Philco 90 - Tuning Gang? - Printable Version

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+--- Thread: Philco 90 - Tuning Gang? (/showthread.php?tid=1396)

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Philco 90 - Tuning Gang? - etech - 10-01-2008

Hi all,

I have noticed in restoring my recent Philco 90 chassis that the tuning gang has a copper braid wire soldered to the three mounting bolts, which is then soldered to ground. Obviously this was a means of providing an additional ground to the tuning gang frame. But why? The tuning gang has three rotary wipers that have wires attached to them that are soldered to ground under the chassis. The other 90 chassis I did, did not have this braid wire soldered to the tuning gang bolts.

Has anyone ever seen this before? Is this a factory installation or did some repairman along the way decide that this was a good idea? I'm just a little curious about this. Both chassis seem to work fine without the braid. I had to remove it to install new grommets. I have not reinstalled it as of yet. I'm waiting for opinions.

Ed

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Re: Philco 90 - Tuning Gang? - Terry Burns - 10-01-2008

Hi Ed,
Both of my 90's have the grounding braids on the tuning cap. I think they were put on at the factory. I put mine back on after changing the grommets. Superhets were still fairly new at the time maybe they thought they were needed. Hope this helps.

Terry

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Re: Philco 90 - Tuning Gang? - etech - 10-01-2008

Hi Terry,

Thanks for the info. I guess the grounding braids were installed at the factory then. On the first chassis I did, someone had previously installed new grommets on the tuning gang, so I suppose that the braids were removed at that time. I can reinstall the braid that I have for one and install a new coax braid on the other, no problem. I'm not sure they are needed, but I guess I might as well keep them original.

Ed

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Re: Philco 90 - Tuning Gang? - Chuck Schwark - 10-01-2008

A short braided bond to a tuning gang frame insures a low impedance RF ground.

Chuck

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Re: Philco 90 - Tuning Gang? - etech - 10-01-2008

Quote:A short braided bond to a tuning gang frame insures a low impedance RF ground.

In general, I am aware of this reason to use a braid type of grounding strap. I have used them many times on homebrew transmitter and/or antenna projects. I have just not seen this used on these Philco radios before.

I took another look at both of my model 90 chassis'. The one that had the ground braid was serial #709734 and the braid was soldered directly to the heads of the tuning gang mounting bolts. The other chassis is serial #535341 and there is no evidence that the ground braid was ever there. That is to say that I see no remaining solder on the heads of the mounting bolts and there is no evidence that there was ever a braid soldered to the top of the bypass condenser can as there is on the other chassis. Now I suppose that it is possible that they soldered the braid to lugs that were attached to mounting bolts and a ground point on the chassis. Or it is possible that some chassis were built with the grounding braid and some were not?

Can anyone else offer an information?

Ed

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Re: Philco 90 - Tuning Gang? - etech - 10-01-2008

Well, take a look at this. Here is one with no grounding braid on it. Just click on the photo of the chassis underside.

http://www.greenhillsgf.com/Project_Philco_90.htm

So, I guess some were made without.

Ed

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Re: Philco 90 - Tuning Gang? - BDM - 10-01-2008

My 116 chassis has these also. Plus, the gang is grounded at the front through the dial support. Using braid copper wire. I'm also wondering how critical as I do not want to damage the new grommets with heat. I'll try it without and see how it operates.

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Re: Philco 90 - Tuning Gang? - BDM - 10-04-2008

Well, it makes no difference with them connected or not. I tried it both ways. Doesn't effect frequency or sensitivity in any way. Regardless if it's on the highest freq (22.5/mc) or the lowest. Sure made getting those tuner gang screws a real "britch" to get off

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