This section is devoted to receivers, receiver accessories, receiver components, and modifications and upgrades to certain receivers. If you want to see a particular article which you think might benefit the Glowbugs community, please send me an e-mail at kgordon2006 "at" frontier "dot" com.

High Frequency Receivers & Accessories.

The two receivers shown here are taken, with permission, from the ARRL's "The Radio Amateur's Handbook", 41st Edition, 1964, pages 118 through 124. Following these receivers are accessories: 3) The "Select-O-Ject", 4) An Audio Clipper, to be followed, ASAP by "A Crystal-Controlled Converter for 20, 15, and 10 meters", "A Regenerative Pre-Selector for 7 to 30 Mc.", and an "Antenna Coupler for Receiving". If you build all of these circuits and use them, you will have a pretty darned good receiver, and it won't cost you much either. The receivers stand alone and work well without the accessories, but what Ham is ever satisfied with the performance of his equipment? ;-)

1) The "Simplex Super"

The "Simplex Super", a handy little 3 tube receiver, covering the 80 and 40 meter Ham Bands, and WWV at 5 mHz. It is easily built and adjusted. There are four pages in this article. These pages have been sized so that you can print them directly from your browser. Page 1 is the description, Page 2 is the schematic and parts list, Page 3 continues the description and building instructions, and Page 4 finishes the adjustment and operation. Either click the title above, or start here.

 2) The "2X4+ Superheterodyne"

This is a 4 tube superhet, covering the 80 and 40 meter Ham Bands, and 5 mHz WWV frequencies, with "single-signal" CW selectivity. There are 5 pages in this article. This receiver and the "Simplex Super" are posted at the suggestion of Jim Bowman, W7HPK. Start here, or above.

 Receiver accessories

3) The "Select-o-Ject"

This accessory can be used with any receiver. It was manufactured commerically by National Radio Corp., the makers of the famous HRO series of receivers. Later model HROs could have this unit incorporated in the receiver as an optional module. Start here, or above.

 4) An Audio Clipper

This accessory can be used with any receiver. It will give those receivers lacking an AGC, or those having one which is un-useable on CW, much of the characteristics of one, and, at the same time, keeps static crashes, etc., from bashing your ears. The tube version is part of the "Clipper/Filter" from the ARRL's 1961 Handbook. We intend to put the complete "Clipper/Filter" up here ASAP. Start here, or above.

 Modifications and Upgrades

5) Packaged Selectivity

G. E. Ham News for March-April 1957, Vol 12 - No. 12, contained an article on how to build a 455 Kc Mechanical Filter Receiver Adapter which plugged into the socket of the first IF tube on several of the better receivers of the era. National later marketed such a factory-built adapter for their HRO-50 and HRO-60 receivers. This is the entire article in .PDF format. It is over 14 megabytes, so it will take a while to download. I have also re-drawn three of the schematics which were included in that article since all the schematics were originally drawn in white-on-black and were hard to read. Please let us know if you build this adapter for your receiver, and how well it works.

For those who find it difficult to download the single, 15 mb file, here are all 8 pages broken out in single .PDFs. Fig1, Fig3, Fig4, Pg1, Pg2, Pg3, Pg4, Pg5. 

7) Nuvista-plug.

Here, in .PDF format, is an upgrade for the 1st RF amplifier in a Hammarlund SP-600 receiver via a tech bulletin dated 1965. This has application to other GB receivers, both commercial and homebrewed. What it essentially consists of is two 6DS4 Nuvistor triodes in a low-noise cascode circuit, mounted on a small board enclosed in a tubular bit of stock with a 9 pin miniature plug at the bottom. One simply removes the first RF amp tube and plugs this creation in its place. Reportedly improves the receiver noise characteristic by from 2 to 9 db depending on frequency tuned to.

A schematic is included. This .PDF file is about 1 megabyte.

If space is NOT a concern, there are other, triodes, and dual-triodes with even LOWER ENR (Equivalent Noise Resistance) than the 6DS4. One excellent candidate is the sub-miniature 7963 dual triode.

 8) Line-Voltage Adjustment.

Most of our older AC line-voltage powered equipment was designed and built to run on 110 - 115 VAC 60 Hz. voltage. However, there has been a trend in the last 10 or more years for line voltages to be much higher than they were then. Here, our line voltage sometimes reaches 130 VAC, and can spike even higher. So, in the interests of protecting our equipment from these high line voltages, ONE of the easiest ways to reduce this, is via a "bucking" transformer. This is simply a filament transformer whose secondary current capability is at least as high as the current your equipment draws (I would double it, myself), connected as per the accompanying .PDF drawing. The secondary winding is "phased" so that it "bucks", or opposes the line voltage. By reversing the cross-connected secondary winding, or "phasing" it correctly, as shown in this .PDF drawing, this circuit will also "boost" the line voltage, in this case, adding 12.6 VAC to the line voltage.

Another way to accomplish this voltage reduction, suggested by Jim Miccolis, N2EY, is shown in this .PDF diagram. It uses the same transformer as above, connected as a tapped "auto-transformer", exactly like a Variac, and will either "buck" or "boost" the line-voltage accordingly. What is written above about sizing the secondary current capability of the transformer applies here also.

Receiver Components.

9) The Pullen Mixer.

This is a .PDF file of the report given by Dr. Keats Pullen describing the so-called "Pullen Mixer", a cathode-coupled mixer of unique design. This mixer is noted for very low noise, good "linearity", and a need for only low injection voltages. This device also makes an excellent product detector.

Here is a .PDF file of one page in size, which is a copy of part of a page from a handbook published in 1972, and which describes a "new" type of mixer, which we know as the Pullen Mixer. Strangely, the handbook in question did not present any analysis of this circuit, and mentioned it "in passing" ! Experience has proven that it very significantly reduces mixer noise.

And here is a schematic of the Pullen Mixer mod for the 75A4. A mod of this type was first described by W2VCZ in 1967, publication unknown. Ray Osterwald, N0DMS, refined the design, then published a description and explanation of it in Electric Radio Magazine #47 of March, 1993, in one of a series of articles he authored on the Collins 75A-Series Receivers. The schematic was drawn by me, W7EKB, using GeneriCad ver 6.0. This is also a .PDF file. File size is 2.11 mb. The schematic had an error which has been fixed. The 4.7K 2W resistor, had been inadvertantly labeled as 47K 2 W. The corrected file has been uploaded today, July 26, 2018.

"A Like-New Mixer Circuit" This PDF article was written in October, 1961. It discusses the Pullen Mixer circuit in some detail, and includes a table with test data taken on several different types of twin-triodes. It also attempts to explain mathematically how the mixer works. It includes a schematic diagram of the circuit as used, which does not vary substantially from the three circuits shown above.

"Another Look at the Like-New Circuit" subtitled, "A low distortion low noise mixer for those who use tubes." In this PDF article, the writer attempts to modify the Pullen mixer circuit so that less pulling on the oscillator involved occurs. However, as mentioned several times on this web site, oscillator pulling can be essentially eliminated by simply including a cathode follower between the oscillator output and the mixer input, as already suggested by Keats Pullen in his article. Also, in this article, the Pullen mixer is used as a product detector, instead of an RF-to-IF mixer.

10) Calculating ENR.

Provided for us by Chris Trask is a PDF of an article by Stolze on how to calculate Equivalent Noise Resistance for tubes which we would use in receivers. Stolze.PDF

11) The Novice Q5'er

Here is a PDF of an article on modifying the BC-453 or R-23/ARC-5 receivers for AC power, PLUS a two-tube crystal-controlled converter for 80 and 40 meters.