Customers Repairs: Bush receivers


Bush VTR103, Repair No. E132

The set, made in 1963, covers Long, Medium and VHF (88-100MHz) and looks similar to the model TR82B which excludes the VHF range

 

VTR103

 

TR82B

 I understand this set was given to my neighbour Ian on his eighteenth birthday. It hadn't been used for some time and had probably been stored in a dampish atmosphere. Sets like this go through a transition phase from being just an old radio to an interesting bit of nostalgia. I guess the recent revival of this style of set and its appearance in shop windows helps to make it more desirable.

The set had a flat battery and refused to make any sound when turned on. This is slightly unusual as generally you get a crackle reducing in volume as the batteries last gasp is expended. My guess is that the damp environment caused some electrolytic action which unplated the contacts in the switch attached to the back of the volume control. With a bit of added dust covering the metal the switch then became defunct. This was proved when a milliameter was inserted in series with the battery and the set switched on. As the switch module was effectively sealed a trick is to drill a tiny hole in a suitable position in the rear plastic, taking care not to let the drill damage the internal workings. Once there is an aperture through the plastic, switch cleaner may be injected and if the switch is operated a few dozen times all will be well. This can also be done with crackly potentiometers.

Connecting an external 9v power supply half brought the set to life but it was very deaf and on its VHF range stations were miles out from the scale markings. The set uses the Mullard AF116.. series of transistors but measurements showed that none of these was faulty. For two reasons I decided to leave the chassis in-situ, firstly I did not want to expend too much time on the set and secondly, removing the tuning knob looks to be very difficult (the servicing information recommends a sink plunger but that would certainly not do the trick after nearly 40 years of the knob freezing onto the spindle!) but to carry out a full restoration would certainly entail its removal. As the knob was rubbing on the case I did however decide to pull it slightly. The method I normally use is to force a couple of lengths of PTFE coated wire under the knob and by carefully pulling and levering I manged to move the knob by an eighth of an inch clear of the case which was sufficient to stop the rubbing. Next alignment...by very gingerly wobbling the dust cores in their transformers I found they would all move with care. First I set the AM IF to exactly 470kHz then set the FM IF to 10.7MHz. This improved sensitivity by a large factor on the two modes. The oscillator coil serves both Long and Medium Waves so primarily must be set to the bottom end of the Medium Waveband then the position of Droitwich on the dial checked for accuracy. As it was miles out I then set the top end of the Medium Waveband with the trimmer and by juggling the various trimmers and oscillator coil core managed to get a good compromise with Droitwich not far from the correct position. Easing the coils on the ferrite rod and adjusting the RF trimmers then helped to liven up reception. Moving to FM... the VHF tuner assembly is mounted in a particularly awkward position making adjustment no easy matter. The metal screening can can be detached after removing two screws, but as this affects the oscillator, further adjustment must be undertaken after it has been refitted. The oscillator and RF coils are permeability tuned by a pair of aluminium slugs carried on a wire moved by the tuning knob. Interestingly the fully meshed position of the Medium and Long Wave tuning capacitor coincides with the highest VHF frequency position of the aluminium slugs. If this wasn't so it would be impossible to adjust the VHF trimmers as the vanes of the tuning capacitor would get in the way (is this design or a happy accident?). Setting the low end of the range, which is 88MHz is done by moving the position of the aluminium slugs. Unfortunately the adjusting screw seems accessible only if the chassis is removed from the case. Because of this I decided that there must be some compromise between frequency and scale markings. Firstly I decided to place Classic FM just within the top of the tuning range which is 100MHz and as locally the station is on 100.3MHz this was OK. In another area one might have to cheat. Fortunately, after some fiddling and refitting the metal screening can, the low end neatly covered Radio 2 reception so as far as dial settings were concerned all was well and with further careful twiddling of the trimmers I manged to get the set to pull in stations with uniform signal strength across the FM band. The set now works tolerably well but I notice interstation noise on VHF is peculiar. There's a sort of popping sound presumably a side effect of a muting circuit? Audio quality is not great, primarily because the speaker is not in very good order. I've found some people are very critical of sound quality. It depends on what you're used to and your expectations. Roberts sound quality is normally excellent and because of this I've been asked to change loudspeakers on two separate occasions when deterioration has occurred.

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