Radio City Products Signal Generator Model 705A - Printable Version

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Radio City Products Signal Generator Model 705A - captainclock1988 - 05-02-2020

Greetings everyone, I just recently bought a 1948 Radio City Products Signal Generator Model 705A which according to the original manual that I downloaded from the BAMA website is an AM and FM Signal Generator that has a frequency range of 100 kilocycles to 25 Megacycles across 6 band selsections and then with the use of Harmonics it has a frequency range entension of up to 150 Megacycles. 

This unit uses Banana Jacks for all but one of the connections, the RF Lo Output uses the old Switchcraft Microphone Jack like my Heathkit SG-8 used, and the RF Hi output and the AF input/output jacks are of the Banana plug variety of jacks, the unit did come with a Switchcraft Microphone jack to RCA plug adaptor (at least I think its an RCA Plug, it could be a Banana Plug but I'm not sure).

I just finished recapping the unit as it had its original paper caps in it yet and an older replacement electrolytic capacitor that I swapped out for a modern set of capacitors.

Anyways I was wondering if there would be a way to make some test leads or adaptors for this thing that would utilize the existing Banana Plug so that I could use the RF Hi output to hook up to a frequency counter to check the unit's accuracy (which according to the original manual its supposed to be a very accurate unit, an accuracy of 2%, with the ability of being able to achieve an accuracy rate of 1% or less.

It also isn't supposed to have issues with drifting or anything else like that as well according to the manual.

The manual is posted below.



Any help with this unit would be appreciated.

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RE: Radio City Products Signal Generator Model 705A - RodB - 05-02-2020

I guess I would start with a connection to the freq counter. If it's a BNC, then use that, whatever it needs. Next use a coax cable that has the same impedance as the freq counter input, probably 50 or 75 ohms. Then,, since the RF has 2 sources, attach aligator clips to the free end of the coax. Now you can switch between the two RF sources. If you want to have it permanent then you need a switch to select RF or HI RF. The switch may make the HI RF act strange or induce noise. Be very careful as to how the grounds of the 2 units are handled.

Rod

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RE: Radio City Products Signal Generator Model 705A - captainclock1988 - 05-02-2020

Quote:I guess I would start with a connection to the freq counter. If it's a BNC, then use that, whatever it needs. Next use a coax cable that has the same impedance as the freq counter input, probably 50 or 75 ohms. Then,, since the RF has 2 sources, attach aligator clips to the free end of the coax. Now you can switch between the two RF sources. If you want to have it permanent then you need a switch to select RF or HI RF. The switch may make the HI RF act strange or induce noise. Be very careful as to how the grounds of the 2 units are handled.

Rod

It already has a switch built-in to it to switch between the high and low RF outputs, so I don't need to worry about that. 

As I already stated previously the RF High ouput on here that I would be using with the Frequency Counter uses a Banana Jack which I need to get a Banana to BNC Cable to hookup between the signal generator and the frequency counter, the Low RF Out which would be the one I would use for the actual alignment process, uses the old style Mic Jack like my Heathkit Signal Generator used, only Difference is that it actually has a plug for it that I could use to make a set of test cables for if I could find some on say Mouser that were just the cables and alligator clips and didn't have a plug on the end.

And Yes, unlike the Heathkit unit I have this unit is fully shielded and grounded for better performance quality, which is why I want to alter this unit as little as possible because they have this setup so that it is wired up with top notch accuracy in mind, and I don't want to ruin that, I believe this might of been a lab quality unit.

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RE: Radio City Products Signal Generator Model 705A - captainclock1988 - 05-03-2020

Ok so from what I've seen of pictures of the RCP Model 705A Signal Generator, it seems that the original RF Output plug was basically just a hot lead all by itself and then the ground lead was independent of it and hooked up to the banana plug jack that's marked "GND" next to the AF Output jack.
So it seems that all I need is some RG-58 Coaxial cable that I could wire one side to my already existing mic plug and then the other side wire up to an insulated red colored alligator clip, and then have a regular black banana plug wired to a 4' length of black wire on one end and the other end a black insulated alligator clip attached for the ground lead. 

Here's the picture I found posted below showing the original RF-Output test lead.

   

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