I got a 60B a while back that had a jumper from the bottom side of the 10k (part #1) to ground someone had put there. I removed it and the BC band went about 50% down, but was still there, however it brought the SW band back. I just got a 60L and both bands work fine, however there was no jumper, so I just decided to try it and the same thing. BC band came up very good, but the SW band is virtually gone.
Is anyone else aware of this and if so, is there a way to provide the ground while the switch is in the BC band position, but remove it from the circuit when the SW band is used? I don't really want to mess things up, but if there is an easy way to do it, I'd sure like to know.
I tried searching for any previous discussions on this, but my search terms failed to come up with anything, so I'm sorry if this has been asked before.
TIA
Brian
Guess no one knows..
I will leave the jumper as it is. The amount of gain obtained with the ground jumper on the BC band is worth reducing that of the SW band. That particular SW range is pretty dead anyway.
I think Philco changed that circuit up later, and maybe the switch too.
Well, since no one else spoke up, I'll take a shot at this...
http://philcoradio.com/phorum/showthread.php?tid=15007
Normally the 10K resistor is grounded through the "police" band primary of antenna coil (4). When in the "police" band position, both the 11 ohm section of coil (4) primary and the 10K resistor (1) are shorted out.
I would check the integrity of coil (4) as well as the cleanliness of the band switch.
The only change Philco made in that circuit was to add a wave trap to keep any low wave beacons in the vicinity of 460 kc out of the antenna input. See the link above.
Thanks Ron.
I was speaking more about later models or variations of the circuit. See attacthments.
Coils on both radios check out fine, and both perform very good with a the jumper to ground. Both also receive fine on the BC band without the jumper, but not nearly as sensitive...
Apples and oranges. Models 60 and 118 are not the same.
Please look at the link I posted in post #3 above - this shows all known changes made to Model 60.
0.7 ohms should be quite sufficient to serve as a ground. If you are needing to put a jumper between the bottom of the 10K resistor (1) and ground to obtain better AM reception, then something is wrong with the 0.7 ohm winding of coil (4). And in the "police" band position (what you are calling SW, actually only 1.5 to 3 or so MC), having a jumper there will effectively tie the antenna to ground, so no wonder the jumper kills police band reception.
Please don't go away in frustration. I have some additional thoughts on this, but I cannot elaborate at this time as I am at work. Tonight when I get home, if I don't forget I'll elaborate further. This is an interesting discussion and I feel it is worthy of exploring further.
Meantime, Terry and Mike, or anyone else, feel free to jump in...
So...where is everyone
Well...anyway...Brian, the more I thought about this the more I found this (what I believe is what you are thinking) to be intriguing.
So...presented here in schematic form is a mod which may do what you are after:
[
attachment=17178]
The only problem is, the lower (grounded) end of the antenna coil primary, the 0.7 ohm end, is likely attached to the coil form at the grounding lug. Which means that you would have to unsolder the grounded lead of the coil and then figure out how to attach it to something else without breaking the wire.
Another thought -
I don't own a 60, but as I recall, the AM primary winding is a large bobbin of wire at the top of the coil form (opposite end of the lugs). The following would be an easier way to perform the mod:
Remove the lower end of the AM primary winding (11 ohms, across one section of the band switch) from one terminal of the 0.7 ohm police band primary winding, and connect it to the grounding lug of the coil.
Now connect the lug you removed the lower end of the 11 ohm winding from to the lug where the top of the 11 ohm winding is connected.
If you can pull this off, it might do what you are looking for.
If you can successfully do this and it really improves the reception, let me know. I never cared much for Model 60 sets simply because in my experience, they never had very good AM reception.
Ron, you were right to begin with. I removed the coil entirely on one radio and sure enough the .7 ohm portion was indeed open! I don't know what I was measuring before, but it was a fluke, no pun intended...
I also found the break. Repaired it, and found another break closer to the ground end, so I gave up. The wire was brittle as could be too.
Sorry to have you run a wild goose chase, but I was certain that coil was okay, and I guess the other 60 has the same problem!! Having two of them with the same problem is no good... Your mod above could get one by. I am thinking I will leave it be for now. BTW, I always call anything above the BC band "shortwave". Just habit. The "police" band in not worth messing with to me, so I may just leave well enough alone for now.
Thanks again and sorry for the goof on my reading the coil to begin with.
Brian
Well, good!
All's well that ends well...
Yes, all 1928-1935 and some 1936 Philco coils are notorious for going open (usually the secondary or tertiary winding but sometimes the primary as well), which is what I suspected at first.
So you don't need a MOD after all and I'll stop going down that path.
P.S. The mod would only work if the 0.7 ohm section of the primary was/is good.
Ron, do you or anyone else happen to know what the inductance of that .7 ohm portion of the coil is? I am tempted to rewind it, but the magnet wire I have is slightly larger and I'm not even sure what size that was they used other than it's very tiny. The existing wire is so brittle now, it's hopeless to try and use any portion of it.
Thanks
Brian
The inner bobbin is either 38 or 40 gauge; the others are likely 32 or 34 gauge. If you have 30 gauge and would like to rewind the 0.7 ohm section, go for it. It's worth a try and will probably work anyway. The older Phico coils such as there are not as finicky about exact wire size as are the later Philco coils (1937 and later models).
Oh, and I don't know what the original inductance was.
Here's a link to the section in my 60MB posts where I rewound that 0.7 ohm coil. Maybe it will help.
http://philcoradio.com/phorum/showthread...5#pid86435
update: the link to Ron's post leads to photobucket pics that are no longer there...perhaps you could add them into this thread Ron?
Thanks! I'll have a look!
Good job Bob. I have nothing to lose by trying it. I will need to get some 37 or 38 wire however. What I have is slightly bigger and without knowing total inductance, I better stick with getting the smaller wire.
Thanks again.
Brian