Grunow difficulty

[csingle]

G'day, All. I am at a loss on a certain problem I am having with an old Grunow set (6G chassis). The problem is that it has(rather used to have) a dynamic 108C5 speaker. As it seems, these particular speakers are pretty much nonexistent. As such, I was wondering if it would be possible to use some choke coils for the humbucking and feild sections, and use a more modern replacement for the voice coil sections. Let me know what you think, or if you know of a resource to find the proper replacement, I would think it would be far better.

Thank you,
-Chris Ingle

[blue_lateral]

You dont need the humbucking thing if youre no longer using a field coil speaker. The field coil can in some cases be replaced with a resistor. I guess a choke would be better if you knew what to use, but field coils are usually rated in ohms, and they dont tell you inductance.

What I have done in the past if the speaker was there, but completely destroyed, was to just disconnnect the voice coil and leave the field coil connnected. I just mounted the old speaker off to the side somewhere, and then used a modern speaker.

If the speaker is missing completely, you can often get away with substituting a resistor for the field coil. This isnt as good as a choke, but often it works fine. There could be slightly more hum. The b+ voltage could be affected. Probably you cant tell the difference.

If the schematic tells you what b+ should be, you can experiment to see what resistance will get you to the right b+ voltage. Use something big and wirewound to experiment. Once you know how much current is flowing and how much voltage is being dropped, you can select an appropriate resistor for a permanent fix. It will likely get hot, so be careful where you put it.

I'm not familiar with this particular Grunow, so kind of shooting from the hip. Is the output transformer there? Often on old sets they were mounted on the speaker. If it's gone you'll need one of those, too.

Another idea, back in those days field coil speakers were sold as universal replacements, just like permanent magnet ones are now. Maybe you can find something close. These usually dont have the humbucking coil, but if hum is a problem (probably not) try increasing the size of the filter capacitor after the field coil.

Have you posted on http://antiqueradios.com/forums ? I'll bet those guys would know what to do.

Good luck,

John