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Philco 90 - Tuning Gang? - Printable Version

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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? Icon_eek 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


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. Icon_biggrin

Terry


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

Hi Terry,

Thanks for the info. Icon_smile 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


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


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


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


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.


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 Icon_confused