Heathkit equipment has consistently proven that you don't need to spend a lot of money to get reasonable test gear. This Found in the Attic feature, the SG-8 RF signal generator, is no exception. It was introduced by Heath in September of 1953, and sold for $19.50. Production continued through May of 1961. Despite the low cost, the stability and accuracy of this RF generator is pretty impressive.
The circuitry is simplicity in itself. The RF section consists of a single 12AU7. One triode section is a Colpitts oscillator, while the other is a buffer between the oscillator and output section. Four coils, for bands A-D, are switched via the band switch. The coil for band E, which covers 25-110 Mhz is really a section of bus bar wire. Additionally, useful calibrated harmonics are available up to 220 Mhz.
The audio oscillator is also a Colpitts circuit, in this case, a 6C4, having a frequency of approximately 400 Hz. It is fed both to the RF section of the SG-8 and to the OUT connector, making it available for testing audio amplifiers, etc. With the modulation switch in the EXT position, an audio oscillator may be connected to the SG-8. In that case, the 6C4 becomes an amplifier for the external signal.
The power supply provides filament voltage to the 6C4 and 12AU7. A selenium rectifier is connected to one side of the transformer as a half-wave rectifier. RC filtering is provided by two 20 µF electrolytic capacitors separated by a 3.3K resistor.
Both sides of the power line are bypassed with .01 uF disc capacitors to discourage RF energy from feeding back into the power lines.
There are no tweaks in the SG-8. What you see is what you get. The instructions claim that this is because all the coils have been pre-adjusted at the factory.
The most common application for the SG-8 is receiver alignment. With some practice, specific alignment instructions are no longer necessary. Superhets are superhets, and IF stages are always aligned first, followed by high frequency oscillator trimmer at the highest frequency, usually 1600 Khz. Then set the oscillator and receiver for 1400 and adjust the RF trimmer for a peak output. Finally, set the RF oscillator to 600 Khz, and tune the receiver to the low end of the dial. Rock the receiver tuning capacitor while adjusting the trimmer for maximum output.
Has been modified from original, by changing the audio in and RF out connectors to modern standards, generally clean, Works! This has been on my bench since 1980, but its time to go to some other needy user.
PLEASE READ: I am standing FIRM with my No Return policy, esp. with electronic & audio equipment!
I have been getting a lot of returns, Simply Because the buyer, A) Does not know what the item is, or how to use it, or B) Is connecting it incorrectly, and inappropriately, and frying the unit, then wanting to return it. If you don't know what this unit is, or how to use it, don't buy it, Sale is Final!
I provide an accurate assesment of an items condition, and if I say it is tested and working when it leaves here, it is. I'm not a pro seller/store, I'm just trying to downsize.