Watt Torino - Cadetto Repair

[real0real]

Hi
Have a Watt Torino - Cadetto
When switched on display light illuminates , but just getting a load Humming noise from speaker ,wonder what possible fault/cause maybe

[Herald1360]

Dried out main smoothing capacitors?

[real0real]

i thought my self possibly capicitor fault, will take out of case later today, take a few pictures of under chassis and upload.

[real0real]

Have attached some pictures of ,couple of the capacitors do look bit frazzled

[Station X]

Circuit available from radio museum. I won't post it here for obvious reasons. There are no component designations shown, only values.

Change the audio coupling capacitor which is connected to the control grid of the 6V6 output valve before it causes any damage.

To get rid of the hum, change the smoothing capacitors, probably located in the dual can on the left of picture 4.

[real0real]

Hi ,
Have downloaed Radio circuit , as mentioned no component designations shown ,so bit confusing , but as far as i can make out as shown in picture attached pointed out what think is audio coupling capacitor could anyone please possibly know if its correct one

Clive

[Station X]

You'll have to trace the wiring from pin 5 (control grid) of the 6V6 output valve and see which cap it goes to.

[real0real]

not sure if this corresponds correctly to wiring schemetic , Tried tracing from pin 5 but found a wire leads to grid , not directly to a capicitor , and found there is restance between where wire soldered and to capicitor across 2 points points there are wires from these 2 points that feed to speaker ,

Clive

[Station X]

The audio coupling capacitor won't necessarily be connected directly to pin 5 of the 6V6. There may be a wire on pin 5 which goes to a tag strip to which the coupling cap is connected. The other end of the coupling capacitor should be connected to a 5000 Ohm resistor.

Also connected directly or indirectly to pin 5 should be a 250,000 Ohm resistor.

[ms660]

Neat reflex job.

Lawrence.

[real0real]

Have had another look at 6V6 Valve socket , noticed there is a melal wire attached to one of pins of 6v6, this runs along length of radio and ends next to 6A7 Socket where it is connected to a capacitor , capacitor appears to have written on it 0.1 Uf and 1000V ,the capacitor is coupled together to a resistor and has a resistance of 0.281 at 20k on vault meter , pictures attached ,could this be audio coupling capicitor ?

Clive

[Station X]

Looks like you're using paint to view the image. Could you try saving the picture as a jpg and uploading it directly to the forums. It'd save you having to photograph the screen, download the image from the camera and then upload it to the forums. The picture would be clearer too.

I'll check on your query.

[Station X]

Looking at your picture the wire you refer to appears to connect to pin 7 ie the seventh pin clockwise counting from the spigot. Pin 7 is one side of the heaters. In this set one side of the heaters is earthed and there'll be any number of components connected to it.

You need to trace the wiring from pin 5 the control grid. If it's difficult to trace visually, connect one lead of your meter to pin 5 and probe around component leads until you find those which show a full short circuit to pin 5.

[real0real]

counting back from pin 7 two pins to pin 5 , just noticed somethink not see before . there are 2 wires connected here , 1 wire easy to see goes into a small hole in chassis and disapears ,but thing not notice before as very hard to see theres a very short wire going to a resistor (meter set on 2m getting .260 ohms resistance) on the end of cetral grid ,attached picture of

Clive

[Tractionist]

When was this set last used? I appreciate that it's been turned 'on' recently - because you have been rewarded with a hum ..... but do the electrolytics require re-forming or changing? Equally, there are quite a few wax-paper axial's in there too - and they are hardly [visually] pristine .... indeed, one of two look as though the end seals are no longer air-tight and ergo moisture-resistant.

Finally, the staining in the area of the mains transformer would be of concern to me too.

It's a nice looking set - if it were me, I'd give it a re-cap and full service ...............

[Station X]

Originally Posted by real0real

counting back from pin 7 two pins to pin 5 , just noticed somethink not see before . there are 2 wires connected here , 1 wire easy to see goes into a small hole in chassis and disapears ,but thing not notice before as very hard to see theres a very short wire going to a resistor (meter set on 2m getting .260 ohms resistance) on the end of cetral grid ,attached picture of

Clive

0.260 Megohms (not ohms) is near enough 0.25 Megohms, so I'd say that's the 0.25 Megohm resistor from the control grid pin 5 to chassis. In fact you should be able to measure 0.25 Megohms from pin 5 to ground. Please confirm. It also appears that the resistor has label with its value.

The other wire from pin 5 should go to the coupling capacitor. As I said previously, if a visual check is difficult, use you meter to find which component leads show a dead short to pin 5.

[Station X]

Originally Posted by Tractionist

It's a nice looking set - if it were me, I'd give it a re-cap and full service ...............

I hesitate to suggest that new members with little technical knowledge indulge in wholesale capacitor replacement. There's just too much scope for fitting the wrong value cap, in the wrong place, the wrong way round, especially when the old caps have non-preferred values when compared to today's values. Also many newbies assume that caps with low pF values need to be replaced and that generally spoils the set's alignment. If a mistake is made it's then a real pig trying to sort things out remotely from photographs.

Having said that the smoothers in this set look relatively easy to replace given that they're in a wire ended can. Replace those along with the coupling capacitor and it should be safe to apply power after checking the mains lead etc. The remaining caps can then be replaced one at a time.

[real0real]

Believe i may have found the capicitor
0.01uF / MFD 10nF 10000pF (MMFD) RATED AT 1500 V
Attached pictures of

Clive

[Station X]

Is that inside one of the IF Transformers?

Is the resistance from one end of that cap to 6V6 pin 5 close to zero ohms? If so it's the correct cap.

[real0real]

Yes found hidden inside the IF transformer , the wire from pin 5 goes directly to capacitor checked is zero ohms ,
Did also check from pin 5 to measure the resistor 0.25 Megohms to ground - o.k