformer. Anyway that's for another thread but thanks to your project and enthusiasm its got me thinking. ?  

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Posted : 29/04/2018 9:28 am
Boingy
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Posts: 136
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Hello all,

More progress today. Rebuilt power supply to accommodate zeners and dropper resistors. The main thing today though was drilling the top plate of the instrument enclosure. Lots of drilling and filing here!

Template on paper before centre punching.

Template

Pilot holes drilled.

Pilots

Switch cut out.

Switch cutout

The drilled plate. There'll be another few small holes for the locating lugs on the various pots and switches.

Drilled

Temporarily mounted bits.

Mounted

Monday's always a hectic day, won't get back to it until Tuesday probably.

I've also decided to add an "offset" pot that operates above 100V. The offset pot makes each voltage division variable. For instance at the 350V setting, the voltage can be adjusted from 350V to 400V, so we can set 375V if we want to.

OK, time to call it a day 🙂

All the best,

Tony 

Standards are like toothbrushes. Everybody needs them, but nobody want to use yours!

 
Posted : 29/04/2018 11:50 pm
Boingy
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Posts: 136
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Here we go, burning the midnight oil again!

So, more progress, got the last few components through today. Tonight it was all about drilling what holes are left to drill, followed by mounting everything. Lacing up and final testing I'll try to get done by Friday.

Anyway, some more pictures.

Top panel, with all parts in place.

Top

Front. 

Front

Left side.

Left side

Rear

Back

Inside enclosure, with transformer, mains connector, PSU, capacitor sockets and fuses.

PSU

Should now be able to have the unit tested in time for the arrival of my KB LR10 radio 🙂

Up again at 06:45, so night night zzzzzzz

Standards are like toothbrushes. Everybody needs them, but nobody want to use yours!

 
Posted : 02/05/2018 1:14 am
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