Help identifying this old AM transmitter

Discussion in '"Boat Anchor" & Classic Equipment' started by W7UUU, Feb 11, 2019.

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  1. W7UUU

    W7UUU Super Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Any ideas which HRO it might be? I have an HRO-50 carcass in the barn - but what's in this rack looks older.


  2. N2EY

    N2EY Premium Subscriber QRZ Page

    My best guess is that it's an HRO Senior from just before WW2. Need more info to be sure.

    73 de Jim, N2EY
    W7UUU likes this.
  3. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    It looks like it started its life as one of the Navy versions of the HRO. The HRO Senior, as well as most of the civilian HRO models had an R / S meter. The HRO Junior did not have an R / S meter (before World War II the "S" meter was often called an "R" meter). However, the knob layout is different from the HRO Junior.

    But, there were a number of different HRO variants made for the U.S. Navy that did not have the meter. The HRO civilian models were not rack mounted but most of the Navy versions were. This receiver does have about the same control layout as the HRO Senior which also leads me to think that the receiver is a Navy variant of that receiver.

    There were quite a number of different Navy models including the RAS- series, the RAW- series, the RBJ- series, and several other nomenclature receivers.

    Glen, K9STH
  4. W7UUU

    W7UUU Super Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Couple more photos of the receiver:

  5. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    The fact that there are some miniature tubes in the receiver screams Navy. The earlier HRO Senior had all large pin tubes and the later versions had a mixture of octal tubes and large pin tubes.

    Glen, K9STH
  6. N2EY

    N2EY Premium Subscriber QRZ Page

    Oh dear. Talk about a hard-knock life!

    A couple of things:

    1) Since the front panel has been replaced and numerous mods made, it is not safe to assume anything about an S-meter or control placement other than what is shown. So @K9STH's observations about Navy sources are...speculative at best.

    2) The lowest row of controls on the front panel are all not original, nor do they go through the chassis.

    3) The IF cans are all non-original, same for the miniature tubes. The chassis is painted, not plated, which pushes the date back somewhat, and the black dial chart on the left plus the gray PW tuning knob pushes it forward. Those factors all intersect in the late 1930s and into the 1940s.

    4) There were all sorts of HRO variants made by National for the Navy, Coast Guard and the British (once Lend-Lease was in place). In addition, when WW2 ended, National used parts on hand to build HROs in various flavors of "HRO-5" while they got set up to make the HRO-7, which came out in 1947 or so. The HRO-7 is quite a bit different in appearance from the earlier models, so the receiver can't be newer than about 1946.

    5) There is no sign of MFP treatment, which was done to many military HROs - even to the point of coating the knobs.

    6) The early HRO was a prime candidate for modifications that improved performance, particularly if one could be had cheaply. It appears this receiver got the full treatment and then some!

    73 de Jim, N2EY
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  7. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    The panel is probably original. It has definitely seen better days.

    Many of the original HRO series receivers had the toggle switches mounted to the chassis and larger holes drilled in the panel that were larger than the nut holding the switch to the chassis. Here are photographs that clearly show the recessed toggle switches:



    The fact that the chassis is painted "battleship gray" and no "fungus" prevent, which was used on Army equipment but not, usually, on Navy equipment, is another clue that the receiver was probably Navy surplus. Yes, some of the civilian HRO series had gray painted chassis as well as black painted chassis. Of course, most of the knobs are a hodgepodge of replacements.

    Here is a photograph of a Navy RAS- series receiver showing the "battleship gray" painted chassis and no "fungus" prevent:


    I know that there were at least 8-different RAS models and maybe even 10. The original RAS through the RAS-7 (I have worked on an RAS-7) and I have heard mentioned an RAS-9. However, I cannot swear to anything past the RAS-7. There were also RAW and RBJ versions of the HRO series and, maybe, even more.

    Glen, K9STH
  8. N2EY

    N2EY Premium Subscriber QRZ Page

    No, it's a replacement. Here's proof:

    Note how far below the coil set the front panel extends, and the control, switch, jacks and pilot light in a row on that part of the panel. No pre-HRO-7 HRO I have ever seen, in pictures or reality, has a panel that extends so far below the coil rack.

    No argument there! The whole setup was clearly built from what was at hand.



    Sure - but that doesn't make the panel original. It would be a simple job to make those holes big enough to clear the switches. Note how, in the pictures above, there is only a narrow strip of panel between the bottom of the coil rack and the bottom of the receiver, while in the picture of the unknown HRO, there's a lot more panel.

    What I suspect happened is that the unknown HRO was a table model (as seen in the pictures above) and the owner wanted a rack model - and didn't want to fuss with the cabinet. So, the front panel was simply replaced with a rack panel - the original table-model panel could be used as a template.

    Yes, it could be Navy surplus. There were many variants made, including some with 175 kc. IFs so that the maritime band below the AM broadcast band could be tuned without interruption or feed-through. Maybe that's why the IFTs were all replaced.

    There were some models (HRO Junior, for example) which did not have the bandspread feature. They are clearly identifiable by the single frequency chart on the coil sets. The unknown HRO clearly isn't one of those.

    I wonder - are there other coil sets in the pile, or just that one?


    It seems to me there are several possible uses for that receiver:

    1) Parts source to keep other HROs alive.

    2) Restoration project of incredible magnitude, requiring a lot of research just to figure out what it is.

    3) Restoration to the former owner's original intent (hard to determine)

    4) As a basis for a semi-homebrew receiver. (Tear it down completely, clean up all the usable parts, make a new front panel, design "the HRO that never was", and build it. )

    You can guess which one I would do.....

    73 de Jim, N2EY

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  9. KB3OUK

    KB3OUK Ham Member QRZ Page

    Probably based on the 6L6-807 exciter in the November 1940 QST. I have 2 versions of that rig, a homebrew copy and a Millen 90800, which was a manufactured version of the same exciter. One question i have looking at the pictures, how can you tell that tube in the one picture is an 852 and not an 860, which looks identical but is a tetrode? The 860 was also used by a few WW2 Navy transmitters.
  10. N2EY

    N2EY Premium Subscriber QRZ Page

    I agree 100%. Versions of that idea appeared in QST and the Handbook for some years. IIRC it evolved into a 6AG7-6146 design. The 5 pin socket and the cathode coil are the give-aways.

    The 852 and 860 may look identical at first glance, but they are not.

    The 852 has two rods coming down from the top of the tube which hold the grid spiral - but the grid spiral is only at the place where the anode is.

    The 860 has the screen mesh running almost the entire length of the tube.

    Here's a picture of an 860:


    and here's the 852 in the transmitter:

    front (4).JPG back (4).JPG

    Zoom in on the rear view and you'll see there's no screen mesh extending upwards from the plate. Dead giveaway that it's an 852 and not an 860.

    73 de Jim, N2EY

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