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Old 15th September 2007, 03:01 PM   #1
Grifon is offline Grifon  Chile
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Smile Philips Tube radio

Hi

I came across an old Philips Tube radio 1960 or there abouts , its an B3X00U model . I am a newbie when it comes to Tube radios so this is my first radio .

Now when I got it it was filthy inside with a resident spider , after a good clean and check for anything blown I switched it on, and to my surprise it was still working......however after about 20 minutes it cut out no sound , no hissing a slight hum coming through the speaker......boooo.....

After some time the signal came back for a 1min or so then go and then comeback.........

Thought it was the antenna , but it wasn't , checked the Tubes just to see if the switched on [do not have a tube checker]....UCH81 , UBF80 , UCL82 and UY89........they all seem to be on.



I was able to locate a schematic of the radio on the web here it is :

Click the image to open in full size.

Click the image to open in full size.


Can someone give me an idea what could be the problem?
Also if you look at some of the values of the capacitors they read 10K or 4.7k what values are these I only know of uf and pf....
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Old 16th September 2007, 12:27 AM   #2
PRNDL is offline PRNDL  United States
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Most likely something went bad.
The two most common are electrolytics and a bad tube.
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Old 16th September 2007, 03:46 PM   #3
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Location: Sussex
Hi,

I learnt somthing recently whilst cruising DIYaudio that seems to be relevant to your issue.

Reflow all the solder joints and clean all tube sockets with switch cleaner or somthing. The problem is occuring when the unit warms/warmed up so it is due to expansion or movement of joints and contacts causing some connection/connections to fail.
Also as mentioned replace all the electrolytic capacitors, if this fails thenget a DMM to check PSU and a scope totrace the signal until you find a problem.
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Old 16th September 2007, 07:43 PM   #4
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I have a similar vintage Philips radio. When I got it I switched it on and it worked fine for a week or so. It then went dead, and I eventually tracked it down to the output transformer which had a partial primary winding which had fried, I rigged up a resistor to do a similar job - but the radio hasn't been the same since.

The point of this little story is that there was excessive DC flowing through this winding. I decided to do some poking around. I found that nearly all of the little black caps were cracked and had badly drifted or were leaking DC across them. I got a schematic and replaced all of these caps as best i could (none of them had readable markings and a lot were difficult to match up to the schematic). Surprisingly the main electro caps have caused no problems as yet, and all of the original valves are still good.

I would strongly advise a recap of all of these little black caps before your radio has a similar melt down to mine.

Shoog
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Old 16th September 2007, 11:42 PM   #5
Stentor is offline Stentor  United Kingdom
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Default Cap values

Current practice is to express cap values less than 1 uF in pF (colloquially "puffs") so 10k = 10,000 pF = 10 nF (because 1,000pF = 1nF); using the same schema makes a 4.7k cap (or, as is more recently expressed, a 4k7 cap) = 4,700 pF = 4.7nF.

Clear as mud? :-)

I think the reason is partially to allow a sensible use of the standard colour code as seen on resistors, and partially to allow fewer characters needing to be printed on small components.


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Old 20th September 2007, 03:40 AM   #6
Grifon is offline Grifon  Chile
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Thanks for the info , this weekend will get out the soldering iron and check everything and see how it goes , also will replace the capacitors. Will let you know what happens.
thanks
rod
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