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 Post subject: Antenna coupling
PostPosted: Apr Thu 02, 2020 11:46 pm 
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Joined: Dec Tue 04, 2012 1:59 am
Posts: 32
Location: marquette, michigan
Does the antenna induce the radio waves into the other side of the antenna coil ( radio side) ? If so why ? I have been working on a zeinth 6s229. I can use an antenna wire an touch one terminal on the band switch and it sounds great . If I see the antenna terminal at the back very little if anything.


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 Post subject: Re: Antenna coupling
PostPosted: Apr Fri 03, 2020 1:39 am 
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Joined: Jun Wed 14, 2006 11:49 pm
Posts: 6889
Location: Leo, IN or Zellwood, FL
dean1673 wrote:
Does the antenna induce the radio waves into the other side of the antenna coil ( radio side) ? If so why ? I have been working on a zeinth 6s229. I can use an antenna wire an touch one terminal on the band switch and it sounds great . If I see the antenna terminal at the back very little if anything.


There is a good chance you have an open antenna coil. Ohms test.. temporarily remove the Z to G jumper and check ohms from the A terminal to the chassis should be some low ohms reading. Replace the jumper from Z to G and recheck A terminal to chassis and flip bandswitch through all three positions. Should show same or lower ohms than first test. Next test the secondary of the Antenna coil. Check ohms from grid cap of 6A8 tube to grid cap of 6K7 tube. Flip bandswitch through all three positions. It should read reasonably low ohm on all three bands. Slightly lower ohms as you do Police and SW bands.
If you get any OL out of limit or high ohm readings then that winding is open.
good luck
John k9uwa

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 Post subject: Re: Antenna coupling
PostPosted: Apr Fri 03, 2020 3:13 pm 
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Joined: Dec Tue 04, 2012 1:59 am
Posts: 32
Location: marquette, michigan
Thanks John for the reply. I have 23.2 ohms with the zg connected. Without on A 23.2 ohms B 0.8 ohms. C .08
Between 6a8 and the 6k7 on A 79.6ohms. B 74 ohms. C 73 ohms . I guess it is time to spin a coil. Thanks for all your help. Dean


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 Post subject: Re: Antenna coupling
PostPosted: Apr Fri 03, 2020 4:26 pm 
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Location: Annapolis, MD
dean1673 wrote:
Does the antenna induce the radio waves into the other side of the antenna coil ( radio side) ? If so why ?

The over-simplified explanation:

The antenna converts the incoming E-M** wave into a current (at the radio frequency). The typical antenna "coil" is a transformer that converts the current in the primary to a voltage on the secondary--which in turn goes to the control grid of the first tube. The secondary is normally tuned--which maximizes this voltage. Ideally, the primary to secondary turns ratio---combined with the antenna design---matches the receiver impedance to that of free space, thereby maximizing the power transfer. To understand the impedance of free space, look at the principles of transmission lines

**An electromagnetic wave is a sort of chain reaction wherein a collapsing magnetic field generates an electric field, which in turn collapses and generates a magnetic field (which then collapses, and......)
If you place a wire in a changing magnetic field, you get a current.

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"Even if you don't understand Ohm's Law, you are still required to obey it."


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 Post subject: Re: Antenna coupling
PostPosted: Apr Fri 03, 2020 5:44 pm 
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dean1673 wrote:
Thanks John for the reply.
I have 23.2 ohms with the zg connected.
Without on A 23.2 ohms B 0.8 ohms. C .08
Between 6a8 and the 6k7 on A 79.6ohms. B 74 ohms. C 73 ohms .
I guess it is time to spin a coil. Thanks for all your help.Dean
??? That sounds correct to me...

What happens is the antenna will also receive the high energy pulses from a nearby lightning strike that surge will burn out a winding, it will go open. Depending on the winding and the number of turns, wire size will have different resistances when good.
On multi-band radios antenna coils as well as the oscillator coils can be a complex group of windings, not easy to duplicate. Go slow and check again, use an analog meter... It places a small amount of current into the winding...

Attachment:
Zenith Radio Corp 6-S-229 - RF_snip.png
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Do check the band switch for poor contacts, avoid drenching the switch with a contact cleaner that leaves a residue.

GL

Chas

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 Post subject: Re: Antenna coupling
PostPosted: Apr Fri 03, 2020 8:15 pm 
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Joined: Jun Wed 14, 2006 11:49 pm
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Location: Leo, IN or Zellwood, FL
dean1673 wrote:
Thanks John for the reply. I have 23.2 ohms with the zg connected. Without on A 23.2 ohms B 0.8 ohms. C .08
Between 6a8 and the 6k7 on A 79.6ohms. B 74 ohms. C 73 ohms . I guess it is time to spin a coil. Thanks for all your help. Dean



Yes Dean as Chas says... those are good numbers on both the primary and secondary of your ANT coil... nothing wrong with it... have to look elsewhere.

You do have the Gimmick Capacitor wound correctly? I don't think this is your problem but want to be sure it is OK. Notice in schematic 6A8 tube input grid cap a one turn wrap of a wire around it that is not connected ... but is just wrapped around the other wire. That would be correct. I have seen radios where someone thought that open ended wire was supposed to be soldered to the grid cap and that for sure messed things up.

So the radio works OK if you touch the antenna to some lug on the bandswitch. The Ant coil is checked and is OK. As Chas stated starting to look perhaps like a switch problem. Or maybe C2 was put to a wrong lug of the bandswitch?

good luck
John k9uwa

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 Post subject: Re: Antenna coupling
PostPosted: Apr Fri 03, 2020 11:25 pm 
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Joined: Dec Tue 04, 2012 1:59 am
Posts: 32
Location: marquette, michigan
Thank you to all of you for the explanation. Sorry Chaz I already hit the switch with deoxit . But I will clean it up with alcohol. This unit was walk rough. I spun a new field coil replace If transformer because of a open and I did spin a new primary side of the antenna it was cooked and broke in 3 spots . It was 55 feet long and .0055 in diameter . I used 36 gauge magnet wire. Not to mention every, I mean every resistor was at least double. Plus someone added a few. 1 mica cap bad also. Never had one of those go before.
John,. when I received this there was no wire at all on the front gang of the tuning cap . I have a new one but I have it wrap twice. Trying to understand that switch on the schematic got my eye crossed. But I have learned a lot on this one . It is still fun . I'm very happy that it plays. Thanks again . I will check c2 and try to shine up that switch. Dean


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 Post subject: Re: Antenna coupling
PostPosted: Apr Sun 05, 2020 2:11 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 12437
Location: Powell River BC Canada
Thank you for the data about the wind of the antenna coil.

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 Post subject: Re: Antenna coupling
PostPosted: Apr Sun 05, 2020 4:12 am 
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Joined: Jun Wed 14, 2006 11:49 pm
Posts: 6889
Location: Leo, IN or Zellwood, FL
dean1673 wrote:
John,. when I received this there was no wire at all on the front gang of the tuning cap . I have a new one but I have it wrap twice. Trying to understand that switch on the schematic got my eye crossed. But I have learned a lot on this one . It is still fun . I'm very happy that it plays. Thanks again . I will check c2 and try to shine up that switch. Dean


The Switch functions. There are three functions of the bandswitch.

#1 The lower wafer on your schematic... it grounds out the larger Z to G section of the primary of the Ant coil for both SW bands leaving only the smaller winding of the primary in the game.

#2 The main wafer 4 lugs on the left side change taps to the ANT coil secondary to the three different bands. Reference your 3 ohm readings of grid cap to grid cap. So the only parts those lugs are connected to are ANT section of the tuner, The L Trimmer for Short wave matching The G trimmer which is on top of the tuner and C2 capacitor which is the drain of any RF left over so it doesn't go on toward the IF and other parts of the radio... which is the AVC line. Voltage readings from This line to chassis should become more negative as you tune into a stronger radio station.

#3 the right side 6 lugs Control the Oscillator frequency.
#3A The upper right three lugs control which portion of the Oscillator primary is in the game for each of the three bands. Other parts are the Osc section of the tuner plus the K N and F trimmers which set the upper frequency of each of the three bands.

#3B section the lower right three lugs select which capacitor is the Padder for each of the three bands. The J is a screwdriver adjusted trimmer to set 600 khz on the BC band. The other two are the "Fixed Double padder Trimmer" for the Police band and the upper short wave band.

As to tracing out the parts and wires on the bandswitch wafer think of counting the 12 lugs starting from one of the rods that holds the switch together. Number like a clock 1 to 12 and from where all the parts are connected you can noodle through what is happening. We didn't do an ohm check on this primary of the oscillator coil. If you want to do that then look for the small mica C7 25 pF from G1 of 6A8 to the bandswitch ohm meter to the switch side of C7 and then find C6 .002 and other meter lead on the switch side of C6. Flip bandswitch and you should have low ohm readings the higher the band the lower the ohm readings. Other than a miswire of C6 or C7 if they have been replaced there really shouldn't be any wiring errors. You should also check the secondary of this oscillator coil Yes for the most part the oscillator coil winding must be OK as the radio works somewhat. But notice R5 is a 4700 ohm resistor. There is also a winding of wire over this resistor making it an RF choke. So check ohms from G2 the Screen grid of 6A8 to the other side of this resistor coil choke. If it reads 4700 ohms then the winding is open... if it reads 4 to 5 ohms or some very small reading then the choke is OK. No way to read the 4700 ohm resistor but if could hardly be open and even if the resistance went up due to age of the part that wouldn't make any difference to the radio work or not work.

Good Luck
John k9uwa

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 Post subject: Re: Antenna coupling
PostPosted: Apr Wed 08, 2020 12:28 am 
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Joined: Dec Tue 04, 2012 1:59 am
Posts: 32
Location: marquette, michigan
A Huge Thanks to Mark,Chaz and John! Explanation of the circuit is Invaluable.

John I did the checks on the oscillator coil and everything is good.
My eyes finally became uncrossed after you explained the switch to me.
I did find c7 out of spec, it measured 32pf rather than 25 pf. New on on order
The real culprit I believe was the band switch. It took quite a few Qtip with alcohol to clean it up.

The radio plays excellent with a 100foot solid core 18gauge wire for an antenna.

"And now you know the rest of the story"

Thanks again guys!

All the best,

Dean


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