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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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16th Feb 2017, 7:48 am | #1 |
Heptode
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Philips 204U
I have a European Philips 204U that I'm hoping to get going. It's been a bit mangled it seems.
I have the circuit, though . I wonder if someone can explain to me what the 56K resistor across the 2 x UCH21 and 1 x UBL21 filaments is doing. At that high a resistance it wouldn't be doing much I wouldn't have thought. The 56K R is missing in my set. These are tubes with 100ma filaments. Also there doesn't seem to be a lot of resistance in series with the filaments to cope with 220volts. The UCH21 has a 20 volt filament, the UBL21 has a 55 volt filament and the UY1N has a 50 volt filament. The circuit shows UY21, but there is a UY1N in the radio. The circuit also shows a neon indicator lamp. In my set the neon is missing and a regular dial lamp has been substituted Thanks Peter |
16th Feb 2017, 9:10 am | #2 |
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Re: Philips 204U
Its a bit difficult to work out the mains voltage selector but if all 3 of the resistors 620, 55, & 180 ohms are in series with all the valve heaters at the 220v setting, its about right.
The lamp is obviously wrong, its shunting the main dropper resistor and the rectifier heater leg. Leave it out for now. But note that this is for 200/220v mains, will yours overrun it? Run it up on a lamp limiter would be a good idea! The 56k would seem rather pointless, it is Philips after all! I would be surprised if the rectifier should be a UY21 as that has a B8G not octal base. Last edited by Boater Sam; 16th Feb 2017 at 9:17 am. Reason: added |
16th Feb 2017, 9:20 am | #3 |
Heptode
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Re: Philips 204U
Thanks. I can run the radio from a 220 volt supply.
My attached circuit obscured the details somewhat. I attach a clearer one. |
16th Feb 2017, 9:42 am | #4 |
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Re: Philips 204U
So all the valves are B8G base except the rectifier? Was it built that way or has it been changed? The UY21 may have been unobtainable, UY1N is fine, has a higher rating, same heater volts @100mA. 60uf maximum reservoir capacitor.
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16th Feb 2017, 10:08 am | #5 |
Dekatron
Join Date: Apr 2011
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Re: Philips 204U
I think the 56k resistor across the series heater chain is to keep the neon lit in the event of a series heater chain failure.
Lawrence. |
16th Feb 2017, 10:34 am | #6 |
Heptode
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Re: Philips 204U
Looks like the rectifier socket has been changed to an octal. The rest are local.
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16th Feb 2017, 11:44 am | #7 |
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Re: Philips 204U
The circuit available on this site from the banner at the top of this page makes the mains voltage selection on this set much easier to understand.
The first picture is a snip from the power supply as printed in the circuit with a table in the bottom right hand corner to indicate the connections for different mains voltages. R38 should be shorted out when using the set on the mains voltages indicated in brackets. The second picture shows the set wired for 125volts (or 110volts) and the last picture for 220volts (or 200volts). Lawrence is generally spot on in matters concerning circuits but on this occasion I must disagree with him. On the higher mains voltages the voltage dropped across R40 and the rectifier heater when in series with 56k ohms will be to low to light the neon. On the lower mains voltages the 56k is not in the same circuit as the neon. However I must say I have no idea what the 56k (R37) is actually doing in this set. |
16th Feb 2017, 12:18 pm | #8 | |
Dekatron
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Re: Philips 204U
Quote:
Lawrence. |
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16th Feb 2017, 12:52 pm | #9 |
Pentode
Join Date: Oct 2016
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Re: Philips 204U
The current in heaters of the three valves E1, E2 & E3 when connected for 220 V will be the sum of the current flow through heater of the rectifier valve E4 and the neon circuit. My guess is that the current (about 1.7 mA) through the 56 kΩ resistor R37 is designed to be about equal to the current through the 27 kΩ resistor R41 in series with the neon so that theoretically all the heaters run at the same current. If this is the case, there is no need for the 56 kΩ resistor R37 if there is no neon fitted.
I agree that the 56 kΩ resistor does not seem to be doing much other than perhaps not giving the valve manufacturer an excuse to not honour the warranty. This may be a moot point if the valves in your set are already out of warranty. |
16th Feb 2017, 12:58 pm | #10 |
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Re: Philips 204U
The neon did occur to me too but I had difficulty in working out how it would get enough voltage to strike on 110v, maybe it will. But why keep the neon lit if the heater chain is open circuit?
They are an unusual set of valves, but its Philips. |
16th Feb 2017, 1:15 pm | #11 |
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Re: Philips 204U
Customer notification if the set is still plugged in and switched on.
Lawrence. |
16th Feb 2017, 1:35 pm | #12 |
Triode
Join Date: May 2006
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Re: Philips 204U
Hi Peter
The 204U was produced at different radio works/countries and there are quite some differencies between the models - some had two, some three wave bands. Different line voltages could have been selected at the time of purchase. So - to get you a correct (not generic) schematic, you will have to find out, who/where your radios was made and for what country the radio was built. Best help for that will be the dial scale markings in the parts not visible in mounted situation. So - let us see pictures. Regards, Walter |
16th Feb 2017, 1:42 pm | #13 |
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Re: Philips 204U
Ok, just to put some numbers on it.
For a potential divider where you have 2 resistors in series (R1 and R2) the output PD is the source PD multiplied by R2 divided by (R1 + R2). If you want to know the PD across R1 it becomes the source PD multiplied by R1 divided by (R1 + R2). The UY21 heater will have a resistance of 500 ohms when hot (50V @ 0.1A) so the PD available for the neon is developed across 500 + 620 ohms. (The 620 ohms being R40). If we work (for simplicity) with a supply of 200 volts our calculation for the PD across E4 htr + R40 when the lower part of the heater chain is open circuit becomes : 200 multiplied by (500 + 620) divided by [56000 + (500 + 620)] VOLTS. = 200 x 1120 / 57120 Volts This comes out at 3.92 volts (to 2 decimal places), far too low to light the neon. The above only applies at the instant the bottom half of the heater chain goes open circuit and the rectifier heater is still hot. The voltage will be even less when the rectifier heater cools. Last edited by ukcol; 16th Feb 2017 at 1:49 pm. |
16th Feb 2017, 2:19 pm | #14 |
Dekatron
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Re: Philips 204U
Yes, I see what you mean now Colin, maybe the draughtsman had a bad day.
EDIT: Maybe not, it's shown in the chassis layout in the manual. Lawrence. Last edited by ms660; 16th Feb 2017 at 2:29 pm. |
16th Feb 2017, 5:18 pm | #15 |
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Re: Philips 204U
Hi Lawrence
Perhaps the idea of the 56k was as suggested by Neutrino in post #9 and then the design team realized that a heater current imbalance of 1.7% was insignificant and the 56k was not needed? As I've said before I can't think what other function that 56k could fulfil. |
16th Feb 2017, 5:23 pm | #16 |
Dekatron
Join Date: Apr 2011
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Re: Philips 204U
I don't know Colin, it's one of those mysteries so far.
Lawrence. |
16th Feb 2017, 11:27 pm | #17 |
Heptode
Join Date: Jan 2007
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Re: Philips 204U
Hi all,
I'm very impressed and grateful for all the detailed replies. Many thanks. Walter, My radio came from a seller in Bulgaria. I attach a scan of the dial glass. Perhaps this will be diagnostic. P |
18th Feb 2017, 4:30 am | #18 |
Heptode
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Re: Philips 204U
I've just realised that there is a detailed write up on this radio in issue 54 of The Radiophile.
Peter |
18th Feb 2017, 5:32 am | #19 | |
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Re: Philips 204U
Quote:
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18th Feb 2017, 6:45 am | #20 |
Heptode
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Re: Philips 204U
Mine is a 204U-37
NR E 89598E03 P Last edited by petervk2mlg; 18th Feb 2017 at 6:53 am. |