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Old 20th Feb 2018, 6:43 pm   #1
Ray G3XLG
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Default National HRO 5T Renovation

I have recently acquired an HRO-5T with a HD psu (non HRO type) plus 23 coilsets, high impedance phones and a few dozen spare valves.
It was made in 1944 I think as it has a stamp saying it was tropicalized in Jan 1945 & the number stamped on the chassis by the antenna terminals is H706. Removing the bottom cover, the coil set cover can be seen and is stamped ARMY
I tried the HRO out today, using a MW coilset & the high impedance headphones with a few feet of copper wire in the living room as an antenna.
It worked …..… & I was able to tune in “5-Live”, “Radio Caroline” running 1kW here in Suffolk, and a few other stations. There was a lot of background sshhhhhh noise but at least its working & a couple of the variable pots on the front panel were a bit crackly, so might need replacing.
I then removed the bottom to check out some of the components. I found that most of the capacitors were way off value & some of the resistors too.
Someone has already replaced a few caps I think & has put in a small speaker transformer - to be able to connect a speaker directly to the rear sockets. Two other sockets at the back which I think should be part of the original muting circuit if the RX is used in conjunction with a TX, were disconnected, so maybe the front switch was being used for muting?
I have bought all the capacitors (600VDC) & a few high wattage resistors from a company in Canada, so I can start working my way through replacing duff ones.
Is there a preferred sequence when renovating an old receiver I wonder & for example should I re-test the RX frequently as I replace components?
Ray
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Old 20th Feb 2018, 7:54 pm   #2
Barraman
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Default Re: National HRO 5T Renovation

I've never had an HRO Ray, but normal procedure with old valve sets is to bring

the volts up with a variac, then check each stage for voltages.

Changing Rs and Cs willy-nilly is not needed.

The pots should respond to a squirt of Servisol.

Richard
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Old 20th Feb 2018, 8:32 pm   #3
G6Tanuki
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Default Re: National HRO 5T Renovation

"I found that most of the capacitors were way off value & some of the resistors too."

How did you test these? If a capacitor/resistor has a resistor/capacitor across it then the generic cheap LCR testers will be horribly confused.

What do you want the final result to be?

An exhibition-piece that *looks* historically-right but has lacklustre performance, or a receiver that can be reliably used for ten hours a day for weeks on end and works as well if not better than it did when new?

A good HRO [with 'period' modifications like voltage-regulation for the BFO/LO] can still perform well as a CW receiver on the 1.8/3.5/7/14MHz amateur bands.

Having a single-crystal filter they're really less-than-ideal for receiving SSB voice transmissions.
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Old 20th Feb 2018, 9:06 pm   #4
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Default Re: National HRO 5T Renovation

I used to have an HRO 5t, aka Reception Set R106 MK11, the HRO is my all time favourite receiver, mine had a full complement of general coverage coils, I also had an original loudspeaker for it with a matching transformer, I refurbished the cabinet and all the coil packs.

Don't forget that when powered up there's HT on the S meter adjustment pot shaft and also on the primary side IF transformer alignment trimmers. Don't forget to switch the B+ (HT) off before changing a coil pack.

I did have a Dog House power supply for another HRO but that frizzled out so I made my own PSU using a 6080 series pass valve a, stabilizer valve and a comparator valve which I used for both receivers (separately)

Capacitors to change first, the output valves g1 coupling capacitor and any across the HT rail (I think there's 3 of them on the schematic) then any between g2's and chassis and any that decouple HT feed resistors, last to change are usually the ones with a low voltage on them such as AGC de-couplers etc.

You might already have the manual but if not the HRO 5 series can be found here:

http://www.cryptomuseum.com/df/hro/files/hro-5.pdf

There's also a copy of the R106 MK1 and MK11 EMER here (copy not too good in places but everything is basically there):

http://n4trb.com/AmateurRadio/Nation...%20and%202.pdf

The receiver part shown in the background is an HRO Senior, rack mount.

Good luck with it all and enjoy.

Lawrence.

EDIT: For easy SSB you will need the band spread coils if you have them, the receiver is designed for single signal CW reception with the crystal but SSB is no problem once you get the hang of it.
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Old 20th Feb 2018, 10:11 pm   #5
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Default Re: National HRO 5T Renovation

Hi Ray, I think you have chosen to do the right thing. I have an HRO which I bought in the late 60's and had lots of fun with it. Then it got put to one one side for very long time, after which it was totally dead and I decided to do a complete rebuild. As pointed out above, it can be difficult to test components while they are in-circuit, but as I began to remove components, I realised how bad many of them were; some of them literally fell apart when they did not have the support of being soldered in position, this included some of the original paper caps and some resistors.

I don't recall adopting a particular strategy for the rebuild, partly because it was totally dead. As you have got something that is working, I might be inclined to start at the back, i.e., the AF stage and work forward. I found the trickiest bit was the combined first AF/detector/AVC, where there are quite a lot of components to accommodate. I chose to mount quite a few components on a piece of Veroboard and positioned that below the valve.

Before you start, you might wish to consider any mods you want to make. Adding a digital frequency counter (possibly as an external unit; see https://www.vintage-radio.net/forum/...d.php?t=141180 ) is a very useful thing to do, in which case you could consider how to include an RF pickup from the LO and take it out of the set. Unless you are interested in CW reception, the existing filter has “limited use”. Good luck with it.

B
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Old 21st Feb 2018, 11:53 am   #6
Ray G3XLG
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Default Re: National HRO 5T Renovation

Firstly my thanks to the members who have replied so far.
To answer a few of the questions posed:

I didn't use a Variac as I knew the PSU was working OK & there are only a couple of electrolytics in the HRO which I intend to replace anyway. OK about the likely errors testing Caps in situ but again I will be replacing the dozen or so original paper capacitors.
At the end of the day, I want a "stable" HRO with voltage regulation & to use it principally for CW & AM, I have less interest in SSB.
As I have a large number of coilsets (some of which are already bandspread) I want to check all these over & end up with B/S versions for the amateur bands.
I had already found the manuals on the internet but thank you for the links. I quite like the idea of a separate set top box to house any additional circuitry such as a speaker, crystal calibrator or a digital frequency counter etc.
73 Ray
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Old 21st Feb 2018, 4:45 pm   #7
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Default Re: National HRO 5T Renovation

As originally supplied, the HRO and its PSU did not have a stabiliser on the HT, and I always found that a certain level of chirp was evident on CW. This was easily eliminated by stabilising the HT supply to the LO and BFO.

In the rebuild, I'm using an HT supply which has a solid-state stabiliser (LR8). I have no real interest in CW, but my impression is that the very early single-crystal filter is probably not very "user friendly", at least not by modern standards. There have been quite a few articles published on adding product detectors to many of the older receivers, I guess mainly for use on SSB, but presumably they would suit CW work also.

When I removed the two large electrolytics riveted to the rear side of the chassis, they were remarkably light (as feathers); I suspect that they had dried out to a serious extent!

B
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Old 21st Feb 2018, 6:37 pm   #8
Ray G3XLG
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Default Re: National HRO 5T Renovation

On looking closer at the capacitors in my HRO it seems very likely that someone re-capped it in the 50's or 60's at they are mostly marked as "TCC Metalpack/Metalmite, Made In England".
I believe these might be caps with paper dielectrics in oil. Either way a number of them look very dodgy & I will replace them. The two large electrolytics are also of TCC manufacture.
73
Ray
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Old 21st Feb 2018, 8:07 pm   #9
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Default Re: National HRO 5T Renovation

The Metalpack/Metalmite ones are just metal-cased waxies. OK they may be a *bit* better sealed than the cheap cardboard-cased versions, but I can assure you that after a few decades they still go leaky: I had a batch of them in some gear a while back and every one failed the "wire a neon in series and feed with 350V" flash-test.
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Old 22nd Feb 2018, 12:01 am   #10
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Default Re: National HRO 5T Renovation

They sound to be the business, just as "Micamolds" do, but G6 is right, a waxie is a waxie by any other name.
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Old 22nd Feb 2018, 10:47 pm   #11
bill knox
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Default Re: National HRO 5T Renovation

Hi Ray

According to your serial number H706, it was made in August/September 1935, you have a really old one there, I thought my one was early at 1938.

I hope you enjoy renovating it

Regards

Bill
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Old 22nd Feb 2018, 11:26 pm   #12
Bazz4CQJ
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Default Re: National HRO 5T Renovation

Quote:
According to your serial number H706, it was made in August/September 1935, you have a really old one there, I thought my one was early at 1938.
Hi Bill - wonder which of the various websites you have used to look up dates?
My HRO has just the number "194" stamped on it with no prefix or suffix letter and I've never been able to make sense of that. The number is located between the S-meter pot and the audio valve, which I think means it was a late WWII model?

B
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Old 23rd Feb 2018, 9:53 am   #13
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Default Re: National HRO 5T Renovation

Quote:
Originally Posted by bill knox View Post
According to your serial number H706, it was made in August/September 1935
That's certainly what the Charles Fisher survey would suggest but surely if it's an HRO-5 (the octal version) it must date from the latter part of WW2?

Perhaps this is a case of serial number re-use, which seems to have been fairly common as wartime production ramped up?

Hugh
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Old 23rd Feb 2018, 10:46 am   #14
Ray G3XLG
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Default Re: National HRO 5T Renovation

Its definitely an octal valve WW2 model so yes, National must have reused the numbering sequence.
Now I'm starting to replace the various capacitors, I realise this is not as easy as I first thought. Its difficult to see into the depths of the under-chassis wiring & the use of the solder tags everywhere, means its difficult to reconcile the actual wiring with the circuit diagram.
Its also apparent that a number of resistors have been replaced sometime in the distant past.
I'm going to have to get a better source of illumination to do it properly. At the moment I'm using a cheap headband magnifier supplemented by an ordinary torch....not good!
Does anybody have any recommendations about the best lights etcs to use?
Ray G3XLG
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Old 21st Mar 2018, 5:57 pm   #15
bill knox
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Default Re: National HRO 5T Renovation

Hi

I would suggest that you have a look at the web site run by Henry Rogers called Radio Boulevard Western Historic Radio Museum, there is a quite a lot on all models of HROs.

He is very knowledgeable on all things HRO.

https://www.radioblvd.com/

Regards

Bill
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Old 21st Mar 2018, 9:47 pm   #16
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Default Re: National HRO 5T Renovation

We like HROs and so did my cat.
Picture to the left <<<

I found adding more decoupling to the screen of the 6V6 (or the 42 in my case - doh!) did wonders for hum - especially using on headphones.

I reckoned this one as 1938. There are 2 others but all are UX5 not Octal types.
I must not hanker after an octal one - but I do...

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Old 30th Mar 2018, 1:30 am   #17
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Default Re: National HRO 5T Renovation

Just following up on the mysterious letter-free number on mine; picture attached. I've searched all over the set with my head-band torch on and with a magnifying glass, but this is the only number I can find (just to the side of the output valve socket).

B
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Old 30th Mar 2018, 10:25 am   #18
bill knox
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Default Re: National HRO 5T Renovation

Hi Bazz

Could I suggest that you have a look at the "Western boulevard museum site"

I have just noticed there that there are some serial numbers with just 3 numbers but they are RAS versions of the HRO, do you know what the IF freq. is on your set, normally it's 455-465 KHz but the RAS versions have an IF freq. of, it's either 150Khz or 175 KHz I cannot remember at the moment though the part numbers you gave me from the side of the IF transformers from memory do relate to the higher IF freq.

When you first go onto the Western boulevard site, in the top left hand side there is 2 chaps looking at an old radio and if you go from the LHS and go down the 4th small block is relative to HRO when you click on it the next page that comes has a rather large lady sitting in front of a lot of radio equipment, scroll down and you will come to the section about serial numbers, the very small section about the RAS version of HROs is there.

Good luck

Bill
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Old 30th Mar 2018, 5:17 pm   #19
Bazz4CQJ
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Default Re: National HRO 5T Renovation

Hi Bill; I've looked again at that page and it's not helping. The RAS models were HRO juniors and mine is a senior. In every aspect other than that serial number, it seems quite standard, being fitted with the UX6 glass valves and looking exactly like the pictures in the original manual.

B
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Old 31st Mar 2018, 12:27 am   #20
bill knox
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Default Re: National HRO 5T Renovation

Hi Bazz

Have you thought of sending Henry Rogers an email at Western Boulevard he really is the font of all knowledge on HROs.

One other thought, a week or two ago I had a problem where I had to take the tuning capacitor out and I have a nagging thought that when I removed the tuning capacitor I seem to remember that I saw my serial number in that area, so it is worth having a look around there, I am not advocating you taking the tuning capacitor out but just to have look around that area.

Regards

Bill
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