National Radio Company's
AN/FRR-24 HF Receiver
(Tuner Module: Amplifier-Converter AM-450B/FRR-24)

--- The Ultimate Big-Iron, Heavy-Metal Receiver ---
--- 420 tubes, 3,121 pounds ---

AN/FRR-24 receiver front panel
AN/FRR-24 left interior
---left front---
AN/FRR-24 right intertior
---right front---
AN/FRR-24 top view
---top view---
AN/FRR-24  bottom view
---bottom view---
AN/FRR-24 top view
---close up of sealed 5-gang main tuning capacitor---
AN/FRR-24  bottom view
---close up of fine tuning scale in kilocycles---

The 1952 National AM-450B/FRR-24 is the tuner module of what is perhaps the most expensive, elaborate HF receiver ever manufactured in the United States. A complete receiver equipped for triple diversity monitoring--with three sets of four RF modules for the full HF range of 2 to 32 MHz--contains a total of 420 vacuum tubes, weighs 3,121 pounds in four six-foot rack cabinets, and sold for $60,000+ in 1947 dollars (or $581,000 adjusted for CPI inflation). It truly is a "Duesenberg" of radios and represents the very best of National Company's engineering talent.

I have only one of the 9-tube tuner modules, the AM-450B/FRR-24, which tunes 2-4 MHz with 3 RF stages and separate mixer and oscillator tubes providing a 1750 kHz IF output for this double-conversion receiver. I set it up for 80-meter operation with a homebrew power supply (+210VDC, +150VDC, -105VDC, 12.6VAC, and 6.3VAC) and a FLEX-1500 as IF amplifier/detector. I am indebted to Nick England, K4NYW, for schematics and other documents and especially his expertise. If you can contribute any information to Nick regarding its development and historical use, he would love to hear from you. His website contains a treasure of photos and information about this receiver and dozens of other military models of research interest to Nick. Its URL is:

Photo and module IDs
---Click here for system photo and module IDs---

National & FLEX receiver
Reception demonstration: W6OM's AM signal (distance: 400 miles) on 3870 kHz
using the FLEX-1500 SDR as IF amp/detector for the AN/FRR-24 RF module.

block diagram of system
---Click here for block diagram of single receiver---

Also see:

YouTube demo by N4LQ of KN4R's AN/FRR-24 receiver

US Navy Radio Communications by K4NYW

A Brief History of the National Radio Company by John J. Nagle, K4KJ

Wikipedia entry for the National Radio Company

National R-1490/GRR-17 HF Receiver

National R1230/FLR Countermeasures HF Receiver

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Updated 2016