Stella ST154U.

[leroygibbs]

Has anyone any experience of modifying or repairing the very difficult to get at wavechange switch in this lovely radio. I bought the set for a fiver, carried out numerous component changes and it works beautifully on AM. FM is poor due to the switch. Thanks.

[ukcol]

Hello leroygibbs and welcome to the forum.

I don't know your set and cannot find any reference to it in my extensive list of service information or the usual sources on the net. Stella model numbers take the form STxxx.. but searches for 158U and ST158U are unsuccessful. It follows that your model may be quite uncommon.

If you are able to post pictures of the set and in particular of the chassis someone may recognise the equivalent Philips model.

It will also be helpful to know more about the symptom, "FM is poor due to the switch" doesn't convey a great deal. Having said that many wave-change switch problems can be solved by cleaning the contacts, but with an FM set extra caution is required because there will be HT on a set of contacts and careless cleaning can cause damage. You will need a good quality electrical switch cleaner (don't use WD40) and will need to wait for it to thoroughly dry before applying power again to the set.

[leroygibbs]

Thanks for your reply UKCOL, my apologies I gave you duff info. Start again- Model is ST154U or the Cossor CR1102U. I do have the circuit diagram and have worked through the whole set. Voltages around the UCC85 are OK as per the spec. Problem arises due to contacts on the FM/AM switch. Tried cleaning with switch cleaner to no avail. Contact resistance is poor. Will try to post a photo, but don`t have much success on other forums.

[Station X]

Thread title updated.

[ukcol]

i have the manual for the Cossor CR1102U which also covers the Philips equivalent model B4G37U.

The under chassis layout drawing shows the wave-change switch as a slider type in the middle of the chassis. It doesn't look particularly difficult to get at but the drawing may be misleading in that respect.

The fact that the UCC85 voltages are about right means the HT switch in the W/C switch is OK. There are another 4 sets of contacts associated with switching to FM.

Forgive me for asking but I have no idea, of course, what experience you have of repairing valve radios. The question is, what has convinced you that the wave-change switch is the cause of the poor FM? Have you managed to measure the contact resistances of the switch or perhaps you find the set works OK sometimes if the switch is "jiggled" about?

If you haven't found the above the first suspect when you have weak reception of VHF/FM is the UCC85 valve being low emission. These valve VHF tuners also require a decent VHF aerial if you are not in a strong signal area.

[leroygibbs]

OK bit of history, now retired, been in electronics all my life, used to build and operate HF radio and was a HAM for many years. So the fixed contacts on the w/c switch seem to have lost tension, and not a lot I can do about it. Must have had lots of use in its heyday. Jiggling wiyh the contacts as you say improves reception. Incidentally, all coupling, decoupling and electrolytics are new as are the valves.

[ukcol]

Hello again,

Just a thought - As there is not a great deal on AM nowadays perhaps you could justify hard wiring the wave-change switch for VHF/FM and disconnect the mechanical linkage?

[leroygibbs]

Yes I was thinking that also. Its deffinitely the switch that's causing the problem. I'm also going to change a few cap values to increase the FM range from 100 Mhz to 108 Mhz. Thanks for your help.

Martyn