08-07-2011, 10:25 PM
A very useful and important thread Roger. I do leave the power on in my workshop as I used the workshop (just 10' x 8') for woodturning as well as radio, so I have a dust extractor suspended from the ceiling which comes on automatically for two hours each night. I have a woodturning dust extractor (like a powerful vac) that I used when sanding on the lathe, but the ceiling mounted one helps keep general dust in the workshop to a minimum. recently I bought a small dehumidifier - not much larger than a kettle, with a 0.25 L tank. Given that it's been sunny and warm for several days, I left the dehumidifier on overnight to see if it extracted any moisture in the workshop. Next morning there was at least a glassful, so hopefully, in the winter it will keep the dampness down. The workshop is heated, the walls are insulated and the windows double glazed.
I do have two isolating transformers - one about 1 amp, the other 2 Amps, so more than adequate for radio repairs. I'm always a bit concerned that often, the first radio that novices cut their teeth on seems to be the Bush DAC90A, which is not at all an ideal radio for a first project, because although not complex, it is an AC/DC live chassis. I also wonder if some of the potential safety hazards on the DAC90A are fully understood. For example, often the rubber insulated wire on the dial lights is in poor condition. Although admittedly it's a remote possibility, what if one of those wires came into contact with the speaker frame and hence, the metal speaker grille with the chassis live? I always replace the speaker wiring and dial light wiring - it's not a big job. Furthermore, for me, safety trumps originality every time, and I consider that instead of restorers searching for reversible Bush 2-pin mains plugs on e-bay, they'd be better to consider hard wiring the mains lead to the pot switch to ensure that the correct polarity is maintained at all times. Of course, what tends to happen with e-bay sales of DAC90As is that they're offered without the mains plug so that the onus is on the restorers to put it back into use, then further down the line, lo and behold, the mains plug pops up on e-bay!
Another safety factor is to do as much testing and diagnosis with the set disconnected from the mains, whereas in reality, often, caution is thrown to the wind, the set plugged in to 'see if any sound comes out of it'. A great deal of testing can be done before a set is even plugged in. Visual observation will highlight perished wiring, which will in any event need replacement, which can, and should, be a first priority. I always use silicone covered heat resistant multi-strand wire in vintage colours, which I stock up with from Phil Marrison at the NVCF. Resistors can be checked to see if they're in spec, valve filaments can be checked for continuity, and heater/cathode shorts, transformer windings, coils, OPTs, IFTs and the 'switchery' can all be checked for continuity and against the circuit. If a set is to be 'restored' rather than just 'mended' most restorers will wish to replace all the waxy caps, and if fitted, to replace the mains suppressor cap across the mains input with an X class cap, or at least clip it out. It makes much more sense to do these things before the set is switched on rather than afterwards. If - due to faults - a set draws excess current, and if it has a mains energised speaker, that excess current can burn out the field coil, which has thousands of turns of fine wire. Similarly, mains transformers and OPTs risk being damaged. Sure, a lamp limiter can reduce the risk, but why put the set under stress? Best to use the lamp limiter after the set has been restored - not before!
Often, rather than poking around a set with two test prods, it's possible to use a croc clip on one lead attached to the chassis, then you only have to look what you're doing with the one prod. Personally, I always make a 'cradle' from scrap wood and bracket in which to suspend the upturned chassis to keep it stable, but I know that many restorers just balance the upside down chassis any way they can. The point we should bear in mind, is that we do this for a hobby - not for a living, so there are no time pressures upon us to do a rush job. There are times when we should therefore temper our natural enthusiasm with a little more discretion. There are two definitions of 'amateur' - someone who isn't up to the standard of a skilled professional, or on the other hand, someone who is highly competent and able to work to a high standard, but doesn't do it for a living. Hopefully most of us would aspire to the latter!
Good lighting is also essential, and personally, I have a magnifying Anglepoise style lamp with a circular florescent tube which I often find very useful.
I hope that these observations don't read like a finger-wagging lecture - it's not meant that way, but a lot of heartache and hassle can be avoided by adopting a cautious rather than tempestuous approach.
Or so it seems to me, having learnt a few hard lessons in 'the university of life'!
Have fun,
Night night,
David
I do have two isolating transformers - one about 1 amp, the other 2 Amps, so more than adequate for radio repairs. I'm always a bit concerned that often, the first radio that novices cut their teeth on seems to be the Bush DAC90A, which is not at all an ideal radio for a first project, because although not complex, it is an AC/DC live chassis. I also wonder if some of the potential safety hazards on the DAC90A are fully understood. For example, often the rubber insulated wire on the dial lights is in poor condition. Although admittedly it's a remote possibility, what if one of those wires came into contact with the speaker frame and hence, the metal speaker grille with the chassis live? I always replace the speaker wiring and dial light wiring - it's not a big job. Furthermore, for me, safety trumps originality every time, and I consider that instead of restorers searching for reversible Bush 2-pin mains plugs on e-bay, they'd be better to consider hard wiring the mains lead to the pot switch to ensure that the correct polarity is maintained at all times. Of course, what tends to happen with e-bay sales of DAC90As is that they're offered without the mains plug so that the onus is on the restorers to put it back into use, then further down the line, lo and behold, the mains plug pops up on e-bay!
Another safety factor is to do as much testing and diagnosis with the set disconnected from the mains, whereas in reality, often, caution is thrown to the wind, the set plugged in to 'see if any sound comes out of it'. A great deal of testing can be done before a set is even plugged in. Visual observation will highlight perished wiring, which will in any event need replacement, which can, and should, be a first priority. I always use silicone covered heat resistant multi-strand wire in vintage colours, which I stock up with from Phil Marrison at the NVCF. Resistors can be checked to see if they're in spec, valve filaments can be checked for continuity, and heater/cathode shorts, transformer windings, coils, OPTs, IFTs and the 'switchery' can all be checked for continuity and against the circuit. If a set is to be 'restored' rather than just 'mended' most restorers will wish to replace all the waxy caps, and if fitted, to replace the mains suppressor cap across the mains input with an X class cap, or at least clip it out. It makes much more sense to do these things before the set is switched on rather than afterwards. If - due to faults - a set draws excess current, and if it has a mains energised speaker, that excess current can burn out the field coil, which has thousands of turns of fine wire. Similarly, mains transformers and OPTs risk being damaged. Sure, a lamp limiter can reduce the risk, but why put the set under stress? Best to use the lamp limiter after the set has been restored - not before!
Often, rather than poking around a set with two test prods, it's possible to use a croc clip on one lead attached to the chassis, then you only have to look what you're doing with the one prod. Personally, I always make a 'cradle' from scrap wood and bracket in which to suspend the upturned chassis to keep it stable, but I know that many restorers just balance the upside down chassis any way they can. The point we should bear in mind, is that we do this for a hobby - not for a living, so there are no time pressures upon us to do a rush job. There are times when we should therefore temper our natural enthusiasm with a little more discretion. There are two definitions of 'amateur' - someone who isn't up to the standard of a skilled professional, or on the other hand, someone who is highly competent and able to work to a high standard, but doesn't do it for a living. Hopefully most of us would aspire to the latter!
Good lighting is also essential, and personally, I have a magnifying Anglepoise style lamp with a circular florescent tube which I often find very useful.
I hope that these observations don't read like a finger-wagging lecture - it's not meant that way, but a lot of heartache and hassle can be avoided by adopting a cautious rather than tempestuous approach.
Or so it seems to me, having learnt a few hard lessons in 'the university of life'!
Have fun,
Night night,
David
