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Old 17th Sep 2019, 2:03 pm   #1
cdm1christopher
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Smile Philips BX281U20 valve radio

Well I picked this up today for 7 not sure if bargain or not.
It's all there including original carry case plus the glass tuning scales although quite rubbed off. Suppose if you could get a good photo of original print you could copy and apply to glass.
I don't think it's been switched on for a long time so not sure if to put it on variac see what happens.
Actual case is very clean no damage and original cloth in nice condition as well. Dials all okay mounted on the side. It looks like it sat in the case could be wrong.

Date wise I think it was pre or in between WW2. As it cost 135 guilder. Just a thought.

Switchable mains to 110v or 220v although think you need to change a resistor. Two pin plug so I would assume it's chasis live when on?

Managed to get manual although in Dutch so expect it was made for that Market.

All valves intact look in good condition visibly but got taylor 47a tester so could shove them on there.

Anyhow my question is is it a worthwhile restoration project? Not found any info on here so I thought I would pose the question in case someone has restored one of these.

Any help very appreciated.

Posted couple pics.

Cheers
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Old 17th Sep 2019, 3:47 pm   #2
HamishBoxer
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Default Re: Philips BX281U20 valve radio

Would not hesitate if it is complete to restore.
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Old 17th Sep 2019, 4:45 pm   #3
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Default Re: Philips BX281U20 valve radio

Hi,Ben Dijkman does repro dials for these but looking at the glass it seems to be a different shape to yours.Link included.
Regards John.
https://www.bendijkman.nl/philips-bx281u-dial?ipath=9
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Old 17th Sep 2019, 8:31 pm   #4
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Default Re: Philips BX281U20 valve radio

If you read Post #5 on this thread David gives a good summary of how to do repro dial glasses. https://www.vintage-radio.net/forum/...d.php?t=100121 I have done a reasonable job on a Philips 170A glass. The key is to first get a really good high definition jpg of the BX281U glass (without the pointer behind it!). Then reverse the image, resize it as necessary and print onto transparent waterslide paper. After the ink has dried spray with clear lacquer so the ink doesn't run when you wet the transfer for application to the glass. The problem you are going to face is that unlike the 170A, on the BX281U the font is white font on clear background so although you should be able to invert the font and background colours most printers cannot print white so you might have to use pale green or pale yellow. Then when backlit the font becomes rather anaemic looking. If you try this out then post some images as we could all learn from this. Cheers, Jerry
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Old 18th Sep 2019, 11:37 am   #5
cdm1christopher
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Default Re: Philips BX281U20 valve radio

Thanks guys.
Yes it complete and internally in pretty good condition no leaky caps, overheating signs and all wiring intact and not brittle. Theres also a small transformer which I did not think this model came with unless read literature wrong!

Only thing puzzled me is someone has added an additional wax 0.1uf cap to aerial input!! There's already 2 which is the original spec!!! Maybe caps playing up then added another to get capacitance up don't know.
Not tested it yet got some flex coming today so will re wire and wind here up on the variac.
I have two sheets of glass but the one with the link is spot on with one I have A3219.01 BX281. The other does have a code but all rubbed off plus glass is slightly thicker. The actual glass case it has is sized for one piece of glass so the other may have come off another radio. I'll try and take a better photo of it. Mind you 25 euro seems pretty good price to me. Plus new sheet of glass. Background print is kinda yellow not white.

Now the end suffex on model number there seems there where a few like 0 or 06 etc. the one I have ends in 20. Any ideas on that?
Plus I have not seen any with a case or a case even mentioned and what limited info I have read says it's not portable! Well this would have been.

But if you guys think it's worth the effort of restoration then I'll go ahead.
Think just replace caps all resistors look fine there's one very large power fixed resistors with three separate ohm readings on the windings according to spec sheet which is in Dutch I think ha be fun. Another looks like it has an insulation cloth wrapped round internally not seen that before.

I'll get some pics taken. I also picked up a Murphy a262 so another project. Still keeps me busy as due to I'll health don't get out much.

Although compact there is quite a bit of kit in there.

Thanks again guys.
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Old 18th Sep 2019, 12:29 pm   #6
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Default Re: Philips BX281U20 valve radio

Looks like one I had and as it was made for 220v, I had to increase the value of the mains dropper to cope with our mains of over 240v. Watch that back cover if it’s metal, I think there are some poor srbp standoffs that isolate it from chassis. I always used rcd protection.

Well worth restoring.

Ken
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Old 18th Sep 2019, 1:52 pm   #7
Herald1360
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Default Re: Philips BX281U20 valve radio

Cunning use of valve types to get a full superhet down to four valves including rectifier.

The -20 suffix may relate to the target market. ISTR -15 was UK.


Maybe that transformer is to provide 220V or buck the 240 to 220?
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Old 18th Sep 2019, 3:01 pm   #8
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Default Re: Philips BX281U20 valve radio

Pic attached, the dropper is attached to the transformer at the back of that silver screen plate. Which is connected to mains switch set at 220v. So should not need to change that.
Yes its metal back with looks like stand offs on chassis but their metal.
Not sure if it's me but does that look like an additional octal base attached on top of another where the uy1n valve sits to the far right was absolute nightmare to pull the valve out seemed stuck. Looks fine underneath.
Pic of aerial connection with additional capacitor.
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Old 18th Sep 2019, 3:38 pm   #9
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Default Re: Philips BX281U20 valve radio

Please be careful, I doubt the standoffs are metal and why do you think it will be ok at 240v plus when it clearly says 220v on the selector ? Over running to that extent will stress the valves and probably other things too. Do you think it has a mains transformer as well as an output transformer ? If no mains transformer, it is virtually certain to have a live chassis. Finally, I believe the aerial coupling cap needs to be replaced with a class X (?) rated component as it’s safety critical.

Ken
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Old 18th Sep 2019, 4:55 pm   #10
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Default Re: Philips BX281U20 valve radio

I don't think it will be okay but it was obviously used at that rating and there does not seem to be any evidence of overheating. That's all I have to go on.
Not sure about the aerial business as that's all new to me not come across caps straight on to the aerial connector. I've also noticed that I think there should be an additional wire from aerial going to ground as the picture posted if you look far left towards far back a wire is missing on that screw terminal. On other sets I've looked at there seems to be 3 wires but only two caps. This has 3? One of which the wax has positive terminal as it has two red rings located on cap one end I'm assuming or it means something else. Again not come across this type wax capacitor before usually marked +/- or electrolytic written on it.
Why a snubber here on aerial is it connected to mains or on/off switch again not had chassis out. Odd there is no ground socket for aerial which is what I have so far come across not just one input.
Sorry your right looks like rusty metal but their bakerlite standoffs. Like say I need to pull it out and have a proper look.
I do have service manual but it's in dutch which is not very helpful.
I was going to plug her in the variac but I think I'll have a good look round first.

This unit seems to be more complicated than I first realised.

Still like say if anyone has restored one then pointers in the direction of the aerial would be most helpful and this business of 220v sw0itch but 240v input from mains. Is that green dropper there for that to bring down voltage rating again just plucking things out of the air.
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Old 18th Sep 2019, 5:34 pm   #11
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Default Re: Philips BX281U20 valve radio

According to the schematic/manual there should be a connection from the rear of the antenna socket to the receivers internal plate antenna, it might be a spring connection.

The three capacitors....there were two originally (the black ones) the end of one of those black capacitors is connected to the antenna socket, the other end of that capacitor would have originally connected to the grey wire which is the feed wire to the RF transformers primary coils, the wax capacitor is just a bodged in replacement for that black one.

The other black capacitor is/should be connected between the metal rear cover and the receivers chassis.

The wax capacitor is not polarized, it has no positive and negative the two red bands usually mean AC rated and the capacitors lead out wire nearest the bands would normally be the capacitors outer foil connection if there's no black band.

The mains voltage selector is marked for either a 220v or 125v mains input voltage setting, that can be shifted down to 200v or 110v by bypassing the 75 ohm section (R37) on the mains dropper.

Replace that wax capacitor and the other black one that's in circuit with suitable Y Class types for safety reasons....this receiver is a live chassis design.

The heater circuit when the voltage selector is set to 220v is a single series circuit, when the voltage selector is set to 125v the heater circuit is two series circuits connected in parallel.

The component marked L1 on the schematic is the scale bulb.

Other must replace capacitors for starters are C83, C85, and C110.

Lawrence.

Last edited by ms660; 18th Sep 2019 at 5:59 pm. Reason: Additional info
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Old 18th Sep 2019, 6:37 pm   #12
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Default Re: Philips BX281U20 valve radio

A heads-up - I came across one of these many years ago and it caused me much confusion. I seem to remember that it had two frequency changer valves (i thought 'wrong valve!) and that the signal doubles back on itself (final detector diode in the output valve, then back to the 'oscillator' section of the 2nd frequency changer which was used as a 1st AF amplifier then back to the pentode of the last valve.) (I may be wrong-was a while ago)

Anyway it was very unconventional. Had me stumped.

As has been said, it's live chassis, so the antenna/earth connections need isolated with reliable capacitors.
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Old 18th Sep 2019, 7:20 pm   #13
cdm1christopher
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Default Re: Philips BX281U20 valve radio

Wow many thanks Lawrence that all makes sense to me it did stump me that wax cap. So that ground lug at the back should have ground wire attached to it from aerial socket but is missing. Y safety cap think makes sense as x type I've only used on mains so y cap is if you have live chasis? I think I read somewhere that when you switch the voltage over it short circuits the dropper resistor so that should be automatic or have I physically got to bypass it? Well I'll have a good look round it tomorrow too tired today no ****** energy.
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Old 18th Sep 2019, 7:29 pm   #14
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Default Re: Philips BX281U20 valve radio

It should all make sense if you look at the manual, a manual is available here if you haven't already got a copy:

https://www.doctsf.com/documents/aff...6042&num_fic=1

Lawrence.
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Old 18th Sep 2019, 9:42 pm   #15
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Default Re: Philips BX281U20 valve radio

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Originally Posted by Croozer View Post
A heads-up - I came across one of these many years ago and it caused me much confusion. I seem to remember that it had two frequency changer valves (i thought 'wrong valve!) and that the signal doubles back on itself (final detector diode in the output valve, then back to the 'oscillator' section of the 2nd frequency changer which was used as a 1st AF amplifier then back to the pentode of the last valve.) (I may be wrong-was a while ago)

Anyway it was very unconventional. Had me stumped.

As has been said, it's live chassis, so the antenna/earth connections need isolated with reliable capacitors.

That's a reasonable summary of the signal path. The UCH21 is deliberately designed with separate grid connections for the triode and heptode sections (it uses the centre metal spigot to provide the extra, 9th, connection needed) so that it can be used in just this way. There's no UBF21 nor UCL21 to do the 4-valve trick in a more conventional way. Presumably the fairly high slope UBL21 was also used in conventional short superhets.
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Old 18th Sep 2019, 10:29 pm   #16
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Default Re: Philips BX281U20 valve radio

Quote:
Originally Posted by Herald1360 View Post

The UCH21 is deliberately designed with separate grid connections for the triode and heptode sections (it uses the centre metal spigot to provide the extra, 9th, connection needed) so that it can be used in just this way. There's no UBF21 nor UCL21 to do the 4-valve trick in a more conventional way. Presumably the fairly high slope UBL21 was also used in conventional short superhets.
Thanks for that Herald
Interesting to learn that the valve was designed to work like that. I had just assumed wartime component shortage and a surplus of frequency changers to use up.

Embarassingly, when the set came to me with a request to fix it, i assumed (with some insistance- " it could never have worked like that!!") someone had been there before me and had been swapping valves.

The radio was a manky set with no dial glass serving a garage. I dont remember any power supply mods re 220/240V and it had daily use.

(Afterthought - maybe the uk model had a differnt dropper?)
(I dont remember the voltage selector markings but i probably wouldnt have paid attention......)
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Old 19th Sep 2019, 1:31 am   #17
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Default Re: Philips BX281U20 valve radio

The GIRA label on the back, means it was sold in Belgium and only imported later into the UK. Execution suffix -20 likely matches that. It was probably also made in Belgium; does the serial number start with an L?

I think it's a bargain for 7 quid, especially with the travel case which I've never seen before.
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Old 19th Sep 2019, 3:19 pm   #18
cdm1christopher
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Default Re: Philips BX281U20 valve radio

the serial number starts PL if any help.
Well I managed to get the chasis out what a nightmare the tunning dial well they have riveted 3 of the pulleys to the baffle board then the side pulleys had to be unscrewed as attached to chassis with dial and dial bar. The front of the pulley has a spring attached one side but other end free not sure if it's supposed to be like that as I know nothing about their construction! Now I think the hardest part for me is actually re doing the pulley mechanism so may need someone on here to do that for me paid of course.
As you can see the underside is just packed full of components making access incredibly difficult but doable. Top of chasis quite easy thank God but I think this one is going to take some time especially cleaning. The silver foil internally needs replacing easy enough. Speaker needs a clean.
Speaker wire well two sizes one normal 28awg the other which goes to output tranny like old cloth cable must be 18 or 16 awg!!!! Bit ott if you ask me.

So I don't think loads will need replacing underside some caps maybe the odd resistor.

Not sure what base it's on but on valve base is two pieces bakerlite sandwiching metal plate directly below the valve metal locator lug Any ideas on that one again not seen that before.

Anyhow be good to see if I can getting looking spick and span.

Attached some picks for you all.
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Old 19th Sep 2019, 3:35 pm   #19
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Default Re: Philips BX281U20 valve radio

Lawrence your right about that spring clip from aerial connected to front of cabinet by the side of the foil pic attached wire was is missing.
Anybody have a NOS dropper as this one is looking a bit tired see pic. It's 3 section 75 ohm, 150 ohm and 190 ohm with 5 solder points. The three in middle are for look like ceramic ferrite beads.

Pics attached.

Cheers
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Old 19th Sep 2019, 7:32 pm   #20
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Default Re: Philips BX281U20 valve radio

Quote:
Originally Posted by cdm1christopher View Post
Well I managed to get the chasis out what a nightmare the tunning dial well they have riveted 3 of the pulleys to the baffle board then the side pulleys had to be unscrewed as attached to chassis with dial and dial bar. The front of the pulley has a spring attached one side but other end free not sure if it's supposed to be like that as I know nothing about their construction! Now I think the hardest part for me is actually re doing the pulley mechanism so may need someone on here to do that for me paid of course.
No need to remove the pulleys from the baffle board and no need to remove the cursors sliding mechanism unless it's duff, there's a clamp screw that clamps the cursors slider to the drive cord, slacken that off and the drive cord can be separated so far as I can make out, it can then be unhitched from the left and right hand pulleys allowing the chassis to be withdrawn whilst leaving the cursors slider/rod etc in place.

The diagram for the routing of the cord(s) is shown in the manual, if you look at Fig 5 you can see that they used a spring clamp (like a large Terry Clip) to keep the cord on the drum, that would have been inserted and fitted from underneath before attempting to remove or refit the chassis.

Lawrence.
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