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Old 24th Jan 2023, 6:56 pm   #21
kalee20
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Default Re: Ferranti U1003 VHF loud and distorted

C45 and the UABC80 would be my bet!

Tuner faults or IF faults would cause a drop in output, but no distortion (unless it's a very weird fault).

These are decent radios when working well, it's worth persevering with.
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Old 25th Jan 2023, 8:04 am   #22
Andy 1964
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Default Re: Ferranti U1003 VHF loud and distorted

Regarding C45 polarity and the other electrolytics, I very carefully noted polarities and marked them on the layout diagram. I thought I had got C61 the wrong way round, on the schematic it is positive to ground, but when I tried it I smoked R34. Referring to the U319 schematic it is indeed negative to ground.

I have previously replaced the detector diode inside the can of a Roberts R200, but this valve stuff is all new to me.

I do not have any kit to perform alignment.

I have been feeding the Gram input with a Bluetooth audio signal, sounds OK but a little quiet like MW/LW, volume at 3/4. VHF 1/4 volume but warbled.

Looks like I need to get a UABC80.
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Old 25th Jan 2023, 8:41 am   #23
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Default Re: Ferranti U1003 VHF loud and distorted

I've starred at the U1003 circuit diagram long and hard. It definitely shows C61 connected negative to ground which is what I'd expect. If in doubt connect your meter across the cap on a suitable voltage range and check that it reads with correct polarity.

I don't understand the reference to a U319.

EDIT. I see you mean an Ekco U319.
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Old 25th Jan 2023, 8:57 am   #24
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Default Re: Ferranti U1003 VHF loud and distorted

Oops, I got confused with that one, there is a mark on my print out.

Just ordered UABC80 7.99 from laroga71 on Ebay
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Old 25th Jan 2023, 12:59 pm   #25
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Default Re: Ferranti U1003 VHF loud and distorted

Let's hope the "tested excellent" includes the two important diodes!

You've gone for the cheapest option and with free postage for a used, but tested Mullard, so I can't really blame you for that. The UABC80 valve is actually four valves inside one glass bottle, being a triode and three diodes, so a lot going on inside it. The triode is an amplifier and D1 is the AM detector, while D2 and D3 are the FM ratio detector - it's all shown on your service sheet. These are one of those valves where a new one is always the best option, but so long as D2 and D3 are good and reasonably matched, then it should be good...and it's a Mullard. It's not stated how the valve was tested, so fingers crossed.

It's likely that all these old sets will be at least slightly out of alignment, but it's best left well alone if you haven't got the gear to perform it properly. You can also cause yourself a lot of grief with stuck slugs in coil formers etc.

Edit: Sorry, it does say how it was tested. It was tested on a Sencore TC154 tester, apparently a calibrated one, too, so should be all good.

Last edited by Techman; 25th Jan 2023 at 1:12 pm. Reason: Correction regarding how valve was tested.
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Old 25th Jan 2023, 4:41 pm   #26
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Default Re: Ferranti U1003 VHF loud and distorted

Hi Techman

Leicester is my local city from Hinckley, so hopefully could be my go-to man for valve testing!
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Old 25th Jan 2023, 5:16 pm   #27
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Default Re: Ferranti U1003 VHF loud and distorted

Yes, a quick look showed that he had quite a few valves for sale at what seemed like not unreasonable prices. When you consider postage and packing costs, the price of that valve was very reasonable if it's a good one. I only had a very quick scan of his valve list, but noticed that they were mostly (if not all) listed as Avo tested, so guess there must be a reason that the one you ordered was tested on a different tester. As you say, he may be willing to test the odd valve for you, although most valve faults can be diagnosed with the valve fitted in the circuit that it was designed to work in.

It's an interesting thing about these particular valves with the three diodes, and it's possibly been discussed before, as to why the diodes seem to fail like they do, it's not as if they're worked hard...perhaps that's the reason and it's cathode poisoning or something similar - certainly something open to interesting debate.
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Old 25th Jan 2023, 5:19 pm   #28
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Default Re: Ferranti U1003 VHF loud and distorted

Hi Andy1964

Many of these 1950's sets had an internal FM aerial option, usually a dipole shortened by fitting it with a "loading coil" inductor and/or by putting tinfoil paddles on the ends. I suspect these were provided mainly so that customers could get a set to "work" as soon as they got it home, before they had time to put up a 'proper' aerial.

Unless you are lucky, the aerial will be in a room with multipath reflections and at the mercy of the distortion these can introduce. The multipath situation will vary with exact postion, frequency and even the position of people in the room ! These older sets didn't have the gain and AM rejection performance of more modern designs, so it's all rather pot luck.

You may well get more stable and reliable results with an outdoor dipole, or even an indoor one placed higher up in the room.

Nearly all these sets used a "Ratio Detector" for FM, which includes a 5 uF or 4.7 uF electrolytic capacitor which unusually always has positive to chassis. If this cap dries out and goes low in value you will get distortion on all FM signals. All the other electrolytics in the set will have positive voltages on them so will be connected the 'normal' way i.e. negative to chassis.
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Old 25th Jan 2023, 5:48 pm   #29
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Default Re: Ferranti U1003 VHF loud and distorted

Quote:
Originally Posted by Mr 1936 View Post
Many of these 1950's sets had an internal FM aerial option, usually a dipole shortened by fitting it with a "loading coil" inductor and/or by putting tinfoil paddles on the ends.

Nearly all these sets used a "Ratio Detector" for FM, which includes a 5 uF or 4.7 uF electrolytic capacitor which unusually always has positive to chassis. If this cap dries out and goes low in value you will get distortion on all FM signals.
I've got one of these sets and the FM aerial is a single wire round the inside of the back cover.

As far as I can gather, Andy has replaced the C45 ratio detector smoothing capacitor and checked that he's connected it in what might seem to some to be an unconventional way round in the circuit.

Talking about this particular set has caused me to get mine down off the shelf for an airing and I'm listening to it right now playing local radio on 94.9 FM. I wouldn't say that mine is absolutely perfect, but it's not a bad performer and at least it doesn't drift on warm up like those wretched Bush VHF61 sets do.
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Old 30th Jan 2023, 10:17 am   #30
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Default Re: Ferranti U1003 VHF loud and distorted

UABC80 arrived this morning, VHF is now working lovely.
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Old 1st Feb 2023, 1:42 pm   #31
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Default Re: Ferranti U1003 VHF loud and distorted

Thanks for the feedback - a good resolution!

With nothing to lose, you could keep the old UABC80 for trial in another set. Or have some fun with it - give it double the heater volts for half a minute, and see if it then comes good!
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Old 2nd Feb 2023, 9:32 am   #32
Andy 1964
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Default Re: Ferranti U1003 VHF loud and distorted

While I was waiting for the postman I examined the resistors, only 2 were within tolerance, the rest were way high. So I changed them all anyway.
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Old 2nd Feb 2023, 11:27 am   #33
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Default Re: Ferranti U1003 VHF loud and distorted

I have now turned my attention to using the Gram input for bluetooth, but I am getting volume dependent hum with nothing connected! I have used a battery powered BT receiver, hum is the same.
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Old 2nd Feb 2023, 12:03 pm   #34
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Default Re: Ferranti U1003 VHF loud and distorted

The Gram input definitely works well with the U1003, with a 'proper' position on the waveband switch rather than forcing the input onto the AF triode on top of the detector's signal, and tuning to somewhere quiet.

I'd be inclined to suspect the switch, give it a good clean.
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Old 2nd Feb 2023, 12:27 pm   #35
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Default Re: Ferranti U1003 VHF loud and distorted

The service notes suggest two core screened lead to prevent hum. See snippet Clause d.

The capacitor connected to the PU socket and chassis needs to be a Y type.
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Old 2nd Feb 2023, 1:28 pm   #36
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Default Re: Ferranti U1003 VHF loud and distorted

Waveband switched cleaned again. What is a 'proper' position? Y type to chassis done.
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Old 3rd Feb 2023, 9:35 am   #37
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Default Re: Ferranti U1003 VHF loud and distorted

Looks like I missed a resistor, its R15 on the gram input, should be 560k but measures 684k, so I will change that.
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Old 9th Feb 2023, 11:05 am   #38
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Default Re: Ferranti U1003 VHF loud and distorted

Update

Fitted NOS UL84. I had noticed that it wasn't glowing as much as the others and strong VHF signals were a little distorted. That is now fixed and glows as brightly as the others.

I had noted C42 & C44 were shielded to chassis, so I have shielded the replacements with some outer braid from a TV aerial cable and heat-shrink tube.

Bluetooth KRC-86b connected directly to gram input at wavechange switch, powered by 5v regulated smoothed supply from the X2 cap. Rear connections removed. Gram hum is minimal and not noticeable when in operation.

A very nice sounding radio.
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Old 10th Feb 2023, 10:27 am   #39
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Default Re: Ferranti U1003 VHF loud and distorted

Quote:
Originally Posted by Andy 1964 View Post
Waveband switched cleaned again. What is a 'proper' position? Y type to chassis done.
The "proper position" is just a reference to there being a dedicated position on the wave change switch for "gram" which substitutes the gram input signal for the detector output. Some sets skimped on this as described by just taking the gram input straight to the volume control leaving the user to simply find a signal free spot on one of the wavebands to avoid unwanted noise on the gram signal.
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Old 13th Feb 2023, 9:39 am   #40
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Default Re: Ferranti U1003 VHF loud and distorted

Thanks, properly switched, there are a lot of contacts in that wave change. If I understand it correctly HT is being cut to the radio only valves in gram mode!
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