Ferranti U1003 VHF loud and distorted

[Andy 1964]

Ferranti U1003 (Ekco U319) VHF is loud and distorted compared to MW/LW/PU. All usual caps replaced and wave change switch contacts very thoroughly cleaned. I can see two possibilities, V1 UCC85 or C52 0.01uF inside the VHF tuner unit, which is very difficult to get at, and I am worried about upsetting the alignment. All the other 0.01uF caps were under half their value! Any opinions please?

[Techman]

I've got one of these.

It's unlikely to be anything to do with the tuner. A bad UCC85 would cause the opposite of loud, although internal leakage can cause a hum. More likely to be a detector fault.

[Radio Wrangler]

Electrolytic in ratio detector, or maybe the dedicated attentions of the phantom twiddler loose on the discriminator.

David

[Andy 1964]

Originally Posted by Techman

I've got one of these.

It's unlikely to be anything to do with the tuner. A bad UCC85 would cause the opposite of loud, although internal leakage can cause a hum. More likely to be a detector fault.

Where is the detector?

Originally Posted by Radio Wrangler

Electrolytic in ratio detector, or maybe the dedicated attentions of the phantom twiddler loose on the discriminator.

David

Which cap number is that?

[Station X]

I assume you have the service sheet?

[Andy 1964]

Yes, the manufacturers.

[Station X]

C45.

Make sure to fit any replacement the right way round. Positive to chassis.

[Andy 1964]

Yes, done that, could it be the internal aerial?

[Station X]

Does it have an internal aerial? I can see connections for an external dipole.

[Andy 1964]

Yes, I am on the internal

[Station X]

An internal aerial is only going to be one or two pieces of wire. Easy to check out visually, mechanically and electrically.

[Andy 1964]

Strong signals are worse, warbled and clipped like the output is too high.

[Techman]

It's either out of alignment or one of the detector diodes in the UABC80 is down. You might be able to bypass them with solid state types as a temporary test/cure. If the set improves slightly the longer it's been on then this is, or could be, indicative of the bad diode section gradually getting some of its emission back as it warms up. There's three diodes in the valve. One is for AM detection and two are for FM.

Make sure that C45 capacitor is connected the correct way round!

[PJL]

Do you have another UABC80 you could try? The set does have a pick-up input BUT it is an AC/DC set and relies on C35 & C42 to isolate the input and they MUST be replaced before trying it with an external signal.

[Radio Wrangler]

It sounds like you are likely to have to do an alignment.

For FM, you're going to need a wobbulator and oscilloscope. Without them, trying to adjust by ear, whether off-air or with a simple sig gen, usually results in a set with its adjustments messed up. These got chucked to one side and forgotten about.

David

[ms660]

Originally Posted by Radio Wrangler

It sounds like you are likely to have to do an alignment.

For FM, you're going to need a wobbulator and oscilloscope.

Not so.

Lawrence.

[Sideband]

Originally Posted by Radio Wrangler

It sounds like you are likely to have to do an alignment.

For FM, you're going to need a wobbulator and oscilloscope.

In an ideal world ....yes. However most manufacturers circuit information will explain how to do a satisfactory alignment without a wobb. Most domestic receivers can be aligned using just a signal generator and a test meter.

Andy, do you have a signal generator that covers 10.7mhz? You WILL need one if you stand any chance of getting your radio anywhere near accurately aligned on FM.

[Techman]

It's best to check the easy things first before going into the alignment business. It's obvious to me that Andy has very little basic radio theory knowledge just by the question regarding where the detector is when he has the manufacturers service sheet in front of him...not a criticism, just a fact!

I'd be looking at a possible bad diode in the UABC80 valve before going all complicated. Easy stuff first, please!

[PYE 405]

Originally Posted by Techman

I'd be looking at a possible bad diode in the UABC80 valve before going all complicated. Easy stuff first, please!

I quite agree and the UABC80 is often prone to be poor. I would get a new one to replace it with first.

[PYE 405]

To amend my above post, it perhaps would be better to establish that C45 is OK first. This would be cheaper than a new UABC80!