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 Post subject: Re: Selecting a osc coil replacement
PostPosted: May Mon 13, 2019 3:36 pm 
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Location: Jamison PA
Thank you Mark

Now this set has been recapped and has nos tubes for 6A7, 6D6 76 75 and good 48’s

The set is 456 but universal 455. Dunno if that’s if any concern.

The only coil that oscillates is the 4034. It only will Wired a certain way

I tried several combinations on the universal and got nothing

Of note this set has a wave trap and I wanted to know if that affects anything. I dunno how to peak it but perhaps it’s 456 through ant lead from generator and peak it that way??

I’ve not run into this issue before so learning as I go

Thank you
Mike


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 Post subject: Re: Selecting a osc coil replacement
PostPosted: May Mon 13, 2019 4:02 pm 
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Exact frequency for oscillator coil: anything around 455 is fine--I would guess the tolerance is at leasst 5%. maybe more with the adjustable "universal" type.

"Wave trap"--I assume you mean a trap at ~455KHz---not relevant--but I would just disconnect it.

When you say that the universal coil does not work, do you mean that it does not oscillate at all? If it's just the frequency that's off, then that could cause the set to not work. If everything is wired correctly, the tube is good, and the tube voltages are right, then the universal coil WILL oscillate.

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-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Selecting a osc coil replacement
PostPosted: May Mon 13, 2019 7:08 pm 
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Joined: Jun Sat 09, 2007 8:14 am
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When using one of the AES coils I remember some kind of confusion as to the terminals and having to check with an ohmmeter to be sure of which was which. One winding has a tap. The tuning cap goes across this entire winding. The other has no tap and is the feedback winding.

You mentioned trying several configurations. The one to try first is as a drop-in with the entire tapped winding across the tuning cap. Try both phases of the feedback winding. If the circuit is oscillating there should be a negative voltage across the grid resistor (the one in parallel with the padder). You need either a VTVM or a DMM with a resistor (1 meg or so) on the probe tip to see this.

I asked in an earlier post of all the other parts in the oscillator circuit had been verified as good.

RRM


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 Post subject: Re: Selecting a osc coil replacement
PostPosted: May Tue 14, 2019 2:33 am 
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Joined: Jan Wed 07, 2015 10:39 pm
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Location: Jamison PA
No oscillation out of universal coil.
I am listening to our 1060 at 1370 on the dial. I have the 4034 coil hooked up via alligator leads.
I have 4 wires to connect to coil. One is the big osc padder to ground, one is B+ fed from 6D6. Next is grid pin 5 coupled with ant tuning sector as one wire, then lastly pin 4 from 6A7. The signal is strong touching too cap of 6A7. Through antenna weak but of course if I touch 6A7 top cap much louder.

I’ve tried the different combos with the universal. If you all have a suggestion I’d take it. As you know there are 5 pins on the universal.


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 Post subject: Re: Selecting a osc coil replacement
PostPosted: May Tue 14, 2019 2:45 am 
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Well--I see one big problem. Most RF circuits cannot be expected to operate predictably---or at all---with those long leads. In addition to adding capacitance, they add a lot of unintended coupling.

Whatever coil you are trying, make the lead length and routing as close as possible to the factory wiring.

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-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Selecting a osc coil replacement
PostPosted: May Tue 14, 2019 4:11 am 
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delco32 wrote:
..... I’ve tried the different combos with the universal. If you all have a suggestion I’d take it. As you know there are 5 pins on the universal.


The one I tried to describe is the one I would use since it doesn't require redesigning the circuit. The entire tapped winding goes across the tuning cap. The tap doesn't go to anything. The untapped winding is the feedback winding. If you can't get oscillation at some frequency with either phase of the feedback winding, I'm more than a little puzzled, but it wouldn't be the first time.

RRM


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 Post subject: Re: Selecting a osc coil replacement
PostPosted: May Tue 14, 2019 1:45 pm 
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The Coronado oscillator is a Hartley---using the "oscillator anode" in the mixer tube as the plate. This is circuit #1 (left side) in the AES spec sheet:
https://www.tubesandmore.com/sites/defa ... sheet2.png
I'm betting that those long leads are the problem......

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"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Selecting a osc coil replacement
PostPosted: May Tue 14, 2019 3:59 pm 
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Thank you for hanging in there with me. I realize it must be a bit tiring to hear less than experienced questions....

Yes, I will ditch the long leads. The leads for the osc coil are original and are uncut. I did attach the 4034 coil to it in the same configuration as shown. I will try again and will also try the universal in the same manner. Now what pins should I use on the universal, and yes its the first diagram I was attempting to use on its data sheet. I describe my original wires above for reference.

Thank you again :mrgreen:


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 Post subject: Re: Selecting a osc coil replacement
PostPosted: May Wed 15, 2019 2:16 am 
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An update:

Soldered 4034 in place with trimmer attached. Found antenna trimmer backed way out.?Also had replaced top clip on 75 tube. I’m still getting crashes and garbage unless in get it just right on top cap. The original was very rusty but perhaps this one isn’t that great either. It clearly seems to be the top cap wire itself. Strange stuff.
So got our strong 1210 in and dial is at 1370. I’ll try to trim it tomorrow, but had same issue before. It does sound good and if it weren’t for that it would be done.

If I can’t trim it then what would be my next step to try?

My lite wire is coming so that might be an option to rewind my original....

Mike


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 Post subject: Re: Selecting a osc coil replacement
PostPosted: May Wed 15, 2019 11:41 pm 
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delco32 wrote:
Now what pins should I use on the universal, and yes its the first diagram I was attempting to use on its data sheet.

You would wire it in accord with the 1st diagram.......

Someone mentioned potential confusion about the pin numbering on the coil. Verify which is which using the DC resistance.

First principles: The winding with the most number of turns is the tuned winding and--in your case---gets wired to the "oscillator grid" ** of the tube. The other winding is the "feedback winding". In you case, it goes in series with the B+ supply to the "oscillator anode" **.

When wired correctly (and the tube is good, etc.,) it will oscillate. If not, reverse the connections to the feedback winding.


** Anything except the cathode can be an ANODE---meaning simply that, with a positive voltage applied, it will behave as an anode. In a mixer such as the 6A7, the cathode and the first 2 grids operate as a triode to provide the gain required to generate the LO signal. Because the "oscillator anode" is really a grid---and therefore passes an electron stream, it allows the LO signal to move on to the rest of the tube.

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-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Selecting a osc coil replacement
PostPosted: May Thu 16, 2019 12:47 am 
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Excellent and very helpful

In my case, the oscillator grid is pin 5 of 6A7. It goes in conjunction with ant tuner cap to bw switch. That’s the one connection. Then pin 4 ithe other grid from bw switch is the other. Lastly is B+ From 6D6 also to sw sic coil is 3 and then padder to ground to make four connections.

The universal is confusing as it has the 5 taps. It shows tap 4 and 5 and also 1 and 3 for my circuit.

Now I’ve done it before but based on my description it appears you look at from tunable slug side.

In your opinion based on my four connections as I described, which one goes to what? The grids confuse me, B + I get not sure which one is considered the ground to padder either

I’m slowly understanding, my wife thinks I’m nuts constantly talking to myself when I’m front of it....


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 Post subject: Re: Selecting a osc coil replacement
PostPosted: May Thu 16, 2019 1:06 am 
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Nomenclature: "tap" means an intermediate point on a winding, The coil has 2 windings, one of which has a tap (which is not used)

Connect the two windings in accord with this:
Attachment:
AES_coil_connections.jpg
AES_coil_connections.jpg [ 14.44 KiB | Viewed 207 times ]

_________________
-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Selecting a osc coil replacement
PostPosted: May Thu 16, 2019 2:03 am 
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Joined: Jan Wed 07, 2015 10:39 pm
Posts: 237
Location: Jamison PA
I’ll give it another shot tomorrow hopefully

As an aside backing the low end padder got me to 1280 for 1210. The trimmer I have in the coil didn’t do anything, yet it is on the ground padder pin and the pin 5. On osc coil itself. seems to be correct connection wise

Backing out low padder probably killed anything below 900. I can still get 990 from Ontario however

This has been interesting and enlightening


Many thanks to you Mark


Mike


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 Post subject: Re: Selecting a osc coil replacement
PostPosted: May Fri 17, 2019 2:20 am 
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Joined: Jan Wed 07, 2015 10:39 pm
Posts: 237
Location: Jamison PA
We have a winner!! :mrgreen:

Although I was close with the 4034 it couldn’t quite be tuned to get accurate dial vs freq.

I carefully soldered in the universal as Mark suggested and it came alive!!

I was able to adjust it and hone it in to the correct dial vs freq.

There was a thread from 10 years ago with a fellow who had the exact same chassis and same problem. I don’t think he ever got it cause no follow up. I am hopeful that this will help anyone else thanks to the generosity of the board members

One tiny problem I have is that the top cap clip on the 75 is intermittently causing crackling loss of signal and crashing noise. It is definitely at the clip. I will have to resolder it.

This was a poor old set that would have been tossed. We saved another one!

Mike


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