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Old 22nd Dec 2016, 11:02 am   #1
indigo.girl
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Default My first valve radio project - Philips 462A

Hello everyone,
Well, I've been tinkering around with transistor radiograms on here for a while now but now its time to dive into my first valve radio project. I picked up a 1947 Philips 462A radio from an auction for a couple of quid and am looking forward to restoring this beauty

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So far I have cleaned and disassembled to I can see what I've got. The case looks nice - it still has the glass panel - but is missing its philips badge and two knobs but overall is in good condition. The valves are all present and correct and none look obviously blown (AZ31, EBL21 and 2 x ECH21). I've read around the topic and have seen quite a few useful threads on the 462A. I have also read the general info on this site about restoring radios so my plan is to first replace some of the old capacitors and go from there.

My questions:
1) From my reading it seems that yellow wax caps are the most likely to go faulty so I'm planning to replace all (there are 5). There are also some black ones - should I also replace these or seeing as they 'look' ok just leave them for now.

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2) What about the caps on the top in tins? Do these need opening up and looking at or just leave for now.

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3) I will download the service data next - there are 3 available - called ERT, manufacturers and traders. Which is the best to use?

4) Mains supply is via the old two prong plug that locates into the back of the radio. I'd like to replace for a fixed mains supply and add an earth. Both wires behind the mains socket are yellow so I can't tell which is live and which is neutral. They both wire into the on/off/volume pot. Is there a way to distinguish? Where can I attach the earth?

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5) Any other obvious tests/replacements before I switch on?
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Old 22nd Dec 2016, 11:20 am   #2
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Default Re: My first valve radio project - Philips 462A

Lot's of answers possible but first the manual, not everyone on here has access to the manufacturers manual but a lot can get access to the Trader sheet(s)

First things first with valved gear, especially radios and record players, with some designs the metal chassis has the potential to become "live" and potentially very dangerous if the mains lead is incorrectly connected, tons about that on this forum including the subject of "earth"

I'll try and dig out a manual or Trader sheet for it and have a mooch.

Yes, wax type capacitors are way past their use by date these days, other types too, the capacitors in the large cans are usually of the electrolytic type and will be polarized ie: they have a +ve and -Ve connection, get that wrong and things can go pop and bang.

At this stage I wouldn't attempt to apply power to the receiver, wait for some tips and advice first but you can give it a clean out if needed making sure you don't pull any wires off or damage any components, especially the tuning gang (large egg slicer looking thing on chassis topside)

You will probably get lots of advice.

Lawrence.
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Old 22nd Dec 2016, 11:21 am   #3
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Default Re: My first valve radio project - Philips 462A

I just want to say - please be careful. If you have an isolating transformer then now is the time to put it to use. Even then, give the HT+ voltage the utmost respect. It may be present in places you don't expect, even the tuning capacitor. I don't have the service info so I can't check but you will want to get that before you dive in.

The black caps are probably Hunts branded and I don't think I've ever found one that didn't need to be replaced. They are probably worse than the yellow 'waxies'.

You may already know about the safety concerns but no harm in being told twice, as my father used to say.

You'll get plenty more advice here but I just wanted to touch on safety given that there were no other posts at the time of writing.

Good luck,

Jon.
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Old 22nd Dec 2016, 11:54 am   #4
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Default Re: My first valve radio project - Philips 462A

This is an AC only radio so will not have a live chassis, it would be an idea to get Trader Sheet 817 and read it thoroughly to get an understanding of how the radio works. It has an unusual negative feedback volume control arrangement. The yellow wax capacitors you refer to are in the tuning or RF section and should be left alone, they are unlikely to be faulty, the small capacitors inside the IF cans should also be left alone, unless there is a specific reason to suspect a faulty RF or IF capacitor they should not be touched. Even the black capacitors can be quite reliable in the lower voltage stages. capacitor C21 the output valve control grid coupling capacitor may need replacing, and the main smoothing capacitors C26 C27 need to be reformed or replaced. The radio should ideally be connected to a variac to bring the voltage up slowly.
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Old 22nd Dec 2016, 12:06 pm   #5
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Default Re: My first valve radio project - Philips 462A

Well, you don't do things by halves do you Indy?

Of all the Radios to choose you have bought a quirky Philips - a complex enough one using a reflexed circuit and 3 gang tuning. These can often challenge those hard-bitten experts.....

I have a feeling that this may turn into a Thread of record length. God speed!
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Old 22nd Dec 2016, 12:34 pm   #6
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Default Re: My first valve radio project - Philips 462A

I have a copy of the Trader sheet for the Philips 462a receiver, the good news is that it's AC mains only so it's not of the live chassis design, you can connect mains earth firmly to the chassis though as a precaution for when you are working on the receiver, but if you want to sell it on I would remove the mains earth connection for liability reasons.

A capacitor that must be replaced no matter what is the grid coupling capacitor (C21) to the audio output valve (V3) it couples the audio signal from the anode of the triode section of V2 to the control grid of V3 via R16, if this capacitor develops an electrical leak (resistance) it will put a +ve voltage on the control grid of V3, that will cause V3 to conduct heavily and can cause the audio output transformer and possibly the mains transformer to fail amongst other things....control grids don't like + voltage, they require a -Ve voltage with respect to the cathode, the -Ve voltage is called the grid bias voltage.

Some typical letters/terms used for valve electrodes etc:

k = cathode.
g1 = control grid.
g2 = screen grid.
g3 = suppressor grid.
a = anode.

The electrolytics might or might not be ok, sometimes they can be reformed if the receiver has been out of use for a long time, any sign of bulging of the can or the seal where the connection tags are would mean replacement, personally I would fit new ones anyways, other folks might have a different view.

Two ways to approach this, replace all suspect capacitors etc and hope you've connected all the components up ok and not introduced any faults or replace the bare bones minimum and trouble shoot any faults that might then develop on a case by case basis.

My method was to replace the bare bones minimum to try and get the receiver to a basic up and running situation, that can help eliminate the painful situation where you spend a pile of time and effort replacing stuff en mass only to find at fire up time that some expensive or unobtainable component starts to fail (transformers etc)

I would replace C28 as a minimum as well, needs to be rated for at least 300 volts AC working but as a temporary measure just snip one end of it out of circuit, the receiver when up and running will work without it while a replacement is sourced.

Recommendation in this instance for first power up would be to power up via a lamp limiter or variac.

Make sure the fuse in the mains plug is suitable, 3 amp fuse maximum.

This post might cross.

Lawrence.
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Old 22nd Dec 2016, 12:55 pm   #7
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Default Re: My first valve radio project - Philips 462A

I'd have a very good look at all of the wiring before applying any power and make sure the wire insulation's intact so you don't short something out. The wires insulating covering either 'melts' or cracks.

Also make a photographic note of how the two smoothing electrolytics capacitors are wired above and below chassis if you're going to replace them with anything underchassis.

These sound pretty good.

Andrew
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Old 22nd Dec 2016, 1:52 pm   #8
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Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by Edward Huggins View Post
- a complex enough one using a reflexed circuit and 3 gang tuning.
The three gang tuner only means an extra RF (radio frequency) amplifier stage, and most, if not all, the components in this stage can be left alone, the same with the IF (intermediate frequency) stage. Not sure where the reflex comes into it unless referring to the more complex audio negative feedback arrangement. It is not a TRF (tuned radio frequency) radio.

The black capacitors used in the Philips sets are very reliable, those decoupling the screen grids along with the output valve control grid coupling capacitor should be changed but the smaller ones can be left in place. The electrolytic C25 should be replaced and as mentioned the mains filter C28 disconnected.

The radio could be connected with the rectifier valve V4 removed to check the valve heaters in the other valves.
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Old 22nd Dec 2016, 2:06 pm   #9
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Default Re: My first valve radio project - Philips 462A

The three gang tuning capacitor just means band pass tuned coupling, band pass on MW & LW only so far as I can make out.

No RF amp, no reflex stage.

No problem.

Lawrence.
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Old 22nd Dec 2016, 2:13 pm   #10
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Default Re: My first valve radio project - Philips 462A

Yes it is a passive band pass coupling, confused the three gang tuner with an earlier model that has a RF amplification stage. All it needs is careful cleaning of the tuner.
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Old 22nd Dec 2016, 2:37 pm   #11
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Default Re: My first valve radio project - Philips 462A

Yes, quite a conventional design circuit wise apart from using a triode heptode valve for the IF amp and AF amp.

Grid bias via HT-ve return resistors, not that unusual either.

Lawrence.
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Old 22nd Dec 2016, 3:36 pm   #12
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Default Re: My first valve radio project - Philips 462A

Thanks guys - I'm focusing in on C21, C25, C26, C27, C28 then. Looking at the service sheet I can identify C21, C27 and C28 but I'm unclear on where C25 and C26 are and what their values might be. Rather than giving me a value it simply says 'see coils'. The coil info lists the caps but with no value or location. Whys that?
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Old 22nd Dec 2016, 3:41 pm   #13
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Default Re: My first valve radio project - Philips 462A

The circuit refs that I referred to were taken from the Trader sheet, you might be referring to the manufactures manual?

Lawrence.
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Old 22nd Dec 2016, 3:54 pm   #14
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Default Re: My first valve radio project - Philips 462A

They are different How annoying! Do I need to download the traders service sheet too? If what ways are they different?

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Old 22nd Dec 2016, 3:57 pm   #15
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Default Re: My first valve radio project - Philips 462A

C21 removal. Will replace with 330 pF. I hope this is right one based on the manufacturers service data sheet
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Old 22nd Dec 2016, 4:16 pm   #16
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Default Re: My first valve radio project - Philips 462A

Check your PM.

Lawrence.
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Old 22nd Dec 2016, 4:18 pm   #17
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Default Re: My first valve radio project - Philips 462A

It's highly unlikely that a 330pF capacitor will need replacing and it certainly isn't the grid coupling capacitor.

Confusion has arisen because the two service sheets being used have different component designations. This is hardly surprising, as component designations are largely arbitrary.

As far as the manufacturer's sheet goes, the cap you need to replace is C31.
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Old 22nd Dec 2016, 4:19 pm   #18
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Default Re: My first valve radio project - Philips 462A

Great Choice ! and I've always had a soft spot for it, as our family owned not one, bit two of these - one of which I 'dismantled' aged around 9 or 10 ( oops )
I always called this the set with 2 frequency changers due to the unusual use of the 2nd ECH21 as the IF amp and audio gain stage.
You'll find it sounds really good, due to Philips usual careful use of 'contouring' the audio output stage to the speaker and cabinet.

I hope that the mains transformer is OK. May be worth running this up gently with no valves in to see if the scale lamps come on. As mentioned above some of the Philips wiring is in rubber coated stuff and is either fine, or very crumbly. If the latter, it will of course need replacing.
I replaced only the 245 V wiring to the voltage selector and removed the rest, otherwise it can take forever. That said, a lot of it is in plastic coated wire, so clearly they were in a changeover period when these sets were made.

As to the black 'pitch' capacitors - I often find they are OK. Not so the Dubilier or TCC 'waxies' which are probably leaky.
Only change one at a time of you do. The vertical stacking of the tagboards under the chassis can encourage wiring errors and makes some very difficult to get to.

Replace those 2 single wet electrolytics that are screw mounted to the chassis whatever happens. They will be beyond salvage. The website 'askjanfirst ( www.die-wuestens.de/eindex.htm ) sells single and double replacements of the same mounting type in a slightly smaller can. All that needs to be done is a slight enlargement of the mounting holes. Ensure that C2 ( philips schem. )is isolated from the chassis as before ( reuse the original washer and tag )

The output transformer on these sets is often found to be a 'Radiospares' replacement. If it's cooked ( open primary ) they can be a bit of a pain to source - the primary is part of the HT smoothing circuit. Worst case, something from another set or a 'generic' new component will usually suffice.

For a safer mains connection, I usually replace the flex with a 3A 3 core one. If you strip the insulation back a few extra inches and then shorten the L/N conductors before wiring into the rear chassis plug, its possible to get the plug's cable grip around the outside of the cable for safety and then apply heat shrink or a hellerman sleeve to the end whilst doubling back the earth conductor. This can then be passed though the back cover and soldered to a tag, which can then be bolted to the chassis ( add a star washer first also ). This gives the ability to remove the back a short distance ( thus removing the power ) for future service whilst maintaining the earth connection.

These are really attractive sets in my view - Hopefully your dial has most of its print left ?
In a darkened room the edge lit glass dial looks really classy

GOOD LUCK

A

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Old 22nd Dec 2016, 5:18 pm   #19
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Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by Station X View Post
It's highly unlikely that a 330pF capacitor will need replacing and it certainly isn't the grid coupling capacitor.

Confusion has arisen because the two service sheets being used have different component designations. This is hardly surprising, as component designations are largely arbitrary.

As far as the manufacturer's sheet goes, the cap you need to replace is C31.
Oh dear - I have been using the manufactures datasheet but the capacitor numbers mentioned above have been from the traders service sheet. This means I've now removed 4 capacitors in error.

I have accidentally removed the C21 (330pF) which is actually C11 on the traders sheet (the osc circ ME fixed tracker). I have also accidentally unsoldered 3 yellow wax DUBILIERS from a tag strip. These were C27, C16 and C29 from the manufacturers datasheet but actually C14, C6, C17 respectively on the traders sheet

Never mind - all good practice and I think I'll just replace them now with new ones now they are out
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Old 22nd Dec 2016, 5:52 pm   #20
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Default Re: My first valve radio project - Philips 462A

In some circumstances it can help to find components by looking at the schematic and tracing back from the valve socket pin number(s)

Here's a link to the most popular site for valve pin connections and valve data:

http://www.r-type.org/inx/main-inx.htm

In the first box is the 1st number or letter of the valves you might be interested in, click on then scroll down for a picture and full name/number of the valve then click on that for the pin connections/data etc.

If not found there then try this site, also excellent:

http://www.shinjo.info/frank/index.html

Click on the first character printed on the valve then look for the valve by scrolling down and clicking on it's link.

Lawrence.
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