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Old 23rd May 2019, 12:12 am   #1
Venom1234
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Default Cord for Melody maker 494c tips about valves wanted

Just restoring one which was left for dead in back of a wardrobe after a relative died.

Thanks for pointing me in direction of the cord replacement. Took me a while but done that and can tune all ok.
I looked at another post of capacitor changes etc.
This actually works fine apart from a small fault and the fact I need to resolder lamp as wire just fell of the soldering !

I dont know much about valves so I hope you can see this picture.

Basically I was getting no radio channels at all.

Then when I moved radio worked ok.

This was not to do with aerial but seems to be this valve with red arrow.

Seems like a lose connection as if I wobble it a bit works fine. I have put it in and out and still the same.

Do I need to replace it or clean contacts cant quite understand when it has legs why it would get no real connection.

I will follow the guide of how to clean chassis but thought would ask for advise in this valve before I start cleaning the chassis.

I also see I should get a new mains cable and something to hold it down for safety. If everything else works and I can fix this valve and lead and will leave at that.

I also did not realise these valves were symmetrical, and seem to fit any way round back in the hole. I noticed there was like a marl on chassis and valve and I assume they need lining up ?

Unless people advise there is anything else I need to do ? Its real quite nice sound.

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Old 23rd May 2019, 10:14 am   #2
Station X
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Default Re: Cord for Melody maker 494c tips about valves wanted

Unless the glass part of the valve is loose in the metal part, there is not likely to be anything wrong with it. Clean the valve pins with Servisol 10. If they're very dirty give them a gentle scrape. Having done this insert and reinsert the valve in its holder several times, whilst it's still wet with Servisol. In some cases you may need to GENTLY "nip up the pin sockets in the holder so they make better contact.

With regards to further repairs you should as a minimum change the audio coupling capacitor. If you don't do this the output valve, output transformer and mains transformer may be destroyed.

Trader Sheet C18. Manufacturer's sheet C26. ERT Sheet C19.
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Old 23rd May 2019, 10:23 am   #3
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Default Re: Cord for Melody maker 494c tips about valves wanted

http://www.r-type.org/static/baseb8b.htm

Lawrence.
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Old 23rd May 2019, 10:23 am   #4
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Default Re: Cord for Melody maker 494c tips about valves wanted

Don't understand how valves can be fitted any old how- they should have a central spigot keyed to fit the base in only one orientation. Loose or dirty contacts in the valve socket can cause the symptoms you describe.

There are at least two capacitors, C25 and C26 on the manufacturer's circuit diagram ( https://www.service-data.com/product...55/1369/m10955 ) which should be replaced if they haven't been already or they can cause expensive problems if they get too leaky (low insulation resistance). Others will likely also be bad, but will only affect performance rather than causing damage.
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Old 24th May 2019, 3:08 pm   #5
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Default Re: Cord for Melody maker 494c tips about valves wanted

Statement of the ******* obvious perhaps but there is also the possibility of a bad soldered joint on one of the wires or components connected to the valve pins underneath the chassis. Also the valve pin sockets can wear loose but can be tightened carefully with a pair of pliers. If you can't get it sorted then PM me and arrange to bring it round and I will sort it for you. Cheers, Jerry
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Old 24th May 2019, 3:47 pm   #6
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Default Re: Cord for Melody maker 494c tips about valves wanted

Hi. I have also one of these radios. There is a mention of various line-ups of valves used in the series of radios of model 494A, and various component changes (which hadn't been done previously in my receiver).
Also in my set, the aerial coil former had been damaged at its base. I have some similar card coil formers and I wonder if I might be better using part of the new ones to rebuild the base of the damaged original. Probably contact adhesive will be useful in this case?
With regards to the speaker leads, I disconnected mine from their plugs and wired them directly to the loud speaker.
Those snap connectors from the mains selector should be disconnected and the mains lead wired directly to the transformer terminal.
Hope this helps?
Mike
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Old 24th May 2019, 7:18 pm   #7
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Default Re: Cord for Melody maker 494c tips about valves wanted

I recall the U series of this type of valve giving me the same problem it turned out to be the pins on the problem valve were slightly shorter than the other valves , Mick.
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Old 25th May 2019, 3:04 pm   #8
Venom1234
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Default Re: Cord for Melody maker 494c tips about valves wanted

Thanks for the great advise.

I have managed to replace the mains lead. Was quite lucky I had a really thick extension cable lead in black I no longer needed and fits really tight in the hole. I have terminated the Earth in the plug with a terminal block both ends as not required.


I've also soldered a new wire and used a lever type terminal block for the lamp so can just use lever to release it.

After resoldering the mains cable, I remind myself I am not greatest at soldering I think I may wait a bit before I re-solder the capacitors you mention, as will need some pratctise on an old board ! Thanks for the offer Jerry and I'll see how I go but may well be in touch.

Going to look at valve tomorrow as get limited time to play !

Thanks for all the advise


I'll leave it off till I sort that.
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Old 25th May 2019, 3:53 pm   #9
cathoderay57
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Default Re: Cord for Melody maker 494c tips about valves wanted

This radio has a mains transformer and, although it was no doubt originally supplied with a 2-wire mains cable, for your safety I recommend that you should connect the mains cable earth wire to the chassis of the set and the other end of the earth wire to the mains plug's earth terminal. Others here might have different views - but for me it's safety first. In the old days when mains sockets were 2-pin the set could still have been earthed via a copper pipe buried in the ground outside an adjacent window with an earth wire plugged into the earth socket (next to the aerial socket). Cheers, Jerry
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Old 26th May 2019, 1:52 pm   #10
Venom1234
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Default Re: Cord for Melody maker 494c tips about valves wanted

Ok must of misread some stuff about overheating. No worries I think I can re-do earth easy enough may just need to extend to the chassis.


The capacitors C25 and C26 I did download a trader service sheet for 1.99 which sees to be a page of wireless electrical trader form 1949 !


C25 says Aerial MW trim value 0.00006 at slot j3
C26 says Aerial tuning slot A1 but had no value for the uF just like blank "__".
What do I need for c26 chaps ??


I am actually finding this less painful than the arcade machines I fiddle with !
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Old 26th May 2019, 2:01 pm   #11
ms660
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Default Re: Cord for Melody maker 494c tips about valves wanted

See Post# 2.

Lawrence.
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Old 26th May 2019, 2:39 pm   #12
Venom1234
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Default Re: Cord for Melody maker 494c tips about valves wanted

Ok need to not rush and read properly !

Will do
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Old 26th May 2019, 2:46 pm   #13
Simon Gittins
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Default Re: Cord for Melody maker 494c tips about valves wanted

Something that always causes confusion is that each type of service sheet allocates a different number to the same component!

You have downloaded the Trader service sheet.

The capacitor referred to in Post 2 is Trader Sheet C18.

The capacitor referred to in Post 4 is Trader Sheet C17. I can only tell this by looking at both sheets as I have the DVD with all 3 versions.

Last edited by Simon Gittins; 26th May 2019 at 2:50 pm. Reason: Clarification.
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Old 26th May 2019, 7:05 pm   #14
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Default Re: Cord for Melody maker 494c tips about valves wanted

I restored a Cossor 494 several years ago and found that the original valve sockets were not good quality exacerbated by the fact that the radio had been stored in damp conditions. I have also found that the pins on Loctal valves are more troublesome than other types and need to be thoroughly clean to make reliable contact.

In the end I replaced two of the valve holders with better quality ones and it was much more reliable.
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