Pennine Ranger Project

[Terry]

Don't forget that not all LW sets had LW oscillator coils!

This was mainly a transistor set bodge but it would be worth trying: simply re-use the MW coil and switch a suitable value of capacitor across it for Long Wave.

It might not track with the aerial coil as well as the proper coil but, as long as it receives Droitwich well, I doubt anybody will notice the difference!

[boater sam]

I've never tried that. It may be difficult as the long & medium wave oscillator coils are  transformers, where would I put extra capacitance? Switching it in could be awkward too.
The circuit is on the CD if you could have a look?

[boater sam]

I've never tried that. It may be difficult as the long & medium wave oscillator coils are  transformers, where would I put extra capacitance? Switching it in could be awkward too.
The circuit is on the UKVRRR  CD and on the web if you could have a look?

[Mike Watterson]

You just parallel the capacitor to the winding that gets switched to the tuning capacitor, but I suspect something else is wrong. Gluing the broken core doesn't reduce Q (it may even increase it). So if the frequency range is correct the failure to oscillate is for some other reason. Lack of gain somewhere. Or core at wrong end of coil / transformer.

[pwdrive]

So far as I can make out you would need some extra switch contacts, I wonder if you could replace the oscillator coil with a Denco as I believe they are slug tuned.

Lawrence.

[boater sam]

Thanks Mike, I have looked at everything else, the cores are unmoved, I cannot establish the frequency range with my equipment, I would not know how to with 2 coupled coils either. Short & medium waves are fine, sensitive and tracking well, Valve voltages/currents are roughly correct, all have been substituted. Components that were suspect have been changed, small value caps seem OK, resistors are all 20% and in tolerance.
Why would a broken pot increase the Q?

Lawrence, I thought of just replacing the coil/pot arrangement but have nothing suitable to hand. It would need to be a pair of coupled coils as per the original because  of the switching. Which Denco?

[pwdrive]

Another alternative for the LW oscillator coil might be to use am old MW RF coil that has an antenna coupling winding.

Lawrence

[pwdrive]

Thanks Mike, I have looked at everything else, the cores are unmoved, I cannot establish the frequency range with my equipment, I would not know how to with 2 coupled coils either. Short & medium waves are fine, sensitive and tracking well, Valve voltages/currents are roughly correct, all have been substituted. Components that were suspect have been changed, small value caps seem OK, resistors are all 20% and in tolerance.
Why would a broken pot increase the Q?

Lawrence, I thought of just replacing the coil/pot arrangement but have nothing suitable to hand. It would need to be a pair of coupled coils as per the original because  of the switching. Which Denco?

Not absolutely sure, might be red, some Denco tech stuff here:

http://www.vintageradio.me.uk/info/MaxiQ...inDTB4.pdf

Lawrence.

[Mike Watterson]

Air core has higher Q (though lower inductance) than Dust Iron or Ferrite. The glue is usually pretty low loss, really the only effect of a glued together broken core is to reduce the inductance a bit.

On LW one winding is connected somehow to the tuning cap and the other winding isn't. The other winding is feedback.

[boater sam]

Its not a broken core Mike but the 2 piece ferrite pot that surrounds the winding all round and above and below. Its like a pill box with a central hole where the tiny core goes through.

Checked everything, it will get major  surgery when I have the time.

Still looking for a picture of the back or indeed any Pennine set back as they may be similar.