Painted Tubes

ID: 184131
? Painted Tubes 
20.Feb.09 18:47

Lars-G. Lundelin (FIN)
Articles: 143
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 Hi Tube Radio Freaks!
  In several European radios from the 30th's, tubes are painted with a conductive silver or gold coating (like AF3). 
My question therefore is: Where can you get get this conductive paint and whtat's the name of it.
My second rq is: should this painted screening be connected to the earth (grounded to chassis) or not?  

There are several swedish sets using american-type (not painted) tubes and these are enveloped with a steel shield which are grounded.
 I would be appreciated if anyone could give an answer to this.



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painted tubes 
20.Feb.09 19:07

Konrad Birkner † 12.08.2014 (D)
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Konrad Birkner † 12.08.2014

On most of these tubes You can find a wire ring just where the bulb enters the base. This ring is connected to a base contact and to the conductive layer. The purpose is simply electrical shielding, ergo the paint must be connected to chassis.

It is a common experience with certain radios, that the IF is oscillating if the screen does not work. There is capacitive coupling from the high level anode to the previous (unscreened) stage anode, which in turn is coupled to the grid of the oscillating tube.

The symptom is then a whistling if a station is tuned in.

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repair painted tubes 
20.Feb.09 20:48

Carlos Alves (P)
Articles: 171
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Hi Lars,

in this link you can see how repair this paint ( in French )



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English translation 
20.Feb.09 22:19

Michele Denber (USA)
Articles: 129
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Michele Denber

Here is an English translation I just did of that article:

Tube shielding repair (Article translated from a Dutch review by Roger Florus)

This is an excerpt of an article written in Dutch by Mr. W. Breij in the revue "Historisch Tijdschrift de la Nederlandse Vereining voor de Historie van de Radio."

The zinc coating covering old tubes which serves as shielding is generally in bad condition or nearly gone.  Furthermore, the copper wire connecting the tube socket to the shielding is often broken and therefore no longer makes good contact with the cathode.

To fix this, we need the following material:

 * 1 fine graphite spray (eg. no. 33 from Kontact Chimie)

* 1 insulating plastic spray (no. 70 plastic from Kontact Chimie)

* 1 "Auto" lacquer spray in gold, silver, or red depending on the type of tube being treated.

* Plastic gloves

* Masking tape

* Dry transfer letters and numbers

* Paint stripper

* Cyanomethacrylate glue ("Crazy Glue")

First verify that the glass bulb and tube base are well joined.  If not, degrease the joint using a Q-tip dipped in acetone.  Use the least possible amount of glue.

It is first necessary to free the copper wire found in the joint by prying it outward without breaking it.

Remove the old coat of shielding with a wooden scraper.  Do not use metal which might scratch the glass.  The slightest scratch could cause the tube to shatter.  Use paint stripper if needed.  Let it react and remove with the wooden spatula.  Don't forget to wear gloves.

Then rinse the glass well in warm water (not the base!)

Carefully replace the copper wire in the groove between the glass bulb and the tube base.

Then srpray a coating of graphite on the glass at a distance of 25 cm. (10") away, very smoothly and evenly.Make sure the joint is well filled.  Let this dry in a hot area at least an hour to avoid bubbles.  Once dry, verify that the coating is uniform, otherwise restart the whole operation.

Apply a coat of paint the same way as the graphite taking the same precautions.  Apply the paint uniformly in thin layers and allow to dry well between coats.

Silver paint for Telefunken, Gold paint for Phillips Miniwatt

Once the paint is dry, you may transfer letters and numbers to the tube and finish the process by applying a coat of plastic laquer No. 70 over the painted portion.

Don't forget to transfer the special markings, for example the big "O"s of the Telefunken RENS 1264 which indicate the application for which the tube is designed.  A big "O" indicates that the tube is used as a mixer and a small "o" that it is used in less critical applications.

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Painted Tubes 
21.Feb.09 09:52

Lars-G. Lundelin (FIN)
Articles: 143
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Hi KoBi!
Thanks a lot for your reply. You spotted immediately my problem i.e. the whistling phenomena in the IF-stage (AF3) in my Philips V6A when I was realigning the set.
When touching the tube I noitced a heavy crackling and whistling. I found that base of the tube was loose and the paint not properly connected to ground.
I checked all of my spare tubes of this kind and found out that almost half of them had the same problem.

Hi Carlos!
Thank you for the link.

And Michele, the translation is certainly welcome, you see I'm not the one having a ready tongue in french, Thank you for taking your time to translate this valuable information.



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Copper spray 
01.Mar.09 18:50

Viktor Cingel (SK)
Articles: 36
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Better for making HF shield than graphite, is a copper spray.

I tested graphite as well as copper, the second one is much better.

eg. in Slovakia we can buy a German product EMV35


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