I’ve had one of these little generators for some years now, which has served me well and works fine.
Last year I bought a non-worker from a rally, so was able to use the existing one for performance comparisons and to check for any wiring errors or whatever I found when I opened up the non-worker – not knowing whether or not someone had got there before me. I think the non-worker may be from the mid to late 1960s, older than the working one as it is darker in colour and has a separate orange and silver dial, whereas the working one I have is lighter in colour and the whole of the front of the case including the dial is screen printed. They’re nicely laid out and a compact size, measuring 24cms x 160cms x 140 cms. (9.5” x 6.5” x 5”).
I fondly remember the Heathkit era on the 1960s – 1980s when I often longingly browsed through the catalogues, but I'm sure I'm not alone in saying that the prices were far beyond my range. I’ve discovered a 1966 catalogue online which lists the RFIU - the kit being £13.18s 0d, and the assembled price being £20.8s 0d. To put this into perspective, when adjusted for inflation, this equates to £250 and £363 respectively in 2018.
http://heathkit.glosnet.com/heathkit.../1966_pg25.jpg
When browsing through the catalogues and seeing the wide range of kits, it’s a reminder of what a huge company Heathkit was in its heyday.
I can’t imagine how many designers, engineers and production staff it must have employed, not just in the USA but at Gloucester:
http://www.heathkit.org.uk/
The generator covers 100kHz to 100 MHz in six ranges, and calibrated harmonics from 100 MHz to 200 MHz as follows:
Range A: 100 KHz – 300 KHz
Range B: 300 KHz - 1 MHz
Range C: 1 MHz – 3 MHz
Range D: 3 MHz – 10 MHz
Range E: 10 MHz – 30 MHz
Range F: 30 MHz – 100 MHz
Calibrated Harmonics – 100 MHz – 200 MHz.
Accuracy, +/- 20% of dial calibration.
Output impedance 75 Ohms.
Voltage: Up to 100mV on all ranges.
Internal modulation approx 400 Hz, 30% depth nominal.
Audio output up to 9 Volts across 1 MegOhm
Valves:
V1: 12AT7/ECC81 - RF Oscillator
V2 ECF80 – Modulator and RF output.
Rectification is via a Sentercell selenium rectifier.
Some Heathkit equipment was factory constructed, but most was home-constructed, made much easier by the renowned Heathkit manuals which detailed every step of the way. Thus, the quality of construction can be variable. To aid the home constructor, the coil and bandswitch unit of the RF1U was pre-wired and factory aligned. Just one coil - the range F coil - consisting of four air wound turns of 22 SWG tinned copper wire - had to be soldered to the tuning capacitor. The turns are later either opened up or squeezed together to align that range. The coils and associated circuitry, along with the circuitry of V1 are contained in a screening box, bolted to the underside of the chassis.
The ‘U’ suffix on Heathkit equipment indicates that it was version modified for the UK market for 230 – 250V AC mains, whereas equipment without the 'U' suffix was for the American market, for 117 Volts mains and often had other diffrences. The first thing that’s evident on removing the case is that the thin two-core mains flex isn’t anchored inside the case – it’s simply tied in a knot as with similar Heathkit mains powered equipment of that era. The cable passes through a grommet on the rear apron of the chassis and poses a safety hazard as it can be twisted round in any direction, risking fracture of the soldered connection over time, which could then touch the metal cabinet. The mains cable doesn’t go directly to the two pole mains switch on the audio control potentiometer – it goes to a tag-strip, and from there, via thin twisted flex to the pot switch and back again to the tag-strip. As the mains cable isn’t earthed, that poses an added hazard. As I’d done with my original one, I fitted a 3-core flex, earthed the case, and fitted a cable restraint in place of the grommet to firmly anchor the flex.
On checking the output of the selenium rectifier, which - from a healthy rectifier would be 160V - it was down at 120V, albeit the AC input from the mains transformer to the rectifier was correct at 150V. Instead of the HT being 125 Volts after the 2k2 load resistor across the reservoir/smoothing capacitor, it was down at 95V, so it was evident that the rectifier was in need of replacement. More about that in the next post.
Pictures attached:
Pic 1: Front of the old (non-working) one that's the subject of this thread.
Pic 2: Front of newer one.
Pic 3: Newer one beneath chassis with the screening box in place.
Pic 4: Sentercel rectifier.
Pic 5 Above chassis.