BushTR130 radio

[Celestial]

I have just obtained this radio form EBay. It is the old original version with MW, LW and bandspread. The radio is working well. However, the scale pointer does not coincide with the scale markings. There is a margin of error on both wavebands. I wondered if this is anything to do with the oscillator setting. I have inspected the radio and not found any components that might be causing this. There are just one or two old Philips Electrolytics that will need changing because of their values.
Also I have a query about C8. In both the manufacturers and Trader service sheet the value given for this component is 0.1mfd. There is a 10mfd capacitor fitted on the circuit board at that point. I cannot find any reference to any circuit modifications having taken place on this radio. Trader Service Sheet 1760 refers.

[ronbryan]

It is quite common on these sets for the vibration damping grommets on the tuning capacitor mounts to go hard or break up and leave the tuning capacitor at an unintended angle and a bit loose. This might contribute to a scale pointer error on both bands, or it could be just the pointer in the wrong position or that the set needs the oscillator trimmers reset. It is awkward to change all three grommets however as the (very tight) tuning gear grub screw has a tendency to break.

I've got a photo of a TR130 which shows a Mullard electrolytic in what I believe to be the C8 location.

Ron

[G6Tanuki]

Yes, as mentioned, the tuning-capacitor support rubbers decay with age [what can you expect after 50 years...?] and this causes errors as well as a horrible amount of backlash which will make accurate tuning a real problem.

[I've reworked quite a few TR130s over the years - it was styled by the late Tom Karen - who worked for and later managed Ogle Design - who designed the likes of the Reliant Scimitar, the Raleigh Chopper, and Luke Skywalker's "Landspeeder" in the original Star Wars movie!]

[Celestial]

The tuning capacitor is at an angle in this radio. I do not intend to try and take the assembly apart to replace the grommets I am going to leave well alone. The other slight problem I have is that the volume control is very noisy certainly at the bottom end when switching on. There is no way that one can give it a dose of switch cleaner as the control is completely sealed. Again, I do not intend to try and take this assembly apart to completely replace the volume control.
Gentlemen, thank you for your replies to my queries.

[Leon Crampin]

Noisy volume controls on the TR130 arise because the electrolytic coupling capacitor connected to the slider has sufficient leakage current to allow DC on the track/slider interface.

An instant fix is to remove the electrolytic and replace with a non-polarised capacitor. Its value is not critical, I think I used a 4.7 microfarad 100 V Mullard 344 series, which exactly fitted the board and just cleared the other parts of the set when re-assembled. Noise fixed instantly.

The Plessey moulded track potentiometers used by Bush are practically everlasting - but in this case, the circuit design is incorrect, and an electrolytic coupling capacitor is unsuitable.

Leon.

[Celestial]

Dear Leon,
Thank you very much for the tip. I did not know that. I will change that component when I next get a chance.
As I said in my previous post, the radio is working fine and it is in reasonably good condition complete with carrying handle. I am going to change a couple of the old Philips electrolytics when I get round to it. I have measured them and they have wandered off their marked value by quite a margin. The electrolytic across the supply always seems to behave like that for some reason.
With all good wishes.

[David G4EBT]

Originally Posted by Celestial

I am going to change a couple of the old Philips electrolytics when I get round to it. I have measured them and they have wandered off their marked value by quite a margin. The electrolytic across the supply always seems to behave like that for some reason.

Where blue Philips are concerned, it's often worse than that - they start to behave like low value resistors.

On any Bush sets, as with Roberts and others of the '60s in which these caps abound, before doing anything it's worth connecting a mA meter in line with the battery to see how the current consumption compares with the spec. The pic below is of a 680uF blue Philips from a Roberts R505 (C40) which showed up on test not as a capacitor, but as a 0.53 Ohm resistor - basically a dead short.

Not a criticism of Philips, given that these sets are more than fifty years old - way past their MTBF. (mean time before failure).

[Leon Crampin]

As an update, I've just checked my TR130 and the capacitor I fitted is actually a 3.3 microfarad 100V 344 series component. This fits the board and just clears the loudspeaker frame - no other mods required. There is no apparent loss of bass.

The blue Philips/Mullard electrolytics are often OK in the larger sizes if they are re-formed before testing. Often, the in-circuit conditions are not optimal for maintaining polarisation.

Any physically small electrolytics of this age need to be changed on sight. Their unfavourable surface area/volume ratio means that by now, they will have dried up.

Leon.

[crackle]

These are nice radios with a good sound.
But I have replaced very few blue Philips electrolytics, in the hundreds of transistor radios of this sort of age, that I have serviced. I find they are normally very reliable. Despite being so old they often have a better ESR reading than modern ones.
But you can get the odd one now and then.

Mike

[Celestial]

Thank you to everyone for all your tips and information.
I will have another look at this radio when I get a chance.
With all good wishes.