Hi All

I am chasing a diagram for my Philips Mod 172. This radio doesn't appear in AORSM but is shown in the July 98 issue of Radio Waves.

Is there anyone out there who has this or another source of the diagram.

The Radio is from the 1950s and Normally has a very good sound for its size. It has been my daily use radio until the problems started!

The problem that I am having with it is when tuned to a known strong station, the volume spikes and then dies off.

I know that this is probably a resistor breaking down but I cant read the bands as they have discoloured over time and some have lost their colour bands altogether.

I have done a recap of the radio in the past and found a few resistors were sus in the power supply section when I did that. Now I think the bulk of the rest need to go.

PS it copped one hellova surge before it started playing up. I have checked both transformers, Speaker, Switches, and Valve jockyed (I don't have a Valve tester) with known good valves. this didn't fix the problem and all parts were good.

Once I can work out the resistor Values I think the set will be able to be fixed up again. Then I will be able listen to the football again!

Flakes

I might be able to help you. Do you have the model with the permeability tuner rather than the conventional tuning capacitor? And is the valve lineup 6AN7, 6EH7(6BH5), 6BD7, 6M5, 6V4?

Regards

Rob

Did you change the Silver Mica caps?
Thats the sort of thing I would expect of one of them. Normally one with HT on it and possibly in the AGC.
Also check plate bypass cap on the output tube.

If the plate bypass lets go and it's plate to ground HT will also drop.

Marc

Hi Marc and Rob

Mine is the one with the permeability tuner. this is the reason I am getting it working again as it is the only set I have with this type of tuner!

I haddent replaced any of the silver Micas yet. I disconnected the AGC line by lifting one let of the resistor that feeds back to these to see if AGC was causing the problem. There is still a sudden spike in volume.

I will try replacing the Micas as I have completly replaced every other cap in the set.

P.S. I now have the diagram and have found a few resistors are out of tollerance so am in the process of changing them out (When I can get time that is)

Ok seems you now have the schematic, so good hunting in tracking the fault down. They are nice little radios those, my model 172 is a great little performer and one which my wife has claimed as "her radio" in the kitchen.

Cheers

Rob

That’s what my wife had done as well. I was only allowed to listen to the football on Saturday when it wasn’t on FTA TV and had something to do in the dining room!

Must be a wife thing with this type of set

(Not slinging of at wives’ here. Mine sometimes reads my posts!!!!)

Do not be deluded into thinking that a newer cap cannot fail. Its rare but it can happen.

I would concentrate on the mica's with HT on them. around 1956 was a bad year when it comes to components, They are the sets that I find have the most failures of everything. I have an 1956 Astor here that complied with that. Rarely do Silver Mica's fail and you can often, in Australian sets, ignore them. Yet this one, an Oscilloscope and a Little Nipper of that era all had to have every capacitor & resistor replaced?

The most likely Resistor I find that fails like that in the audio is the 1st AF Plate resistor when the Valve is used as voltage amp. Normally these Just go high.

Check also for dry joints, faulting with vibration. Plastic Chopstick makes a good probe.

I have a 132L similar fault was converter. It's got a 6.25 inch speaker, with feedback & that helps the sound quality. Clutz had holed the original speaker & It was polling. Now has modern foam suspension type out of a car (more efficient).

Marc

Thanks for the tips Marc.

At the end of this I guess I will have built a bran New Philips 172. The only origional parts are speaker, O/P TX and Power TX! Have already replaved 2 valves (the 6M5 and 6V4) due to being smashed when I got the set!

Oh well I like this radio so I guess its worth it!

I will let you know how it goes when I replace the Micas.

Where is the best place to get them. RS seems a little expensive for a simple component!

Noticed some of the prices ...scary

EVATCO has some, unless they have changes recently, it was not a full range, especially down low.

WES components has ceramics 500V, which I have used. Use the higher voltage types on Audio output plates.

Also note the EVATCO has 2&3 Watt resistors.

Marc

Thanks Marc

I keep forgetting about evatco. I used to have a WES account but since I am not in a place with an ABN now I cant get trade prices.

I have put this restore on hold because of the HRSA National Radio Fest that is being held this weekend here in Canberra.

I plan to tackle it after the weekend.

Will let you know what I find.

I found a few of the high resistors in the cct (1M ohm and above) have gone well high. I plan replacing them as I go.

Test as you go is good policy, nothing worse than having to go and redo connections to replace resistors after you have replaced caps or wiring.

I am replacing the previously rubber coated wire, in an Astor, with insulated wire, as required. Two resistors have already been evicted for being out of spec. The plate resistor on the 6AV6 is high and it is rare to fine the grid resistors on a 6V6 in spec.

Amusing one was when I pushed a cap, that looked poorly soldered & it fell off (chassis craned on end)?

Marc

Addendum: Note on Astor / Pye Apart from a couple of feral resistors so far. It's actually got a 500K grid stopper that should be 50K? Coupling cap's leaking as well.