Marconi 559

[davidrt]

Could anyone advise on the above requiring probably a new valve. The set was restored in 2000 and is used daily. Couple of years a go the sound was reducing (had to increase volume) until no sound at all. It was repaired with a new rectifier valve. Now same symptons. Also at one point it kicked back into life and I had to turn the volume right down. Now sometimes works OK, then volume down to very faint or not at all (as of this morning). It will probably worse this evening.

The person I normally take it to is not available. So, would it be easy for me to identify this valve (assuming you agree it is this) and could I buy one and fit it myself?

[Herald1360]

As you found, a dying rectifier produced an ongoing reduction in performance.

The symptoms you describe, though they could be a valve problem, sound more like the result of a poor connection somewhere or perhaps a failing resistor or capacitor. It wouldn't do any harm to switch off and disconnect from the supply, then take the back off and carefully remove each valve in turn (wiggle by the base only, not by the glass body) to give the pins a clean. If you find that any of the valves is loose between the body and the base come back with details.

The wavechange switch and volume control may also benefit from some repeated back and forth operation to ensure that the contacts are wiped a bit.

If none of this is successful, it gets potentially more difficult. At that point, come back and I'm sure we'll try to talk you through it, if you feel up to having a go.

[ukcol]

Although a valve fault cannot be ruled out valves are much more reliable than is generally supposed. Many sets of your sets age (75 years) are still working fine on the original set of valves.

The sort of things that do fail include wax capacitors, electrolytic capacitors and resistors. If a full electronic restoration was done in 2000 these components will have been dealt with.

Changes in volume can be caused by bad connections such as dirty valve bases, dirty wave-change switches and faulty solder joints.

The possible causes for your fault symptom are many and valve failure is possible but it is not possible to guess which one.

I am sure there is likely to be someone on this forum who lives near you who could sort this nice set out.

Colin M

EDIT: I note that I have duplicated some of the advice given by Chris above who posted whilst I was typing.

[Silicon]

I have the version with Octal valves. Earlier ones had B7 based valves.
I suggest looking for bad connections first.

I cleaned the valve socket contacts with an 'interdental' brush held by a long nosed (radio) pliers. The brush was approximately 4mm in diameter.
8 or 9 strokes cleaned a lot of dirt from them.

I found that the wavechange switches were initially difficult to clean.
They now work OK.

Good luck.
Brendan

[davidrt]

Many thanks to all for the feedback. I have cleaned in general and also removed a couple of valves that was in easy access. I think, touch wood, this has improved 100% because it seems to come on quicker and you only require minimum volume.

[Herald1360]

Let's hope it stays OK for a while.....

[davidrt]

Following on from the above I need to replace the MU14 valve. I noticed that it seemed to be sort of arcing. Took it out and assume it is broken because there are bits rattling around. I did put a bid in for a Marconi MU14 so I guess 99% sure that would be OK. However outbid. My question is providing it says MU14, is that OK?

Some say eg "VU39 MU14 UU5 BRIMAR AM 10E/9600 102 NOS VALVE " or "CV1039 MU14 UU5 MULLARD VU39 NOS VALVE" etc I know NOS is new old stock and I assume Mullard and Brimar would be the makes. No need for complete electronics lesson but some sort of idiots guide to make sure it is the correct one.

[Herald1360]

The list of hieroglyphics look like a reasonable set of other manufacturer's part numbers for valves equivalent to the MU14.

There's some relevant info here:

http://www.r-type.org/exhib/aaa0272.htm

It would seem that the MU14 itself at any rate wasn't the best of the alternatives.......

In any case NOS is rather pricey.

Colomor seem to have used/tested UU4 which would also do.

[davidrt]

9 years ago posted asking for advice on radio and replacing a valve. I did this (MU14) and the radio has been working fine until today.

For whatever reason turned on this morning not a crackle.

Would like to be able to get it going again. Have taken out & put back in MU14 and KT42 and they seem OK ie no loose bits.

My question is, are there valves underneath the aluminium round covers with screws? The painted valves cannot tell, the transparent ones all light up except the magic eye which I believe is for cosmetic purposes only.

Quite frankly it's a shot in the dark and don't want to poke around too much in case I have problems There is a motherboard underneath which could come into question as well.

Obviously open to suggestions.

[Simon Gittins]

Originally Posted by davidrt

My question is, are there valves underneath the aluminium round covers with screws?

No, I think you are describing the IF cans and you don't want to be disturbing these. You should be able to see 7 valves in total (including the magic eye tuning indicator).

As you have the valves lighting up but no sound, the next logical step would be voltage measurements. We could guide you through this.

A possibly better suggestion would be to place a request in the Repair and Restoration Services Wanted section:

https://www.vintage-radio.net/forum/...play.php?f=145

As the set has been restored and was working until recently, it should be fairly easy for someone experienced to establish what is wrong.

[davidrt]

Now fixed, with thanks to another member. It was in fact one of the valves.

[Station X]

Tell us more. These are discussion forums after all.

[Glowing Bits!]

Which valve would be nice to know, it could be the output, rectifier or detector, all these things can cause those symptoms.

[davidrt]

Mullard TDD4

[Station X]

A Double Diode, Triode as shown by the type number then.

[cathoderay57]

Hi folks, I was the repairer. I had a DH42 in spares, which is the correct Marconi replacement for this set (TDD4 being Mullard equivalent) so fitted that. The set had previously been restored very competently and the refinished cabinet was stunning. A nice set that worked well. Cheers, Jerry