AVO CT160 buzzing with certain valves - UK Vintage Radio Repair and Restoration Discussion Forum

kosunen · 26th May 2008, 5:24 pm

Hello, I'm new here, looks like a good forum.

I am in the process of testing lots of valves on an AVO ct160 which seems to be working well. The only problem so far has been a buzzing noise when testing valves with "CL" in the name eg. ECL80, PCL83 etc. This isn't the warning buzz, it sounds different and the warning light doesn't come on when it happens. It seems to happen on just about every valve with "CL" in the name when I rotate the knob to "test". Does anyone know what causes this and is it anything to worry about?

Thanks.

Dave Moll · 26th May 2008, 5:46 pm

xCLnn signifies a valve containing a triode, and a power tetrode or pentode, if that helps at all.

Sean Williams · 26th May 2008, 6:12 pm

It could be that the internal connections to the valves are connected to "spare pins" - Ct160 does not like this!

Alf Fisher · 29th May 2008, 8:09 pm

I think the buzzing sound can come from the mains transformer when it is called upon to supply more current than about 30mA. I don't think it is anything to worry about. Sometimes when testing high current rectifiers, I get the impression that the overload trip is about to operate so that could also be a possible cause of the buzzing as the valve types mentioned contain power output pentodes.

Alf

wave solder · 29th May 2008, 8:36 pm

The buzzing sound can also be caused by an incorrectly adjusted cutout .........

kosunen · 7th Jun 2008, 1:35 pm

Thanks for the advice everyone. I will have a look inside the machine at some point. I think it needs some calibration too but thats a whole other topic!

26th May 2008, 5:24 pm	#1
kosunen Retired Dormant Member Join Date: May 2008 Location: Plymouth Posts: 2	AVO CT160 buzzing with certain valves Hello, I'm new here, looks like a good forum. I am in the process of testing lots of valves on an AVO ct160 which seems to be working well. The only problem so far has been a buzzing noise when testing valves with "CL" in the name eg. ECL80, PCL83 etc. This isn't the warning buzz, it sounds different and the warning light doesn't come on when it happens. It seems to happen on just about every valve with "CL" in the name when I rotate the knob to "test". Does anyone know what causes this and is it anything to worry about? Thanks.

26th May 2008, 5:46 pm	#2
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,127	Re: AVO CT160 buzzing with certain valves xCLnn signifies a valve containing a triode, and a power tetrode or pentode, if that helps at all. __________________ Mending is better than Ending (cf Brave New World by Aldous Huxley)

26th May 2008, 6:12 pm	#3
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,517	Re: AVO CT160 buzzing with certain valves It could be that the internal connections to the valves are connected to "spare pins" - Ct160 does not like this! __________________ Engineers make things work and have spare bits when finished

29th May 2008, 8:09 pm	#4
Alf Fisher Hexode Join Date: Sep 2005 Location: Potton, Bedfordshire, UK. Posts: 293	Re: AVO CT160 buzzing with certain valves I think the buzzing sound can come from the mains transformer when it is called upon to supply more current than about 30mA. I don't think it is anything to worry about. Sometimes when testing high current rectifiers, I get the impression that the overload trip is about to operate so that could also be a possible cause of the buzzing as the valve types mentioned contain power output pentodes. Alf

29th May 2008, 8:36 pm	#5
wave solder Hexode Join Date: Feb 2007 Location: Chesterfield, Derbyshire, UK. Posts: 483	Re: AVO CT160 buzzing with certain valves The buzzing sound can also be caused by an incorrectly adjusted cutout .........

7th Jun 2008, 1:35 pm	#6
kosunen Retired Dormant Member Join Date: May 2008 Location: Plymouth Posts: 2	Re: AVO CT160 buzzing with certain valves Thanks for the advice everyone. I will have a look inside the machine at some point. I think it needs some calibration too but thats a whole other topic!