AVO CT378B signal generator - UK Vintage Radio Repair and Restoration Discussion Forum

QWENIX · 9th Jul 2016, 11:31 pm

I have bought a Signal Generator two weeks ago. The military version 378B it came with those blue adapter and two attenuators and one big thing the modulator. I haven't fired it up jet. I know how to soft start this thing wth variac and glowing bulb placed in series. Is there something I should take a look at wile starting up.. such as the smoothing capacitors electrolytics?

The mains lead is in bad shape so I wil cut off the plessey mark IV 3 way mains plug and solder on a better cable...

See pics....

QWENIX · 20th Jul 2016, 6:19 pm

The signal generator works. But the 1000 HZ internal modulation can not be heard if modulated on a signal. If I turn the switch halfway between the sinus and the rectangular wave form then I can hear it a slight bit. Anyone has some tips were to look at?

kind regards Qwenix

ms660 · 20th Jul 2016, 7:18 pm

The modulation Osc packed up completely on mine, C1 (0.01uf) had gone almost short circuit, that capacitor is connected across the modulation Osc inductor.

Lawrence.

mole42uk · 20th Jul 2016, 9:49 pm

Mine has a u/s attenuator so I can only get an output by clipping a cable to the attenuator input :-(

The service manual is available somewhere in the ether but I don't remember where I got it. Google should know.

9th Jul 2016, 11:31 pm	#1
QWENIX Pentode Join Date: Jan 2006 Location: Amsterdam, The Netherlands Posts: 180	AVO CT378B signal generator I have bought a Signal Generator two weeks ago. The military version 378B it came with those blue adapter and two attenuators and one big thing the modulator. I haven't fired it up jet. I know how to soft start this thing wth variac and glowing bulb placed in series. Is there something I should take a look at wile starting up.. such as the smoothing capacitors electrolytics? The mains lead is in bad shape so I wil cut off the plessey mark IV 3 way mains plug and solder on a better cable... See pics.... Attached Thumbnails Last edited by AC/HL; 10th Jul 2016 at 12:25 am. Reason: Thread split

20th Jul 2016, 6:19 pm	#2
QWENIX Pentode Join Date: Jan 2006 Location: Amsterdam, The Netherlands Posts: 180	Re: AVO CT378B signal generator The signal generator works. But the 1000 HZ internal modulation can not be heard if modulated on a signal. If I turn the switch halfway between the sinus and the rectangular wave form then I can hear it a slight bit. Anyone has some tips were to look at? kind regards Qwenix

20th Jul 2016, 7:18 pm	#3
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: AVO CT378B signal generator The modulation Osc packed up completely on mine, C1 (0.01uf) had gone almost short circuit, that capacitor is connected across the modulation Osc inductor. Lawrence.

20th Jul 2016, 9:49 pm	#4
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,613	Re: AVO CT378B signal generator Mine has a u/s attenuator so I can only get an output by clipping a cable to the attenuator input :-( The service manual is available somewhere in the ether but I don't remember where I got it. Google should know. __________________ Richard Index: recursive loop: see recursive loop