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Old 27th Dec 2016, 12:29 pm   #81
indigo.girl
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Default Re: My first valve radio project - Philips 462A

Well, the rectifier heaters light up but very faintly compared to the other valves in the set. The voltage across the heater is only 2V rather than the expected 4V. The continuity of the heater is OK with resistance just 2 OHMS. So, apart from the voltage across the heater being a bit low the rest seem ok.
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Old 27th Dec 2016, 12:31 pm   #82
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Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by crackle View Post
Is the transformer hot or cool after an hour of being on with no valve heater load?
Hi Mike - I was too impatient to wait a full hour but after a while, say 30 mins, the transformer was mildly warm, certainly not hot to touch, but not 'cold as metal either'. I have it on again now with no load to test properly if needed.
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Old 27th Dec 2016, 12:40 pm   #83
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Default Re: My first valve radio project - Philips 462A

If you remove the rectifier valve from the valve holder and then measure the heater connections in the valve holder what what is the A.C. voltage.

As it won't have the superimposed rectified DC voltage it should measure the 4 Volts A.C.

Though EXTREME caution is need if this is carried out as the transformer anode connections will be at the peak high tension secondary voltage of over 300 Volt A.C.

It could be that the rectifier valve has a partial short circuit.

It might be useful if you took a few pictures of the work you have carried out, what type of capacitors where fitted as the main smoother and reservoir.

With all valves removed the heater voltage to the other valve holders and pilot bulbs should be 6.3 Volts A.C.
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Old 27th Dec 2016, 12:48 pm   #84
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Default Re: My first valve radio project - Philips 462A

Also with the rectifier fitted measure the DC voltage across C26 that should be consistent with the rectifier symptoms already observed...Just to get the whole picture.

Lawrence.
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Old 27th Dec 2016, 1:40 pm   #85
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Default Re: My first valve radio project - Philips 462A

With all the valves removed I can measure 2-3V AC across the base for pins 2 & 8 of AZ31 (for rectifier heater) and 5 VAC across the bases for pins 1 & 8 for all the other valves. There is also 5VAC across the pilot bulbs.

There is no voltage measurable across C26.

Here are come photos of my work so far: please excuse the colour of the green & yellow wire coverings that I have used to insulate the bare legs of the capacitors. All I had available...
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Old 27th Dec 2016, 1:41 pm   #86
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Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by indigo.girl View Post
Quote:
Originally Posted by crackle View Post
Is the transformer hot or cool after an hour of being on with no valve heater load?
Hi Mike - I was too impatient to wait a full hour but after a while, say 30 mins, the transformer was mildly warm, certainly not hot to touch, but not 'cold as metal either'. I have it on again now with no load to test properly if needed.
Now been on 1 hour+ . Transformer is warm to touch but not hot. All seems ok.
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Old 27th Dec 2016, 1:48 pm   #87
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Default Re: My first valve radio project - Philips 462A

This radio has complex voltage selector arrangements for the mains transformer primary. Is the selector "disc" correctly to make the appropriate connections for your mains voltage?
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Old 27th Dec 2016, 1:59 pm   #88
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Default Re: My first valve radio project - Philips 462A

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This radio has complex voltage selector arrangements for the mains transformer primary. Is the selector "disc" correctly to make the appropriate connections for your mains voltage?
Hi Graham - As far as I know yes.
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Old 27th Dec 2016, 2:18 pm   #89
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Default Re: My first valve radio project - Philips 462A

I agree that the disc is correctly placed for a 245V supply. I was just wondering whether the wire links within the disc itself were correctly placed.

WITH THE VALVES OUT, you could check the heater voltages with the disc set to 220V and 200V to see if they are higher.
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Old 27th Dec 2016, 2:32 pm   #90
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Default Re: My first valve radio project - Philips 462A

For the low range pF capacitors (usually 3pF to 3000pF range), if you have to replace them, such as ones that get damaged ,fail, or removed by mistake, these are always better replaced with 500V silver mica types. These usually have a dark brown look. The better quality ones are the American mil spec types, if you use these you will never have any trouble again, especially in a domestic tube radio where the voltages are generally nowhere near 500v. Here is a typical one on UK ebay:

http://www.ebay.co.uk/itm/CAP-SILVER...wAAOxyaTxTPxin

There are some cheaper 330pF Sangamo ones that are also good on ebay. Last time I looked RS components also stocked a range of 500V silver mica caps which are very good. (any capacitors on the mains power side of the transformer need special ratings like X2 types)

Don't be upset with the occasional mistake along the radio restoration trail, by the time you have restored a few radios you will have mastered the art.

I would be cautious with the 330V electrolytics, since when the set hasn't warmed up the voltage could easily go to 300v x 1.4 , so 450V electrolytics might be better, but if the peak voltage is only 300V its probably ok.

Last edited by Argus25; 27th Dec 2016 at 2:47 pm.
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Old 27th Dec 2016, 2:34 pm   #91
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Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by Station X View Post
I agree that the disc is correctly placed for a 245V supply. I was just wondering whether the wire links within the disc itself were correctly placed.

WITH THE VALVES OUT, you could check the heater voltages with the disc set to 220V and 200V to see if they are higher.
Well here's an interesting result!

At 245V I get 2-3V AC and 5 VAC across the heaters of AZ31 and EBL21

At 220V I get 3V AC and 6 VAC

At 200V I get 3-4 VAC and 6 VAC which matches the valve specs

So I do seem to get a higher transformer output when a lower voltage is supplied

I moved the disc to 145V and something made a vibrating/humming noise so I pulled it straight out (same for 125V and 110V)

With the 200V disc setting giving me valve spec values I checked for HT output from the EBL21 anode (pin 2 to chassis) but ZERO HT DC voltage :-(. The valves are illuminating nicely at this 200V setting - in all cases though the rectifier is much less bright than the other (I guess to be expected because heaters are only powered by 4 not 6 V AC.)
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Old 27th Dec 2016, 2:51 pm   #92
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Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by Argus25 View Post
I would be cautious with the 330V electrolytics, since when the set hasn't warmed up the voltage could easily go to 300v x 1.4 , so 450V electrolytics might be better, but if the peak voltage is only 300V its probably ok.
Yes, I thought the 330V max working voltage of the electrolytics sounded low compared to the advice on this thread of always going for a 630V for all caps to be sure. The 330V electrolytic was the spec used previously and on the trader service data. Were higher voltage caps more difficult to obtain back in the 70s?
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Old 27th Dec 2016, 2:51 pm   #93
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Default Re: My first valve radio project - Philips 462A

The radio might have looked better if you had just put the smoothing and reservoir capacitors underneath the radio, and saved a lot of work.

From the experiments with the voltage tap it could be there is a 'shorted turn' in the primary of the mains transformer and putting the tap on 200V is boosting the winding as 240Volts is being applied to the 200 Volts setting, but if this is the case then it is not a good condition for the transformer to operate at.

The lower tapping settings definitely should not be used, the vibration is because of severe overload.
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Old 27th Dec 2016, 3:04 pm   #94
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Default Re: My first valve radio project - Philips 462A

Ah, I see - in all cases 240V is being applied to the transformer each time (being the UK supply from the mains) and the disc position denotes the ideal place for the supply voltage to be added across the transformer depending on the mains supply you have. This should normally be the 245V position for UK. When I move the dial to the 200V setting 240V is still being applied across the transformer windings but across fewer of them, and perhaps bypassing a shorted turn, hence a better output. In the case when I set the dial to 145V this means I am putting the 240V across an even smaller section of the windings and hence over load and vibration.
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Old 27th Dec 2016, 3:07 pm   #95
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Default Re: My first valve radio project - Philips 462A

Assuming that everything we've been told is true, I think we're reaching the inevitable conclusion that the mains transformer is faulty.

You could try selecting the 220V setting, inserting the rectifier, checking the on load heater voltage on the rectifier and if OK checking the HT voltage across the smoothers.

This isn't a long term solution though.
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Old 27th Dec 2016, 3:23 pm   #96
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Default Re: My first valve radio project - Philips 462A

Hi Graham - at 220V setting I still get no HT voltage measureable across the smoother capacitor C26. I'm measuring across the two tails of the C26 itself or from pin2 of AZ31 to chassis. So does this mean that I have a faulty mains transformer AND a faulty rectifier?

(I get 310 VAC from either anode to chassis - pins 4 or 6 to chassis on AZ31)

Last edited by indigo.girl; 27th Dec 2016 at 3:37 pm.
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Old 27th Dec 2016, 3:24 pm   #97
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Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by indigo.girl View Post
Well, the rectifier heaters light up but very faintly compared to the other valves in the set. The voltage across the heater is only 2V rather than the expected 4V. The continuity of the heater is OK with resistance just 2 OHMS. So, apart from the voltage across the heater being a bit low the rest seem ok.
Quote:
Originally Posted by indigo.girl View Post
With the 200V disc setting giving me valve spec values I checked for HT output from the EBL21 anode (pin 2 to chassis) but ZERO HT DC voltage :-(. The valves are illuminating nicely at this 200V setting - in all cases though the rectifier is much less bright than the other (I guess to be expected because heaters are only powered by 4 not 6 V AC.)
Should be pointed out that the rectifier valve is meant to operate from the separate isolated 4 Volt winding so will light with the same level of brightness at 4 Volts as the other Valves at 6.3 Volts.

With the rectifier removed there will be no D.C. high tension voltage with the 4 Volts A.C. voltage that is there to light the rectifier heater.
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Old 27th Dec 2016, 3:39 pm   #98
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Default Re: My first valve radio project - Philips 462A

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So no DC voltage from chassis to pin 7 of the rectifier?
Which pin on the rectifier?

I get measure 345V on DC settings on my mulitmeter between the anode pin 4 and chassis (same as anode pin 6 and chassis). I get 310V on AC setting on multimeter.
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Old 27th Dec 2016, 3:43 pm   #99
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Default Re: My first valve radio project - Philips 462A

Sorry. I meant chassis to pin 2 or 8 of the rectifier.
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Old 27th Dec 2016, 3:50 pm   #100
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Default Re: My first valve radio project - Philips 462A

If still no HT, check that R2 and R3 (manufacturers sheet) aren't open circuit.
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