Derailleur compatibility

[johnnyb47]

Hi again.
I've been thinking about replacing my aging Simplex rear derailleur with a new one, but I'm a little confused on what would be compatible. My bike is an old school 12 speed road bike with friction shifter's with a 6 speed cassette on the rear wheel. I'm looking to pay around £25/30 for one which should get me a low end Shimano jobbie.
When I look for one though, most state that they are 7/8 speed , and was wondering would these actually work on a 6 six cassette. The cassette fitted to my bike is a 14/24 (if that has any bearing on my choice of derailleur).
Many thanks.
Johnny

 

[Drago]

You'll have to fiddle with the limit screws, but it will work.

Somewhere I have a silver Sora mech, very low mileage in near mint condition you could have cheap.

 

[Cycleops]

I got one of these when I converted my old Dawes with a seven speed and it worked fine. It had indexed shifters.

They're on clearance at Evans currently for about £27.
Edit: I see @raleighnut used the same one on a Carlton which I think was 6 speed.

 

[raleighnut]

If you're using friction shifters then anything will work fine (unless its 11 speed when chain width could be an issue) and @Cycleops is correct I fitted a 'New 105' (it was the model that replaced 'Golden Arrow') to my Carlton but that's a 1987 model which is capable of being 'indexed' to 6 speed but I run it with friction shifters (indexing was a new thing at the time and I didn't trust it)

 

[johnnyb47]

That's brilliant. Just the news I wanted to hear. Thank you all for your good advice ..