[Techman]

Hi, sorry for the delay in replying.

You don’t say whether you’ve still got the limiter in line now you’ve got it connected up to the original gram speakers in the cabinet. If you’ve still got the lamp in line, then I wouldn’t connect full mains just yet. It may well be ok with full mains and I have to say that if it were me I would have done by now, but I would certainly be feeling all those large electrolytic capacitor cans for any signs of warming.

So, assuming that you’ve still got the lamp in line, the next step is to see which of the large electrolytic capacitors in the power supply smoothing circuit has failed either o/c or just low capacitance. The ones that show signs of distress may not actually be the ones causing the hum and I’ve certainly run some of my old gear with capacitors in that state with no problems. It could be that the set was left switched on for several days sometime in its life and the capacitors just vented a little bit due to heat, but it could also be that they’re just not in a very good state and really need replacing.

The electrolytic smoothing capacitors all seem to be 8uf with a 16uf reservoir. You could buy a nearest value 10uf and either solder it or attach it with crock clip leads across each of the ‘can’ capacitors in turn to see which one significantly reduces the hum. If you bought a couple, you could connect them in parallel to make 20uf and connect them across the 16uf can to test that. It may, however, be easier to buy all the ones you need in one go and replace most/all of them – they’re not that expensive. You need the ‘axial’ type with the wires coming out of each end for the 8uf type. They’ll need to be no less than 450 volt working and should be 105 c temperature rated for best reliability. For permanently replacing the 16uf reservoir, you’ll ideally need the best fit type you can get, paying particular attention to the ‘ripple current’ rating and this one doesn’t look like it wants to be an axial type. This is all, of course, if you decide to replace them all, it’s up to you. I myself, have various ‘test’ capacitors to hand for doing this type of testing so I don’t need to buy anything in until I actually know what I need. Some would advise you to just replace all of them regardless, the choice is yours, if you’ve got the time, then why not do the tests to see which one/s are faulty – you’ll learn a lot more doing it that way. A little word of warning – always make sure you connect electrolytic capacitors the correct way round (the same way as the originals) as they go off with an awful bang if you don’t and can be quite dangerous. Also, always make sure they’re fully discharged before touching the connections, as a shock will, at the very least, make you jump!

You’ll have to decide how you’re going to replace any faulty electrolytic capacitors. The replacements will be a lot smaller than the originals. You could fit them inside the hollowed out cases of the originals (re-stuffing). I’m a bit ‘iffy’ about re-stuffing. I never ‘re-stuff’ capacitors, although I wouldn’t say that I ‘never’ would. Replacement capacitors are designed to be in the open for cooling and not sealed inside an airless extra container. I suspect that many of the sets that have re-stuffed electrolytic capacitors don’t get continuous all day long use, or the slight heating of a capacitor is insignificant enough for it to make little difference. It is also likely to cause confusion for the future – we’ve already encountered cases of newcomers starting to restore a vintage radio where the old wax capacitors they’ve removed have turned out to have already been re-stuffed with new components and this situation is only going to get worse. I like to see a good honest repair, which is what you’ve done so far, as all the capacitors you’ve replaced have actually needed replacing. At least one of the electrolytics shown in the picture is fitted under a clamp. What I tend to do in this situation is disconnect it electrically from the circuit and just leave it there and fit the replacement along side it in the circuit. Depending on how the others are fitted, you could perhaps do the same with them if you’re going to replace them. All original smoothing electrolytics that are being replaced should be electrically disconnected from the circuit if they’re going to be left in place for historical reference. This means that the positive connection should be disconnected and isolated, the chassis side connection can be left in place if desired. So the choice is yours, test and replace as necessary, replace all, re-stuff, leave originals in place but disconnected and replace along side. Remember, nearest preferred value, working voltage as high or higher than the original (check that 16uf capacitor can in case it’s a 500 volt rating) if you need to replace it, and check the replacement for temperature and ripple rating. Be mindful of polarity as they’ll explode if you get it wrong and be careful of them holding their charge and giving you a shock, especially the new replacements.