Philips 272 power supply rebuild - UK Vintage Radio Repair and Restoration Discussion Forum

ColinB · 29th Oct 2010, 7:37 pm

Hi,

I've been meaning to start on this set for a while now, the valve lineup is FC13C, VP13C, TDD13C, PEN36C and UR1C.

I guestimate HT consumption to be around 75mA, from the trader sheet.

Thus far I've found out that the rectifier gives no output (heater OK, AC on anode, no DC on cathode). Also the filter caps are dry, and the choke is O/C - otherwise, it's in good shape

My plan is (Maplins to the rescue!) to use two 1N4007s in series, followed by a 47uF cap, a 10w 470R resistor and another 47uf cap to rebuild the HT supply. Does this sound reasonable?

I'd be tempted to bridge rectify the AC, but there doesn't really seem much point over half wave.

Any thoughts?

Cheers,

Colin

vinrads · 29th Oct 2010, 9:39 pm

Don't do it fit the propper valve rectifier every time ,these are not to difficult to find .

G8UWM-MildMartin · 30th Oct 2010, 2:56 am

The UR1C = CY1C and a CY2C would also do, or even a UY85 with 380-ohm (say 390R) heater shunt and base adaptor if you're going with valves, as the barretter will keep the heater current OK over that range.

1 1N4007 would be sufficient.
With the existing 250-ohm surge limiter, though I suspect you'd need nearer 1K rather than 470R instead of the choke.
(Rough calcs: Rectified AC on 1st cap. 300V, expected HT around 200V, 75mA through 1K gives 225V ignoring the ripple left after the 1st cap. Near enough to start with.)
Martin.

ColinB · 30th Oct 2010, 9:14 am

Hi Martin,

Thanks, I did wonder if the R value was a bit low. As luck would have it, I did buy two high wattage 470R resistors, so will use both in series between the caps.

I only mentioned the two diodes as a 'just in case', they just look smaller than I would have expected them to.

Eventually the diodes may get replaced with a valve again, but for now I'd like to get the rest of the set up and running fairly cheaply - the valve would be preferable to give the HT line a slower start, however.

Thanks again,

Colin

Tony1951 · 30th Oct 2010, 2:55 pm

I did this sort of mod to help out a very tired AZ31 on my Philips 371a, only I used a 180ohm resistor. It worked, except the voltage was quite high, HT of 304v as against the designed value of 270v. The radio seemed happy enough, but I took the advice of forum members and cut the thing out again. The radio is now running happily enough on a rather low HT supply around 220v, about 50v less than Philips expected.

I could have used a higher wattage resistor and got to the correct level I suppose, but the thing works anyway, so why worry. Obviously, you are not in the same situation.

ColinB · 30th Oct 2010, 4:24 pm

Well, its done

I went for two 470s in series in the end, and have 220v HT at the filter output. In the end the CY1C wasn't faulty, but it's 130R surge limiter was O/C. I can only think that when I thought I had AC on the anode, I had measured one or other of the heater pins which goes to AC line as well...

I must be getting old, it simply won't do...!

I've got life on SW, and one faint station on MW, so I think it's time to recap the set, and (hopefully) listen to it improve as I go then do the drive cord...

Cheers,

Colin

29th Oct 2010, 7:37 pm	#1
ColinB Heptode Join Date: Apr 2003 Location: Newton Abbot, Devon, UK. Posts: 761	Philips 272 power supply rebuild Hi, I've been meaning to start on this set for a while now, the valve lineup is FC13C, VP13C, TDD13C, PEN36C and UR1C. I guestimate HT consumption to be around 75mA, from the trader sheet. Thus far I've found out that the rectifier gives no output (heater OK, AC on anode, no DC on cathode). Also the filter caps are dry, and the choke is O/C - otherwise, it's in good shape My plan is (Maplins to the rescue!) to use two 1N4007s in series, followed by a 47uF cap, a 10w 470R resistor and another 47uf cap to rebuild the HT supply. Does this sound reasonable? I'd be tempted to bridge rectify the AC, but there doesn't really seem much point over half wave. Any thoughts? Cheers, Colin

29th Oct 2010, 9:39 pm	#2
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,766	Re: Philips 272 power supply rebuild Don't do it fit the propper valve rectifier every time ,these are not to difficult to find .

30th Oct 2010, 2:56 am	#3
G8UWM-MildMartin Heptode Join Date: Jan 2004 Location: Stockport, Greater Manchester, UK. Posts: 827	Re: Philips 272 power supply rebuild The UR1C = CY1C and a CY2C would also do, or even a UY85 with 380-ohm (say 390R) heater shunt and base adaptor if you're going with valves, as the barretter will keep the heater current OK over that range. 1 1N4007 would be sufficient. With the existing 250-ohm surge limiter, though I suspect you'd need nearer 1K rather than 470R instead of the choke. (Rough calcs: Rectified AC on 1st cap. 300V, expected HT around 200V, 75mA through 1K gives 225V ignoring the ripple left after the 1st cap. Near enough to start with.) Martin.

30th Oct 2010, 9:14 am	#4
ColinB Heptode Join Date: Apr 2003 Location: Newton Abbot, Devon, UK. Posts: 761	Re: Philips 272 power supply rebuild Hi Martin, Thanks, I did wonder if the R value was a bit low. As luck would have it, I did buy two high wattage 470R resistors, so will use both in series between the caps. I only mentioned the two diodes as a 'just in case', they just look smaller than I would have expected them to. Eventually the diodes may get replaced with a valve again, but for now I'd like to get the rest of the set up and running fairly cheaply - the valve would be preferable to give the HT line a slower start, however. Thanks again, Colin

30th Oct 2010, 2:55 pm	#5
Tony1951 Tetrode Join Date: Sep 2010 Location: Tyne Valley, Northumberland Posts: 79	Re: Philips 272 power supply rebuild I did this sort of mod to help out a very tired AZ31 on my Philips 371a, only I used a 180ohm resistor. It worked, except the voltage was quite high, HT of 304v as against the designed value of 270v. The radio seemed happy enough, but I took the advice of forum members and cut the thing out again. The radio is now running happily enough on a rather low HT supply around 220v, about 50v less than Philips expected. I could have used a higher wattage resistor and got to the correct level I suppose, but the thing works anyway, so why worry. Obviously, you are not in the same situation.

30th Oct 2010, 4:24 pm	#6
ColinB Heptode Join Date: Apr 2003 Location: Newton Abbot, Devon, UK. Posts: 761	Re: Philips 272 power supply rebuild Well, its done I went for two 470s in series in the end, and have 220v HT at the filter output. In the end the CY1C wasn't faulty, but it's 130R surge limiter was O/C. I can only think that when I thought I had AC on the anode, I had measured one or other of the heater pins which goes to AC line as well... I must be getting old, it simply won't do...! I've got life on SW, and one faint station on MW, so I think it's time to recap the set, and (hopefully) listen to it improve as I go then do the drive cord... Cheers, Colin