Re: [MELB TRAM] Buzzing Noise (Xmas Spirits!)

["Tom Boles" <mousewithglasses@NO.CANNED.HAM.hotmail.com>]

It is probably some kind of chopper control. It is a kind of thyristor
semiconductor, that controls acceleration and deceleration by 'chopping'
the current (switching it very fast?). The description that it "varies in
pitch" seems to confirm this. On C, T, and some V sets in Sydney, the high
pitch whine jumps up and down in perfect musical octaves, and a jump of one
octave up, indicates a doubling of frequncy of current and sound. At low
speeds, the noise is at a lower frequency so it is audible. I have heard it
is the motor coils vibrating at the frequency of the electrical 'chopping',
but on Sydney C/T/V sets, it comes from the overhead compartments,
especially noticeable in the C sets, just as in the tram you described.

> ... a high-pitched buzzing noise  <<Snip, snip, snip>>