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 Post subject: National HRO 56A1
PostPosted: Feb Fri 23, 2018 5:12 am 
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Joined: Feb Fri 23, 2018 3:25 am
Posts: 1
A HRO 5A1 followed me home from the Orlando FLa Hamfest last weekend. It is rack mounted, with power supply, Receiver, and speaker at top. It came with 9 coils covering from 50 Khz to 30 Mhz. Having never owned one before, it works much better than I expected. I real joy to use. Now the problem. Two of the coils are for the Navy RAS 5 receiver, which cover 190 Khz to 450 Khz and 450 Khz to 900 Khz.
My question is does anyone have any information to adding inductance to the existing coils to force them from 175 Khz to 456 Khz. I guess only the mixer and oscillator coils need to be changed. I do not want to damage the coils. I guess the capacitance may also need to be changed.

Thanks for any help
Joe Munson

 Post subject: Re: National HRO 56A1
PostPosted: Feb Fri 23, 2018 8:37 pm 

Joined: May Fri 01, 2015 2:33 am
Posts: 1658
Location: Roslyn,Pa 19001
Hi Joe and welcome,
As you mentioned the RAS coil sets are designed to operate w/an if of 175kc this makes the local osc lower that the HRO @ 455kc. So you would need to reduce the inductance to raise the lo fq. The RAS osc tunes 625kc to 1075kc on the 450-900kc coils. On the HRO the F coil set cover 480-900kc (it doesn't cover the receiver's if fq) and the osc tunes 935-1355kc.
I have a 1936 HRO and have 8 of the HRO coil sets (50-100kc I'm missing) I also have a set of RAS coils and have done a little experimenting to see if I can reconfigure the two BCB coil to work on the HRO. The rf and mixer coils align ok and after removing some turns from the osc coil I got it to tune the proper range but it seem to cause the osc to not have enough output the run the mixer properly (poor sensitivity). If I switch the two osc coils the RAS pack works ok. I'm thinking that maybe if I add little more feedback winding maybe this will increase the output.

Terry N3GTE

 Post subject: Re: National HRO 56A1
PostPosted: Feb Sat 24, 2018 2:58 am 

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1571
Location: Morris Plains, N.J. 07950
Joe, this site will give you a lot of information, including restoration advice.

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