Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Sep Wed 30, 2020 11:22 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 9 posts ] 
Author Message
 Post subject: Philips b2x85u
PostPosted: Mar Sat 28, 2020 4:18 am 
Member

Joined: May Wed 31, 2006 6:41 am
Posts: 255
around 20 years ago i found this radio at my grandfayher's house and i had it on my shelf since then.
Now, for a few weeks i will be at home, so i want to make it work again.
i have adoubt about an NTC in parallel with the pilot bulb. the schematic says only NTC, but not a value. on the parts list there is a part number:49 379 55.
this NTC is cracked so i will have to change it, but i have no idea what NTC to use. i know this NTC is here to protect the lamp at startup,


Top
 Profile  
 
 Post subject: Re: Philips b2x85u
PostPosted: Apr Mon 06, 2020 5:25 am 
Member

Joined: May Wed 31, 2006 6:41 am
Posts: 255
Anyone?

In this location makes more sense a PTC than an NTC


Top
 Profile  
 
 Post subject: Re: Philips b2x85u
PostPosted: Apr Mon 06, 2020 5:27 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 36010
Location: SoCal, 91387
What the hell is an NTC? How about posting a link to the schematic, and designating what you are referring to?

_________________
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins/////////////////////////


Top
 Profile  
 
 Post subject: Re: Philips b2x85u
PostPosted: Apr Mon 06, 2020 6:07 am 
Member

Joined: May Wed 31, 2006 6:41 am
Posts: 255
An NTC is like a resistor, but the resistance changes with temperature. more temperature, less resistance.

Here is the schematic for the power supply on the radio.:

Attachment:
b2x85u.PNG
b2x85u.PNG [ 233.15 KiB | Viewed 609 times ]

R13 is the NTC and L1 is the pilot lamp


Top
 Profile  
 
 Post subject: Re: Philips b2x85u
PostPosted: Apr Mon 06, 2020 10:41 am 
Member
User avatar

Joined: Nov Mon 02, 2009 7:01 am
Posts: 4611
Location: Lincoln City, OR 97367
Greetings to alfonsol and the Forum:

I was at a loss to know what "NTC" was out of context also, but now we can assume it is an abbreviation for "Negative Temperature Coefficient". Unfortunately, without some cross-reference information from the original manufacturer, there is no way to get the specification for that part, and it is likely not available any longer in any case.

I would suggest a pair of back-to-back zener diodes (in series) of sufficient wattage to handle the current drawn by the radio at their rated voltage. Their voltage rating should be that of the lamp's nominal voltage rating less the forward drop of one diode.

Regards,

_________________
Jim T.
KB6GM


Top
 Profile  
 
 Post subject: Re: Philips b2x85u
PostPosted: Apr Mon 06, 2020 3:40 pm 
Member
User avatar

Joined: Dec Sat 24, 2011 9:17 pm
Posts: 6549
Location: Vancouver Island, Canada
Also, it is just a light bulb. A resistor will do the job.

https://www.radiomuseum.org/r/philips_b2x85u.html

It is not that complex of a circuit. Millions of pilot lights all over the globe used to glow bright for a second at startup. :lol:

_________________
Watch the doughnut, not the hole.
Burl Ives, RIP, oldtimer.
[:l>)


Top
 Profile  
 
 Post subject: Re: Philips b2x85u
PostPosted: Apr Mon 06, 2020 4:25 pm 
Member
User avatar

Joined: Jan Tue 31, 2012 1:55 am
Posts: 14048
Location: Mountains of Mourne. Ireland.
As john says, a 100Ω resistor will suffice.
https://www.vintage-radio.net/forum/sho ... stcount=12

voir... 26 modèles avec ces lampes
https://www.doctsf.com/philips-b2x-85-u/f11285/o=y


Top
 Profile  
 
 Post subject: Re: Philips b2x85u
PostPosted: Apr Tue 07, 2020 3:36 am 
Member

Joined: May Wed 31, 2006 6:41 am
Posts: 255
The radio sunsumption is 52w, that is at 220V 240mA

the lamp is 6,3V 250mA so the resistance is around 25 ohms and under normal circumstances it dissipates 1,6 watts

So if the cold resistance of the NTC is high enough there will be little or no effect on the current through the lamp.
If the lamp opens, all the current will pass through the NTC and it will get hot. and when hot the resistance will be lower. so if the hot resistance is near 25 ohms the NTC will have around 6,3v across it dissipating the same 1,6 watts of the lamp. i think the hot resistance of the NTC is not important as long is low enough. the only caveat here is finding one capable of 1,6W at least.

if i remove the NTC, i think there will be little effect on the voltages inside the radio, but if the lamp burns the radio will not work.

If i replace the NTC with a 100 ohm resistor, when the lamp is good, there will be 20 ohms( resistor and lamp in parallel) , so if the same 240mA are passing through this, there will be a drop of 4V instad of around 6,3, so the lamp will be dimmer. but otherwise no side effects. If the lamp opens all the current will pass through the 100 ohm resistor. the current will be lower than 240mA. let's say 210mA. for this current the resistor will drop 21V. it will have little effect in the performace of the radio, but the resistor will dissipate roughly 4,41 watts so i will need a big resistor that will put lots of heat if the lamp opens.

If i put a 2 zeners back to back they will put a fixed voltage on the lamp. when the lamp is fine this will protect a little the lamp from the startup current. If the lamp opens the zeners will take all the current, maintaining the voltage. Using 2 5,6V zeners, will do 5,6+0,6V=6,2V
at 240mA, the zeners will dissipate roughly 1,344W, so i will need a 5,6V 5W zener. the only caveat is the current limiting effect of the lamp will be lost, but i don't think that will be a problem. the lamp is only 25 ohms

I think the zeners are the best solution, and is cheap and are readily available.

Correct me if i am wrong


Top
 Profile  
 
 Post subject: Re: Philips b2x85u
PostPosted: Apr Thu 09, 2020 1:58 am 
Member

Joined: May Wed 31, 2006 6:41 am
Posts: 255
waiting for the parts to start with this one


Top
 Profile  
 
Post New Topic Post Reply  [ 9 posts ]  Moderators: Norm Leal, Marcc

All times are UTC [ DST ]


Who is online

Users browsing this forum: torotoro and 25 guests



Search for:
Jump to:  


































-->


Privacy Policy :: Powered by phpBB