HRO Identification Help Please

[rutlandboy]

Hi,

I purchased this HRO and 'Dog House' 697 from the Peterborough rally (remember those at the showground?) in the late 90's. It was working and my late father used it for a year or so and then gave it back to me.

Its been under several of my workbenches since then.

Recently my mind turned to putting this back to a restored and working condition along with a couple of AR-88's and an HRO-7 that I've got as well.

I'm very used to slightly more modern valve equipment having restored and repaired many, many collins and drake valve equipment and so doing that side of things doesn't worry me too much BUT I would like to know a little more about its age and what you think of its condition.

The Dog house is standard but quite interesting - it has a date stamp inside of Jan 1944 and at some time has had the pitch removed and transformer replaced, so probably had the standard 'meltdown' !! - the coil looks original as did the other components. I've re-stuffed the capacitor with the three 8uF electrolytics, the transformer has a 240 V winding so I used that and after replacing the badly worn mains cord with a good quality modern cotton covered cable, bringing it up on a variac resulted in a suitable output - I'm thinking of introducing some stabilisation on the HV line but that can come later

To me, the HRO looks in quite good/original condition - but I'd appreciate your views on this ! it has a serial number of A297 between the aerial connector and the Audio O/P valve, has what looks like an original fitted audio output transformer, some of the capacitors have been replaced (most likely in the 60's) so I think many (if not all) are original and so will need to be replaced, resistors measured and replaced etc. where needed as a start.

My question is what age do you think age-wise - the badge has HRO-M with what looks like a scratched 'X' - what do you think? contemporaneous with the dog house unit as 1944 ?

I've attached some pictures - advice/views as ever gratefully received - you guys are so knowledgeable

[Bazz4CQJ]

That looks to be in fine condition, and I speak as someone who bought their HRO back in 1968. Someone will be a long in a minute to give us the link to the website where all the serials numbers are spelled out in terms of their origins – I cannot currently find the link.

However, you still have all the paper caps, which I have replaced, and I can tell you that many of them fell apart in my hands once they did not have soldered connections to keep them intact. Looks like many of your resistors have been replaced, I'd replace all the originals, they too can fall apart.

Re HT stabilization, it’s good enough if you just supply it to the local oscillator and BFO, which need only a few mA, rather than the whole set.

B

[Bazz4CQJ]

The website with all the serial numbers is here https://www.radioblvd.com/National_HRO_Part2.htm.

Looks like your receiver is 1938. Mine is just numbered 194, which doesn't fit in to any production run listed on the site.

B

[ms660]

MX denotes Xtal inside the phasing unit, prior to that the Xtal was a plug in job on top of the phasing unit, apparently the MX version started production in 1942.

My favourite receiver, have owned a few in the past.

The audio output transformer would have been a later addition.

The original transformers in the Dog House supply don't seem to like 50Hz.....The ones I had didn't.

Lawrence.

[G3PIJpeter]

My HRO-MX (purchased in 1959) has the -MX suffix on the front panel name-plate. The S-meter is an uncalibrated 'Marion' wartime job - your S-meter looks to be the earlier version. Also, you have a pull-switch for the S-meter, further evidence of the set originally being an earlier version. The HRO-MX also has a round 'National' knob labelled 'Phasing' and not the pointer knob.

Could it be that your HRO was upgraded by National by substituting the more modern phasing unit with the internal crystal - possibly to meet the wartime export specification for the UK? The scratched-on X would indicate a rushed job but the wiring is fully professional.

Peter

[HamishBoxer]

Yes, my HRO has MX on the name plate too. Also have "Phasing " written on the knob.

[Jon_G4MDC]

I'm very jealous of your S meter scale. Mine was black to S9 and Red above.
Now pretty much nothing left above S9. That's a job for a round tuit...

[Bazz4CQJ]

I know it's daft, but I wish these sets to talk and tell us about their lives .

B

[rutlandboy]

Hi Everyone !

Wow thank you for all the information !- most useful definitely worth doing the work on I think

I'm putting together a BOM for the capacitors etc.

Any recommendations on where to buy from?

I've previously found one eBay seller to have very good quality capacitors at a reasonable cost, and I'm tempted to do the same again, but wondered where other people get their stock from ?

Thanks for all the information - much appreciated !!

I'll post updates as and when I get the chance

Not daft at all Bazz4CQJ ! - I agree it would be wonderful to get the radios to let us know what they'd heard or did wouldn't it - fascinating to think what they might have received or where they'd been!

[Bazz4CQJ]

The replacements for the paper caps are probably not very critical; 400VDC working, film caps of far-eastern origin would do (check them before installing). The resistors will need to be replaced with suitable wattage; something like Vishay would be good.

There are at least 2, possibly 3 electrolytics inside the receiver which will probably need replacement. When I took mine out, they were light as a feather (dry!) with little or no capacitance.

B

[rutlandboy]

Originally Posted by Bazz4CQJ

The replacements for the paper caps are probably not very critical; 400VDC working, film caps of far-eastern origin would do (check them before installing). The resistors will need to be replaced with suitable wattage; something like Vishay would be good.

There are at least 2, possibly 3 electrolytics inside the receiver which will probably need replacement. When I took mine out, they were light as a feather (dry!) with little or no capacitance.

B

Thanks as ever Bazz4CQJ all noted