**National HRO-500** Premium SIGINT Intercept Type Communications Receiver

Description: Where do I start?I bought this receiver as I LOVE the tuning knob and HOW it calculates frequency mechanically. So fun to use and tune this. But a famous movie star said "Life is like a box of chocolates" I read blogs on HOW to repair this receiver. I have 3 years repairing Ten Tec Paragon and Omni's. Drake TR7's and TR4's and T4XB, R4A and R4B and R4C. So I figured I was ready to take on this super receiver. This receiver DOES work on Band #4. It will lock and you can listen from 10 to 20 Mhz just fine.I tried HARD to get the receiver to work on ONE band to verify the possibility of getting the rest of the bands working. I noted the band switch was NOT totally in sync the front most wafer was out of sync with the rest of the wafers.AAnd the front wafer was pretty beat up - people in there trying to fix it. So I decided to replace the fiber glass band switch ROD with an aluminum rod to assure more alignment with the rest of the wafers.I had a hard time removing the fiberglass band switch wafer and ended up damaging the front wafer a bit more. After all this I did find that band #4 was still working. So back track - how did I get the receiver to work at all? It was dead when I got it. ====1) First thing I did was replace ALL the 25uf and 5uf and .1 uf capacitors. About 15 of them. This brought audio back to the receiver.2) Get the Synthesizer working. Synthesizer mixer was dead.. Synthesizer mixer takes signal from Spectrum Harmonic generator and combines it wtith the HF oscillator to give a difference signal of 4.75 Mhz thru the two IF cans marked in the pictures on the Synthesizer. Replace Synthesizer mixer transistor. Align the cans for 4.75 Mhz with a scope.3) Verify lock. You can force a 4.75 signal into the beginning of the Synthesizer right after the mixer and align the 4.75 cans for best IF signal to the comparator.4) Verify Spectrum harmonic generator - Used RTL-SDR and CubicSDR to see the harmonics were present.5) Alignment of HF oscillator. Pulled the scanning transistor and was able to line up each band HF oscillator (injection LOcal oscillator) to the chart in the manual.6) Verify LOCK. Put the scanning transistor back in and the HF oscillator will be subject to a sawtooth wave. When 4.75 IF in the right Synthesizer module matches 4.75 Mhz from an onboard reference crystal and oscillator - it LOCKS and the lght goes out.7) Added Synthesizer lock LED to the bottom chassis for debugging Synthesizer lock. After all this I could and can receive on 10 to 20 Mhz.The receiver works fine. Probably could stand an alignment to get it perfect. The real work needed is to get the HF oscillator working on all bands 1, 2,3 and 5. I can see the HF oscillator working on band #5 but no lock. I was trying to sort out putting in a new band switch wafer. Sadly I think that the band switch wafer is very custom from CentraLAB to National Company for the HRO 500. I am pondering putting in RELAYS. I am not sure HOW to put in PIN diodes but that may work too. Then just use a normal 5 position rotary wafer EASY to find. I have put a week of 8 hour days into this radio - 40 to 60 hours so far to get this far. My motivation for selling the radio is - well do I want to put in 40 to 80 MORE hours?Will people in my life tolerate the obsession fo fix this radio?Probably NOT. One of the ways to NOT fix a radio you are obsessed with is SELL it. Ha. So I offer it for sale.As someone else is offering an HRO 600 for $6000 or more dollars - I figure this one is a bargain at $999. I have described HOW to fix the radio the rest of the way.This HRO 500 has excellent audio and receives WELL even without a full alignment yet. This radio is aimed at a collector or extreme tinkerer.The circuit is not hard ONCE you understand the intent.This is a totally Analogue Phase Lock loop.It is REALLY COOL. As you can see the case needs a good repaint.I did my best to clean up the front of the receiver.and I gave the chassis a good cleaning and it came out very nice. I may end up keeping this radio if it does not sell and time passes by and I eventually fixthe wafer or put in PIN diodes. As this section deals with the HF oscillator - aka LOCAL oscillator PIN diode loss should not be a really big issue.DEMOS: Listening on Band #4 20 meters on HRO 500 https://www.youtube.com/watch?v=1OO6VcY_xiA Band #4 demo showing sync lock and some WWV reception https://www.youtube.com/watch?v=wxlD5EIjcC0

Price: 999 USD

Location: Las Vegas, Nevada

End Time: 2024-09-06T22:03:02.000Z

Shipping Cost: 79 USD