[Boatanchors] National RX?

Wed Feb 1 17:26:18 EST 2012

----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: "David Stinson" <arc5 at ix.netcom.com>; <boatanchors at mailman.qth.net>
Sent: Wednesday, February 01, 2012 2:05 PM
Subject: Re: [Boatanchors] National RX?

>
> ----- 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.

The first run D series was heavily rack mount and sold to commercial
customers likely to recoup some engineering and production costs.
Im sure most were pre sold.

> 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.

Up thru the HRO 5-1 at least. The 7 required careful handling
and had to be inserted so as to not jam the mating contacts in the radio.

>    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.

There were no sliding jumpers on any HRO until the HRO-50 in 1950.
A screw had to be moved from one set of contacts to the next. Very
 inconvenient and why I picked up a set of A to D Junior coils for mine
for general coverage. I now have the complete A to J set with the thick 
panel plus the Juniors.

>    I believe the HRO was also the first receiver to contain
> a crystal filter.

Far from it. At National the AGSX and FBX(or FBX-A) preceeded it.

>The filter was invented by James Lamb, who
> worked for National.

Lamb never worked for National but Millen used several of his ideas 
published in QST
 but never adapted his noise blanker which did show up in the SX-28 and much 
later in the
 HQ-180. Millen and the ARRL were attached at the hip and he had advance 
info months
 before articles were published.

Early National filters were not very spectacular and it wasnt until 1939 
that Hammarlund got
it right for the SP-200. Later Nationals sort of copied it but avoided 
patent infringement.

>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.

The AGS had an RF stage as well as some consumer sets such as
the 1931 Scott AW-12 2 dialer.

Drift was a problem in the HRO when coils were changed and many commercial
 customers had a receiver for each range they used, hams had to learn to 
live with
the drift until cold coils warmed up or got creative with their storage 
placement.
TC capacitors hadnt been invented yet.
The major benefit of the HRO coils was in sensitivity and image rejection. 
With no
bandswitch, rats nest wiring and strays to contend with the HRO was hot on 
20M and even
 did a credible job on 10 if you read various QST DX and contest results. 
The resultant high Q of the coils
and air variable trimmers and padders were the reason.
OTOH the ugly RME-69 with the same front end tubes needed 2 more noise 
generators in
 the DB-20 preselector even on 20M. Many period photos showed the two pieces 
together
but not with HRO's.
Even the single RF stage in the NC-100 thru NC-240 did a decent job on 10M 
thanks to
another Millen innovation and the high Q coils result in much better image 
rejection than single RF stage
 bandswitched receivers.

> Its possible that
> RME had a set about the same time. I suspect Carl, K1MH
> would know.

The RME-9 was announced in Dec 1933 but the AGS was on the market in 1933 
and the HRO was already
 in the 1934 Catalog as a mockup which also announced a version with a built 
in PS.
 The same goes for the crystal filter. Lamb designed it and both National 
and RME copied it but the
AGSX was first to market. The FB-7 had a matching preselector and needed it 
on 20M and up. I use mine a lot
 (the FB-XA version) on 30M where its been pretty decent.

> I was a remarkable design for its time and, as I
> said previously, is still a respectible receiver.

I can sometimes be found on 20, 40 and 80 CW with my 1935 E series and some 
30's version of a HB or factory transmitter.
Ive even added some all time new countries and band countries with them.

Carl
KM1H

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