HRO-500
The National HRO-500 was the first complete solid state receiver manufactured by National. It is a real transition unit as it is built just like a vacuum tube radio, except that transistor sockets replace the tube sockets. It is all point-to-point wiring and thus straightforward to get at the components, and uses also the famous National PW dial, found in older HROs. It weighs 32 lbs, not bad for a solid state device!. So I classify it as a 'semi-BA'.
With respect to serial numbers, the first two digits specify the series. Here are the series and (approximate) dates of manufacture:
The largest circuit changes occured beween series 75 and 88, and there were some factory bulletins specifying most of the upgrades.
My unit is serial number 75 1257, so it is from the first series. It was made in 1965, according to the dates found in some of the components.
There are a couple of common troubles in the HRO-500. One of them is the crystal calibrator, which tends to have difficulty starting. One of the recommended mods is to use a larger emitter bypass cap in the oscillator in order to raise the gain. The capacitor is C127, and the original 0.1uF should be replaced with a 1-10uF. But the biggest problem with the HRO-500 pertains to all series, and that is audio distortion in SSB and CW. There are some very nice articles dealing with these and other HRO-500 troubles in Electric Radio issues 88 (August 1996) and 95 (March 1997).
In these pages, I will show the restoration process of my HRO-500 receiver. This is a 'live page', as I am going to update it regularly as I progress with the restoration. I would like to hear from anybody who has an HRO-500 and/or experience aligning them. Thanks!.
Series Year (approximate) 75 1964 88 1966 102 1967 122 ???? 140 1972
Frequency range 5kc to 30Mc in sixty 500kc bands, continuous coverage Modes USB, LSB, AM, CW Calibration accuracy Within 1kc over the entire 500kc selected tuning range; within 250cps when zeroed at nearest 50kc calibration point Synthesizer accuracy Within 250cps over entire tuning range when zeroed at 10Mc Dial backslash Less than 50cps Frequency stability Over-all stability fron turn-on NMT 100cps in any 10 min period RF input impedance 50 Ohms unbalanced, separate high impedance unbalanced AM sensitivity 5kc to 30mc (with LF-10 preselector) better than 2.0uV for 10dB S/N
5kc to 500kc (without LF-10), 25-50uV for 10dB S/N
Preselector not required for 500kc to 30Mc operation.SSB/CW sensitivity 5kc to 30mc (with LF-10 preselector) better than 1uV for 10dB S/N
Preselector not required for 500kc to 30Mc operation.Selectivity at -6dB points 500cps, 2.5kc, 5.0kc, 8.0kc Shape factor of filter 2.5:1 at 2.5kc bandwidth Passband tuning range 6kc Rejection tuning notch 50dB Image rejection min 60dB between 500kc and 30Mc AGC merit Less than 10dB change in output for input change between 5 and 50000 uV Tuning ratio 10kc per revolution Audio response 200cps to 7000cps +/- 6dB Speaker impedance 3.2 Ohm Size 7 5/8" H, 16 1/2" W, 12 3/4" D Weight 32 lbs Semiconductor complement 37 transistors, 20 diodes
HRO-500 page INDEX
Any contribution or idea to enhance this page would be welcomed!.