AVO test results - UK Vintage Radio Repair and Restoration Discussion Forum

PJL · 1st Feb 2023, 5:54 pm

I have broken out the grid and anode connections from my Mullard Tester so I can take accurate anode current readings and do static gm tests (it's very easy as the connections can be taken from the push switches).

In the past I have been using the 'AVO Valve Data Manual' as a guide to what a valve should do but I am now not so sure this is valid.

I tested an EL37 using test card 262 that has Va=250, Vsg=250, Vcg=-13.5 (77 is the official card but 262 is the AVO test conditions) and it measures 87mA. The AVO data says 100mA and that appears to roughly match the datasheet.

I then tested a KT66 using test card 262 again and the anode current measures 95mA. The AVO data sheet implies it should be 65+10 (adjusting for -15V) or about 75mA. Then if I go to the datasheet 95mA looks about right.

My measured currents may be a little low as I don't wait till they fully settle (anode dissipation exceeds specs) but my assumption that the AVO data corresponds to manufacturers DC specification is clearly wrong and why test a KT66 at 65mA and an EL37 at 100mA?

1st Feb 2023, 5:54 pm	#1
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	AVO test results I have broken out the grid and anode connections from my Mullard Tester so I can take accurate anode current readings and do static gm tests (it's very easy as the connections can be taken from the push switches). In the past I have been using the 'AVO Valve Data Manual' as a guide to what a valve should do but I am now not so sure this is valid. I tested an EL37 using test card 262 that has Va=250, Vsg=250, Vcg=-13.5 (77 is the official card but 262 is the AVO test conditions) and it measures 87mA. The AVO data says 100mA and that appears to roughly match the datasheet. I then tested a KT66 using test card 262 again and the anode current measures 95mA. The AVO data sheet implies it should be 65+10 (adjusting for -15V) or about 75mA. Then if I go to the datasheet 95mA looks about right. My measured currents may be a little low as I don't wait till they fully settle (anode dissipation exceeds specs) but my assumption that the AVO data corresponds to manufacturers DC specification is clearly wrong and why test a KT66 at 65mA and an EL37 at 100mA?