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WaveyDipole · 26th Jun 2020, 12:53 pm

While I am waiting for parts to turn up for the radio I am working on, I have investigated the sig gen a bit further. There is good news and there is bad news.

The electrolytic capacitors in the power supply circuit had already been replaced and I replaced the remaining handful of paper caps in the power supply filtering chain with quality high voltage ceramics. The generator was then powered up gradually on and isolating transformer and variac with no problems. At this stage I haven't touched any components in the signal generating circuit nor any of the input/output decoupling caps.

The good news is that the generator circuit itself seems to be working. The valve warms up and I am getting output up to and out of the Output Voltage control. I can see modulated AM in the "30% AM" position and a clean sine wave on the CW and Crystal Check positions. Observing on an oscilloscope, the sine wave frequency can be adjusted. Using the built in counter it was possible to determine that the output frequency is about spot on across all frequency bands and a signal is present all the way up to the top of the band 230-100MHz band, although at varying amplitude. So far, so good.

Now for the bad news. I was advised that the sig gen had no output and indeed there was no output at the R.F Output terminal, except, as it turns out, when the control is turned to the X1 position in the μV range. There was no output in any other position so It would seem that there is some problem with the resistor chain in the attenuator circuit which will need to be investigated.

There is also a mechanical problem with the frequency range control. One of the rivets pops out every now and then from under the spring plate as the control is rotated, with the couplings distorting as it does so. I am concerned that it may give way at some point if not repaired, but unfortunately getting access to this will require a complete dis-assembly.

Looking carefully at the unit, I believe that the oscillator can be removed in one complete piece by disconnecting the 3 wires to the coils fed from the power supply, the co-ax from the Output Voltage pot, disconnecting the linkages to the Frequency, Frequency Range and Modulation controls and removing 4 large screws from the rear plate. Disconnecting the tuner shaft looks the trickiest as it uses some rather small grub screws. Hopefully the oscillator circuit will not need to be disturbed in any critical way.

If anyone has any notes on how to disassemble the unit, or has done so in the past and provide any insights this would be appreciated.

26th Jun 2020, 12:53 pm	#6
WaveyDipole Nonode Join Date: Mar 2013 Location: Leicester, UK Posts: 2,535	Re: Advance type 63A While I am waiting for parts to turn up for the radio I am working on, I have investigated the sig gen a bit further. There is good news and there is bad news. The electrolytic capacitors in the power supply circuit had already been replaced and I replaced the remaining handful of paper caps in the power supply filtering chain with quality high voltage ceramics. The generator was then powered up gradually on and isolating transformer and variac with no problems. At this stage I haven't touched any components in the signal generating circuit nor any of the input/output decoupling caps. The good news is that the generator circuit itself seems to be working. The valve warms up and I am getting output up to and out of the Output Voltage control. I can see modulated AM in the "30% AM" position and a clean sine wave on the CW and Crystal Check positions. Observing on an oscilloscope, the sine wave frequency can be adjusted. Using the built in counter it was possible to determine that the output frequency is about spot on across all frequency bands and a signal is present all the way up to the top of the band 230-100MHz band, although at varying amplitude. So far, so good. Now for the bad news. I was advised that the sig gen had no output and indeed there was no output at the R.F Output terminal, except, as it turns out, when the control is turned to the X1 position in the μV range. There was no output in any other position so It would seem that there is some problem with the resistor chain in the attenuator circuit which will need to be investigated. There is also a mechanical problem with the frequency range control. One of the rivets pops out every now and then from under the spring plate as the control is rotated, with the couplings distorting as it does so. I am concerned that it may give way at some point if not repaired, but unfortunately getting access to this will require a complete dis-assembly. Looking carefully at the unit, I believe that the oscillator can be removed in one complete piece by disconnecting the 3 wires to the coils fed from the power supply, the co-ax from the Output Voltage pot, disconnecting the linkages to the Frequency, Frequency Range and Modulation controls and removing 4 large screws from the rear plate. Disconnecting the tuner shaft looks the trickiest as it uses some rather small grub screws. Hopefully the oscillator circuit will not need to be disturbed in any critical way. If anyone has any notes on how to disassemble the unit, or has done so in the past and provide any insights this would be appreciated.