National HRO 5TA-1 T/R ideas.

[N6YW]

Greetings

I just purchased my first HRO receiver, the 5TA-1, built in 1946. While I understand that many of the HRO features from the late 30's thru mid 40's had much in common, I assume the standby condition during transmit dealt with removing HV from the front end. I reasoned that this jalopy could use a little updating!
So, I thought, why not interrupt the Cathode of the first RF stage? Do any of you have experience with inserting this fine receiver into an every day ham radio station without having 240 vdc or better on a set of relay contacts?
I plan to use this radio with my BC-610E, along with an AR-88 as a diversity rig. While I love the SX-28, I just want to do things a little different.
What say you guys?
73 de Billy N6YW

[KA2DZT]

I have a HRO-M (1942) that I use for my main station receiver.  I use the contacts on a Dowkey antenna relay to mute the receiver.  My receiver has a B+ switch on the front that you would use while changing the plug-in coils.  The receiver has a terminal strip on the back where the relay gets connected.  I think the relay opens the same B+ line as the front panel B+ switch.  I can check the schematic later today to be sure.

The Dowkey relay is controlled by the transmit switch circuit in my HB xmtr.

And you're right, there is 250VDC on the terminal strip on the back (like many other receiver do).  So, don't touch the terminals when the receiver is on.

Fred

[WX1WX]

You I considered the very same modification years back but never got around to it… please post your results if you do

WX1WX

[WQ9E]

I like the method used in a number of Hallicrafters models where the normal connection to the RF gain control was opened and the muting contacts choose either the regular RF gain control (receive) or an auxiliary resistor (transmit) which reduces the gain to minimum.  A variation of this is used in the SX-88 so that the auxiliary resistor is a second variable pot which allows you to set a monitor level of gain during transmit which is very useful for CW monitoring.

I don't like switching the B+ since this increases the drift as the receiver alternates between receive and standby condition.

[N6YW]

I like the method used in a number of Hallicrafters models where the normal connection to the RF gain control was opened and the muting contacts choose either the regular RF gain control (receive) or an auxiliary resistor (transmit) which reduces the gain to minimum.  A variation of this is used in the SX-88 so that the auxiliary resistor is a second variable pot which allows you to set a monitor level of gain during transmit which is very useful for CW monitoring.

I don't like switching the B+ since this increases the drift as the receiver alternates between receive and standby condition.

Rodger
That's an excellent idea that deserves investigating. The schematic of the HRO 5 suggests this would be a pretty easy mod to implement. Seeing how there is 6 volts present in the radio, a simple 5 volt mini relay could be used to mute or switch in an RF gain pad. COOL!
Thanks.

[WQ9E]

Billy,

You are welcome and it provides very smooth muting.  Basically the auxiliary resistor (or pot) is put in series with the regular gain control and this resistor is shorted for receive.

[w3jn]

I like the method used in a number of Hallicrafters models where the normal connection to the RF gain control was opened and the muting contacts choose either the regular RF gain control (receive) or an auxiliary resistor (transmit) which reduces the gain to minimum.  A variation of this is used in the SX-88 so that the auxiliary resistor is a second variable pot which allows you to set a monitor level of gain during transmit which is very useful for CW monitoring.

I don't like switching the B+ since this increases the drift as the receiver alternates between receive and standby condition.

BINGO.  This is the correct answer.  It's dangerous to have the B+ floating around the shack on exposed relay contacts or T/R switches.  Ask me how I know this.

It's a very, very easy mod and keeps the oscillator running so it doesn't wander off into never never land while the B+ is off.

This is an easy mod very well worth doing and the Collins Collectors mafia will never know the difference.

[N6YW]

I like the method used in a number of Hallicrafters models where the normal connection to the RF gain control was opened and the muting contacts choose either the regular RF gain control (receive) or an auxiliary resistor (transmit) which reduces the gain to minimum.  A variation of this is used in the SX-88 so that the auxiliary resistor is a second variable pot which allows you to set a monitor level of gain during transmit which is very useful for CW monitoring.

I don't like switching the B+ since this increases the drift as the receiver alternates between receive and standby condition.

BINGO.  This is the correct answer.  It's dangerous to have the B+ floating around the shack on exposed relay contacts or T/R switches.  Ask me how I know this.

It's a very, very easy mod and keeps the oscillator running so it doesn't wander off into never never land while the B+ is off.

This is an easy mod very well worth doing and the Collins Collectors mafia will never know the difference.

Bwahahahahahahahahaha! Hey, I was a CCA "Made Man" and now am in the witness protection program. There is a bounty on my head for using National and "God Forbid", RCA equipment in my shack. My hypocrisy has no limits!

[N6YW]

By the way, speaking of Collins...
This is the same arrangement used on my R-390 mated with the ART-13. RF gain muting works great.
Thank you for mentioning this when I should have known all along. Go ahead and give me the dunce
cap for the day.

[N6YW]

And here's a photo of the schematic place as discussed.

[w3jn]

Bwahahahahahahahahaha! Hey, I was a CCA "Made Man" and now am in the witness protection program. There is a bounty on my head for using National and "God Forbid", RCA equipment in my shack. My hypocrisy has no limits!

LOL - Join the club.  I offended them when I advocated pulling a turn off the 51J endpoint adjust coil so the PTO would track correctly. 

[N6YW]

I wonder if they would be offended if I did that to my Flex 5000A... wait, uh...

[WQ9E]

LOL - Join the club.  I offended them when I advocated pulling a turn off the 51J endpoint adjust coil so the PTO would track correctly. 

JN, several years ago on the boatanchors mailing list I was taken to task by a list member who went postal over my recommendation to remove, clean, and lubricate the thrust bearing in a SX-101 tuning capacitor as part of the process to address stiff tuning.   In all of these vintage receivers the original lube has long lost its lubricating quality and I do this as part of standard maintenance on every old receiver that goes across the bench.  My detractor was convinced the entire capacitor would fall apart and could never be assembled again.  Since I do this with the plates fully meshed nothing is going to fall apart and I had written a very sarcastic response opining that anyone who couldn't perform a simple cleaning and lubrication without disaster had no business even trying to replace an open fuse in a piece of vintage gear but I guess my "south Mississippi hospitality" is deeply ingrained so I deleted my reply and wrote a much more diplomatic (and boring) reply

For many years I avoided Collins gear because of the bizarre behavior of some of that tribe.  But several years ago at the Princeton IL hamfest I picked up a nice Collins made R-390A with original meters, covers, manuals, spare set of new tubes, and the vernier/counter BFO dial for $100.  Shortly after that I ended up with an S-3 line, a KWM-2, 2A, 51S-1, 30L-1, speakers, power supplies, and a couple of station consoles for under $1,000 so the sickness started   I soon added a 30S-1, 51J3, 51J4, and 75A-1 through 4 receivers and I now have a KWS-1 awaiting my attention.  But I don't worship them any more than I do my lowly Hallis, RMEs, etc. although maybe I do respect the St. James Gray alter just a little more than some of the stuff that Howard manufacturing turned out. 

John,  next time your run into one of those hard core types tell them you had a problem with the PTO not turning smoothly but once you poured in a pint of STP oil treatment and sealed it back up it seems to be OK.  That should cause a stroke or two.

[N6YW]

LOL - Join the club.  I offended them when I advocated pulling a turn off the 51J endpoint adjust coil so the PTO would track correctly. 

JN, several years ago on the boatanchors mailing list I was taken to task by a list member who went postal over my recommendation to remove, clean, and lubricate the thrust bearing in a SX-101 tuning capacitor as part of the process to address stiff tuning.   In all of these vintage receivers the original lube has long lost its lubricating quality and I do this as part of standard maintenance on every old receiver that goes across the bench.  My detractor was convinced the entire capacitor would fall apart and could never be assembled again.  Since I do this with the plates fully meshed nothing is going to fall apart and I had written a very sarcastic response opining that anyone who couldn't perform a simple cleaning and lubrication without disaster had no business even trying to replace an open fuse in a piece of vintage gear but I guess my "south Mississippi hospitality" is deeply ingrained so I deleted my reply and wrote a much more diplomatic (and boring) reply

For many years I avoided Collins gear because of the bizarre behavior of some of that tribe.  But several years ago at the Princeton IL hamfest I picked up a nice Collins made R-390A with original meters, covers, manuals, spare set of new tubes, and the vernier/counter BFO dial for $100.  Shortly after that I ended up with an S-3 line, a KWM-2, 2A, 51S-1, 30L-1, speakers, power supplies, and a couple of station consoles for under $1,000 so the sickness started   I soon added a 30S-1, 51J3, 51J4, and 75A-1 through 4 receivers and I now have a KWS-1 awaiting my attention.  But I don't worship them any more than I do my lowly Hallis, RMEs, etc. although maybe I do respect the St. James Gray alter just a little more than some of the stuff that Howard manufacturing turned out. 

John,  next time your run into one of those hard core types tell them you had a problem with the PTO not turning smoothly but once you poured in a pint of STP oil treatment and sealed it back up it seems to be OK.  That should cause a stroke or two.

I am flailing around wildly laughing with uncontrolled spasms gasping for air. Well done Sir, well done!!! Bravo! Curtain call, curtain call!!!!

[KA3EKH]

I have a 1938 HRO RAS Navy receiver that I used for some time on AM with a TBW transmitter. I had a little relay that I put in a Bud box that hung off the back of the power supply that interrupted the B+ when the transmitter was keyed. This is accomplished by using the terminal strip on the back of the radio. Running AM never had any issues with just turning off the B+ and drift. The receiver was wide anyway in AM mode. The old HRO is still one of my favorite radios being its fairly low noise, sensitive and just complex enough to scare away the easily frightened. Trying to determine what frequency you’re on is fun also. The only problem is that when using the external relay and the rear terminal strip you cannot turn off the B+ with the front switch and have to turn off the power supply to change bands.

[N6YW]

I am loving these responses and it has the feel of us sitting around a table at a pub having a pint, talking shop and having a few laughs.
You may have seen this radio on Ebay last week, I am including a photo of it here.
The former owner (SK) was rather proud of his ownership, enough so that he installed those Italics silk screened aluminum mailbox letters with the self adhesive backing... eh, well I think I can get them off
without having to repaint the faceplate. A little bit of oil based "Stuff" ought to do the trick but still will be a little tricky. This is a true buzzard box and I look forward to lashing this wrinkled breadbox alongside the BC-610E. A true beauty of WWII era electronic excellence.
Any hints and kinks here? I am all about preserving the past as long as I preserve my present brain function.

[w8khk]

The paint looks like it is in excellent condition.  You should have no trouble getting those call letters removed.

When I helped my dad restore his HRO, cleaning the paint turned it an ugly gray.  I found that spraying it with gloss enamel after thorough cleaning restored the lustre and preserved the wrinkle finish.  

I never saw a square meter in the HRO, I only remember seeing round meters.  But that one seems to have the national logo on it, so it might be original.  

The knob to the right of the headphone jack, and the switch and light to the right of the tuning dial do not seem to be original, I am curious what they are.  Good luck on your restoration.  It is a very easy receiver to recap and restore, and it should perform very well when you are finished.  Have fun!

[N6YW]

The paint looks like it is in excellent condition.  You should have no trouble getting those call letters removed.

When I helped my dad restore his HRO, cleaning the paint turned it an ugly gray.  I found that spraying it with gloss enamel after thorough cleaning restored the lustre and preserved the wrinkle finish. 

I never saw a square meter in the HRO, I only remember seeing round meters.  But that one seems to have the national logo on it, so it might be original. 

The knob to the right of the headphone jack, and the switch and light to the right of the tuning dial do not seem to be original, I am curious what they are.  Good luck on your restoration.  It is a very easy receiver to rescap and restore, and it should perform very well when you are finished.  Have fun!

Mine is a 1946 model 5TA 1, which used parts left over from the war effort. Apparently, there were several variants from the original type M and Seniors produced prior to WWII. Some of the common thoughts seem to be that National wanted to use up leftover parts from the war effort, so you see an example here. The square Marion Electric S-Meter is what you see. I would have preferred to find an M or Senior but I got impatient and found this one which I won for 380 dollars complete with matching speaker and 5 coil units with storage box. I thought that was a heck of a deal, seeing the that the speakers seem to bring serious dollars by themselves. There is a mod with the switch and some banana plugs on the back of the receiver and dog house supply. I won't know until they arrive in a few days. I cannot wait. I also came into an NC-100A restoration project that is a real prospect. It will take some serious work but it will be a killer radio when I am done with it. At least, it's complete but without tubes. I think it will be fun to have the 100 as a spotting and general coverage receiver while the HRO will be Ham band specific, 160, 75, 40 & 20 meters as lashed up with the BC-610E. The buzzard boxes will thrive here.

[KA3EKH]

A picture of my HRO RAS in the center of the shot, its huge with the rack, receiver, power supply and coil box and the whole mess must weighs about a hundred pounds and takes up quite a bit of space for a receiver with just four knobs and two switches. The Navy version has only a BFO, RF and AF gain control along with a switch for AVC and B+ with the external power supply having the power switch. No crystal filter or other stuff although this receiver has the 1942 modification of a noise limiter on a little chassis that fits into the tube socket where the detector tube was located. Also the RAS has an IF frequency of only 175 KHz to accommodate a coil pack that allows the radio to receive the 200 to 500 KHz band.

[w8khk]

I never saw a square meter in the HRO, I only remember seeing round meters.  But that one seems to have the national logo on it, so it might be original.  

Well, after doing some research, I found I was wrong about the apparent mods.  With the exception of the toggle switch, your HRO looks completely original.  Here is a link that provides a great deal of historical detail on the evolution of the HRO:

http://www.radioblvd.com/National%20HRO.htm

I have been helping a friend restore an HRO-50T, but I really prefer the original HRO Senior or HRO-5 series.  By the way, the NC-100 and NC-101 series is a really neat design.  I have been hoping to find a 100 or 100A for years, still looking for a nice one.  You scored a great find!

[N6YW]

Ray, that's a beautiful setup. I love how you have everything arranged. Reminds me of a typical war time operating position where everything was of utilitarian application and comfort was seemingly an afterthought. Remember the SCR-299 vehicle?
http://www.vwoa.org/images/ARMTRUCK.jpg
I also found a rather cool website devoted to war time radio intercept topics that include the various equipment used. Pretty fascinating stuff.
http://www.cryptomuseum.com/df/hro/
The more I get into this stuff the more fun it becomes.
73 de Billy N6YW

[Ralph W3GL]

Bill,

You have a BC-610 and at times mention the SCR 299, so if you really want to match that 610 box to a correct receiver, look for a BC-342 ( the 110VAC receiver in the 299 set-up ) or a BC-312, the 12 volt version that was used in the remote location, in the field, when the 299 was deployed...  Then look for a PE-95 on its trailer (good for power outages at home) to complete the full SCR-299 experience...

Way back when, I spent a fair amount of time in one of those systems...  While stationed in Hawaii, I picked up, from the MARS warehouse, a space heater from  the SCR 299 and still have it in my bath room to kill the chill with out turning up the oil burner on cool mornings...

[N6YW]

Bill,

You have a BC-610 and at times mention the SCR 299, so if you really want to match that 610 box to a correct receiver, look for a BC-342 ( the 110VAC receiver in the 299 set-up ) or a BC-312, the 12 volt version that was used in the remote location, in the field, when the 299 was deployed...  Then look for a PE-95 on its trailer (good for power outages at home) to complete the full SCR-299 experience...

Way back when, I spent a fair amount of time in one of those systems...  While stationed in Hawaii, I picked up, from the MARS warehouse, a space heater from  the SCR 299 and still have it in my bath room to kill the chill with out turning up the oil burner on cool mornings...

I WISH!!! My wife would have a COW!
I have a BC-348, but not a 342. Imagine doing field day with the mighty SCR-299? I am sure it has been done in the past. While I am casually looking for the matching items for the 610, as they pop up, I am content with using period type equipment. The look and performance fills the need quite nicely.
On the other hand, I would imagine a fully equipped SCR-299 with generator wagon would command a very high price these days. Good post.

[N6YW]

Radio bliss...
I am happy to say that the HRO 5 showed up in perfect shape. Aside from installing a new AC mains
cable and redoing the tips of the speaker leads, all is well. It fired right up as described and is dead nuts on frequency with 10 Megacycles WWV. It will need just a touch of control cleaning. I have not peered inside the cabinet yet but suffice to say, no negative artifacts are showing their ugly faces yet.
The S meter movement is perfect. The mailbox letters came off the front of the face without any problem.
I put the radio on it's right hand side, and using a folded paper towel as a blotter, I gently coaxed some WD-40 behind each of the letters using a new single edge razor. This allowed the fluid to rush in and free the adhesive backing off of the paint. After final cleanup, you cannot tell the letters were ever there.
The mystery switch was terminated to some zipcord that exited out the rear apron through a grommet.
I removed the wire but left the switch because I do not have a knockout plug (chrome) that will fit.
Once I find one, I will paint it black wrinkle to match the cabinet. Otherwise, the switch does no harm.
Some collectors would have passed on this one entirely but not me. It's a player! A damn nice radio.
There are a couple of mysteries to unravel with this radio yet, but for now I am pleased.
Check it out...