Part 3 – Things that go bang in the night

The thing about working on a 40+ year old instrument is that certain critical parts are well…. 40 years old. Wiring, capacitors, motors, switches. Fortunately a lot of Hammonds are built like tanks. It’s not unknown for an organ to be stood outside for a couple of years and fire up after a bit of cleaning and oil.

The T series are a little different. Yes they still have the tank like tone generator but instead of valves (sorry – tubes in the USA) they use solid state circuits. Most Hammond aficionados throw their hands up in horror at the thought of a valveless instrument but there are a few advantages to the T series. They are easier to work on with less lethal voltages flying about. Replacement electronics are widely available and cheap. Tolerances can be tightened up with newer parts – remember that Hammond used relatively cheap electronic components as they didn’t expect them to last for decades.

Later on I’ll start running through these electronic replacements and upgrades but the first thing to do was make the organ safe. The mains lead is usually hard wired into the power supply and on this T it was no different. Forty year old mains cable is liable to crack and perish and most of the time you can’t actually see it. So the first and least expensive job to do is replace this cable. I’ve wired mine into a fused IEC socket – the normal three pin socket – so that I can use standard power cables. In the UK and Europe the cable is also earthed to the power supply chassis.

With the introduction of the cheaper spinet organs Hammond moved away from the traditional Start/Run double switching method of starting up the tone generator to a self starting motor with just one switch. It relies on a motor run capacitor to regulate the voltage to the motor. These take the form of a large can capacitor that is clamped in place just in front of the generator motor.

hammond caps-1-2 hammond caps-1-3

Now these capacitors can be filled with a foul concoction which in some cases is downright nasty and have a finite shelf life – it was certainly never spec’d to last 40 years. symptoms of a dodgy capacitor include – tones starting to fluctuate, motor running very hot, difficulty with the motor starting.  If you experience any of these then turn off the Hammond immediately. If you’re lucky then you can quickly replace the motor capacitor. If you’re unlucky then the can capacitor explodes and throws this gunk everywhere (photo courtesy of the unfortunate Alpine from Organforum.com). The explosion below happened 10 minutes after the organ had been switched off due to the fluctuating tones issue. Here’s the thread on Organforum.com where he talks about the episode.

blown cap

An exploded can cap.

If you’ve just bought a ‘new’ Hammond then don’t even bother testing the capacitor – just change it as it costs next to nothing. It’s a bit like buying a used car and you don’t know if the timing belt has been changed – just change it. Now if you’re in the USA then replacements are available from a couple of sources and match the original in both spec and dimensions. In Europe it’s a different story. The 50Hz capacitor is a 1.25uf – pretty much impossible to find here.  What I ended up using was a couple of 2.5uf 440v motor run capacitors from Maplin which I then wired together in series to give me 1.25uf. Note – you must use motor run capacitors rather than start capacitors. There is a big difference although the ones labeled for both start and run should be okay. A bit of self amalgamating tape around the caps and it fitted quite snugly in the original clamp.

The new caps in place

The new caps in place

Part 4 – Down and dirty with the drawbars

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