Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Feb Thu 21, 2019 4:22 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 16 posts ] 
Author Message
 Post subject: Antenna coil replacement
PostPosted: Jan Tue 02, 2018 11:00 pm 
Member

Joined: Jan Wed 07, 2015 10:39 pm
Posts: 196
Location: Jamison PA
This is continuation of the alignment issues had with my Silvertone 1863.

After a lot of trial and error, it appears that the culprit in my motorboating and non reception lower than 800mhz was the original antenna coil. Not poor alignment. The original coil had some of its winding come loose of its adhesive and was laying about on the solder lugs. I thought I had rescued it by carefully rewinding the loose stuff, but there must be some insulation missing, and its not really working unless I had clipped the grid cap with an alligator directly to the house antenna. It seemed electrically intact, but must be touching itself somewhere in the wrap. When clipped in this fashion, I had reception across the whole band. When not clipped, only motorboating and normal reception above 900.

I've bought the AES antenna coil, and clip leaded it to ensure it will work. It appears to and no more motorboating.

My question is that it is markedly smaller, and I don't know if I need to mount it up in the can, or how I should install it. You can see how the original used stand offs to mount it inside the can.

Suggestions welcome :mrgreen:


Attachments:
IMG_24791.JPG
IMG_24791.JPG [ 30.26 KiB | Viewed 866 times ]
Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Wed 03, 2018 1:07 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 12525
Location: San Jose, CA USA
You probably don't need to mount it in the can. As long as there is no motorboating, shielding of the antenna coil might not be necessary.

Once you've got it mounted and wired, then tune a station near the top of the dial and adjust the antenna trimmer for max signal. Then tune a station near the bottom of the dial and adjust the core in your new antenna coil for max signal. Go back and forth between these two until there is no more improvement. It may take as many as 10 iterations when installing a brand new antenna coil like this.

_________________
Tom K6VL


Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Wed 03, 2018 1:42 am 
Member

Joined: Jan Wed 07, 2015 10:39 pm
Posts: 196
Location: Jamison PA
Thanks Tom!

Glad you mentioned tuning it, as I had noticed there was a allen headed piece in the coil itself, but didn't realize I had to tune it as well. Thank you for the heads up!!

Mike


Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Wed 03, 2018 2:00 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30217
Location: SoCal, 91387
Don't use a metal Allen Wrench to adjust the Ferrite core; use a plastic hex-head tool.

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Wed 03, 2018 3:48 am 
Member

Joined: Jan Wed 07, 2015 10:39 pm
Posts: 196
Location: Jamison PA
Yup, roger on the plastic tool.

It still is not really receiving anything low on the dial. I can get a hint of a station, but as before, excellent reception above 900. The old antenna coil would receive well below 900 if you had a lead out clipped to the grid of the ant tube.

I ran the ferrite coil many times, along with the low end padder and ant trimmer. It is being stubborn, and with the new coil, and clipping the grid of the ant tube, still wont pick up the low end stuff. I barely can decipher a low station, but not intelligble......high end very sensitive.....

What is left at this point, pulling the tuner condenser and giving it a bath?. It looks clean enough, and was washed with contact cleaner much earlier in the game.

Thank you

Mike


Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Wed 03, 2018 4:12 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 12525
Location: San Jose, CA USA
Here's the procedure I would suggest:

0. Make sure dial pointer moves properly over all the dial, not overshooting on one end or the other. Sometimes there is a mark on one end of the dial to show where the pointer should be at end of travel. If the pointer isn't in exactly that spot at end of travel, physically move the pointer so that it is.

1. Adjust oscillator trimmer so that station near top of dial comes in at the right position on the dial.
2. Adjust broadcast padder so that station near the bottom of the dial comes in at the right position on the dial.
3. Repeat steps 1 and 2 several times until both ends of the dial are correct in terms of frequency calibration.
4. Tune in a weak station near the top of the dial and adjust the antenna trimmer and the mixer trimmer for maximum signal strength.
5. Tune in a weak station near the bottom of the dial and adjust the slug in the antenna coil for maximum signal strength.
6. Repeat steps 4 and 5 until no further improvement can be made.

When you perform steps 4 and 5, do you get a clear peak within the available adjustment range of both trimmers and the slug? Or is it loudest at the end of adjustment range? Or is there no discernable peak?

Note that for the antenna coil, one "end" of the adjustment range (max inductance) is when the core is centered in the coil. Other "end" of the range is all the way out of the coil on either side. What you're looking for is a peak in signal strength with the core partially out of the coil on one side or the other (either side is equivalent).

If you're not seeing the clear peaks in steps 4 and 5, that means there is still some problem in the antenna transformer circuitry.

By the way, when you get better reception with the antenna clipped to the top cap of one of the tubes, is it the RF tube (6D6) or the mixer tube (6K7)?

_________________
Tom K6VL


Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Wed 03, 2018 2:44 pm 
Member

Joined: Jan Wed 07, 2015 10:39 pm
Posts: 196
Location: Jamison PA
Hi Tom,

The original issue was the inability to tune in anything below 900. I had performed an alignment and got a tone at 600, so assumed tuning capacitor was not shorting. I also removed the antenna coil, and dressed up the sagging wiring on the bottom of the cylinder. After putting it back together, I had motorboating on below 800 with antenna connected to external antenna. I then clipped on the grid cap for the 6D6 with test lead, and clipped that to the external antenna. I then had good reception across the dial. 610 is our local sports channel and it came in well. I had cleaned the trimmers and mica (which is intact and OK). I have a digital radio to confirm dial tracking, and have another tube set on the bench that receives across the dial when using the same external antenna.

Thinking the antenna coil might have an issue, I swapped it for the AES universal one. I have been back and forth with the trimmers and padder, plus the slug in the coil. The dial is accurate at 940-1700 and receives fine up there. Below, no matter what I do, I can get a hint of station at 610, but so feeble, you cannot understand it. Just noise anywhere else down that end of the dial. Clipping the 6D6 as before does not change or improve the reception. Slug in coil seemed to peak on lower station noise near center of coil.

I'm thinking the original coil was OK now, but out of ideas.......

Thank you

Mike


Attachments:
Silvertone%25201863%2520schem%25201.JPG
Silvertone%25201863%2520schem%25201.JPG [ 124.5 KiB | Viewed 757 times ]
Silvertone%25201863%2520schem%25202.JPG
Silvertone%25201863%2520schem%25202.JPG [ 115.42 KiB | Viewed 757 times ]
Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Wed 03, 2018 4:48 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 12525
Location: San Jose, CA USA
Key thing to diagnose this problem is whether or not you are getting a nice peak during alignment. At the top of the dial do you get a nice peak on the antenna trimmer?

How long is your antenna? At bottom of dial, a longer antenna is needed.

When you wired up the new antenna coil, which terminals did you attach to what? I see on the AES website that they recommend connecting the smaller coil as the secondary (connected to tuning cap) and the larger coil as the primary. I'd suggest turning that around -- using the larger coil for the secondary and the smaller coil for the primary. See if that works better.

Is the AVC cap good and properly wired? That’s the cap below the sntenna coil on the schematic.

_________________
Tom K6VL


Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Wed 03, 2018 8:24 pm 
Member

Joined: Jan Wed 07, 2015 10:39 pm
Posts: 196
Location: Jamison PA
I wired the AES coil as it is in their schematic. In this case you are suggesting swapping 1 and 2?.
Terminal 1 is tuner cap and grid cap
Terminal 2 is through .05 cap and resistors
Terminal 3 is to the volume control and ground
Terminal 4 is Antenna

The picture is before the recap, and antenna coil. However the AES coil is situated exactly in the same position, so you can see terminal 1 is on the right top, terminal 2 right bottom, terminal 3 left bottom, antenna terminal 4 top left of the picture.

All caps are new, and are the correct values. The antenna is a two foot braided wire that is attached to a basement grid drop down ceiling with a alligator clip. That seems to work well, and in the previous post, I did get good reception on the low end of the band after clipping the 6D6 grid cap with the old antenna coil.

As for peak, by ear I hear it peak up on the end of the dial. The upper end stations are OK and tracks accurate.
Sorry for the questions, I need to win on this one :P


Attachments:
11.JPG
11.JPG [ 210.7 KiB | Viewed 712 times ]
Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Wed 03, 2018 9:03 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 12525
Location: San Jose, CA USA
Try swapping 1 with 3, and 2 with 4. In other words, swap the two coils completely.

Still would like a more precise description of the peak. When you say you hear "it" peak up "on the end of the dial," I'm not quite clear on what you mean. If you tune in a station near the top of the dial, but not really all the way at the end of the dial (say around 1300 - 1500 kHz), do you get a clear peak while you adjust both the antenna trimmer and the mixer trimmer (leaving the dial fixed)? And neither is all the way loose or tight? Here we are not talking about adjusting the slug in the coil yet.

_________________
Tom K6VL


Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Wed 03, 2018 10:48 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30217
Location: SoCal, 91387
One cause of reception degradation on the lower end of the dial is a weak converter tube. You might try another 6A7.

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Wed 03, 2018 11:01 pm 
Member

Joined: Jan Wed 07, 2015 10:39 pm
Posts: 196
Location: Jamison PA
Thank you, I'll look at my other sets, I think I have a NOS one in another 32v set.

To answer Toms response, the tuning gang has 3 trimmers sections, osc, int and ant.

Interestingly, I tuned to 1490 and attempted to trim the ant, with no real discernable difference, I could screw it all the way in and out.. The int section trimmer did a little, but not a huge difference. So at this point, with replacement ant coil wired as described, no trimming going on here..... That was not the case when I first aligned it for sure with old ant coil....

Thank you for hanging in on this growing thread, I really want to get this right again.


Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Thu 04, 2018 12:29 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 12525
Location: San Jose, CA USA
Try reversing the coil next. Wire it like this:

3 - grid cap and tuning cap stator
4 - AVC cap

1 - antenna
2 - ground

To confirm it's wired correctly, now measure resistance from 6D6 grid cap to AVC cap. Should be 40-ish ohms. Measure from antenna terminal to chassis. Should be 10-ish ohms.

See if you have better luck with that.

Start at the bottom end (or middle if no signal at bottom end) of dial. Set the ant trimmer to middle of range. Then adjust core in antenna coil to see if you get a peak that is not all the way out, or all the way centered in the large coil. Use the position of the core that has the core off center in the big coil and toward the small coil (core overlaps both large and small coil).

_________________
Tom K6VL


Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Thu 04, 2018 3:02 am 
Member

Joined: Jan Wed 07, 2015 10:39 pm
Posts: 196
Location: Jamison PA
Well I was not successful. I had reception again above 900 but no ant trimmer action at all obviously it's all pointing there
I then clipped in the original coil. Same thing and clipping the 6D6 netted 610 station
I've been staring at the bottom of the chassis. There is a .5meg resistor in the circuit seen on the pic that has a strange gimmick on it. It's a few turns of copper wire. I cannot get a resistance reading on it. I've checked the others and I had replaced 2 1meg resistors with modern ones. I think I'll need to replace this .5. It is in this antenna circuit.
It seems that my antenna trimmer is not doing much of anything yet
Original ant coil measured term 1 and 2 34 ohms, term 3 and 4 3.8 ohms
New coil 1 and 2 9.7 ohms 3 and 4 41.4 ohms


Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Thu 04, 2018 4:15 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 12525
Location: San Jose, CA USA
Replace that resistor as your next step. Not sure why it has wire wrapped around it. You can wrap it around the new one, although I'm doubtful it's necessary. Don't see what it would do in that part of the circuit. Where does the wire that's wrapped around the resistor come from?

If that resistor is open, your RF tube may simply not be amplifying properly. Clipping an antenna to the grid then has somewhat unpredictable results. Let's see what happens with the new resistor.

Then we can try the old antenna coil again.

I didn't realize there were still resistors in here that you had not checked.

_________________
Tom K6VL


Top
 Profile  
 
 Post subject: Re: Antenna coil replacement
PostPosted: Jan Thu 04, 2018 4:44 am 
Member

Joined: Jan Mon 16, 2012 4:15 pm
Posts: 5126
Location: Near Brandon, Iowa
So far it appears that the problem search has focused on the antenna coil. It seems to me that if the new antenna coil causes the radio to perform approximately the same way as with the original antenna coil, maybe another fault vector should be explored.

If the oscillator is not tracking correctly or has a discontinuity/dead zone, the sort of problem ascribed to the antenna coil can be experienced: part of the band receives OK but other parts are weak. This is caused by the IF filters rejecting the frequency that results from mixing a correct Tuned Frequency and an incorrect Local Oscillator Frequency.

Probably the quickest way to rule this out would be to use an o'scope and/or counter and verify that the Local Oscillator is "on frequency" for the two band endpoints and several midrange points. Or, you might also be able to disable the Local Oscillator and use an RF signal generator (unmodulated) to take its place as a check on correct band-wide operation of the onboard L.O. If the set can be made to tune a station in the "dead zone" by forcing in an external L.O. frequency, that suggests that the onboard L.O. is wonky.


Top
 Profile  
 
Post New Topic Post Reply  [ 16 posts ]  Moderators: Marcc, Norm Leal

All times are UTC [ DST ]


Who is online

Users browsing this forum: Google Adsense [Bot], Ken Layton, processhead and 15 guests



Search for:
Jump to:  


























Privacy Policy :: Powered by phpBB