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 Post subject: Where are all those Zenith Z-G Links?
PostPosted: Dec Wed 15, 2010 11:31 pm 
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It seems that on every Zenith I acquire the Z-G antenna strip link is missing. Since I doubt many owners actually used a doublet antenna, why would these be removed? Maybe so a ground lead can be connected and it gets in the way?

Almost 100% of the Zeniths I acquire have this link missing. A very few have a jumper wire installed. But most are just left open. Yet the links on Wavemagnet type receivers always seem to be there!

I wonder what affect this has on performance? I have never been able to figure this out from schematics, since the functions of the bandswitch are so difficult to figure out.

I once asked Blacksmith if he could reproduce these! I think there would be a market!

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 Post subject:
PostPosted: Dec Wed 15, 2010 11:52 pm 
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I dunno, Dave. Most of the links I've seen have a hole on one side and a cut-away on the other. To completely remove the link you actually have to force the captive screw that goes through the hole end. Beats me why people do that. I guess they somehow figure that's what they're supposed to do. Probably most of the owners of the sets didn't have the instruction manual and were confounded by the three terminals and probably didn't know the difference between a dipole and a diaper anyway.

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 Post subject:
PostPosted: Dec Wed 15, 2010 11:54 pm 
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I'll be watching this post for the answers.

The one I am working on is a "Wavemagnet" kind; "A" & "Z" jumper ed with "G" not connected to anything external.

With the Wavemagnet laying on the bench, the set is quite sensitive (on the B.C. Band), but trying to hook a sig gen to A or Z and G, etc. to do sensitivity evaluation shows poor, in the millivolts range. I was going to bypass the complicated bandswitch and measure right at the grid of the r.f. tube but I am busy at the moment eliminating the 6X5G hazard.

Charlie


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 Post subject:
PostPosted: Dec Thu 16, 2010 12:50 am 
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Location: Northport wa. USA.
It would not suprise me if a change to a jumper wire was made as a cost cutting measure.


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 Post subject:
PostPosted: Dec Thu 16, 2010 4:49 pm 
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tinwhisker wrote:
The one I am working on is a "Wavemagnet" kind; "A" & "Z" jumper ed with "G" not connected to anything external.


The only wavemagnet types (1940-1942) I have seen only had two terminals on the back of the wavemagnet. The wavemagnet functions as the broadcast antenna. At least two sets I restored had a "line cord" (3rd wire in the cord) that served as the short wave/police antenna. If you wish to use an EXTERNAL antenna (and ground), you would then REMOVE the link on the back and connect your antenna and ground (optional). IIRC, these two terminals go to a coil that acts as the primary, with the secondary being the wavemagnet on broadcast. But the same antenna wire also feeds a signal to the shortwave circuits.

I have not seen a wavemagnet type set with A Z G connections. What model are you working on?

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 Post subject:
PostPosted: Dec Thu 16, 2010 5:33 pm 
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Dave Mc:

It is a 10A1 chassis. The schematic shows a jumper between
"A" and "Z", which is how it seems the most sensitive, using the wavemagnet. ("G" is ground).

Connecting a sig gen in every combination A,Z,G, with and w/o the wavemagnet connected, and with and w/o going through a balun, comes to sensitivity in the Milli-volt range. However, with A&Z tied together and the wavemagnet connected, I get stations everywhere on the B.C. band.

I just remembered, the balun I made did NOT have a center tap to tie to "G". (something I forgot to try).

I am trying to spec the r.f. sensitivity for general information for others, if needed. I have measured turns ratio and inductance's of some of the coils and transformers and other measurements in case I or others ever need this info.

I feel that I am hi-jacking this post, sorry.

Charlie


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 Post subject:
PostPosted: Dec Fri 17, 2010 2:11 am 
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Here's the info from my 9S262 owner's manual. It says to use a jumper wire for the shorting link. I guess mine has the "original" bit of cotton-covered wire in place, so I'm probably sittin' on a Gold Mine! :lol:

I keep a 20' length of wire connected to the A terminal, tucked behind the radio which I drape around when the set is operated and Z to G are shorted. I've never bothered with adding a ground.

-Ed

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 Post subject:
PostPosted: Dec Fri 17, 2010 6:43 am 
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Location: Dayton, Ohio
Ed in SoDak;

"Old Radio Zone" has a similar "copy" of the Zenith manual, showing
"Z" and "G" connected together, which conflicts with the schematic for the ch#10A1 (A & Z connected).

As to "where the jumpers all went to", probably taken off and saved (lost) in the wife's sewing basket or put in a drawer with "odds and ends" until needed, (also lost or forgotten).

:|

Charlie

P.S. Dave: My neighbors Zenith has its link. The Zenith's first owner, my neighbor's aunt, had it in an upstairs room. The old lady got so she couldn't climb the stairs, so it set unmolested for many years, until her death and it went to her niece.

C.


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 Post subject:
PostPosted: Dec Fri 17, 2010 9:38 am 
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My manual came with the 9S262 when I bought it in 1976 from the original owner. The instructions apply to 1938-era shutterdial sets and it's called a Zenith Doublet instead of the Wavemagnet. The schematic for the 5905 chassis does show the link between Z & G, but doesn't state in the schematic which position the antenna Local/DX or bandswitch is set at, so we're left to guess or trace it out, but I agree it's pretty inscrutable how exactly the three terminals are interconnected by the antenna coils and various switch positions.

The manual does state to "remove" the link, so that may explain why it's typically gone instead of merely turned aside. Of course in 1938 it's just a jumper wire, so it may have been deemed expendable, rather than run a risk of people seeing it hanging loose and wondering why. Then, in their ignorance, determining a loose link probably needed to be connected, thereby shorting out the Wavemagnet! Perhaps Zenith was taking the safer route by saying to remove the link and thus the temptation to reattach it incorrectly would be gone.

-Ed


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 Post subject:
PostPosted: Dec Fri 17, 2010 9:44 pm 
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Since I had a 6S322 on the bench, I though it was finally time to understand the circuit regarding the A-Z link. Turns out that with the Z-G link in place, on the Short Wave and Police bands, the broadcast band antenna coil primary is shorted out. The antenna signal passes through the Short Wave/Police antenna coil primary directly to ground.

The Short Wave and Police band primary winding is only a few turns of wire. The broadcast band primary is quite large and on the other end of the antenna coil. So with the Z-G link OPEN and using a long wire antenna connected to the A terminal, there would likely be some loss of sensitivity on Short Wave and Police bands due to the high impedance broadcast band antenna coil primary in series with the cold end of the short wave primary and ground.

With a DOUBLET antenna connected to A and Z, and with the link open, the doublet is connected to the Short Wave/Police antenna coil primary in Short Wave and Police mode. In Broadcast band mode, ONE SIDE of the doublet acts as the antenna, and the other side is not connected to anything.

In broadcast band mode, the antenna signal always passes through the short wave/police antenna coil primary before the broadcast band primary.

Many other Zeniths work the same way.

This tells me that most of us should leave the A-Z jumper or link in place (since very few use a doublet antenna).

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 Post subject:
PostPosted: Dec Sat 18, 2010 2:14 am 
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Dave Mc;

The info you provided is what I was searching for earlier.

I hope someone later on, when doing the ARF search and the Google search, stumble across your last post.

It makes sense to allow the B.C. signal to go through the S.W. coil, as the reactance is low for those frequencies and simplifies the connections somewhat at the expense of understanding. :)

Charlie


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 Post subject:
PostPosted: Dec Sat 18, 2010 1:23 pm 
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tinwhisker wrote:
It makes sense to allow the B.C. signal to go through the S.W. coil, as the reactance is low for those frequencies and simplifies the connections somewhat at the expense of understanding.


On other sets, perhaps higher quality, all unused windings are often shorted out by the bandswitch. But this greatly increases the complexity (and COST) of the bandswitch. The Z-G link is a sort of shortcut, IMHO.

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