radiomuseum.org
Please click your language flag. Bitte Sprachflagge klicken.

gemeinsch: DAF1011 (DAF 1011);

Moderators:
Martin Renz Ernst Erb Vincent de Franco Martin Bösch Mark Hippenstiel Bernhard Nagel Dietmar Rudolph Otmar Jung Heribert Jung Eilert Menke 
 
Please click the blue info button to read more about this page.
Forum » Radios and other type of sets (Physics) etc. » MODELS DISPLAYED » gemeinsch: DAF1011 (DAF 1011);
           
Michele Denber
Michele Denber
 
USA  Articles: 129
Schem.: 5
Pict.: 64
12.Jan.08 23:02

Count of Thanks: 8
Reply  |  You aren't logged in. (Guest)   1 I have just successfully removed the guts from one of the block capacitors on the DAF-1011 so that I could hide modern capacitors inside.  The problem is how to remove the hard tar-like substance that fills the box.  I removed the bottom bakelite plate and then put the capacitor in a toaster oven at 400 deg.  After 15 minutes, the material started to drip from the bottom into the tray.  Tilting the oven slightly helps the matreial to flow away.  After 25 minutes most of it had slowy flowed out like lava.  I removed the capacitor and then used a knife to remove the capacitor innards.  They came right out.  Neither th silver paint on the case nor any of the ink markings were harmed.  If you do this, do NOT use your kitchen oven.  The tar smokes and smells horrible.  I did this outdoors.  Use a toaster oven you don't plan to use again for food.  The only problem I had was that one side of the metal case came apart but this can easily be glued back on.  Other than that, it worked fine.  Nothing caught fire.  And I saved the tar.  I could probably pour it back in around the new capacitors but I don't think I'll bother with that.
Detlef Boeder
Detlef Boeder
 
D  Articles: 371
Schem.: 240
Pict.: 140
13.Jan.08 20:17

Count of Thanks: 5
Reply  |  You aren't logged in. (Guest)   2

Hi Michele,

when the tar smokes, the temperature is too high. Pls test it again with a lower temp. But the situation differs from condenser manufacturer to condenser manufacturer. I mount condenser blocs headfirst. So the "lava" floats perfectly out in a old metal cake box and not over the cabinet. But i work with a old kitchen oven in the cellar. I could never work in our kitchen oven with tar, because my girlfriend would eject me ;-)

Regards

DeBo

 

Michele Denber
Michele Denber
 
USA  Articles: 129
Schem.: 5
Pict.: 64
14.Jan.08 01:48

Count of Thanks: 6
Reply  |  You aren't logged in. (Guest)   3

Hi Detlef,

Well, the smoke was actually kind of gray.  I saw another post somewhere where the recommended temperature was 350 deg. F (177 deg. C).  However, that was taking too much time and I'm not known for my patience.  Even at 400 deg. F (204 deg. C) it still took 25 minutes to get the tar to melt.  And even at 350 I got smoke.  At least I did not get fire :-)

I have two more capacitors to melt in my DAF-1011.  I will try them at 350.  They are smaller so it may work OK that way.

On a related note, is there any point in keeping the original capacitors that I extracted from the can?  Do they have any historical value?  Do they affect the value of my radio?  Is there any point in saving the resolidified lump of tar?  Danke sehr1

Detlef Boeder
Detlef Boeder
 
D  Articles: 371
Schem.: 240
Pict.: 140
15.Jan.08 22:31

Count of Thanks: 3
Reply  |  You aren't logged in. (Guest)   4
 

Hello Michele,

well, i think 350C° are heavy! 200C° up to 250 C° are o.k. Please spend enough time, because the power supply condenser bloc is a big lazy mass. About your other questions:

 "On a related note, is there any point in keeping the original capacitors that I extracted from the can? "

No, i don't think. No historical value.

"Do they affect the value of my radio?"

Standpoint electrical: The value from the condensers in these positions are not critical. Example: 1µF you can change it into 820nF or 1,2µF. 0,5µF in 470nF, 560 or 680nF (IEC international standard). But please the first charging condenser 8µF in the power supply after the rectifier not higher! The absolute value is "Cmax" in the datasheet. The second 8µF after the choke should be 8µF, but the radio works also with for example 6µF.

Standpoint optical: This is my personal opinion. I mean, it is nice and the collectors are proud when the radio plays after the restoration, but the work should be professionel, reversible and invisible. Make a photo before you start your restoration and collect original replaced parts - for example small condensers and resistors in a plastic bag inside the cabinet. If you sell your radio, the next owner can restore it into the original state. So the value from the radio keeps in time.

"Is there any point in saving the resolidified lump of tar?"

Do not eat ;-) Keep out from children. Its trash. I use new material in a form of repair material from DIY-markets for roof repair to fill out the condenser cabinets.

Kind regards,

Detlef

 

 

This article was edited 15.Jan.08 22:41 by Detlef Boeder .

Rüdiger Walz
Rüdiger Walz
Officer
D  Articles: 671
Schem.: 146
Pict.: 208
16.Jan.08 00:35

Count of Thanks: 5
Reply  |  You aren't logged in. (Guest)   5
Dear Michele,
there are several methods of restoring a block capacitor. It depends on the intention and the restoration philosophy of the owner of the set. Enjoying the optimal performance of a historical set is very often the dream and the target of the owner. To achieve it without destroying the historical value of the set is always difficult. Every change should be ideally reversible.
 
Detlef already stated that removed parts of a radio should be stored in the set as a minimum measure to keep the value of the set. I agree to him: To my opinion this is not necessary with the contents of a block condenser.
 
I personally put only new condensers into the old can if the can is destroyed by the old condensers. Old capacitors mostly fail due to water take up by the paraffin wax. The wax is hygroscopic and because of that the resistance of the condenser insulation is reduced. Very seldom the condensers fail due to spark and short circuit. Due to the reduced resistance the condensers became hot and increased their volume. So in many cases the tin can of the block condenser is destroyed.
The German Post Office used following method in the 1940ies to restore capacitors with a resistance out of specification (because no spare parts were available after the war), which left the capacitor absolutely original.
First remove the bakelite cover and unsolder the wires. Second I use a heat gun to remove the bituminous tar which is much more efficient than the method using an oven. Then the condenser is put into a pot with molten paraffin wax (about 80 °C) and slowly heated up to 120 °C. (check temperature !) Evolving bubbles show that the water which is absorbed by the wax is evaporating. After about 30 min the water is completely evaporated and the block condenser is cooled down while replenishing molten wax. The wax reduces its volume significantly while cooling down. Now you can apply new tar and close the bakelite cover again. For the next decades the condenser will work again. This method can also be used at small capacitors.
 
If the tin can of the condenser is burst it is not possible to put in the old condensers again. You have to hide modern capacitors inside. If you use a heat gun you will be much faster but take care of the silver colour of the tin can. Use a big screw like a corkscrew to remove the old capacitors. The risk to bend the tin can is much lower than to use a knife. How to equip an old block condenser with new capacitors you will see some pictures under Mende 180W the next days.
 
I always kept the bituminous tar to seal the enclosure of small axial capacitors. It looks absolutely original.
Rüdiger Walz
 
 

This article was edited 16.Jan.08 00:37 by Rüdiger Walz .

Konrad Birkner † 12.08.2014
Konrad Birkner † 12.08.2014
Officer
D  Articles: 2334
Schem.: 700
Pict.: 3655
16.Jan.08 13:38

Count of Thanks: 6
Reply  |  You aren't logged in. (Guest)   6

This is a good method if You are careful:

1)  Never put anything in the white wax if it is above 95°C. Water will vaporize immediately , the piece can burst, and the liquid paraffin will splash and can do real bad harm.
When I was an undergraduate I jobbed in a telephon central office. New dial selectors had to be wired. The multi-wire cables (63 wires) used wrapped paper insulation, which after stripping and harness forming had to be cooked in paraffin. You had to be extremely careful not to import any water, not even one drop. It happened once (I was not an eyewitness, but I saw the consequences) that such a harness cable end was obviously wet (nobody knew why) and dunking it into the hot stuff about 2 litres from a total of 6 were spouted around... the worker luckily wore eyeglasses, so "only" his cheeks, nose, forehead,  chin and one ear got burned. To remove the undesired hair-spray was an extra task...

2) Heat up slowly ! The white wax has to melt inside, before it reaches 100°C. This allows bubbles to escape on the spot before steam pressure builds up and discharges suddenly.

3) Control the temperature ! Overheated wax tends to self-ignition.

Be careful !
Good luck !

PS: For emptying block capacitors I got best results using a hot air gun, too. The tin boxes are often soldered, which is easily redone.

Michele Denber
Michele Denber
 
USA  Articles: 129
Schem.: 5
Pict.: 64
16.Jan.08 19:20

Count of Thanks: 3
Reply  |  You aren't logged in. (Guest)   7
 

Danke sehr to everyone who replied to my post.  To re-emphasize, I was heating at 400 deg. Fahrenheit, not 400 deg. Centigrade.  I appreciate Detlef's comments on restoration philosophy.  Since I do not personally know anyone else restoring these radios, I'm not really familiar with how other people go about it.  I want to restore my radio to playing condition while keeping it safe and with minimum possible disruption to its original state.  I know some people even avoid cleaning the chassis to preserve the original 60 year old dust, but I think that's going a bit too far :-)

I also appreciate the electrical considerations.  The capacitor I'm working on is indeed the power supply filter block and my replacement capacitors are rated at 8.2 uF.  This should be well within the tolerences of the originals.  I'm curious about the suggestion that 6 uF would be OK because I've always heard that one can safely go up in capacitance but not down.

Thanks also to Ruediger about block capacitor restoration.  I thought about using a heat gun but it seemed like it might be too messy and I was worried about uneven heating.  Fortunately, my can withstood the toaster oven at 400 deg. F.  The paint was unharmed and the ink markings were also fine.  The solder did let go on one side but as Konrad mentions, this is easily fixed.  Ruediger also mentions saving the tar to refill small axial capacitors.  This is an excellent idea and I can use it for my DKE-38 capacitors which are almost always bad.  Great idea about using a corkscrew as a puller too.  I'll try that on the next one.

Finally, I had thought about trying to reform the capacitor but I decided it would be more prudent to replace it with modern components, especially given its position in the radio.  I do not want to risk damaging the power transformer or the rectifier tube.  I know that the old capacitor was very leaky and the radio was drawing far too much power.

Ernst Erb
Ernst Erb
Officer
CH  Articles: 5664
Schem.: 13754
Pict.: 31025
16.Jan.08 20:17

Count of Thanks: 7
Reply  |  You aren't logged in. (Guest)   8

Dear Michele
Having lesser capacity will cause more hum but no other problem, having higher capacity can harm the rectifier tube. If you know the data of your rectifier tube you can work out what the maximum is but you might have to consider the 60 Hz instead of 50.

For such a set best is to stay with the original value and your 8.2 is really fine. Then you get also (almost) the same performance as when it was new. It is not a HiFi gear ;-)

The rectifier has to work for a smaller resistance if you go up with the capacity and has therefore to deliver a much higher power (Amps) resulting in shorter life up to sudden "death" depending on the value.

Michele Denber
Michele Denber
 
USA  Articles: 129
Schem.: 5
Pict.: 64
18.Jan.08 02:06

Count of Thanks: 4
Reply  |  You aren't logged in. (Guest)   9 Thank you for the comments, Ernst.  It turns out to be not so easy to find exactly 8 uF in a high voltage capacitor.  8.2 was the closest I could find and that is within 3% of the original value.  I don't think the original tolerences were that tight.  I could not even find any electrolytic capacitor at all that was this close.  I note that the voltage on the original is 1500 V!  My replacements are film capacitors (from Mouser Electronics, see http://www.epcos.com/inf/20/20/ds/b32674_8.pdf) that are rated Vop = 800 VDC, VR = 630 VDC, Vp = 950 VDC, and Vrms = 350 VAC.  Is there any reason they should not work?  Is there something more suitable?  Danke.
Bernhard Nagel
Bernhard Nagel
Officer
D  Articles: 1504
Schem.: 2148
Pict.: 6171
18.Jan.08 12:21

Count of Thanks: 2
Reply  |  You aren't logged in. (Guest)   10
Hi Michele,

the choosen Epcos (formerly Siemens) MKP capacitors would be a very good solution for your replacing job. Even the mentioned voltage rating is more than enough for this application and gives you operational safety for your set.

The usual tolerances of old (historical) block capacitors was about 10...20% when they was new produced. So the usage of 8,2µF instead of originally 8µF is absolutely irrelevant.

Good luck!

Bernhard Nagel
Michele Denber
Michele Denber
 
USA  Articles: 129
Schem.: 5
Pict.: 64
18.Jan.08 18:04

Count of Thanks: 4
Reply  |  You aren't logged in. (Guest)   11

Hi Bernhard,

Thank you very much for confirming my choice of capacitors.  I have simliar capacitors for the other two blocks.  I want to proceed very carefully with this radio.  I have worked on DKE's and VE-301's before, but never a DAF.  I had a hard time finding one so I want to do a good job on it.  I am carefully documenting each step with photographs.  Hopefully by the time I'm done I will have a guide to restoring DAF-1011's that might be helpful to others.

 

 

  
rmXorg