My first valve radio project - Philips 462A

[GeoffK]

Might be best if you stopped any further work until you have read the trader sheet and become more familiar with the chassis and of basic radio operation, better knowledge would have told you that a 330pF capacitor was in the wrong place and the wrong value to be the output valve grid coupler. Not so bad that the three Dubiliers have been removed, these can be replaced with new capacitors. But the radio needs assessing first before just replacing components.

[indigo.girl]

OK - so I have now downloaded the Traders sheet and worked out which cap need replacing. From now on I'll use the TRADERS nomenclature for components.

C21 (C31 in manu) : AC coupling to V3 pentode = 22nF
The old cap was broken when I removed it


C26 & C27 : Smoothing capacitors = 47 microF / 330 V wkg / electrolytic
The smoothing caps (C26/27) are in cans - should I empty them out and put new caps inside or can they just be replaced with a new cap?

C28 (C15 in manu) : Mains RF bypass = 22nF

C25 (C3 in manu) : V1, V2, V3 bypass = 250 microF / 12V wkg / electrolytic

[indigo.girl]

Originally Posted by Hetrodyne

Might be best if you stopped any further work until you have read the trader sheet and become more familiar with the chassis and of basic radio operation, better knowledge would have told you that a 330pF capacitor was in the wrong place and the wrong value to be the output valve grid coupler. Not so bad that the three Dubiliers have been removed, these can be replaced with new capacitors. But the radio needs assessing first before just replacing components.

You are quite right. To be honest, the suggestion of the capacitors didn't seem to make much sense to me as I read the manufacturers service sheet but I didn't query it because I presumed it must be because I simply didn't understand it yet...

[ms660]

Originally Posted by indigo.girl

OK - so I have now downloaded the Traders sheet and worked out which cap need replacing. From now on I'll use the TRADERS nomenclature for components.

Yes, thems the ones, the large can electrolytics can be replaced either by empting the can if you can get into it and stuffing a new one in there and arranging suitable connections, or by removing the old cans completely and discarding then fit the replacements either chassis top side or underneath the chassis which ever suits, or disconnect the can but leave it in place for aesthetics and fit the replacement underneath the chassis or take the route posted earlier of obtaining similar replacement can electrolytics.

Modern replacement 47uF's are usually 400 or 450 volts DC rated, replacement 250uF usually come as 25 or 50 volts DC rated.

Replacing old capacitors with ones with a higher rated voltage is no problem, replacing with a lower rated voltage is, in general, a no no.

You're doing ok, keep at it.

Lawrence.

[indigo.girl]

Replacement caps ordered....will update once they have arrived

[crackle]

Hi
Can I suggest, don't remove any more components or wires until you have the replacements at hand, and then just do one at a time.

it is so easy to forget where a wire came from.

Mike

['LIVEWIRE?']

Wouldn't the modern replacement for a 250uf Capacitor be either 220 or 330uf, these being the nearest preferred values?

[indigo.girl]

I've ordered a 220uF / 16V

[GeoffK]

Originally Posted by pwdrive

Yes, thems the ones, the large can electrolytics can be replaced either by empting the can if you can get into it and stuffing a new one in there and arranging suitable connections, or by removing the old cans completely and discarding then fit the replacements either chassis top side or underneath the chassis which ever suits, or disconnect the can but leave it in place for aesthetics and fit the replacement underneath the chassis or take the route posted earlier of obtaining similar replacement can electrolytics.

In a similar set I left the original capacitor cans in place and fitted new axial types (with a lead at each end) capacitors underneath the chassis. Disconnect the live feed to the original and solder the new ones in place taking the 'chassis' side of the new capacitor to a suitable chassis connection. Use sleeving on the new capacitor leads. Make sure the electrolytic capacitors are the right way round, check twice, fit once.

Also make sure the voltage selector on the back of the radio is set to 240V, The wiring here should be checked as the rubber insulation can be crumbling and cause shorts between connections.

Again it is worth repeating, the smaller capacitors and any around the RF and IF stages are best left alone until the radio is in a working condition, then any individual ones can be looked at further, if needed.

[ms660]

Yes, that reminds me, safety first with this sort of stuff, one hand in the pocket or behind your back if probing around with power applied.

Lawrence.

[crackle]

C28 needs to be quite a high voltage as it is connected across one side of the AC supply to the rectifier, I would use a 630v 22nF polyester type.

Mike

[indigo.girl]

I've order some 22nF @ 50V wkg - sounds like this is far too low then. I'll have to get some 630V ones in too.

Should I do the same for C21 (also a 22nF cap).

[GeoffK]

C28 doesn't have to be fitted just yet, it is there to supress mains borne interference, the value isn't critical a 0.01uF can work just as well, it is important to get a main rated one. A X rated capacitor should be fitted here ( Capacitors used for these applications are categorized as X and Y rated capacitors. These capacitors are also known as EMI/RFI suppression capacitors or AC Line filter safety capacitors).

The audio coupling capacitor should be a high voltage type, a polyester 630V will be quite suitable. The modern yellow ones are the types to look out for.

[ms660]

Originally Posted by indigo.girl

I've order some 22nF @ 50V wkg - sounds like this is far too low then. I'll have to get some 630V ones in too.

Should I do the same for C21 (also a 22nF cap).

For C28 I would go for one at 1,000 volt DC working, that should be good to 350 volts AC.

For the rest and anything for future valve restorations a lot of folks including me would use 630 v DC working ones, those will cover most applications except if X Class and Y Class capacitors are required which are specials for interference suppression across the mains (X Class) and ones for interference suppression between mains and earth (Y Class) and ones to provide isolation between the chassis and any external inputs on potential live chassis stuff such as antenna, earth and pickup inputs etc, those also need to be Y Class types, no need to think about those for your present project though so far as I can tell but it's something you can Google about to understand what's what about X Class and Y Class types.

PS. Some folks use 400 v DC working capacitors, it's for you to decide but 400 volt DC working is the minimum really even if a particular circuit position doesn't demand it, it makes ordering easier and your own "stock control" simpler and reduces the chances of unknowingly fitting a low voltage one where a higher voltage one should be...such as a grid coupling or screen decoupling capacitor.

Anyways East Enders is on now gotta go.

EDIT: Whoops...Post crossed.

Lawrence.

[indigo.girl]

Hi everyone,
Not sure if I'll find anyone on here on Xmas day but just in case ....

I've replaced all the capacitors as discussed above (except C28 for now). My next task will be to construct a lamp limiter in preparation for power up. In the meantime however I have a query about the attachment of the mains supply to the radio. There are 2 pins protuding from the radio and I have a Bakelite plug with two sockets. My question is which way round to plug it in i.e. which is live and which is neutral. In the service data one pin is labelled A and the other is E. Can someone advise as to what these labels refer to.

Many thanks,
Nicola

[julie_m]

By convention, the lead that goes to the power switch should be mains live. If the switch is double-pole, it does not matter so much. You might find you get less power hum with the neutral to the outermost end of the transformer primary winding. But, it's alternating current; and everything is insulated anyway.

[indigo.girl]

Thanks Julie - both pins are wired into the on/off/volume pot. With it being AC does it not really matter which way round then?

[mole42uk]

Originally Posted by indigo.girl

My question is which way round to plug it in i.e. which is live and which is neutral. In the service data one pin is labelled A and the other is E. Can someone advise as to what these labels refer to

Alarm bells start ringing here......

A & E refer to Aerial and Earth respectively and do not relate in any way to the mains connector! The mains connector is in a different place on the chassis!

If the L & N of the mains do indeed go straight to a double-pole switch, without passing GO or collecting £200, and from there straight to the mains transformer primary, without connecting to any other component at all, then it doesn't matter which way around the L&N are connected. If any of the aforementioned conditions are not met, then it does matter and you need to seek more advice.

[julie_m]

Terminals labelled "A" and "E" are more likely to be for Aerial and Earth, than mains in, and the drawing seems to confirm this by showing them connected to soms of the radio coils. The actual mains input will be via those pins next to the voltage selector.

If both wires go through the power switch, it must be a double-pole one .....

An alternating current is going to be flowing in each direction for half the time, by definition. So one would naïvely expect it not to make any difference which way around it is connected.

The neutral of the mains is connected to Earth at the substation, and should therefore be safe to touch -- although it's supposed to be properly insulated anyway, because there are many reasons in practice why it might not be safe to touch. (There are nevertheless a few sets out there, that relied on mains neutral being near Earth potential for their safety .....)

Having the neutral on the outside of the transformer can help to shield the rest of the circuitry from 50 Hz. pickup. I had a set once, fitted with a reversible mains inlet connector, that sometimes would hum really badly, and other times would be silent ..... That took a great effort to find!

[TonyDuell]

According to the Trader Sheet (817), the mains input pins do indeed go to the double pole switch and from there to the voltage selector panel and mains transformer primary. There are no other components (such as fuses or filter capacitors) shown.

So I feel that the polarity of the mains input is unimportant.

And as others have said, the A and E sockets are for Aerial and Earth. They are sockets on the chassis, not pins, and are at the other side of the chassis to the mains input.