HMV Barn Project

[Nowhere-Man]

I was struggling a bit with terminology in this thread. I think what you are calling a "ladder" is tag strip. There are various types but here's a picture of one type: http://creativity103.com/collections/Tec...al2620.jpg There is also tag board such as: http://www.brimal.co.uk/components/com_v...988106.jpg

Both tagstrip and tagboard are commonplace in sets that pre-date printed circuit boards. It was also common proactice to make a solid mechanical joint before soldering. This makes it hard to remove a component. Many of us will simply cut the lead of the old component and solder on the new one. We can debate the merits of making a mechancial joint - I usually hook the component lead into the tag but don't wind it round.

First thing I find is the volume pot is kaput. Resistance was infinity between live and neutral so I feared the transformer primary was shot. It soon turned out there was actually no feed via the switch to the transformer and when I did locate the actual transformer primary leads, Ohms was about 40 R.

This reads strangely. When you say "volume pot" I think you mean the mains switch which is commonly combined with the pot. It's quite common to get an infinity reading even when the switch is closed. This is usually due to oxidation of the contacts. The low voltage of the meter won't punch through the oxidation. When you apply mains, even with a lamp limiter it usually works just fine. Though I've see some that need some Servisol and repeated switching on/off to get them to work.

Of course it's possible for the switch to fail completely. Sometimes it's possible to get a repalcement pot with switch, other times you may have to do transplant surgery and graft on a good switch from another pot. The last resort is to bypass the switch and rely on the mains switch on the wall. Not ideal but at least the set can work. It's a good idea to switch off at the wall anyway.

Actually there was no electrical contact through the two fuses due to the grime and dirt you referred to. On this set they fused the incoming mains before rectification but the metal was so aged, no ohms reading showed. I had to start by scraping the fuse-holders.

As to the switch, basically the on and off function was clapped from the start. No click, I'm afraid. There was also no feed through  the switch to the transformer primary. Given the wires were so tangled, I ended up scraping a tiny bit of insulation off what I believed to be the transformer wires and then finally I got a 40 Ohm or so reading. So, the primary may be O.K.

It would be nice to get a pot and switch as a unit and just rewire it as it should be. Then I should get 40 Ohms reading between live and neutral with the switch on.

The "ladder" as I call it had me thinking very carefully about how to approach the soldering. I gave it lots of thought and tried to weigh up the chances of snipping the ladder out so I could thread in the new capacitors. I did think of dabbing different colour paint on all severed leads. I suppose it's possible but you have to ask whether there might be an easier way around. In the end, I decided to just have a got at soldering across the ladder. That means, if the soldering joint isn't good enough, you'll have more stress later on. Anyway, here is how I did it:

I have some thick cable that's insulated and very rigid. If you start by tinning the end of the wire and tinning the lug on the furthermost end of the ladder, you can get lots of heat and solder and virtually weld it on. You can then tug the whole wire forwards, loop under the opposite rung a couple of turns (needs a bit of force) and you end up with an overhang. Snip off a bit of insulation and you then have a large soldering base. It's taken the rear to the front. You can then just solder the capacitor at the front of the ladder rather than across. Again, lots of solder and heat helps. You do have an inconvenient possibility of a future short this way but I'll insulate these joints later on and take safety measures. I'm afraid there is always a chance of a joint coming off because you lack the secure mechanical anchor of the original method, but it's the best I can do at this point. I've tugged on my joints and they seem O.K. so I'm off to Maplins tomorrow to get some 0.047's.

So, the chassis has been hugely cleaned up and looks a lot better. The transformer and valves might be O.K., we'll see. I could do with a 500 K switch/pot. There is surface rust on the waveband switch.