Ferguson 387RG - Loud Humming (constant)

[peanut369]

Hi all,

In 2019 I bought this lovely radiogram at auction. I cleaned it up, new cartridge, etc. It was working lovely.

About a year ago it developed a very loud hum/buzz (very loud!) when powered on. Regardless of whether it was on radio mode or record playing mode, the hum was constant, even if the volume was set to minimum.

I've bought service manuals from service-data but it's a bit above me when it comes to capacitors and valves.

Any idea what might be the problem?

I've taken the back panel off, I'll post some pictures below.

[Station X]

Originally Posted by peanut369

I've bought service manuals from service-data but it's a bit above me when it comes to capacitors and valves.

That being the case I suggest you get someone with the right skill set to replace the smoothing capacitors for you.

Alternatively there are members here who will be able to guide you through the process.

[peanut369]

Originally Posted by Station X

That being the case I suggest you get someone with the right skill set to replace the smoothing capacitors for you.

Alternatively there are members here who will be able to guide you through the process.

Thanks for your reply and help, Graham.

I can probably get some family members to help with the electrical side.
But I wouldn't know where to start with ordering replacements.

I'm working my way through the service manual, but it'd a little tricky. I was thinking of posting some screenshots so as to be guided to finding the right part, but as the manual was bought from service-data I don't want to publish any screenshots which may go against the rules.

[peanut369]

Having a look at the service manual, I think I've found the part. Could anyone confirm?

I'm assuming it's the silver thing in the final picture: 40-40-32-MFDS

[EDIT] - Okay, so according to another thread. The silver canister contains the 3 smoothing caps.

Is it possible to order replacements for these? As a whole, or would I need to order 3 separate caps?

Thanks!

[Edward Huggins]

You may have trouble in finding an original "three-in-one" can today. Best to order 3 seperate ones, ideally rated at 350V. But if you have no real experience of these, do get a local Member to fit them. There are lethal voltages here.

[peanut369]

Originally Posted by Edward Huggins

You may have trouble in finding an original "three-in-one" can today. Best to order 3 seperate ones, ideally rated at 350V. But if you have no real experience of these, do get a local Member to fit them. There are lethal voltages here.

Yes, I couldn't find any online. So I'll have to go the route you mentioned. Thanks Edward

[paulsherwin]

Almost certainly, the smoothing caps have died. The standard solution is to replace the old double or triple cap with several modern caps on a tagstrip underneath the chassis (the modern caps will be very much smaller).

This isn't a difficult job, but it does need basic soldering skills and at least beginner level electronics knowledge.

However, if this radiogram is unrestored then there will be other components that will be on the point of failing and need to be replaced. If this isn't done, the performance will steadily deteriorate until you get an expensive failure like an output transformer, or even a fire. Getting professional help is probably the best way forward.

[peanut369]

Thanks Paul! That makes complete sense now.

And yes, you're right, there's a small blob of goop on the cabinet frame underneath the mains voltage adjustment, so I imagine it'll begin to fail soon.

If it lasts me just 3 months through this winter then I'll be happy.

[PaulR]

It is actually a nice, usable radiogram with VHF FM. It would be a shame to run it into the ground by not replacing the other essential capacitor(s). You have done the first step by researching and correctly identifying the cause of the hum.

Have a look at this thread https://vintage-radio.net/forum/showthread.php?t=131732 and this information https://www.vintage-radio.com/repair...ut-stages.html which give information about the most problematic capacitor. If you can get the person who is going to replace the smoothing caps to replace this one as well then the set should be a lot safer. The capacitor itself will probably only cost a pound or two.

[Michael Maurice]

What I do is to replace the cap with a 50+50+50uf in one can which I keep in stock.

[peanut369]

I've managed to find a direct replacement (see attachments)

But, underneath the cap is 4 terminals, not 3 as was on the original.
And there's no markings, colour codings on the capacitor. Do I have a way of finding out which is which?

Have I bought a capacitor that someone has re-stuffed? Or is the 4th terminal perhaps used for attaching the cap to the board as support?

[Station X]

I wouldn't be inclined to trust a capacitor dating from 1963 unless you have a means of testing it for electrical leakage at the full working voltage and can measure the capacitance of each section.

Tag 3 is probably the common negative with the other tags used as designated on the can. I'll hazard a guess that the tags number clockwise from the gap, but you'd need to check with a capacitance meter to be sure.

[PaulR]

It isn't re-stuffed but, as StationX says it is old. Unlike valves, electrolytic capacitors deteriorate with age and lack of use. It will need reforming if it is at all viable.

It would be better to replace the original with new discreet capacitors. If there is nobody nearer I can test and try to reform it at its working voltage but in view of postage costs it may be better to write it off to experience and buy new capacitors from a reliable source such as CPC, RS or Cricklewood Electronics. I would be a little wary of Ebay if the capacitors you see on there are a lot cheaper as there are many fake ones around.

[peanut369]

Thanks Graham and Paul. Definitely a write-off as experience. Thank you for offering to reform it Paul.

I think you're right, 3 new separate capacitors is the way forward. Thank you!

[Ed_Dinning]

Hi, you should be able to get modern , separate caps easily and fit them under the chassis.

While you are on, change all the waxies to save trouble later

Ed

[Sideband]

Originally Posted by peanut369

Thanks Graham and Paul. Definitely a write-off as experience. Thank you for offering to reform it Paul.

The other problem you'll have with that capacitor is mounting it. It is designed for printed circuit boards which clearly your radiogram doesn't have. I suspect that capacitor was made for a specific set and would only fit the circuit board one way.....so you wouldn't need to know which one is which. Having said all that, an experienced person could make it work (assuming the capacitor is any good) by fitting a bracket and chassis-mounting it and then measuring the value of capacitor at each tag. I wouldn't like to trust that one though without reforming it.

Three separate caps is the best way as already suggested, but for a long, reliable life, it should be serviced properly.

[PaulR]

Originally Posted by Sideband

but for a long, reliable life, it should be serviced properly.

You really need to note this. If you don't change some of the wax capacitors all your work will be in vain. Been there had the transformer rewound!

[peanut369]

Thanks everyone. I've finally got an hour or two to research this.

Looking at the service manual...."THAT capacitor" I believe is : 0.02uF (22nF) 150 V. Audiocoupling (F.M.)
Is that correct? (Service manual screenshot attached).


Finding the components online:

I'm looking online at RS components as they have a local store.

For THAT capacitor.
I honestly don't know if I'm correct assuming it's the 0.22nF cap. If it is,
would it be a film capacitor or a ceramic capacitor? And would 160V do? I can't find a 150v one.
https://uk.rs-online.com/web/p/film-capacitors/1854123


Smoothing Caps:
Needing 40 / 40 /32 @ 275V.
Would 3 of these do? They're 47uF @ 250V
https://uk.rs-online.com/web/p/alumi...citors/9213218

Wax Caps:
According to the manual, one of the wax caps is "4uF Electrolytic 150V. Ratio det. stabiliser"
Would the following work?
https://uk.rs-online.com/web/p/alumi...citors/1620722


Thank you in advance

[PaulR]

Others have more expertise then I do and I defer to any more expert opinions on this but..

I don't have the circuit diagram of your set to hand but I do have one for a 384U which I assume is similar. The audio coupling cap in that one is 0.01uf. The equivalent on yours is C50. It is described as V5 CG (control grid) coupling. The .02 described as Audio Coupling FM doesn't actually HT on it as far as I can see. Having said that, I see from other threads on this set that the capacitors are Hunts Moldseals. These are particularly troublesome and you should replace them all. They are brown cylindrical plastic ones and often split where the two halves were joined. I have gone down the route of only replacing bad ones on a Bush FM set and more failed as it was brought into use so I replaced them all.

I would replace the smoothing electrolytics with one of the same voltage or higher. Using lower rated ones is a bit risky.

By definition an electrolytic capacitor is not a wax one. They have different construction and different failure modes. The one you link to would be suitable. Watch out the polarisation - unusually for electrolytics the positive of the one in that situation goes to ground. The one already fitted may be ok.

Looking at other threads about similar sets a solid state selenium rectifier rather than a valve rectifier is mentioned. Those can cause problems including hum. Apparently they give off an awful, unforgettable smell when they fail. I have never experienced this but it is something to think about replacing if yours has one.

[DMcMahon]

Originally Posted by peanut369

Thanks everyone. I've finally got an hour or two to research this.

Looking at the service manual...."THAT capacitor" I believe is : 0.02uF (22nF) 150 V. Audiocoupling (F.M.)
Is that correct? (Service manual screenshot attached).

Unless you are looking at a different service manual/schematic, it is not correct. That capacitor is C46, the "THAT capacitor" is C50 0.01uF coupling the anode output of V4 to the control grid input of V5.

I am looking at The Service manual for the Ferguson 382U, which is shown as the manual for the 387RG in the "Downloads available" link above.


Finding the components online:

I'm looking online at RS components as they have a local store.

For THAT capacitor.
I honestly don't know if I'm correct assuming it's the 0.22nF cap. If it is,
would it be a film capacitor or a ceramic capacitor? And would 160V do? I can't find a 150v one.
https://uk.rs-online.com/web/p/film-capacitors/1854123

Note that the voltage rating references on the schematic for the capacitors are DC, your 160V reference above for the RS capacitor is AC, this RS capacitor has a 250V DC rating. But is not the correct uF value as previously explained.


Smoothing Caps:
Needing 40 / 40 /32 @ 275V.
Would 3 of these do? They're 47uF @ 250V
https://uk.rs-online.com/web/p/alumi...citors/9213218

You should not really use a lower voltage rating than original stated value.


Wax Caps:
According to the manual, one of the wax caps is "4uF Electrolytic 150V. Ratio det. stabiliser"
Would the following work?
https://uk.rs-online.com/web/p/alumi...citors/1620722

It would but it is not a wax capacitor.


Thank you in advance

David