Vidor Gem.

[G8UWM-MildMartin]

With a multimeter on the apppropriate voltage range connected across the battery with the set switched on, or a filament lamp (bulb) rated at anything between 6 and 12 V briefly connected across the battery and its brightness compared to either another set of cells giving 6V or being a touch brighter than when connected to a common 5-V "USB" supply (mobile phone charger or from a computer USB port.)

[pepmin 1]

Hi. Thanks for the advice. I will give it a try tomorrow.

[pepmin 1]

Out off curiosity what is the small red and yellow component X1 in the service data pic that I sent? You can see it better in the photo at the start off this post. According to to the service data it says that it is CG12E. A diode maybe ?

[Cobaltblue]

Yes it's the detector diode

Incidentally ISTR this set has amplified AGC using the first audio transistor you need to make sure that the AGC decoupling is good it's just I notice that this set has several Plessey red black and yellow electrolytic capacitors and these tend to fail at this age. Chee



Cheers

Mike T

[pepmin 1]

Hi Thanks for that Mike. As I have said I have Piggy backed the old electrolytics with new capacitors of the same value or as near as I can get. Doing this one at a time until I had lightly tacked them all on made no difference. Are we saying that the old ones have to be taken out off circuit? In the past I have jumped new capacitors onto old transistor radios and the difference would sometimes be immediate with them bursting into life or audio distortion being corrected etc. I had been hoping for a similar scenario with this radio.

[ms660]

Leaving old capacitors in circuit with replacements connected across them is bad practice.

Lawrence.

[Techman]

I think he means that he's only tacking the replacements across the old ones for test purposes. You can get away with this with electrolytic types as they normally lose capacitance when faulty, and due to their generally high value, any leakage usually won't affect the results of this test. You can also get away with this test on the lower value paper types on this occasion, as this is a low voltage transistor circuit, and again, due to this, leakage that the old ones will/may have won't 'usually' affect the test results. Please note that you will NOT be able to do this test with low value paper (Hunts) types in valve radios with high voltage circuits, as leakage in the old components rather than lack of capacitance will VERY likely be the fault, so in this case the old capacitor MUST be removed/disconnected first to perform the test.

[poppydog]

Just a thought, with regard to your whines and whistles, in your pics you have your radio on a shelf next to what looks like cordless phone and a BT router.
regards poppydog

[pepmin 1]

Hi lawrence. I realise that. It was just my way off fault finding. I have a mechanical background but no electronic skill levels to speak off so can only do what I can do. I have a graveyard off old radios, transistor and valve that I have pulled out off skips and the recycle centre and that I have managed sometimes with the help off this site, and sometimes down to my own sheer determination to get them all working. I have surprised myself in what I have achieved with little or no skill level. I have recapped radios, replaced transistors,resistors and diodes. I even managed to to solder in a flimsy looking audio chip to a 70,s HMV transitor radio and got that going. All with a cheap soldering iron and multi metre and little or no knowledge to what I was really doing. All off these radios would have been crushed or in landfill by now if it was not for me having a go. My interest in old radios has now waned somewhat and I only bought the Vidor Gem for nostalgic reasons but the fact that I cant get it going properly is annoying me more than anything else. But I am the same way with everything!

[pepmin 1]

Hi. The radio is not near the phone and only put there for the pic. Thanks anyway, Colin.

[pepmin 1]

Hi Techman. I would never do this sort of a test to a mains valve radio and as you say only transistor radios that are low in voltage. Colin

[Techman]

It's good to see that you're trying to preserve as many of the original components as possible. It's likely that ALL the old capacitors will have some degree of leakage, but it's a case of understanding that in much of the circuit that this leakage will have no effect on the operation of the set. Let's be realistic, these capacitors probably had a very slight leakage when they were brand new due to how they were manufactured. The set would probably have been prototyped around these components with there shortcomings being taken into account. There's not a lot to go wrong with a typical 0.1uf paper type capacitor other than leakage, as it's just a couple of long strips of of metal foil with a strip of paper in between and rolled up like a toilet roll. There are possibilities of how it could lose some of its capacitance, but usually it's a total loss due to one of the connections coming off one of the foils. The usual fault will be electrical leakage through that separating paper strip between the foils, and it's understanding whether the leakage that it's likely to have, will have any effect on the operation of the circuit that it's in.

There may be a possibility that if all the capacitors had very bad leakage that this could all combine and add up to manifesting itself as a fault condition, but again, as we're dealing with low voltage and relatively low impedance circuitry here, we have to ask ourselves how much leakage in capacitors would there have to be to cause a fault.

[ms660]

For those not in the know, bridging capacitors for diagnostics can be hit/miss, consider a short circuit (in effect) capacitor, according to the Bridgeomatic it must be a good'un.

Lawrence.

[pepmin 1]

Thanks for that Techman that was very interesting to read. You are right I do want to preserve the components if I can. I also understand that this is not always possible if you want a reliable working radio. With some battered old radios I have no problem with the scatter gun approach ( in my case )regarding capacitors etc as getting the radio going was my only concern. Ordinarily I try not to do this as I like to see the radio working in as far as possible in original condition. I have transistor radios with the problematic germanium transistors and they are still working years later when the general advice is to replace them. I have a bush VTR103C that I use everyday with all off the original transistors. When I received the radio it was not working but a tap with a screwdriver on one off the transistors brought it back to life and it hasn't missed a beat yet 3 years later, but I know it could fail at any time. The Vidor Gem would never be an everyday radio but would have been nice to get working properly on MW. You guys with your expertise could narrow the fault down fairly quickly and only replace the required component.I on the other hand would be be replacing everything in the vain hope that I would get it going that way. I take more satisfaction in looking at the radio even if not working properly and imagining the life that it had. Not quite the same for me if it is full off modern electronics.

[Techman]

Lawrence has picked me up on the fault condition that I forgot to mention, and that is the 'short circuit' capacitor. Hopefully, the OP would have tested for this with a multimeter on a low ohms range across each one before bridging them, keeping in mind that there could be another component of low value in the associated circuit that could be shunting it to give a false low reading.

The transistor that you mentioned in another set that responded to a 'tap' with a screwdriver handle was probably suffering from tin whiskers. Certainly tapping them can clear the fault and sometimes this can be a permanent fix. It's often the four legged AFxxx type that suffer from a short from the outer screen to part of the internal junction. I actually never replace these in my own stuff, I just disconnect the screen connection of the transistor, I don't even cut it, I just un-solder it from the board and bend it back out of the way. Although this has worked for me every time, there could be the situation where the whiskers of tin short out the whole junction and just disconnecting the screen would not correct this problem. Then there's the standard three legged transistors that are fitted to a grounded heat sink, where other than replacement, electrically isolating either the heat sink or the transistor from it, effects a cure.

I have to admit that the fault you have on your radio does seem to be a little bit 'capacitorish' if I'm honest, unfortunately, this is where an understanding of the circuit and proper test equipment and fault finding methods come to be needed.

[pepmin 1]

Yes I think that you are right that a capacitor is at fault. A silly question maybe but I will ask it anyway. Considering that it is MW that I am having the problems with...is there any off the electrolytic capacitors that I can discount that may only be in use when on LW ? I did say that my knowledge off electronics was minimal!

[julie_m]

Usually, the only bit of circuitry that is not common to both wavebands is the coils. But, if the LO is feeding into the audio stages via poor decoupling, it's not beyond the bounds of feasibility for the set to be just about OK on LW but misbehave on MW.

Replace the red, yellow and black Plessey electrolytics with modern ones of the nearest modern preferred value. You may have to be somewhat creative with the wiring, as modern capacitors tend to have both leads coming out the same end rather than one lead each end. Be sure to get the + and - the right way round.

[pepmin 1]

Hi Julie. Thanks for the reply. I think that you may have a point. I only noticed tonight that although LW works fine when switched on first it doesnt appear 100% audio wise for the first few seconds. A bit like a valve radio warming up. The volume starts to rise ever so slightly and the audio then sounds better. After that it behaves itself for as long as I want to keep it on. I did take C17 out of circuit a few nights ago and tried a new there but that made no difference. As I have said previously I dont want to tear everything out but I guess in my case thats what I may have to do to get the radio to work properly.

[marconi_pete]

To test the battery under load, make sure the set is switched on and that the back is off. Then connect the probes of your tester to the positive and negative of the battery connector on the set and set your tester to DC range. I too think it is a capacitor causing the problem. Depending on the size of the original capacitor, you may be able to restuff the capacitor with a modern replacement retaining the original look. The red and black Plessey caps are tricky to restuff but I have done it so know it's possible.

Thanks,
Peter

[pepmin 1]

Cheers for that Peter. I have given my multi-meter to someone and just waiting to get it back. I will try that when I do. Colin