[Boatanchors] National RX?

[Richard Knoppow]

----- Original Message ----- 
From: "David Stinson" <arc5 at ix.netcom.com>
To: <boatanchors at mailman.qth.net>; 
<boatanchors at theporch.com>
Sent: Wednesday, February 01, 2012 10:17 AM
Subject: Re: [Boatanchors] National RX?


>I haven't recieved it yet, but it includes the rack,
> speaker, power supply/coil box with the coils.
> Here are more photos.  A good friend snagged it
> for me from an estate for an excellent low price.
> It might be a "mix-n-match," but I'm still excited ;-).
> It's so clean it might even work.
> I never worked on an HRO before.
> Gonna be fun.
>
> 73 Dave S.

    The QTH boatanchors list does not support attachments. 
If you have more photos please post them where we can see 
them
    National sold the HRO as a system almost from the first. 
This version had a rack mount receiver in a table rack with 
a combination power supply and coil holder and a speaker. 
The photo you sent does not look like a special, just a 
regular HRO. Power supplies were sold in rack mount and 
table versions, the table version usually in a case with a 
peaked top often called a doghouse supply due to its shape. 
Also available were table and rack speakers and a coil 
storage box.
    Coils were pretty much unchanged for years and most 
coils will fit most receivers.
    When 15 meters became available a new coil set was 
issued that was a 15 meter band spread coil. There were also 
accessory coils for low frequencies, including the broadcast 
band and a couple of others. Normal coils have sliding 
jumpers on each coil to switch from general coverage to band 
spread of one ham band.
    I believe the HRO was also the first receiver to contain 
a crystal filter. The filter was invented by James Lamb, who 
worked for National. The original filter is a bit tricky to 
use for those used to the later version patented by 
Hammarlund but will still give very sharp tuning for CW.
    Because of the way the S-meter is arranged a switch is 
provided for it to prevent burn out. The switch is a 
push-button on the front near the meter.
    Some of the older HRO's have very high impedance audio 
output, around 5K ohms, like older Hallicrafters receivers. 
They were intended to be used with the plate transformers 
used for single-ended amplifiers, these have about the right 
impedance.
    Handbooks for all the HRO receivers are available at 
BAMA and advertising can be found in QST for nearly any date 
after its introduction. QST is available to ARRL members at 
their web site.
    While the plug-in coils look old fashioned they have the 
advantage of short connections to the rest of the circuit 
which remain constant with the band. They are also at the 
bottom to avoid heating and consequent drift.
    I am not sure but think the HRO was the first 
communications receiver with an RF stage. Its possible that 
RME had a set about the same time. I suspect Carl, K1MH 
would know. I was a remarkable design for its time and, as I 
said previously, is still a respectible receiver.

--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com