A bit of HRO history

A couple of people have asked me why I find the HRO receiver interesting enough for me to have two in my collection.

 

I'm interested in World War Two history, and in particular the code breaking activities of Bletchley Park. The HRO played a very significant role in this work as it was the standard receiver used for intercepting the encrypted German radio traffic.

The HRO has its origins in the mid 1930's. The National Radio Company of Malden, Massachusets had previously produced a receiver for the aviation industry, known as the AGS. The successor to the AGS was intended to meet the needs not only of airlines and commercial users, but also Amateur (Ham) Radio Operators who wanted a very high performance shortwave receiver.

The HRO was brought to the market very quickly, and it's name may reflect this. It is said that staff who worked on the project  wrote 'HOR' on their timesheets, meaning 'Hell Of a Rush'. Apparently National thought HOR was inappropriate, and rearranged it as HRO (subsequently said to mean 'Helluva Rush Order'). It went on sale in 1935 at a cost of around $200, which must have been a lot of money at the time!


Very early in WW2, the War Office decided that the receivers in use by British armed forces might not be good enough for the anticipated needs of the war, and a search for a better and commercially available receiver was undertaken.  A number of types were evaluated but the National HRO was considered to be most suitable. At first the British Government was not able to buy HROs in quantity (I assume this was when the USA was neutral), so British officers traveled to the USA to buy sets and import them personally. Many thousands of HROs were subsequently sent to Britain under the Lease-Lend arrangement, and there were probably more than 10,000 in use by the end of the war.

HROs were used as a general purpose HF receiver by all British Forces. The 'Y' stations (I believe the name came from Wireless Intercept, or WI) operated by the Army, Royal Navy, RAF and the Radio Security Service all used HROs. They were also issued to civilian Volunteer Interceptors, who used them at home under control of the RSS.

RSS intercept station at St Erth, Cornwall.

The HRO was very advanced for its time. There were several versions produced over the years but due to its superb performance and ease of operation, even the early ones remained in use by both commercial and military users into the late 1950s, and possibly later. After the war many came onto the surplus market and were eagerly bought by Amateur Radio Operators, and HROs were prized posessions in many radio shacks for several decades. In fact, the first one I ever saw was in the shack of a local Ham who introduced me to the hobby around 1975.

There are a number of good websites where information on HRO receivers can be found. One of the best in my opinion ( I have no connection with it) can be found here

Keep listening!

National HRO MX receiver

I started the restoration of this classic receiver by removing the cabinet to allow a close visual inspection of the chassis. 

My first impressions were that the set was complete, although unfortunately not in original condition.

Many of the capacitors and some of the resistors have been changed, and there is an octal based 6V6GT valve in place of the original amplifier valve.

Whoever fitted this didn't fit an audio output transformer, which was a popular modification for amateur use. (The external HRO speaker had a built in transformer, and presented an impedance of around 7000 ohms to the radio.)

Somebody had cut wires to the meter backlight, to the lamp on the front panel, and also two wires between the IF stages and the crystal filter unit on top of the chassis!

Whilst I was a bit disappointed that the radio isn't in original condition (and therefore somewhat rare) it does give me more flexibility with the restoration. For example, I don't see the need to re-stuff the capacitors as I did with my Wartime Civilian Receiver, and I can use modern resistors where necessary.

I think I'll keep the exterior and above chassis areas looking as original as I can. Under the chassis I'll make whatever changes I need to get the best performance, whilst keeping the circuit as standard as possible.

The first tasks will be to replace the damaged wiring, and then replace all the wax paper and electrolytic capacitors.

It's going to be a fairly big job, but I'll post more updates as I go. 

Keep listening!

Even more radios!

A few weeks ago I decided to pick up a few more sets as 'winter projects'.  I now have a couple more than I originally intended, and the workshop is now overflowing.

National HRO HF receivers

The latest acquisition (the black one in the picture above)  is a National HRO MX, a classic HF receiver that was used extensively in World War Two. The design originates from the 1930s; I haven't had chance to do much research on this particular one, but I think it was probably built around 1942 onwards.

There were tens of thousands of these in use by British forces during the war and for some time afterwards. As a result they are not particularly rare, but finding one that is complete and unmodified can be difficult. This one is complete apart from its power supply, which was a separate unit.

The blue radio is also an HRO that I bought in 2013, but so far I've not been able to find out much about it. The person who restored it assured me that the colour was the same as the original, or as close as he could get.  It might be a variant known as the RAS which was used by the navy, but that tale will have to wait for another day.

I'm looking forward to starting work on the HRO-MX after Christmas, by which time there should be sufficient space in the workshop again.

Keep listening!