AVO CT160 and testing 2A3 valves - UK Vintage Radio Repair and Restoration Discussion Forum

HBWOODY · 26th Mar 2020, 11:47 am

As the neg grid volts for testing a 2A3 are set at 45, does that mean that it cannot be tested on an AVO160 which has a highest neg grid volts setting of 40?

retailer · 26th Mar 2020, 3:28 pm

After 15 yrs of sitting on the shelf I've just got my MKI working - I've been running a few valves through to gauge how it is working and some of these included some 2A3's that I have - I tried various grid volt settings from 35 up to 50 - going lower than 45 will increase the anode current which may possibly go over 60mA, 2A3 data gives 60mA as typical operating figure, the absolute maximum is probably higher, as long as you don't linger too long with the anode current much over 60 then you should be able to get a Gm reading. I tried up to 70mA and down to 50mA and while the Gm did vary with anode current it was not a huge difference. One of them was slow coming up to anode current and increasing it much over 50mA reduced the Gm I suspect that valve was well used. I would try it at 40volts and keep an eye on the anode current.

The MkI and MKII have grid volts up to 100 - not sure about the MKIII and MKIV, I think that the CT160 was intended for the military and can only think that the military did not have a use for valves that required a bias voltage higher than 40volts

chriswood1900 · 26th Mar 2020, 6:31 pm

I believe a 2A3 is equivalent to a CV1831.
In my Admiralty guide for the CT 160 it has settings as follows for the CV1831
264 300 000 - Vf 2.5 - Neg volts 40 - Anode 300 - Ia 60 - mA/V 5.2
Hope that helps

HBWOODY · 26th Mar 2020, 7:29 pm

Chris
Thank you for solving that problem for me.
Haydn

26th Mar 2020, 11:47 am	#1
HBWOODY Pentode Join Date: Mar 2020 Location: Bodmin, Cornwall, UK. Posts: 212	AVO CT160 and testing 2A3 valves As the neg grid volts for testing a 2A3 are set at 45, does that mean that it cannot be tested on an AVO160 which has a highest neg grid volts setting of 40?

26th Mar 2020, 3:28 pm	#2
retailer Heptode Join Date: May 2005 Location: Adelaide, South Australia Posts: 541	Re: Avo160 and testing 2A3 valves After 15 yrs of sitting on the shelf I've just got my MKI working - I've been running a few valves through to gauge how it is working and some of these included some 2A3's that I have - I tried various grid volt settings from 35 up to 50 - going lower than 45 will increase the anode current which may possibly go over 60mA, 2A3 data gives 60mA as typical operating figure, the absolute maximum is probably higher, as long as you don't linger too long with the anode current much over 60 then you should be able to get a Gm reading. I tried up to 70mA and down to 50mA and while the Gm did vary with anode current it was not a huge difference. One of them was slow coming up to anode current and increasing it much over 50mA reduced the Gm I suspect that valve was well used. I would try it at 40volts and keep an eye on the anode current. The MkI and MKII have grid volts up to 100 - not sure about the MKIII and MKIV, I think that the CT160 was intended for the military and can only think that the military did not have a use for valves that required a bias voltage higher than 40volts

26th Mar 2020, 6:31 pm	#3
chriswood1900 Octode Join Date: Jan 2007 Location: Dorridge, West Midlands, UK. Posts: 1,479	Re: Avo160 and testing 2A3 valves I believe a 2A3 is equivalent to a CV1831. In my Admiralty guide for the CT 160 it has settings as follows for the CV1831 264 300 000 - Vf 2.5 - Neg volts 40 - Anode 300 - Ia 60 - mA/V 5.2 Hope that helps __________________ Chris Wood BVWS Member

26th Mar 2020, 7:29 pm	#4
HBWOODY Pentode Join Date: Mar 2020 Location: Bodmin, Cornwall, UK. Posts: 212	Re: Avo160 and testing 2A3 valves Chris Thank you for solving that problem for me. Haydn