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 Post subject: What type of connector is this?
PostPosted: Apr Sat 17, 2021 3:48 am 
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I have a general radio 804-b UHF signal generator and I just wanted to know if anyone could identify the connector on the lower right side of the face. I think it might work with a female GR-874 connector but I have no clue. Any help would be appreciated.

[EDIT]: Also, here's an article from the General Radio experimenter if that helps
https://worldradiohistory.com/Archive-C ... 941_02.pdf


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 Post subject: Re: What type of connector is this?
PostPosted: Apr Sat 17, 2021 4:42 am 
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Looks like it could be a GR Type 774 cable jack.

The attached PDF has the specs if you need to change it out...
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 Post subject: Re: What type of connector is this?
PostPosted: Apr Sat 17, 2021 2:25 pm 
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It is a General Radio Type 774 connector. The 774 was the standard coaxial connector used by GR in their instruments prior to their introduction of the (far superior) 874 series of coaxial connectors.

Many years ago an article in one of the ham magazines concerned the GR Type 821-A Twin-T Impedance-Measuring Circuit, which also used the 774. The author described taking a double female UHF connector and turning down the threads on one end so it would fit inside the 774 jack, creating a homemade adapter.

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 Post subject: Re: What type of connector is this?
PostPosted: Apr Sat 17, 2021 5:20 pm 
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Thanks for the ID guys! I still wonder if it would be possible to use a GR-874 since i cant really machine my own connector. but if someone knows how modify some other kind of connector to fit I am all ears. I know the impedance for the 874 is 50 ohms and the jack is 72 or 75 ohms. Do the impedances have to match(I'm pretty new to this)?

-Greg


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 Post subject: Re: What type of connector is this?
PostPosted: Apr Sat 17, 2021 8:13 pm 
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GoldenAgeOfRadio wrote:
I still wonder if it would be possible to use a GR-874 since i cant really machine my own connector ...

The only way to use a GR 874 connector would be to remove the 774 panel mount connector and replace it with an 874 panel mount connector. The 874 connectors are genderless - any 874 (of a given impedance - 50 ohms is by far the most common) can mate with any other 874 (of the same impedance), but they cannot mate with any other connectors.

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 Post subject: Re: What type of connector is this?
PostPosted: Apr Sat 17, 2021 8:17 pm 
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GR 874 connectors are hermaphroditic (some prefer the term sexless). Because both the center and outer contacts are split, they simply fit together. There are no males or females, just chassis mount and cable end varieties.

The GR 774 connectors are basically banana plugs or jacks in round shields. GR introduced the original banana plug, which was known as the GR 274, in 1924. The 774 was 1941 update intended to bring it into the UHF range. They were not hermaphroditic and never intended to interchange with the 874 series. GR did make adapters to go from 774 to 874 but those are rare. They were special order items GR reps could get to keep their customers happy. If you try to force an 874 into a 774 without one of the adapters, one or both will likely end up ruined. The inner and outer contacts on an 874 are set to very particular angles so they slide together tightly; if you jam something into them it is possible to distort the mechanical alignment to the point where they won't even work properly other 874s any more.

If the correct 774 series adapter or connector cannot be found, one might consider making an adapter as suggested, or perhaps replacing the front panel connector with something easier to deal with.

(Note: Composed while Dale was replying; redundancy unintentional).

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 Post subject: Re: What type of connector is this?
PostPosted: Apr Sat 17, 2021 10:46 pm 
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Chris108 wrote:
GR 874 connectors are hermaphroditic (some prefer the term sexless). Because both the center and outer contacts are split, they simply fit together. There are no males or females, just chassis mount and cable end varieties.

The GR 774 connectors are basically banana plugs or jacks in round shields. GR introduced the original banana plug, which was known as the GR 274, in 1924. The 774 was 1941 update intended to bring it into the UHF range. They were not hermaphroditic and never intended to interchange with the 874 series. GR did make adapters to go from 774 to 874 but those are rare. They were special order items GR reps could get to keep their customers happy. If you try to force an 874 into a 774 without one of the adapters, one or both will likely end up ruined. The inner and outer contacts on an 874 are set to very particular angles so they slide together tightly; if you jam something into them it is possible to distort the mechanical alignment to the point where they won't even work properly other 874s any more.

If the correct 774 series adapter or connector cannot be found, one might consider making an adapter as suggested, or perhaps replacing the front panel connector with something easier to deal with.

(Note: Composed while Dale was replying; redundancy unintentional).


Yeah I figured as much. Those 774's are basically unobtanium and I don't want to really replace the connector since I want to keep the generator as original as possible. As it turns out, I do have some scrap aluminum around so I actually might be able to make my own replacement 774. If the prototype works Ill probably make another thread about it. Thanks again for the info.


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 Post subject: Re: What type of connector is this?
PostPosted: Apr Sat 17, 2021 11:11 pm 
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Although I did make the suggestion to replace the front panel connector on the signal generator with something else, I am glad you won't take that route. I don't like to modify my equipment either, especially not when it is an older GR item.

The 774 was introduced in 1941 but by 1948 it was already superseded the 874 and it appears GR wasted no time getting the earlier connector out of circulation. That tells you right there that it had some issues like leakage and reliability. With a heavy piece of coax cable, it was pretty easy to accidentally pull apart. The 874 was one of the best connectors ever made for low leakage situations, and it is a lot harder to pull apart.

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 Post subject: Re: What type of connector is this?
PostPosted: Apr Sat 17, 2021 11:31 pm 
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Chris108 wrote:
I don't like to modify my equipment either, especially not when it is an older GR item.

I have purchased GR instruments that came with 874 panel connectors that had been replaced with other connectors such as SO-239 or BNC because a previous owner didn't like "funny connectors." To me they are not funny - they are my favorite coaxial connectors. I stock 874 panel connectors, and so I returned those modified GR instruments to stock. I own a dozen or so GR instruments with 874 connectors and a large assortment of 874 cables, between-series adapters, line sections, filters, and other items. For me 874 connectors are standard equipment.

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 Post subject: Re: What type of connector is this?
PostPosted: Apr Sun 18, 2021 12:23 am 
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I know you said you want to keep as original as possible. How ever if you do replace it My suggestion is just install a BNC and keep the original Just in case.

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