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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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1st Jan 2019, 8:08 pm | #1 |
Retired Dormant Member
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Ferguson 771 repair
Evening folks. My first post in this section. I am a novice new owner of a Ferguson 771 purchased a few months back for £5. It powers up and hums but nothing else. The two glass valves glow.
As an idiot in this, it would be great to get a list of the most obvious things I should check first. I have multimeters both analogue and digital and i have downloaded and printed out the service sheet. Many thanks in advance! |
1st Jan 2019, 8:21 pm | #2 |
Dekatron
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Re: Ferguson 771 repair
This section will give you much information that will help you understand your radio.
https://www.vintage-radio.com/repair...ion/index.html
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1st Jan 2019, 10:32 pm | #3 |
Nonode
Join Date: Oct 2017
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Re: Ferguson 771 repair
Hello and welcome. You say 2 valves are glowing. This radio has 5 valves. Are the other 3 missing? I recommend you don't power it on again until after you have completed some basic checks using the guidance in the hyperlink from the previous post. If you are also able to post a pic of the underside and top view of the chassis it woild help us to get a visual idea of what state it is in. You will inevitably need to replace some parts unless it has recently been restored by someone else. Cheers, Jerry
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1st Jan 2019, 10:38 pm | #4 |
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Re: Ferguson 771 repair
It’s possible the other 3 valves are metal enveloped I.e 6K8, or they could be missing as you note.
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2nd Jan 2019, 10:36 am | #5 |
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Re: Ferguson 771 repair
Or the valves are in the wrong places.
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2nd Jan 2019, 6:24 pm | #6 |
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Re: Ferguson 771 repair
Many thanks for your replies. The link above is exactly what I need.
I am hoping five of my pictures have attached below: |
2nd Jan 2019, 6:26 pm | #7 |
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Re: Ferguson 771 repair
...and hopefully three more here:
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2nd Jan 2019, 8:56 pm | #8 |
Nonode
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Re: Ferguson 771 repair
Thanks for the pics. Possibly not the easiest of sets to begin with; the 5-valve line-up is not particularly unusual but the 3 wavebands and lots of wafer switches operating the pre-set station buttons will make the front end circuit tricky to trace. As you've powered it up already, and it hums, that probably means the audio output transformer, loudspeaker speech and energising (electromagnet) coils are OK. With power off and the mains unplugged I would check them with a multimeter and compare the resistance of the coils with the data listed on the service sheet (L14-L16 and T1). Assuming you are using a digital ohmmeter you'd expect the resistance values to be a bit less than shown in the data. If they all check out OK do the same for the mains transformer T2. Also check it has the correct valves fitted. To do this you'll need to carefully remove the metal screening cans. The top cap twists off and the cans should then separate into 2 interlocking halves as you remove them from the clamp rim at the base. If you can read the valve numbers without pulling them out then don't remove them. If you have to, be careful removing the connector from the top cap because sometimes the top cap comes loose. Ease the connector apart and hold the top cap down with a pair of tweezers or long nosed pliers while you pull the connector off. The hum you heard is probably the main smoothing capacitors. If they are the original ones then replacements will be needed before you power it up again. I guess then it's decision time - do you want to have a go or leave it someone more experienced. There will be no shortage of advice here if you decide to have a crack at it yourself. Best of luck - you have a nice radio here. Cheers, Jerry
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3rd Jan 2019, 12:39 am | #9 |
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Re: Ferguson 771 repair
The lack of glow looks likely down to the full metal jackets on all but the output and rectifier valves.
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3rd Jan 2019, 9:38 am | #10 |
Octode
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Location: Llandeilo, West Wales, UK.
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Re: Ferguson 771 repair
Hi Jake,
You say you are a 'novice' can you give a few details of your experiences? Reason I ask is that the set you have there is not an ideal starter project for some one with no electronic or mains voltage working knowledge. For example can you read the circuit diagram, have you tested or measured equipment with high voltage and mains power applied before, etc.? What you answer would help others to give the best and safest advice. As cathoderay says a straight forward set with a fair number of 'gotchas' for the unwary... Alan |
5th Jan 2019, 9:55 am | #11 |
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Re: Ferguson 771 repair
Hi Alan,
I did a GCSE in electronics in 1988 so fairly basic exposure to circuit diagrams. I can identify the components but I do not know what they all do. The testing I do using the multimeter is to check fuses, batteries, mains circuits, chainsaws, generators, etc. I don't really know what to do with the set if I don't have a go at it myself. Seems a shame to let it rot. Thanks for all the advice - I will perform the basic power off investigation suggested and report back. Cheers, Jake |
5th Jan 2019, 11:31 am | #12 |
Triode
Join Date: Jan 2018
Location: Wrexham, Clwyd, Wales, UK.
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Re: Ferguson 771 repair
i see you live in wrexham area as i do if you cant manage it yourself then i dont mind looking at it with you.unfortunatly i am just about to go into hospital and because they are going to kill off my imune system(hopefully not me) i wont be able to see anyone until the end of february you will have to bring the radio over to if that will help you
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5th Jan 2019, 6:35 pm | #13 |
Nonode
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Re: Ferguson 771 repair
Hi Jake, it would be helpful to know what service data you are using so that we are all singing to the same hymn sheet. I have access to Trader Sheet #678 (Supplement to Wireless and Electrical Trader, July 1st 1944). Hopefully you have the same? Sometimes people have the Manufacturer's data sheet which is the same circuit but the component numbering often differs which can confuse. As you say, you can identify components and connections from the circuit, so that's a good start. Safety first: if the mains lead is only 2 wire or if it is 3 wire and the insulation has crumbled or frayed, replace it and fit a 13A plug on the end with a 3A fuse. The earth wire needs to be soldered to a wire connected directly to the chassis. Some will say that earthing the set puts stress on the mains transformer insulation. However, back in the day with 2-pin plugs, sensible folks plugged an earth wire into the radio's earth socket (below the aerial socket) connected to a copper pipe buried in the garden so what's the difference today? To run this type of radio nowadays without an earth at all is potentially unsafe in my view. When you eventually reapply mains, if you have a variac, you can take the precaution of powering the radio up gradually. However if, as I suspect, the main smoothing capacitors are going to be replaced there isn't a great deal of benefit doing this. If the mains transformer has failing insulation it will fail eventually regardless; let's hope not! If the valves are correct and inserted in the right places, and the radio hummed with the volume control set at minimum, then I recommend as a first step you should replace C25 (16uF) and C26 (8uF) with modern electrolytic capacitors rated at least 450v (preferably 500v) working. C25 should be a high-ripple type. You can buy suitable replacements from RS components or Farnell (other reputable suppliers are available!) When you fit them there is a gotcha - the negative terminals (aluminium can) goes to the centre-tap of the high voltage secondary windings (the centre of the windings connected to the rectifier valve) and not the chassis. It is also worth replacing C21 (0.01uF) connected between V3 anode and v4 grid (the valve connections are shown pictorially on the Trader Sheet and are viewed looking at the base of an inverted valve, not looking down on top of the valve holder). Replacement C21 should be easy to find as a poly film capacitor and needs to be rated at least 400v and preferably 630v. Once you get that far try powering up again and let us know if the hum is cured. Remember that the high voltage electrolytics can retain lethal voltage even after the set has been switched off. Best to check with a multimeter before fingers. Good luck. Jerry
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5th Jan 2019, 7:48 pm | #14 |
Nonode
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Re: Ferguson 771 repair
Hello again, just spotted another safety issue. C28 (0.01uF) is connected between mains line and chassis. Before you reapply power with an earth connection, you must remove C28. Otherwise it could explode or at least trip your mains circuit breaker. The set will function happily without it because it is only a mains-borne interference suppressor. It won't do much to eliminate noise from any switch-mode power supplies around your house, but if you want to replace it, you must use a Class Y capacitor that is specifically designed for purpose insofar as if it fails it fails open circuit such that it will not short mains onto the chassis. Cheers, Jerry
Last edited by cathoderay57; 5th Jan 2019 at 7:56 pm. |
12th Jan 2019, 8:32 am | #15 |
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Re: Ferguson 771 repair
Thank you for your replies and please accept my apologies for taking a while to respond. I am hoping to get some time this weeknd and I shall report back.
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12th Jan 2019, 5:57 pm | #16 |
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Re: Ferguson 771 repair
Right so I had an hour to spend on the radio today. I checked the position and type of each of the five valves and they all match the 678 service sheet which is promising I guess.
I am struggling a little with testing because I don't think I am doing it correctly. For instance, L14 is the speaker speech coil. Is that the three terminals pictured below? If so, the circuit diagram on the service sheet gives 2ohm resitance, but the speaker itself has three terminals but I got a zero resitance reading accross all three terminals in the picture above. Is the following picture T1? In the picture above, I get 1.8ohms between F and F, 2.25ohms between left hand F and 3 and 0.5ohms between right hand F and 3. I am starting to think my multimeter is faulty, although I suspect the fault lies with the user rather than the tool! |
12th Jan 2019, 7:00 pm | #17 | |
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Re: Ferguson 771 repair
My replies in bold
Quote:
Last edited by ms660; 12th Jan 2019 at 7:10 pm. Reason: addition |
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12th Jan 2019, 7:10 pm | #18 | ||
Octode
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Re: Ferguson 771 repair
Quote:
Yes L14 is the speaker's speech coil. The readings in the service sheet are for the coils and transformers in isolation and not connected to the rest of the circuit. You have to unsolder various wires to do those tests. You have a lower reading because L14 is in parallel with the output coil of T1 and the hum buck coil L15. Leave that for a while it will most likely be OK in the end. Quote:
Now I am guessing a little, but I would think that F and F indicate the Field coil (L16 on the circuit) connections. Now that should be measure 1.8k ohms out of circuit and even in circuit should measure a lot higher than a couple of ohms? (I suspect there is a sort somewhere or C24/25 have gone very leaky.) And again a bit of a guess is that '1' and '3' are the primary of T1 and should measure about 500 ohms. Now you need to unsolder the wire going to F on the right of your picture, next to 1, and measure F to F and 1 to 3 again. It might be an idea to measure from the chassis to those points as well. Let us know what you get. This is one of the gotchas by the way... Alan Last edited by snowman_al; 12th Jan 2019 at 7:16 pm. Reason: Sorry slower than ms660... |
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13th Jan 2019, 12:06 pm | #19 |
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Re: Ferguson 771 repair
Morning,
Lawrence- You were spot on regarding the multimeter - I was reading it incorrectly. Alan - I unsoldered the right hand F terminal and measured 1,800ohms accross those terminals and 460ohms accross the middle two. I get 415ohms between each of the F terminals and the chassis. Thank you for your patience! |
13th Jan 2019, 12:20 pm | #20 | |
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Re: Ferguson 771 repair
Quote:
Lawrence. |
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