Philips FX824A Radiogram 1953 - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

baff1957 · 3rd Jun 2020, 2:47 pm

So, i am getting the message restore rather than repair? i am happy with that as long as it fits my budget but i am also now worrying about how much time it will take, any estimates on the cost to restore as it would be such a shame not to breath life back into her.

Station X · 3rd Jun 2020, 3:17 pm

Whether to repair or restore is up to you. I don't claim to have restored any item of electronic equipment. I just put them into go working order. That includes replacing any components, failure of which could cause problems further down the line. Repair once should be the aim.

I have the advantage over you in that I have a capacitor reformer so that I can easily check out electrolytic capacitors. I also have a test lamp and Variac so I can slowly wake up old equipment, being ready to switch off at the first sign of distress. It'd cost you more to purchase test equipment than it would for new capacitors.

Don't forget that we don't know why the smoothing choke burned out, we're just guessing. Did you do the test described in post #13?

One approach to repairing this set would be to remove the valves apart from the rectifiers and get the power supply section working first.

baff1957 · 7th Jun 2020, 10:16 am

Quote:

Originally Posted by Station X

Whether to repair or restore is up to you. I don't claim to have restored any item of electronic equipment. I just put them into go working order. That includes replacing any components, failure of which could cause problems further down the line. Repair once should be the aim.

I have the advantage over you in that I have a capacitor reformer so that I can easily check out electrolytic capacitors. I also have a test lamp and Variac so I can slowly wake up old equipment, being ready to switch off at the first sign of distress. It'd cost you more to purchase test equipment than it would for new capacitors.

Don't forget that we don't know why the smoothing choke burned out, we're just guessing. Did you do the test described in post #13?

One approach to repairing this set would be to remove the valves apart from the rectifiers and get the power supply section working first.

Hi, do you have any guidance on price, i guess parts are relatively unknown until you find what needs doing, a ballpark max and min will be fine. If you dont mind.

baff1957 · 7th Jun 2020, 12:58 pm

Hi all, i have a smoothing choke which has become very hot and leaked some bitumen , i have removed it and tested it and it measures 447 ohm and 6.6 H Inductance.
The book says it should be 320 ohms and in my experience it is unusual for resistance to increase after it has become very hot and effectively crossed windings would reduce the resistance.
I really would like to replace as it could easily fail if not already. But i cant find anything with similar inductance and resistance of 320ohm.
Any experience of what i could replace with as i am guessing it is used to smooth the AC.
I wind chokes and transformers which are toroidal but not like this and also without perfect layering i am sure i would find it difficult to achieve the same values although i have all the correct materials.

Any thoughts please.

Thank You

Skywave · 7th Jun 2020, 1:17 pm

You ask "any thoughts": here are some.

When you measured 447 Ohms, was this measurement made when the choke was hot? If so, let it cool down to room temperature and measure its resistance again. Any resistance will increase its value as its temperature rises - especially in a choke, where the heat generated has a difficult path to escape to the surrounding air.
The choke may have overheated due to it passing excessive current due a fault in the items that are drawing the current through the choke. If so, that cause needs to be discovered first and eliminated prior to replacing that choke - a replacement choke might actually not be needed.
A perfect choke has zero resistance, so any replacement choke that has a resistance less than 320 Ohms should be suitable, provided that its inductance is of an appropriate value. You state that its inductance value was measured as 6.6 H. A suitable replacement value will probably be in the range 6 to 7 H. But you will also need to chose a choke whose direct current capacity is adequate for your application.
Also of consideration is what type of choke is this? Is it a 'swinging choke' or a 'constant inductance' type?

Al.

AC/HL · 7th Jun 2020, 3:30 pm

Has it actually burned out? It's overheated, but still seems to test as a choke, unless it's leaking to the core?

Herald1360 · 8th Jun 2020, 10:36 am

Quote:

Originally Posted by Skywave

A perfect choke has zero resistance, so any replacement choke that has a resistance less than 320 Ohms should be suitable, provided that its inductance is of an appropriate value. You state that its inductance value was measured as 6.6 H. A suitable replacement value will probably be in the range 6 to 7 H. But you will also need to chose a choke whose direct current capacity is adequate for your application.
Also of consideration is what type of choke is this? Is it a 'swinging choke' or a 'constant inductance' type?

Al.

Be wary of chokes with too low a resistance in a psu circuit subject to sudden changes in loading- the Q at the L-C resonant frequency can produce some nasty voltage swings and in the case of solid state rectifiers, voltage overshoot on switch on! Maybe more of a problem for low voltage high current supplies with small L and large C but worth considering.

A swinging choke is normally only used in a choke input filter where load currents vary between low and high values as in a class B amplifier, to stop the psu output voltage rising excessively at low load.

baff1957 · 9th Jun 2020, 10:39 am

Ok thanks a lot for your information, it is very helpful, i have taken the choke to our workshops and flash tested it at 600vac and it held up ok, i used our Wayne Kerr Bridge to get an accurate reading and it is 429.5 ohms with a 130k resistor to case.
One thing is if the manual says 320 ohms and another has been fitted (but it looks original) could the increased resistance create the heat i am seeing? I can not find out what the inductance should be as to insure if i replace it, what i should use, if you agree?

3rd Jun 2020, 2:47 pm	#21
baff1957 Triode Join Date: May 2020 Location: Monfaucon, Hautes-Pyrénées, France Posts: 14	Re: Philips FX824A Radiogram 1953 So, i am getting the message restore rather than repair? i am happy with that as long as it fits my budget but i am also now worrying about how much time it will take, any estimates on the cost to restore as it would be such a shame not to breath life back into her.

3rd Jun 2020, 3:17 pm	#22
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,286	Re: Philips FX824A Radiogram 1953 Whether to repair or restore is up to you. I don't claim to have restored any item of electronic equipment. I just put them into go working order. That includes replacing any components, failure of which could cause problems further down the line. Repair once should be the aim. I have the advantage over you in that I have a capacitor reformer so that I can easily check out electrolytic capacitors. I also have a test lamp and Variac so I can slowly wake up old equipment, being ready to switch off at the first sign of distress. It'd cost you more to purchase test equipment than it would for new capacitors. Don't forget that we don't know why the smoothing choke burned out, we're just guessing. Did you do the test described in post #13? One approach to repairing this set would be to remove the valves apart from the rectifiers and get the power supply section working first. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

7th Jun 2020, 12:58 pm	#24
baff1957 Triode Join Date: May 2020 Location: Monfaucon, Hautes-Pyrénées, France Posts: 14	Smoothing Choke Inductor Hi all, i have a smoothing choke which has become very hot and leaked some bitumen , i have removed it and tested it and it measures 447 ohm and 6.6 H Inductance. The book says it should be 320 ohms and in my experience it is unusual for resistance to increase after it has become very hot and effectively crossed windings would reduce the resistance. I really would like to replace as it could easily fail if not already. But i cant find anything with similar inductance and resistance of 320ohm. Any experience of what i could replace with as i am guessing it is used to smooth the AC. I wind chokes and transformers which are toroidal but not like this and also without perfect layering i am sure i would find it difficult to achieve the same values although i have all the correct materials. Any thoughts please. Thank You

7th Jun 2020, 1:17 pm	#25
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Smoothing Choke Inductor You ask "any thoughts": here are some. When you measured 447 Ohms, was this measurement made when the choke was hot? If so, let it cool down to room temperature and measure its resistance again. Any resistance will increase its value as its temperature rises - especially in a choke, where the heat generated has a difficult path to escape to the surrounding air. The choke may have overheated due to it passing excessive current due a fault in the items that are drawing the current through the choke. If so, that cause needs to be discovered first and eliminated prior to replacing that choke - a replacement choke might actually not be needed. A perfect choke has zero resistance, so any replacement choke that has a resistance less than 320 Ohms should be suitable, provided that its inductance is of an appropriate value. You state that its inductance value was measured as 6.6 H. A suitable replacement value will probably be in the range 6 to 7 H. But you will also need to chose a choke whose direct current capacity is adequate for your application. Also of consideration is what type of choke is this? Is it a 'swinging choke' or a 'constant inductance' type? Al.

7th Jun 2020, 3:30 pm	#26
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Philips FX824A Radiogram 1953 Has it actually burned out? It's overheated, but still seems to test as a choke, unless it's leaking to the core?

9th Jun 2020, 10:39 am	#28
baff1957 Triode Join Date: May 2020 Location: Monfaucon, Hautes-Pyrénées, France Posts: 14	Re: Philips FX824A Radiogram 1953 Ok thanks a lot for your information, it is very helpful, i have taken the choke to our workshops and flash tested it at 600vac and it held up ok, i used our Wayne Kerr Bridge to get an accurate reading and it is 429.5 ohms with a 130k resistor to case. One thing is if the manual says 320 ohms and another has been fitted (but it looks original) could the increased resistance create the heat i am seeing? I can not find out what the inductance should be as to insure if i replace it, what i should use, if you agree?