Model 70 tone control - Printable Version
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Model 70 tone control - 37silverstreak - 04-26-2011
I'm working on my model 70. I had it working pretty good and I just couldn't leave well enough alone!!!! I tried aligning it with limited success. I noticed that there was a lot of looseness on the tone control and if i bump it it will cause the set to howl. I pulled the control out and I adjusted the contact arm so that it is snug and cleaned the contacts. I noticed that in the Riders schematic I have it shows the tone control as having a capacitor in it. It's item 48, part number 03140 on the schematic, but it doesn't give a value for the capacitor. Does anyone know the value of this cap? I have completely recapped this set and am wondering if I should replace this one too? Any info would be great! Thanks!
Kevin
Re: Model 70 tone control - Steve Davis - 04-26-2011
Kevin, that would be .015 uf.
Steve
Re: Model 70 tone control - 37silverstreak - 04-26-2011
Steve, Thank you so much for the info!
Kevin
Re: Model 70 tone control - 37silverstreak - 04-27-2011
Okay, an update on my tone control problem. I replaced the capacitor in the tone switch with a new .015 mfd one (Thanks to Steve for providing me with the value!). I replaced the brittle rubber coated lead wire as well. Now the set plays great as long as I have the tone control switch turned clockwise, which is the switch is closed and connecting the capacitor to ground. If I turn the switch counterclockwise which is open the set growls/howls loudly and I can barely hear any stations. Anyone have any ideas? Could I have the set misaligned in some way? I'm confused
Kevin
Re: Model 70 tone control - Radioroslyn - 04-27-2011
Doubt it's an alignment problem. Seems like a decoupling issue. The quick and easy to fix it is to install a small cap from the plate of the 47 tube to ground. Size would be a .005@630v should do it.
Terry
Re: Model 70 tone control - Steve Davis - 04-27-2011
Hi Kevin
Is your tube shield in place?
Steve
Re: Model 70 tone control - 37silverstreak - 04-28-2011
Hey Terry and Steve,
Thanks for the posts! I did have the tube shield installed and was still having the issue. Terry I tried you extra cap fix and it worked like a charm!!!!! the growling is completely gone and the set works fantastically!!! I have it going now as I'm writing this. Even with just a 15ft wire antenna it's pulling in stations all over the dial, so I must have the alignment pretty close!!
Now all I have left to do is the cabinet! Thanks for all your help! Kevin
Re: Model 70 tone control - Radioroslyn - 04-29-2011
Your welcome!
Most sets will have a cap there to prevent the output stage from going in to oscillation. Philco may have thought that there was enough distributive capacity in the winding that it would not break into oscillation. And in 1933 the cost of that cap .15c could buy you lunch. The common value is .01mfd sometimes you'll find a.02mfd. I find that both size tend to make less bright (cuts highs). So I'll adjust the value to my liking.
Terry