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 Post subject: ARC-5 radio IF transformer question
PostPosted: Jan Thu 18, 2018 1:28 am 
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Location: Milwaukee,WI
I am in need of the 2830khz 2nd IF transformer but the only one I can locate online is the 3rd IF transformer. They look identical in the schematic including the cap values. Is there a good chance I can get by with installing the 3rd in place of the 2nd and get decent results? I see I would have to switch pins 5 and 6 to match but thats not a big deal.

I wound my own on a base from an old 455khz transformer. But attaching it without hacking the chassis is a challenge. My only solution is soldering on to the new transformer base, 4 very short stiff wires with small alligator clips at the ends. Then I can just clip those on to the male pins sticking up from the original chassis socket. But I'd rather stick and original on the chassis instead of my makeshift one.

On a related note, I had no idea how far down to make the tap on each coil. I decided on about 20 percent down from the top of the coil. Was that a decent guess or way too much and it should only be a few turns? Plus I know the 2 coil's shape, length and spacing were not close to original but the darn thing works. I don't know how well compared to original though. Another reason why I would like to use original instead.


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Thu 18, 2018 3:02 am 
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Not directly.
The connections at transformer pins 5 and 6 are reversed.

It's possible you could reverse the wires at the IFT socket pins.
But I don't know if the secondary tap is at the same place.

It's been many moons since I worked on any ARC-5 sets.
I seem to remember that the IFTs were polarized in some manner so you could only install one in its proper location. Something about rotation of the base contacts, location of the mounting ears, etc.

- Leigh

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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Thu 18, 2018 4:16 am 
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Location: Milwaukee,WI
I don't have the radio in front of me to look right now to see if there is any diff in the pin layout. I do know that the mounting ears at the 2 corners are different but I'm not too worried about that.

I thought that parts and people that have and work on these radios would be plentiful. At least thats what I thought when doing Google searches. But then I started noticing the dates of the info I found online. It seems the majority of posts I read was in the 2004-2009 era. Not nearly as much since then. So maybe the popularity of this radio peaked and has dropped.


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Thu 18, 2018 5:26 am 
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Posts: 90
What is the freq. of the radio you're working on? I've restored a couple over the last two years. Fortunately I had access to a lot of spare parts but they're gone now. Sorry. Brad Whiting (KD&GDT) is a collector who buys and sells military equipment and I bet he'll have one for you, or point you in the right direction. Contact him at kd7gdt@arrl.net or 541-760-5053.

I had my IF can all apart and can tell you it is not a big deal to relocate a couple of wires going to the pins inside there. I would think the windings on the second and third transformer are the same.......but then why the different pin out? Maybe the guy with one on the web could give you some resistance readings on his so you could compare it with the 2nd IF can you have. I assume you have the schematic and pictorial layout of the receiver you're working on. I was lucky to find a few parts from people who wrote articles about the ARC-5s over the years. It seems that people who are really interested in the ARC-5 also have a good stash of spare parts. Best wishes in your search.


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Thu 18, 2018 3:18 pm 
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I assume from the IF frequency that it is the 6-9.1 Mhz. model. It has been been a long time since I have been in one but I do recall one of the differences between the Navy and the other variants is some of these do not have a tapped IF transformer except for the detector (IF output) transformer. If buying one online make sure exactly what you are getting.

In general the turns ratio may differ for the IF output transformer compared to the input and interstage IF transformers since the diode detector load impedance is lower. This could be addressed through the tap on either the primary or secondary side of the transformer; the entire winding is used with the parallel capacitor to provide the proper resonant frequency but the tap point is chosen for the correct impedance ratio.

In reality an impedance mismatch in this set isn't likely to cause that much difference. Total IF gain would be reduced a bit but probably not enough to notice. In many tube type sets the same 1 to 1 ratio transformers were used throughout the set because perfect impedance transformation wasn't a concern.

Rodger WQ9E


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Thu 18, 2018 9:18 pm 
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Location: Milwaukee,WI
I will try contacting the guy from Michael w's post before ordering the 3rd IFT from Fair Radio Sales.

Even with a possible slight mismatch it couldn't be worse than the IFT I hacked together. I'll take a look at the pinouts on the chassis to verify the 3rd IFT can plug into the 2nd IFT socket with only switching pins 5 and 6.

Thanks for the help so far.


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Sat 20, 2018 11:21 pm 
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Darn. I'm batting 0 for 7. I sent out an email to 7 different people asking about an IFT and all 7 were no replies. I would have expected 1 or 2 not responding, but not all 7. :cry:


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Sun 21, 2018 12:38 am 
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It could be old email addresses. If any of them are hams maybe check QRZ for their email address also.

Also if you use your ISP email instead of one of the major players if one of the other customers of your ISP got infected with a virus and started sending out spam email your domain could be blacklisted and your email isn't going through.

Rodger WQ9E


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Sun 21, 2018 1:18 am 
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Thanks for the tips. A few of the emails were sent to hams. Most of the email addresses came from recent posts in forums so I assume they are up to date.


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Mon 22, 2018 7:07 am 
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Location: Newport, Oregon, 97365 U.S.A.
Roger, really, some tube radios used the same IF can type all the way thru? ( I assume we mean AA5 type things with 1 IF, actually )
? I am not doubting you, but I have never seen this myself.
This question, last IF can impedance, is something I was thinking about myself just recently. I have a National NBS-1 which is a NC-173 with one more IF stage. The last can, the diode driver, is only a single tuned circuit and is heavily damped with a resistor. I am
thinking of replacing it with a standard "IF output" can to gain some more selectivity. That's why I was puzzling over the transformer
impedance. I will look for a diode driver can that fits the cutout. I am just guessing, but I would think a normal IF interstage can would be around 500k - 1M ohms impedance and the diode driver a fraction of this, maybe 300k? That is just a guess. I need to look up some parts specs and learn more about this.
-Hue


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Mon 22, 2018 1:17 pm 
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Hue,

I was surprised when I found an open IF transformer in the last stage of a Hallicrafters SX-133 I was working on that it had the same part number as the others in the set and then for curiosity I checked some other sets and found the same was true. The Hallicrafters SX-101A which is currently being discussed in another thread is another example as is their lower cost SX-140. I noticed that Hammarlund also uses the same approach in the HQ-170 although it does have a final untuned IF stage (choke fed plate) that serves as an impedance converter between the final high selectivity transformer and the detector stage.

You will also see advertisements for "universal" IF transformers and at first I assumed that meant they could be tuned in a fairly broad range around 455 Khz. but it really meant they were for use in any stage. Most simple IF transformers don't have tapped windings and if you dissect one most have the same winding size (and presumably number of turns) on both the primary and secondary.

Feeding the diode load, impedance match is definitely incorrect but apparently the gain lost is considered to be of no consequence. You might first try a standard IF transformer in your NBS-1 and do some before/after gain measurements just to see how much it changes.

Rodger WQ9E


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Mon 22, 2018 4:55 pm 
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I'm still holding on to hopes of finding a proper IFT someday but this makeshift one will do until then. I couldn't find my roll of thinner wire so unfortunately I had to use thicker wire and I had to overlap a second winding layer part way over the first layer. The 2 coils are closer than I would have prefered. Also I didn't have any trimmer caps small enough so I ended up using slug tuned coils with fixed value caps. It looks goofy with the 4 alligator clips soldered to the transformer base pins but its sturdier than I thought it would be plus I didn't have to butcher up the original socket. But hey, the darn thing peaked when adjusted and I was able to confirm the radio works. So now I can go on to recapping and any other mods I might want to make.


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Mon 22, 2018 5:09 pm 
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There is nothing wrong with a non-destructive use of a part to allow you to complete restoration and enjoy some radio usage while waiting to find an exact replacement. Sometimes an exact replacement is very difficult to find or you may not even want an original replacement if the original part has a designed in defect that results in a high failure rate.

Nicely done.

Just be glad it wasn't a radio with a 50 Khz. IF that you had to wind :)

Rodger WQ9E


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Mon 22, 2018 6:14 pm 
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I am enjoying reading your thread and really like the photo. I have a home brew underway that requires some Miller IF transformers that I will never be able to find, so I have plans to make my own. I have been studying IF transformers for a while--what there is out there as far as information. In general; for wire, the smaller and more strands the better, the coils should be square in cross-section, and the distance separating the two windings helps selectivity (Q) but hurts transfer of energy. Ferrite cores increase Q. The reason most transformers are inductance adjusted is probably to save space as trimmers don't fit in small cans. If your transformer works, that's great. Like Rodger said, it will get you through the other parts of the restoration and in the future you can come back and either find a replacement or wind an improved version. Another thing to consider is adding some capacitance by way of external silver micas to a 3 MC transformer to bring it down to the range that works with that radio. I may even have several on an octal base--I will check next weekend when I am back at the bench.

Norm

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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Mon 22, 2018 8:03 pm 
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+1 to norm's text about how to wind coils. I broke just about every rule.

As a test I plugged the original 3rd IFT into the 2nd IFT socket and my homebrew into the 3rd IF socket. My homebrew didn't work good at all BUT the 3rd IFT did peak and work in the 2nd IF socket. So that tells me that I should be able to use either a 2nd or 3rd IFT for the 2nd IF section. IIRC, Fair Sales Radio has a 3rd IFT for sale. If their version has the secondary taps like mine uses, it should work.

But since we're talking fractions of an ohm difference between the 2 versions with or without the tap I'm not 100 percent confident I'll get what I need. Providing they even want to bother to measure. It can't hurt to ask. Lets hope this isn't email number 8 to be ignored. :wink:


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Mon 22, 2018 8:56 pm 
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I've got a bad feeling.
The IFTs in my radio have part numbers of 9693, ????, 9699... 2830khz

The IFTs on Fair Radios's website are 7277, ----, 7279... 2830 khz

I'm guessing their version with the different numbers are going to be without the secondary taps like mine.

EDIT: Now I'm really getting lost. According to a chart I just found, my radio model supposedly does not use tapped IFTs. But the schematic I have does show them. They can't both be right. I tell you, its very confusing if some people on these information websites are confusing arc-5 with scr-274. Also, if this radio does not use taps why are there 2 different sets of part numbers for the IFTs? If i'm lucky the parts are identical and the difference is because one set is for the SCR version and the other for the ARC version. AARRGG!!!! My brain hurts. :wink:

I sure could use the wisdom of Curt Reed right now. In an old post from 2006 he said he had been messing with these radios for 45 years already.


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Mon 22, 2018 10:04 pm 
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The challenge continues. I decided to grab the bull by the horns so to speak, and order up the 3rd IFT from Fair Radio. It costs $7.50 but minimum order is $10.00 so I added the 1st IFT to the order to exceed that minimum. I go to checkout and discover that I see only Mastercard, Visa and Discover credit cards are displayed in the payment section. I have a Capital One card. :cry:


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Mon 22, 2018 10:16 pm 
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forumuser wrote:
The challenge continues. I decided to grab the bull by the horns so to speak, and order up the 3rd IFT from Fair Radio. It costs $7.50 but minimum order is $10.00 so I added the 1st IFT to the order to exceed that minimum. I go to checkout and discover that I see only Mastercard, Visa and Discover credit cards are displayed in the payment section. I have a Capital One card. :cry:


Isn't your Capitol One card under MC or Visa? I use the GM Mastercard and Capitol One took over service of it several years ago. Capitol One is big but I assume they would use one of the major network groups for their cards.

Rodger WQ9E


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Mon 22, 2018 11:51 pm 
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I'll be darned. Its got the Mastercard logo in the bottom corner. I use a credit card so seldom I didn't notice. My previous card was canceled because I didn't use it for over a year.

Thankyou very much. Now lets hope the parts didn't sell to someone else. :lol:

Parts have been ordered. Now the waiting game.


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 Post subject: Re: ARC-5 radio IF transformer question
PostPosted: Jan Tue 23, 2018 3:19 pm 
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A look at the manual for the AN/ARC-5 system (I assume your receiver actually is an R-27 since it has a 12SF7 in it) reveals that your IF transformers should not have taps. A note on the schematic for the communication receivers states that the tap connections are made at the top of the coil on the 6-9.1 Mc receiver. Your 2nd IF transformer should be part number 9697. This is from AN 16-30ARC5-2 available here:

http://tonnesoftware.com/Manuals/ARC5manual.pdf

The schematic for the communications receivers starts on PDF page 141. Drawings of the IF transformers are on pages 342-345.

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