A stalwart of the 50s radio & tv service department that’s been long forgotten by many. This Model 1 valve signal generator covers the 100KHz to 60MHz in 6 ranges. There’s a 400Hz audio oscillator that provides amplitude modulation and a separate audio output along with RF. Dad retained the original service sheet along with advertising brochure.

Update

Warning: Do not operate your mains powered equipment with the case removed. Dangerous voltages are present inside.

After many years of devoted service, albeit more infrequent, the Advance generator stopped working. Carrier waves were being output without the 400Hz amplitude modulation I relied on. I’d picked up a smaller Tech TE-200 for £1 at a vintage fair and been using that instead. But the Tech’s output was far from a true sine wave and its harmonics poured spurious signals over the wavebands.

Taking another look at the Advance I found the audio working on low frequency ranges E&F but stopped on higher frequency D-A bands. After several minutes, switching between mod/cw and RF bands the 400Hz audio showed on D-B but intermittently. RF also appeared to stop on higher ranges.

So time to restore the Advance E1. Opening the case by removing the rear thumbnut and carefully unscrewing each of the four corner fixings, I found the original 8µF reservoir and smoothing electrolytic capacitors still in place. Each suffered from age related warts and wrinkles and the component tester confirmed one was ‘unknown’ and the other had a very high ESR.

Downloading the circuit diagram from the Radio Museum suggested 4µF 450v types but I decided to fit 10µF 350v which I had in stock. Why Advance would fit 450v working when the AC feed from each of the centre tapped transformer only outputs 140v RMS is a puzzle. Advance increased the supply voltage for the Model E2 and fitted 16µF 450v capacitors as the 300v working voltage is much higher. But my Model E1 reaches just 170v DC so a 350V rating should be fine.

I added a 100mA fuse after the 6X5G rectifier just in case one of the caps fails as no internal fuse is fitted. The 3A fuse (you did check it’s not 13A didn’t you!) in the mains plug is rather too high to protect the rectifier valve.

It’s worth noting Advance included a pair of 5000pF capacitors on the live and neutral mains feed to reduce RF escaping via the mains lead. Both capacitors are before the single pole on/off switch so I recommend you don’t leave your Advance signal generator plugged in. If these aging filter capacitors fail short circuit it could trip your house RCB and may be the last place you expect to find a neutral-earth fault!

With capacitors replaced I checked the ripple and found just 230mV at 100Hz. The 6J5G anode supply voltage now measured a healthy 130v instead of 117v. Audio was restored with modulation across all wavebands. RF levels were also consistent with no instability or drop out. There was some reduction in RF level on the 30-60MHz highest frequency band but this could be my scope.

Safety Advice

Note for safety reasons your Advance Signal Generator must be fitted with a 3 core mains lead and its chassis earthed. Originally only twin core cable was used so the output was isolated. But as noted above, there are capacitors fitted internally between the live and chassis which can provide a nasty shock and serious injury if they fail and the chassis is not earthed.